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1
Saiz-Lopez, A., J. F. Lamarque, D. E. Kinnison, S. Tilmes, C. Ordóñez, J. J. Orlando, A. J. Conley, et al. "Estimating the climate significance of halogen-driven ozone loss in the tropical marine troposphere." Atmospheric Chemistry and Physics 12, no. 9 (May 4, 2012): 3939–49. http://dx.doi.org/10.5194/acp-12-3939-2012.
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Abstract. We have integrated observations of tropospheric ozone, very short-lived (VSL) halocarbons and reactive iodine and bromine species from a wide variety of tropical data sources with the global CAM-Chem chemistry-climate model and offline radiative transfer calculations to compute the contribution of halogen chemistry to ozone loss and associated radiative impact in the tropical marine troposphere. The inclusion of tropospheric halogen chemistry in CAM-Chem leads to an annually averaged depletion of around 10% (~2.5 Dobson units) of the tropical tropospheric ozone column, with largest effects in the middle to upper troposphere. This depletion contributes approximately −0.10 W m−2 to the radiative flux at the tropical tropopause. This negative flux is of similar magnitude to the ~0.33 W m−2 contribution of tropospheric ozone to present-day radiative balance as recently estimated from satellite observations. We find that the implementation of oceanic halogen sources and chemistry in climate models is an important component of the natural background ozone budget and we suggest that it needs to be considered when estimating both preindustrial ozone baseline levels and long term changes in tropospheric ozone.
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Stevenson, D. S., P. J. Young, V. Naik, J. F. Lamarque, D. T. Shindell, A. Voulgarakis, R. B. Skeie, et al. "Tropospheric ozone changes, radiative forcing and attribution to emissions in the Atmospheric Chemistry and Climate Model Inter-comparison Project (ACCMIP)." Atmospheric Chemistry and Physics Discussions 12, no. 10 (October 4, 2012): 26047–97. http://dx.doi.org/10.5194/acpd-12-26047-2012.
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Abstract. Ozone (O3) from 17 atmospheric chemistry models taking part in the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) has been used to calculate tropospheric ozone radiative forcings (RFs). We calculate a~value for the pre-industrial (1750) to present-day (2010) tropospheric ozone RF of 0.40 W m−2. The model range of pre-industrial to present-day changes in O3 produces a spread (±1 standard deviation) in RFs of ±17%. Three different radiation schemes were used – we find differences in RFs between schemes (for the same ozone fields) of ±10%. Applying two different tropopause definitions gives differences in RFs of ±3%. Given additional (unquantified) uncertainties associated with emissions, climate-chemistry interactions and land-use change, we estimate an overall uncertainty of ±30% for the tropospheric ozone RF. Experiments carried out by a subset of six models attribute tropospheric ozone RF to increased emissions of methane (47%), nitrogen oxides (29%), carbon monoxide (15%) and non-methane volatile organic compounds (9%); earlier studies attributed more of the tropospheric ozone RF to methane and less to nitrogen oxides. Normalising RFs to changes in tropospheric column ozone, we find a global mean normalised RF of 0.042 W m−2 DU−1, a value similar to previous work. Using normalised RFs and future tropospheric column ozone projections we calculate future tropospheric ozone RFs (W m−2; relative to 1850 – add 0.04 W m−2 to make relative to 1750) for the Representative Concentration Pathways in 2030 (2100) of: RCP2.6: 0.31 (0.16); RCP4.5: 0.38 (0.26); RCP6.0: 0.33 (0.24); and RCP8.5: 0.42 (0.56). Models show some coherent responses of ozone to climate change: decreases in the tropical lower troposphere, associated with increases in water vapour; and increases in the sub-tropical to mid-latitude upper troposphere, associated with increases in lightning and stratosphere-to-troposphere transport.
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Stevenson, D. S., P. J. Young, V. Naik, J. F. Lamarque, D. T. Shindell, A. Voulgarakis, R. B. Skeie, et al. "Tropospheric ozone changes, radiative forcing and attribution to emissions in the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP)." Atmospheric Chemistry and Physics 13, no. 6 (March 15, 2013): 3063–85. http://dx.doi.org/10.5194/acp-13-3063-2013.
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Abstract. Ozone (O3) from 17 atmospheric chemistry models taking part in the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP) has been used to calculate tropospheric ozone radiative forcings (RFs). All models applied a common set of anthropogenic emissions, which are better constrained for the present-day than the past. Future anthropogenic emissions follow the four Representative Concentration Pathway (RCP) scenarios, which define a relatively narrow range of possible air pollution emissions. We calculate a value for the pre-industrial (1750) to present-day (2010) tropospheric ozone RF of 410 mW m−2. The model range of pre-industrial to present-day changes in O3 produces a spread (±1 standard deviation) in RFs of ±17%. Three different radiation schemes were used – we find differences in RFs between schemes (for the same ozone fields) of ±10%. Applying two different tropopause definitions gives differences in RFs of ±3%. Given additional (unquantified) uncertainties associated with emissions, climate-chemistry interactions and land-use change, we estimate an overall uncertainty of ±30% for the tropospheric ozone RF. Experiments carried out by a subset of six models attribute tropospheric ozone RF to increased emissions of methane (44±12%), nitrogen oxides (31 ± 9%), carbon monoxide (15 ± 3%) and non-methane volatile organic compounds (9 ± 2%); earlier studies attributed more of the tropospheric ozone RF to methane and less to nitrogen oxides. Normalising RFs to changes in tropospheric column ozone, we find a global mean normalised RF of 42 mW m−2 DU−1, a value similar to previous work. Using normalised RFs and future tropospheric column ozone projections we calculate future tropospheric ozone RFs (mW m−2; relative to 1750) for the four future scenarios (RCP2.6, RCP4.5, RCP6.0 and RCP8.5) of 350, 420, 370 and 460 (in 2030), and 200, 300, 280 and 600 (in 2100). Models show some coherent responses of ozone to climate change: decreases in the tropical lower troposphere, associated with increases in water vapour; and increases in the sub-tropical to mid-latitude upper troposphere, associated with increases in lightning and stratosphere-to-troposphere transport. Climate change has relatively small impacts on global mean tropospheric ozone RF.
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Lu, Xiao, Lin Zhang, Tongwen Wu, Michael S. Long, Jun Wang, Daniel J. Jacob, Fang Zhang, et al. "Development of the global atmospheric chemistry general circulation model BCC-GEOS-Chem v1.0: model description and evaluation." Geoscientific Model Development 13, no. 9 (August 31, 2020): 3817–38. http://dx.doi.org/10.5194/gmd-13-3817-2020.
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Abstract. Chemistry plays an indispensable role in investigations of the atmosphere; however, many climate models either ignore or greatly simplify atmospheric chemistry, limiting both their accuracy and their scope. We present the development and evaluation of the online global atmospheric chemical model BCC-GEOS-Chem v1.0, coupling the GEOS-Chem chemical transport model (CTM) as an atmospheric chemistry component in the Beijing Climate Center atmospheric general circulation model (BCC-AGCM). The GEOS-Chem atmospheric chemistry component includes detailed tropospheric HOx–NOx–volatile organic compounds–ozone–bromine–aerosol chemistry and online dry and wet deposition schemes. We then demonstrate the new capabilities of BCC-GEOS-Chem v1.0 relative to the base BCC-AGCM model through a 3-year (2012–2014) simulation with anthropogenic emissions from the Community Emissions Data System (CEDS) used in the Coupled Model Intercomparison Project Phase 6 (CMIP6). The model captures well the spatial distributions and seasonal variations in tropospheric ozone, with seasonal mean biases of 0.4–2.2 ppbv at 700–400 hPa compared to satellite observations and within 10 ppbv at the surface to 500 hPa compared to global ozonesonde observations. The model has larger high-ozone biases over the tropics which we attribute to an overestimate of ozone chemical production. It underestimates ozone in the upper troposphere which is likely due either to the use of a simplified stratospheric ozone scheme or to biases in estimated stratosphere–troposphere exchange dynamics. The model diagnoses the global tropospheric ozone burden, OH concentration, and methane chemical lifetime to be 336 Tg, 1.16×106 molecule cm−3, and 8.3 years, respectively, which is consistent with recent multimodel assessments. The spatiotemporal distributions of NO2, CO, SO2, CH2O, and aerosol optical depth are generally in agreement with satellite observations. The development of BCC-GEOS-Chem v1.0 represents an important step for the development of fully coupled earth system models (ESMs) in China.
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Wang, Y., P. Konopka, Y. Liu, H. Chen, R. Müller, F. Plöger, M. Riese, Z. Cai, and D. Lü. "Tropospheric ozone trend over Beijing from 2002–2010: ozonesonde measurements and modeling analysis." Atmospheric Chemistry and Physics 12, no. 18 (September 18, 2012): 8389–99. http://dx.doi.org/10.5194/acp-12-8389-2012.
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Abstract. Using a combination of ozonesonde data and numerical simulations of the Chemical Lagrangian Model of the Stratosphere (CLaMS), the trend of tropospheric ozone (O3) during 2002–2010 over Beijing was investigated. Tropospheric ozone over Beijing shows a winter minimum and a broad summer maximum with a clear positive trend in the maximum summer ozone concentration over the last decade. The observed significant trend of tropospheric column ozone is mainly caused by photochemical production (3.1% yr−1 for a mean level of 52 DU). This trend is close to the significant trend of partial column ozone in the lower troposphere (0–3 km) resulting from the enhanced photochemical production during summer (3.0% yr−1 for a mean level of 23 DU). Analysis of the CLaMS simulation shows that transport rather than chemistry drives most of the seasonality of tropospheric ozone. However, dynamical processes alone cannot explain the trend of tropospheric ozone in the observational data. Clearly enhanced ozone values and a negative vertical ozone gradient in the lower troposphere in the observational data emphasize the importance of photochemistry within the troposphere during spring and summer, and suggest that the photochemistry within the troposphere significantly contributes to the tropospheric ozone trend over Beijing during the last decade.
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Revell, Laura E., Andrea Stenke, Fiona Tummon, Aryeh Feinberg, Eugene Rozanov, Thomas Peter, N. Luke Abraham, et al. "Tropospheric ozone in CCMI models and Gaussian process emulation to understand biases in the SOCOLv3 chemistry–climate model." Atmospheric Chemistry and Physics 18, no. 21 (November 13, 2018): 16155–72. http://dx.doi.org/10.5194/acp-18-16155-2018.
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Abstract. Previous multi-model intercomparisons have shown that chemistry–climate models exhibit significant biases in tropospheric ozone compared with observations. We investigate annual-mean tropospheric column ozone in 15 models participating in the SPARC–IGAC (Stratosphere–troposphere Processes And their Role in Climate–International Global Atmospheric Chemistry) Chemistry-Climate Model Initiative (CCMI). These models exhibit a positive bias, on average, of up to 40 %–50 % in the Northern Hemisphere compared with observations derived from the Ozone Monitoring Instrument and Microwave Limb Sounder (OMI/MLS), and a negative bias of up to ∼30 % in the Southern Hemisphere. SOCOLv3.0 (version 3 of the Solar-Climate Ozone Links CCM), which participated in CCMI, simulates global-mean tropospheric ozone columns of 40.2 DU – approximately 33 % larger than the CCMI multi-model mean. Here we introduce an updated version of SOCOLv3.0, “SOCOLv3.1”, which includes an improved treatment of ozone sink processes, and results in a reduction in the tropospheric column ozone bias of up to 8 DU, mostly due to the inclusion of N2O5 hydrolysis on tropospheric aerosols. As a result of these developments, tropospheric column ozone amounts simulated by SOCOLv3.1 are comparable with several other CCMI models. We apply Gaussian process emulation and sensitivity analysis to understand the remaining ozone bias in SOCOLv3.1. This shows that ozone precursors (nitrogen oxides (NOx), carbon monoxide, methane and other volatile organic compounds, VOCs) are responsible for more than 90 % of the variance in tropospheric ozone. However, it may not be the emissions inventories themselves that result in the bias, but how the emissions are handled in SOCOLv3.1, and we discuss this in the wider context of the other CCMI models. Given that the emissions data set to be used for phase 6 of the Coupled Model Intercomparison Project includes approximately 20 % more NOx than the data set used for CCMI, further work is urgently needed to address the challenges of simulating sub-grid processes of importance to tropospheric ozone in the current generation of chemistry–climate models.
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Gauss, M., G. Myhre, I. S. A. Isaksen, V. Grewe, G. Pitari, O. Wild, W. J. Collins, et al. "Radiative forcing since preindustrial times due to ozone change in the troposphere and the lower stratosphere." Atmospheric Chemistry and Physics 6, no. 3 (February 24, 2006): 575–99. http://dx.doi.org/10.5194/acp-6-575-2006.
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Abstract. Changes in atmospheric ozone have occurred since the preindustrial era as a result of increasing anthropogenic emissions. Within ACCENT, a European Network of Excellence, ozone changes between 1850 and 2000 are assessed for the troposphere and the lower stratosphere (up to 30 km) by a variety of seven chemistry-climate models and three chemical transport models. The modeled ozone changes are taken as input for detailed calculations of radiative forcing. When only changes in chemistry are considered (constant climate) the modeled global-mean tropospheric ozone column increase since preindustrial times ranges from 7.9 DU to 13.8 DU among the ten participating models, while the stratospheric column reduction lies between 14.1 DU and 28.6 DU in the models considering stratospheric chemistry. The resulting radiative forcing is strongly dependent on the location and altitude of the modeled ozone change and varies between 0.25 Wm−2 and 0.45 Wm−2 due to ozone change in the troposphere and −0.123 Wm−2 and +0.066 Wm−2 due to the stratospheric ozone change. Changes in ozone and other greenhouse gases since preindustrial times have altered climate. Six out of the ten participating models have performed an additional calculation taking into account both chemical and climate change. In most models the isolated effect of climate change is an enhancement of the tropospheric ozone column increase, while the stratospheric reduction becomes slightly less severe. In the three climate-chemistry models with detailed tropospheric and stratospheric chemistry the inclusion of climate change increases the resulting radiative forcing due to tropospheric ozone change by up to 0.10 Wm−2, while the radiative forcing due to stratospheric ozone change is reduced by up to 0.034 Wm−2. Considering tropospheric and stratospheric change combined, the total ozone column change is negative while the resulting net radiative forcing is positive.
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Zanis, P., P. Hadjinicolaou, A. Pozzer, E. Tyrlis, S. Dafka, N. Mihalopoulos, and J. Lelieveld. "Summertime free tropospheric ozone pool over the Eastern Mediterranean/Middle East." Atmospheric Chemistry and Physics Discussions 13, no. 8 (August 23, 2013): 22025–58. http://dx.doi.org/10.5194/acpd-13-22025-2013.
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Abstract. Observations show that the Mediterranean troposphere is characterized by a marked enhancement in summertime ozone with a maximum over the Eastern Mediterranean. This has been linked to enhanced ozone photochemical production and subsidence under cloud-free anticyclonic conditions. The Eastern Mediterranean region has among the highest levels of background tropospheric ozone around the globe and it can be considered as a global air pollution hotspot. A 12 yr climatological analysis (1998–2009) of free tropospheric ozone was carried out over the region based on ECMWF (European Centre for Medium-Range Weather Forecasts) ERA-interim reanalysis data and simulations with the EMAC (ECHAM5-MESSy for Atmospheric Chemistry) atmospheric chemistry climate model. EMAC is nudged towards the ECMWF analysis data and includes a stratospheric ozone tracer. A characteristic summertime pool with high ozone concentrations is found in the middle troposphere over the Eastern Mediterranean/Middle East (EMME) by ERA-interim ozone data, which is supported by Tropospheric Emission Spectrometer (TES) satellite ozone data and simulations with EMAC. The enhanced ozone over the EMME is a robust feature, propagating down to lower free tropospheric levels. The investigation of ozone in relation to potential vorticity and water vapour and the stratospheric ozone tracer indicates that the dominant mechanism causing the free tropospheric ozone pool is downward transport from the upper troposphere and lower stratosphere associated with the enhanced subsidence and the limited outflow transport that dominates the summertime EMME circulation. The implications of these summertime high free tropospheric ozone values on the seasonal cycle of near surface ozone over the Mediterranean are discussed.
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Zanis, P., P. Hadjinicolaou, A. Pozzer, E. Tyrlis, S. Dafka, N. Mihalopoulos, and J. Lelieveld. "Summertime free-tropospheric ozone pool over the eastern Mediterranean/Middle East." Atmospheric Chemistry and Physics 14, no. 1 (January 3, 2014): 115–32. http://dx.doi.org/10.5194/acp-14-115-2014.
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Abstract. Observations show that the Mediterranean troposphere is characterized by a marked enhancement in summertime ozone, with a maximum over the eastern Mediterranean. This has been linked to enhanced photochemical ozone production and subsidence under cloud-free anticyclonic conditions. The eastern Mediterranean is among the regions with the highest levels of background tropospheric ozone worldwide. A 12 yr climatological analysis (1998–2009) of free-tropospheric ozone was carried out over the region based on the ECMWF (European Centre for Medium-Range Weather Forecasts) ERA-Interim reanalysis data and simulations with the EMAC (ECHAM5–MESSy) atmospheric chemistry–climate model. EMAC is nudged towards the ECMWF analysis data and includes a stratospheric ozone tracer. A characteristic summertime pool with high ozone concentrations is found in the middle troposphere over the eastern Mediterranean–Middle East (EMME) in the ERA-Interim ozone data, Tropospheric Emission Spectrometer (TES) satellite ozone data and simulations with EMAC. The enhanced ozone over the EMME during summer is a robust feature, extending down to lower free-tropospheric levels. The investigation of ozone in relation to potential vorticity and water vapour and the stratospheric ozone tracer indicates that the dominant mechanism causing the free-tropospheric ozone pool is the downward transport from the upper troposphere and lower stratosphere, in association with the enhanced subsidence and the limited horizontal divergence observed over the region. The implications of these high free-tropospheric ozone levels on the seasonal cycle of near-surface ozone over the Mediterranean are discussed.
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Saiz-Lopez, A., R. P. Fernandez, C. Ordóñez, D. E. Kinnison, J. C. Gómez Martín, J. F. Lamarque, and S. Tilmes. "Iodine chemistry in the troposphere and its effect on ozone." Atmospheric Chemistry and Physics 14, no. 23 (December 10, 2014): 13119–43. http://dx.doi.org/10.5194/acp-14-13119-2014.
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Abstract. Despite the potential influence of iodine chemistry on the oxidizing capacity of the troposphere, reactive iodine distributions and their impact on tropospheric ozone remain almost unexplored aspects of the global atmosphere. Here we present a comprehensive global modelling experiment aimed at estimating lower and upper limits of the inorganic iodine burden and its impact on tropospheric ozone. Two sets of simulations without and with the photolysis of IxOy oxides (i.e. I2O2, I2O3 and I2O4) were conducted to define the range of inorganic iodine loading, partitioning and impact in the troposphere. Our results show that the most abundant daytime iodine species throughout the middle to upper troposphere is atomic iodine, with an annual average tropical abundance of (0.15–0.55) pptv. We propose the existence of a "tropical ring of atomic iodine" that peaks in the tropical upper troposphere (~11–14 km) at the equator and extends to the sub-tropics (30° N–30° S). Annual average daytime I / IO ratios larger than 3 are modelled within the tropics, reaching ratios up to ~20 during vigorous uplift events within strong convective regions. We calculate that the integrated contribution of catalytic iodine reactions to the total rate of tropospheric ozone loss (IOx Loss) is 2–5 times larger than the combined bromine and chlorine cycles. When IxOy photolysis is included, IOx Loss represents an upper limit of approximately 27, 14 and 27% of the tropical annual ozone loss for the marine boundary layer (MBL), free troposphere (FT) and upper troposphere (UT), respectively, while the lower limit throughout the tropical troposphere is ~9%. Our results indicate that iodine is the second strongest ozone-depleting family throughout the global marine UT and in the tropical MBL. We suggest that (i) iodine sources and its chemistry need to be included in global tropospheric chemistry models, (ii) experimental programs designed to quantify the iodine budget in the troposphere should include a strategy for the measurement of atomic I, and (iii) laboratory programs are needed to characterize the photochemistry of higher iodine oxides to determine their atmospheric fate since they can potentially dominate halogen-catalysed ozone destruction in the troposphere.
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Grewe, V. "The origin of ozone." Atmospheric Chemistry and Physics 6, no. 6 (May 10, 2006): 1495–511. http://dx.doi.org/10.5194/acp-6-1495-2006.
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Abstract. Highest atmospheric ozone production rates can be found at around 30 km in the tropical stratosphere, leading to ozone mixing ratios of about 10 ppmv. Those stratospheric air masses are then transported to extra-tropical latitudes via the Brewer-Dobson circulation. This is considered the main mechanism to generate mid- and high latitude ozone. By applying the climate-chemistry models E39/C and MAECHAM4/CHEM, this view is investigated in more detail. The origin of ozone in the troposphere and stratosphere is analysed, by incorporating a diagnostics ("marked ozone origin tracers") into the models, which allows to identify the origin of ozone. In most regions the simulated local ozone concentration is dominated by local ozone production, i.e. less than 50% of the ozone at higher latitudes of the stratosphere is produced in the tropics, which conflicts with the idea that the tropics are the global source for stratospheric ozone. Although episodic stratospheric intrusions occur basically everywhere, the main ozone stratosphere-to-troposphere exchange is connected to exchange processes at the sub-tropical jet-stream. The simulated tropospheric influx of ozone amounts to 420 Tg per year, and originates in the Northern Hemisphere from the extra-tropical stratosphere, whereas in the Southern Hemisphere a re-circulation of tropical tropospheric ozone contributes most to the influx of ozone into the troposphere. In the model E39/C, the upper troposphere of both hemispheres is clearly dominated by tropical tropospheric ozone (40%–50%) except for northern summer hemisphere, where the tropospheric contribution (from the tropics as well as from the Northern Hemisphere) does not exceed 20%.
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Griffiths, Paul T., Lee T. Murray, Guang Zeng, Youngsub Matthew Shin, N. Luke Abraham, Alexander T. Archibald, Makoto Deushi, et al. "Tropospheric ozone in CMIP6 simulations." Atmospheric Chemistry and Physics 21, no. 5 (March 18, 2021): 4187–218. http://dx.doi.org/10.5194/acp-21-4187-2021.
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Abstract. The evolution of tropospheric ozone from 1850 to 2100 has been studied using data from Phase 6 of the Coupled Model Intercomparison Project (CMIP6). We evaluate long-term changes using coupled atmosphere–ocean chemistry–climate models, focusing on the CMIP Historical and ScenarioMIP ssp370 experiments, for which detailed tropospheric-ozone diagnostics were archived. The model ensemble has been evaluated against a suite of surface, sonde and satellite observations of the past several decades and found to reproduce well the salient spatial, seasonal and decadal variability and trends. The multi-model mean tropospheric-ozone burden increases from 247 ± 36 Tg in 1850 to a mean value of 356 ± 31 Tg for the period 2005–2014, an increase of 44 %. Modelled present-day values agree well with previous determinations (ACCENT: 336 ± 27 Tg; Atmospheric Chemistry and Climate Model Intercomparison Project, ACCMIP: 337 ± 23 Tg; Tropospheric Ozone Assessment Report, TOAR: 340 ± 34 Tg). In the ssp370 experiments, the ozone burden increases to 416 ± 35 Tg by 2100. The ozone budget has been examined over the same period using lumped ozone production (PO3) and loss (LO3) diagnostics. Both ozone production and chemical loss terms increase steadily over the period 1850 to 2100, with net chemical production (PO3-LO3) reaching a maximum around the year 2000. The residual term, which contains contributions from stratosphere–troposphere transport reaches a minimum around the same time before recovering in the 21st century, while dry deposition increases steadily over the period 1850–2100. Differences between the model residual terms are explained in terms of variation in tropopause height and stratospheric ozone burden.
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Parrella, J. P., D. J. Jacob, Q. Liang, Y. Zhang, L. J. Mickley, B. Miller, M. J. Evans, et al. "Tropospheric bromine chemistry: implications for present and pre-industrial ozone and mercury." Atmospheric Chemistry and Physics 12, no. 15 (August 1, 2012): 6723–40. http://dx.doi.org/10.5194/acp-12-6723-2012.
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Abstract. We present a new model for the global tropospheric chemistry of inorganic bromine (Bry) coupled to oxidant-aerosol chemistry in the GEOS-Chem chemical transport model (CTM). Sources of tropospheric Bry include debromination of sea-salt aerosol, photolysis and oxidation of short-lived bromocarbons, and transport from the stratosphere. Comparison to a GOME-2 satellite climatology of tropospheric BrO columns shows that the model can reproduce the observed increase of BrO with latitude, the northern mid-latitudes maximum in winter, and the Arctic maximum in spring. This successful simulation is contingent on the HOBr + HBr reaction taking place in aqueous aerosols and ice clouds. Bromine chemistry in the model decreases tropospheric ozone mixing ratios by <1–8 nmol mol−1 (6.5% globally), with the largest effects in the northern extratropics in spring. The global mean tropospheric OH concentration decreases by 4%. Inclusion of bromine chemistry improves the ability of global models (GEOS-Chem and p-TOMCAT) to simulate observed 19th-century ozone and its seasonality. Bromine effects on tropospheric ozone are comparable in the present-day and pre-industrial atmospheres so that estimates of anthropogenic radiative forcing are minimally affected. Br atom concentrations are 40% higher in the pre-industrial atmosphere due to lower ozone, which would decrease by a factor of 2 the atmospheric lifetime of elemental mercury against oxidation by Br. This suggests that historical anthropogenic mercury emissions may have mostly deposited to northern mid-latitudes, enriching the corresponding surface reservoirs. The persistent rise in background surface ozone at northern mid-latitudes during the past decades could possibly contribute to the observations of elevated mercury in subsurface waters of the North Atlantic.
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Wallington, T. J., J. H. Seinfeld, and J. R. Barker. "100 Years of Progress in Gas-Phase Atmospheric Chemistry Research." Meteorological Monographs 59 (January 1, 2019): 10.1–10.52. http://dx.doi.org/10.1175/amsmonographs-d-18-0008.1.
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Abstract Remarkable progress has occurred over the last 100 years in our understanding of atmospheric chemical composition, stratospheric and tropospheric chemistry, urban air pollution, acid rain, and the formation of airborne particles from gas-phase chemistry. Much of this progress was associated with the developing understanding of the formation and role of ozone and of the oxides of nitrogen, NO and NO2, in the stratosphere and troposphere. The chemistry of the stratosphere, emerging from the pioneering work of Chapman in 1931, was followed by the discovery of catalytic ozone cycles, ozone destruction by chlorofluorocarbons, and the polar ozone holes, work honored by the 1995 Nobel Prize in Chemistry awarded to Crutzen, Rowland, and Molina. Foundations for the modern understanding of tropospheric chemistry were laid in the 1950s and 1960s, stimulated by the eye-stinging smog in Los Angeles. The importance of the hydroxyl (OH) radical and its relationship to the oxides of nitrogen (NO and NO2) emerged. The chemical processes leading to acid rain were elucidated. The atmosphere contains an immense number of gas-phase organic compounds, a result of emissions from plants and animals, natural and anthropogenic combustion processes, emissions from oceans, and from the atmospheric oxidation of organics emitted into the atmosphere. Organic atmospheric particulate matter arises largely as gas-phase organic compounds undergo oxidation to yield low-volatility products that condense into the particle phase. A hundred years ago, quantitative theories of chemical reaction rates were nonexistent. Today, comprehensive computer codes are available for performing detailed calculations of chemical reaction rates and mechanisms for atmospheric reactions. Understanding the future role of atmospheric chemistry in climate change and, in turn, the impact of climate change on atmospheric chemistry, will be critical to developing effective policies to protect the planet.
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Zhang, H., S. Wu, Y. Huang, and Y. Wang. "Effects of stratospheric ozone recovery on photochemistry and ozone air quality in the troposphere." Atmospheric Chemistry and Physics 14, no. 8 (April 23, 2014): 4079–86. http://dx.doi.org/10.5194/acp-14-4079-2014.
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Abstract. There has been significant stratospheric ozone depletion since the late 1970s due to ozone-depleting substances (ODSs). With the implementation of the Montreal Protocol and its amendments and adjustments, stratospheric ozone is expected to recover towards its pre-1980 level in the coming decades. In this study, we examine the implications of stratospheric ozone recovery for the tropospheric chemistry and ozone air quality with a global chemical transport model (GEOS-Chem). With a full recovery of the stratospheric ozone, the projected increases in ozone column range from 1% over the low latitudes to more than 10% over the polar regions. The sensitivity factor of troposphere ozone photolysis rate, defined as the percentage changes in surface ozone photolysis rate for 1% increase in stratospheric ozone column, shows significant seasonal variation but is always negative with absolute value larger than one. The expected stratospheric ozone recovery is found to affect the tropospheric ozone destruction rates much more than the ozone production rates. Significant decreases in surface ozone photolysis rates due to stratospheric ozone recovery are simulated. The global average tropospheric OH decreases by 1.7%, and the global average lifetime of tropospheric ozone increases by 1.5%. The perturbations to tropospheric ozone and surface ozone show large seasonal and spatial variations. General increases in surface ozone are calculated for each season, with increases by up to 0.8 ppbv in the remote areas. Increases in ozone lifetime by up to 13% are found in the troposphere. The increased lifetimes of tropospheric ozone in response to stratospheric ozone recovery enhance the intercontinental transport of ozone and global pollution, in particular for the summertime. The global background ozone attributable to Asian emissions is calculated to increase by up to 15% or 0.3 ppbv in the Northern Hemisphere in response to the projected stratospheric ozone recovery.
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Revell, L. E., F. Tummon, A. Stenke, T. Sukhodolov, A. Coulon, E. Rozanov, H. Garny, V. Grewe, and T. Peter. "Drivers of the tropospheric ozone budget throughout the 21st century under the medium-high climate scenario RCP 6.0." Atmospheric Chemistry and Physics 15, no. 10 (May 27, 2015): 5887–902. http://dx.doi.org/10.5194/acp-15-5887-2015.
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Abstract. Because tropospheric ozone is both a greenhouse gas and harmful air pollutant, it is important to understand how anthropogenic activities may influence its abundance and distribution through the 21st century. Here, we present model simulations performed with the chemistry–climate model SOCOL, in which spatially disaggregated chemistry and transport tracers have been implemented in order to better understand the distribution and projected changes in tropospheric ozone. We examine the influences of ozone precursor emissions (nitrogen oxides (NOx), carbon monoxide (CO) and volatile organic compounds (VOCs)), climate change (including methane effects) and stratospheric ozone recovery on the tropospheric ozone budget, in a simulation following the climate scenario Representative Concentration Pathway (RCP) 6.0 (a medium-high, and reasonably realistic climate scenario). Changes in ozone precursor emissions have the largest effect, leading to a global-mean increase in tropospheric ozone which maximizes in the early 21st century at 23% compared to 1960. The increase is most pronounced at northern midlatitudes, due to regional emission patterns: between 1990 and 2060, northern midlatitude tropospheric ozone remains at constantly large abundances: 31% larger than in 1960. Over this 70-year period, attempts to reduce emissions in Europe and North America do not have an effect on zonally averaged northern midlatitude ozone because of increasing emissions from Asia, together with the long lifetime of ozone in the troposphere. A simulation with fixed anthropogenic ozone precursor emissions of NOx, CO and non-methane VOCs at 1960 conditions shows a 6% increase in global-mean tropospheric ozone by the end of the 21st century, with an 11 % increase at northern midlatitudes. This increase maximizes in the 2080s and is mostly caused by methane, which maximizes in the 2080s following RCP 6.0, and plays an important role in controlling ozone directly, and indirectly through its influence on other VOCs and CO. Enhanced flux of ozone from the stratosphere to the troposphere as well as climate change-induced enhancements in lightning NOx emissions also increase the tropospheric ozone burden, although their impacts are relatively small. Overall, the results show that under this climate scenario, ozone in the future is governed largely by changes in methane and NOx; methane induces an increase in tropospheric ozone that is approximately one-third of that caused by NOx. Climate impacts on ozone through changes in tropospheric temperature, humidity and lightning NOx remain secondary compared with emission strategies relating to anthropogenic emissions of NOx, such as fossil fuel burning. Therefore, emission policies globally have a critical role to play in determining tropospheric ozone evolution through the 21st century.
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Newsome, Ben, and Mat Evans. "Impact of uncertainties in inorganic chemical rate constants on tropospheric composition and ozone radiative forcing." Atmospheric Chemistry and Physics 17, no. 23 (December 4, 2017): 14333–52. http://dx.doi.org/10.5194/acp-17-14333-2017.
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Abstract. Chemical rate constants determine the composition of the atmosphere and how this composition has changed over time. They are central to our understanding of climate change and air quality degradation. Atmospheric chemistry models, whether online or offline, box, regional or global, use these rate constants. Expert panels evaluate laboratory measurements, making recommendations for the rate constants that should be used. This results in very similar or identical rate constants being used by all models. The inherent uncertainties in these recommendations are, in general, therefore ignored. We explore the impact of these uncertainties on the composition of the troposphere using the GEOS-Chem chemistry transport model. Based on the Jet Propulsion Laboratory (JPL) and International Union of Pure and Applied Chemistry (IUPAC) evaluations we assess the influence of 50 mainly inorganic rate constants and 10 photolysis rates on tropospheric composition through the use of the GEOS-Chem chemistry transport model. We assess the impact on four standard metrics: annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime. Uncertainty in the rate constants for NO2 + OH →M HNO3 and O3 + NO → NO2 + O2 are the two largest sources of uncertainty in these metrics. The absolute magnitude of the change in the metrics is similar if rate constants are increased or decreased by their σ values. We investigate two methods of assessing these uncertainties, addition in quadrature and a Monte Carlo approach, and conclude they give similar outcomes. Combining the uncertainties across the 60 reactions gives overall uncertainties on the annual mean tropospheric ozone burden, surface ozone and tropospheric OH concentrations, and tropospheric methane lifetime of 10, 11, 16 and 16 %, respectively. These are larger than the spread between models in recent model intercomparisons. Remote regions such as the tropics, poles and upper troposphere are most uncertain. This chemical uncertainty is sufficiently large to suggest that rate constant uncertainty should be considered alongside other processes when model results disagree with measurement. Calculations for the pre-industrial simulation allow a tropospheric ozone radiative forcing to be calculated of 0.412 ± 0.062 W m−2. This uncertainty (13 %) is comparable to the inter-model spread in ozone radiative forcing found in previous model–model intercomparison studies where the rate constants used in the models are all identical or very similar. Thus, the uncertainty of tropospheric ozone radiative forcing should expanded to include this additional source of uncertainty. These rate constant uncertainties are significant and suggest that refinement of supposedly well-known chemical rate constants should be considered alongside other improvements to enhance our understanding of atmospheric processes.
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Finney, D. L., R. M. Doherty, O. Wild, and N. L. Abraham. "The impact of lightning on tropospheric ozone chemistry using a new global lightning parametrisation." Atmospheric Chemistry and Physics 16, no. 12 (June 17, 2016): 7507–22. http://dx.doi.org/10.5194/acp-16-7507-2016.
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Abstract. A lightning parametrisation based on upward cloud ice flux is implemented in a chemistry–climate model (CCM) for the first time. The UK Chemistry and Aerosols model is used to study the impact of these lightning nitric oxide (NO) emissions on ozone. Comparisons are then made between the new ice flux parametrisation and the commonly used, cloud-top height parametrisation. The ice flux approach improves the simulation of lightning and the temporal correlations with ozone sonde measurements in the middle and upper troposphere. Peak values of ozone in these regions are attributed to high lightning NO emissions. The ice flux approach reduces the overestimation of tropical lightning apparent in this CCM when using the cloud-top approach. This results in less NO emission in the tropical upper troposphere and more in the extratropics when using the ice flux scheme. In the tropical upper troposphere the reduction in ozone concentration is around 5–10 %. Surprisingly, there is only a small reduction in tropospheric ozone burden when using the ice flux approach. The greatest absolute change in ozone burden is found in the lower stratosphere, suggesting that much of the ozone produced in the upper troposphere is transported to higher altitudes. Major differences in the frequency distribution of flash rates for the two approaches are found. The cloud-top height scheme has lower maximum flash rates and more mid-range flash rates than the ice flux scheme. The initial Ox (odd oxygen species) production associated with the frequency distribution of continental lightning is analysed to show that higher flash rates are less efficient at producing Ox; low flash rates initially produce around 10 times more Ox per flash than high-end flash rates. We find that the newly implemented lightning scheme performs favourably compared to the cloud-top scheme with respect to simulation of lightning and tropospheric ozone. This alternative lightning scheme shows spatial and temporal differences in ozone chemistry which may have implications for comparison between models and observations, as well as for simulation of future changes in tropospheric ozone.
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Shindell, D. T., O. Pechony, A. Voulgarakis, G. Faluvegi, L. Nazarenko, J. F. Lamarque, K. Bowman, et al. "Interactive ozone and methane chemistry in GISS-E2 historical and future climate simulations." Atmospheric Chemistry and Physics 13, no. 5 (March 5, 2013): 2653–89. http://dx.doi.org/10.5194/acp-13-2653-2013.
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Abstract. The new generation GISS climate model includes fully interactive chemistry related to ozone in historical and future simulations, and interactive methane in future simulations. Evaluation of ozone, its tropospheric precursors, and methane shows that the model captures much of the large-scale spatial structure seen in recent observations. While the model is much improved compared with the previous chemistry-climate model, especially for ozone seasonality in the stratosphere, there is still slightly too rapid stratospheric circulation, too little stratosphere-to-troposphere ozone flux in the Southern Hemisphere and an Antarctic ozone hole that is too large and persists too long. Quantitative metrics of spatial and temporal correlations with satellite datasets as well as spatial autocorrelation to examine transport and mixing are presented to document improvements in model skill and provide a benchmark for future evaluations. The difference in radiative forcing (RF) calculated using modeled tropospheric ozone versus tropospheric ozone observed by TES is only 0.016 W m−2. Historical 20th Century simulations show a steady increase in whole atmosphere ozone RF through 1970 after which there is a decrease through 2000 due to stratospheric ozone depletion. Ozone forcing increases throughout the 21st century under RCP8.5 owing to a projected recovery of stratospheric ozone depletion and increases in methane, but decreases under RCP4.5 and 2.6 due to reductions in emissions of other ozone precursors. RF from methane is 0.05 to 0.18 W m−2 higher in our model calculations than in the RCP RF estimates. The surface temperature response to ozone through 1970 follows the increase in forcing due to tropospheric ozone. After that time, surface temperatures decrease as ozone RF declines due to stratospheric depletion. The stratospheric ozone depletion also induces substantial changes in surface winds and the Southern Ocean circulation, which may play a role in a slightly stronger response per unit forcing during later decades. Tropical precipitation shifts south during boreal summer from 1850 to 1970, but then shifts northward from 1970 to 2000, following upper tropospheric temperature gradients more strongly than those at the surface.
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Saiz-Lopez, A., R. P. Fernandez, C. Ordóñez, D. E. Kinnison, J. C. Gómez Martín, J. F. Lamarque, and S. Tilmes. "Iodine chemistry in the troposphere and its effect on ozone." Atmospheric Chemistry and Physics Discussions 14, no. 14 (August 1, 2014): 19985–20044. http://dx.doi.org/10.5194/acpd-14-19985-2014.
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Abstract. Despite potential influence of iodine chemistry on the oxidizing capacity of the troposphere, reactive iodine distributions and their impact on tropospheric ozone remain nearly unexplored aspects of the global atmosphere. Here we present a comprehensive global modelling experiment aimed at estimating lower and upper limits of the inorganic iodine burden and its impact on tropospheric ozone. Two sets of simulations without and with the photolysis of IxOy oxides (i.e., I2O2, I2O3 and I2O4) were conducted to define the range of inorganic iodine loading, partitioning and impact in the troposphere. Our results show that the most abundant daytime iodine species throughout the middle to upper troposphere is atomic iodine, with an annual average tropical abundance of (0.15–0.55) pptv. We propose the existence of a "tropical ring of atomic iodine" that peaks in the tropical upper troposphere (∼11–14 km) at the Equator and extends to the sub-tropics (30° N–30° S). Annual average daytime I / IO ratios larger than 3 are modelled within the tropics, reaching ratios up to ∼20 during vigorous uplift events within strong convective regions. We calculate that the integrated contribution of catalytic iodine reactions to the total rate of tropospheric ozone loss (IOxLoss) is 2–5 times larger than the combined bromine and chlorine cycles. IOxLoss cycles, without and with IxOy photolysis, represent approximately (17–27)%, (8–14)% and (11–27)% of the tropical annual ozone loss for the marine boundary layer (MBL), free troposphere (FT) and upper troposphere (UT), respectively. Our results indicate that iodine is the second strongest ozone depleting family throughout the global marine UT and in the tropical MBL. We suggest (i) iodine sources and its chemistry need to be included in global tropospheric chemistry models, (ii) experimental programs designed to quantify the iodine budget in the troposphere should include a strategy for the measurement of atomic I, and (iii) laboratory programs are needed to characterize the photochemistry of higher iodine oxides to determine their atmospheric fate since they can potentially dominate halogen-catalysed ozone destruction in the troposphere.
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Prados-Roman, C., C. A. Cuevas, R. P. Fernandez, D. E. Kinnison, J.-F. Lamarque, and A. Saiz-Lopez. "A negative feedback between anthropogenic ozone pollution and enhanced ocean emissions of iodine." Atmospheric Chemistry and Physics 15, no. 4 (February 27, 2015): 2215–24. http://dx.doi.org/10.5194/acp-15-2215-2015.
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Abstract. Naturally emitted from the oceans, iodine compounds efficiently destroy atmospheric ozone and reduce its positive radiative forcing effects in the troposphere. Emissions of inorganic iodine have been experimentally shown to depend on the deposition to the oceans of tropospheric ozone, whose concentrations have significantly increased since 1850 as a result of human activities. A chemistry–climate model is used herein to quantify the current ocean emissions of inorganic iodine and assess the impact that the anthropogenic increase in tropospheric ozone has had on the natural cycle of iodine in the marine environment since pre-industrial times. Our results indicate that the human-driven enhancement of tropospheric ozone has doubled the oceanic inorganic iodine emissions following the reaction of ozone with iodide at the sea surface. The consequent build-up of atmospheric iodine, with maximum enhancements of up to 70% with respect to pre-industrial times in continental pollution outflow regions, has in turn accelerated the ozone chemical loss over the oceans with strong spatial patterns. We suggest that this ocean–atmosphere interaction represents a negative geochemical feedback loop by which current ocean emissions of iodine act as a natural buffer for ozone pollution and its radiative forcing in the global marine environment.
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Williams, Ryan S., Michaela I. Hegglin, Brian J. Kerridge, Patrick Jöckel, Barry G. Latter, and David A. Plummer. "Characterising the seasonal and geographical variability in tropospheric ozone, stratospheric influence and recent changes." Atmospheric Chemistry and Physics 19, no. 6 (March 21, 2019): 3589–620. http://dx.doi.org/10.5194/acp-19-3589-2019.
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Abstract. The stratospheric contribution to tropospheric ozone (O3) has been a subject of much debate in recent decades but is known to have an important influence. Recent improvements in diagnostic and modelling tools provide new evidence that the stratosphere has a much larger influence than previously thought. This study aims to characterise the seasonal and geographical distribution of tropospheric ozone, its variability, and its changes and provide quantification of the stratospheric influence on these measures. To this end, we evaluate hindcast specified-dynamics chemistry–climate model (CCM) simulations from the European Centre for Medium-Range Weather Forecasts – Hamburg (ECHAM)/Modular Earth Submodel System (MESSy) Atmospheric Chemistry (EMAC) model and the Canadian Middle Atmosphere Model (CMAM), as contributed to the International Global Atmospheric Chemistry – Stratosphere-troposphere Processes And their Role in Climate (IGAC-SPARC) (IGAC–SPARC) Chemistry Climate Model Initiative (CCMI) activity, together with satellite observations from the Ozone Monitoring Instrument (OMI) and ozone-sonde profile measurements from the World Ozone and Ultraviolet Radiation Data Centre (WOUDC) over a period of concurrent data availability (2005–2010). An overall positive, seasonally dependent bias in 1000–450 hPa (∼0–5.5 km) sub-column ozone is found for EMAC, ranging from 2 to 8 Dobson units (DU), whereas CMAM is found to be in closer agreement with the observations, although with substantial seasonal and regional variation in the sign and magnitude of the bias (∼±4 DU). Although the application of OMI averaging kernels (AKs) improves agreement with model estimates from both EMAC and CMAM as expected, comparisons with ozone-sondes indicate a positive ozone bias in the lower stratosphere in CMAM, together with a negative bias in the troposphere resulting from a likely underestimation of photochemical ozone production. This has ramifications for diagnosing the level of model–measurement agreement. Model variability is found to be more similar in magnitude to that implied from ozone-sondes in comparison with OMI, which has significantly larger variability. Noting the overall consistency of the CCMs, the influence of the model chemistry schemes and internal dynamics is discussed in relation to the inter-model differences found. In particular, it is inferred that CMAM simulates a faster and shallower Brewer–Dobson circulation (BDC) compared to both EMAC and observational estimates, which has implications for the distribution and magnitude of the downward flux of stratospheric ozone over the most recent climatological period (1980–2010). Nonetheless, it is shown that the stratospheric influence on tropospheric ozone is significant and is estimated to exceed 50 % in the wintertime extratropics, even in the lower troposphere. Finally, long-term changes in the CCM ozone tracers are calculated for different seasons. An overall statistically significant increase in tropospheric ozone is found across much of the world but particularly in the Northern Hemisphere and in the middle to upper troposphere, where the increase is on the order of 4–6 ppbv (5 %–10 %) between 1980–1989 and 2001–2010. Our model study implies that attribution from stratosphere–troposphere exchange (STE) to such ozone changes ranges from 25 % to 30 % at the surface to as much as 50 %–80 % in the upper troposphere–lower stratosphere (UTLS) across some regions of the world, including western Eurasia, eastern North America, the South Pacific and the southern Indian Ocean. These findings highlight the importance of a well-resolved stratosphere in simulations of tropospheric ozone and its implications for the radiative forcing, air quality and oxidation capacity of the troposphere.
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Hess, P., D. Kinnison, and Q. Tang. "Ensemble simulations of the role of the stratosphere in the attribution of northern extratropical tropospheric ozone variability." Atmospheric Chemistry and Physics 15, no. 5 (March 4, 2015): 2341–65. http://dx.doi.org/10.5194/acp-15-2341-2015.
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Abstract. Despite the need to understand the impact of changes in emissions and climate on tropospheric ozone, the attribution of tropospheric interannual ozone variability to specific processes has proven difficult. Here, we analyze the stratospheric contribution to tropospheric ozone variability and trends from 1953 to 2005 in the Northern Hemisphere (NH) mid-latitudes using four ensemble simulations of the free running (FR) Whole Atmosphere Community Climate Model (WACCM). The simulations are externally forced with observed time-varying (1) sea-surface temperatures (SSTs), (2) greenhouse gases (GHGs), (3) ozone depleting substances (ODS), (4) quasi-biennial oscillation (QBO), (5) solar variability (SV) and (6) stratospheric sulfate surface area density (SAD). A detailed representation of stratospheric chemistry is simulated, including the ozone loss due to volcanic eruptions and polar stratospheric clouds. In the troposphere, ozone production is represented by CH4–NOx smog chemistry, where surface chemical emissions remain interannually constant. Despite the simplicity of its tropospheric chemistry, at many NH measurement locations, the interannual ozone variability in the FR WACCM simulations is significantly correlated with the measured interannual variability. This suggests the importance of the external forcing applied in these simulations in driving interannual ozone variability. The variability and trend in the simulated 1953–2005 tropospheric ozone from 30 to 90° N at background surface measurement sites, 500 hPa measurement sites and in the area average are largely explained on interannual timescales by changes in the 30–90° N area averaged flux of ozone across the 100 hPa surface and changes in tropospheric methane concentrations. The average sensitivity of tropospheric ozone to methane (percent change in ozone to a percent change in methane) from 30 to 90° N is 0.17 at 500 hPa and 0.21 at the surface; the average sensitivity of tropospheric ozone to the 100 hPa ozone flux (percent change in ozone to a percent change in the ozone flux) from 30 to 90° N is 0.19 at 500 hPa and 0.11 at the surface. The 30–90° N simulated downward residual velocity at 100 hPa increased by 15% between 1953 and 2005. However, the impact of this on the 30–90° N 100 hPa ozone flux is modulated by the long-term changes in stratospheric ozone. The ozone flux decreases from 1965 to 1990 due to stratospheric ozone depletion, but increases again by approximately 7% from 1990 to 2005. The first empirical orthogonal function of interannual ozone variability explains from 40% (at the surface) to over 80% (at 150 hPa) of the simulated ozone interannual variability from 30 to 90° N. This identified mode of ozone variability shows strong stratosphere–troposphere coupling, demonstrating the importance of the stratosphere in an attribution of tropospheric ozone variability. The simulations, with no change in emissions, capture almost 50% of the measured ozone change during the 1990s at a variety of locations. This suggests that a large portion of the measured change is not due to changes in emissions, but can be traced to changes in large-scale modes of ozone variability. This emphasizes the difficulty in the attribution of ozone changes, and the importance of natural variability in understanding the trends and variability of ozone. We find little relation between the El Niño–Southern Oscillation (ENSO) index and large-scale tropospheric ozone variability over the long-term record.
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Zyryanov, D., G. Foret, M. Eremenko, M. Beekmann, J. P. Cammas, M. D'Isidoro, H. Elbern, et al. "3-D evaluation of tropospheric ozone simulations by an ensemble of regional Chemistry Transport Model." Atmospheric Chemistry and Physics 12, no. 7 (April 3, 2012): 3219–40. http://dx.doi.org/10.5194/acp-12-3219-2012.
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Abstract. A detailed 3-D evaluation of an ensemble of five regional Chemistry Transport Models (RCTM) and one global CTM with focus on free tropospheric ozone over Europe is presented. It is performed over a summer period (June to August 2008) in the context of the GEMS-RAQ project. A data set of about 400 vertical ozone profiles from balloon soundings and commercial aircraft at 11 different locations is used for model evaluation, in addition to satellite measurements with the infrared nadir sounder (IASI) showing largest sensitivity to free tropospheric ozone. In the middle troposphere, the four regional models using the same top and boundary conditions from IFS-MOZART exhibit a systematic negative bias with respect to observed profiles of about −20%. Root Mean Square Error (RMSE) values are constantly growing with altitude, from 22% to 32% to 53%, respectively for 0–2 km, 2–8 km and 8–10 km height ranges. Lowest correlation is found in the middle troposphere, with minimum coefficients (R) between 0.2 to 0.45 near 8 km, as compared to 0.7 near the surface and similar values around 10 km. A sensitivity test made with the CHIMERE mode also shows that using hourly instead of monthly chemical boundary conditions generally improves the model skill (i.e. improve RMSE and correlation). Lower tropospheric 0–6 km partial ozone columns derived from IASI show a clear North-South gradient over Europe, which is qualitatively reproduced by the models. Also the temporal variability showing decreasing ozone concentrations in the lower troposphere (0–6 km columns) during summer is well reproduced by models even if systematic bias remains (the value of the bias being also controlled by the type of used boundary conditions). A multi-day case study of a trough with low tropopause was conducted and showed that both IASI and models were able to resolve strong horizontal gradients of middle and upper tropospheric ozone occurring in the vicinity of an upper tropospheric frontal zone.
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Voulgarakis, A., O. Wild, N. H. Savage, G. D. Carver, and J. A. Pyle. "Clouds, photolysis and regional tropospheric ozone budgets." Atmospheric Chemistry and Physics 9, no. 21 (November 3, 2009): 8235–46. http://dx.doi.org/10.5194/acp-9-8235-2009.
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Abstract. We use a three-dimensional chemical transport model to examine the shortwave radiative effects of clouds on the tropospheric ozone budget. In addition to looking at changes in global concentrations as previous studies have done, we examine changes in ozone chemical production and loss caused by clouds and how these vary in different parts of the troposphere. On a global scale, we find that clouds have a modest effect on ozone chemistry, but on a regional scale their role is much more significant, with the size of the response dependent on the region. The largest averaged changes in chemical budgets (±10–14%) are found in the marine troposphere, where cloud optical depths are high. We demonstrate that cloud effects are small on average in the middle troposphere because this is a transition region between reduction and enhancement in photolysis rates. We show that increases in boundary layer ozone due to clouds are driven by large-scale changes in downward ozone transport from higher in the troposphere rather than by decreases in in-situ ozone chemical loss rates. Increases in upper tropospheric ozone are caused by higher production rates due to backscattering of radiation and consequent increases in photolysis rates, mainly J(NO2). The global radiative effect of clouds on isoprene, through decreases of OH in the lower troposphere, is stronger than on ozone. Tropospheric isoprene lifetime increases by 7% when taking clouds into account. We compare the importance of clouds in contributing to uncertainties in the global ozone budget with the role of other radiatively-important factors. The budget is most sensitive to the overhead ozone column, while surface albedo and clouds have smaller effects. However, uncertainty in representing the spatial distribution of clouds may lead to a large sensitivity of the ozone budget components on regional scales.
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Hu, Y., Y. Xia, and Q. Fu. "Tropospheric temperature response to stratospheric ozone recovery in the 21st century." Atmospheric Chemistry and Physics 11, no. 15 (August 2, 2011): 7687–99. http://dx.doi.org/10.5194/acp-11-7687-2011.
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Abstract. Recent simulations predicted that the stratospheric ozone layer will likely return to pre-1980 levels in the middle of the 21st century, as a result of the decline of ozone depleting substances under the Montreal Protocol. Since the ozone layer is an important component in determining stratospheric and tropospheric-surface energy balance, the recovery of stratospheric ozone may have significant impact on tropospheric-surface climate. Here, using multi-model results from both the Intergovernmental Panel on Climate Change Fourth Assessment Report (IPCC-AR4) models and coupled chemistry-climate models, we show that as ozone recovery is considered, the troposphere is warmed more than that without considering ozone recovery, suggesting an enhancement of tropospheric warming due to ozone recovery. It is found that the enhanced tropospheric warming is mostly significant in the upper troposphere, with a global and annual mean magnitude of ~0.41 K for 2001–2050. We also find that relatively large enhanced warming occurs in the extratropics and polar regions in summer and autumn in both hemispheres, while the enhanced warming is stronger in the Northern Hemisphere than in the Southern Hemisphere. Enhanced warming is also found at the surface. The global and annual mean enhancement of surface warming is about 0.16 K for 2001–2050, with maximum enhancement in the winter Arctic.
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Koo, J. H., Y. Wang, T. P. Kurosu, K. Chance, A. Rozanov, A. Richter, S. J. Oltmans, et al. "Characteristics of tropospheric ozone depletion events in the Arctic spring: analysis of the ARCTAS, ARCPAC, and ARCIONS measurements and satellite BrO observations." Atmospheric Chemistry and Physics 12, no. 20 (October 29, 2012): 9909–22. http://dx.doi.org/10.5194/acp-12-9909-2012.
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Abstract. Arctic ozone depletion events (ODEs) are caused by halogen catalyzed ozone loss. In situ chemistry, advection of ozone-poor air mass, and vertical mixing in the lower troposphere are important factors affecting ODEs. To better characterize the ODEs, we analyze the combined set of surface, ozonesonde, and aircraft in situ measurements of ozone and bromine compounds during the Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS), the Aerosol, Radiation, and Cloud Processes affecting Arctic Climate (ARCPAC), and the Arctic Intensive Ozonesonde Network Study (ARCIONS) experiments (April 2008). Tropospheric BrO columns retrieved from satellite measurements and back trajectory calculations are also used to investigate the characteristics of observed ODEs. In situ observations from these field experiments are inadequate to validate tropospheric BrO columns derived from satellite measurements. In view of this difficulty, we construct an ensemble of tropospheric column BrO estimates from two satellite (OMI and GOME-2) measurements and with three independent methods of calculating stratospheric BrO columns. Furthermore, we select analysis methods that do not depend on the absolute magnitude of column BrO, such as time-lagged correlation analysis of ozone and tropospheric column BrO, to understand characteristics of ODEs. Time-lagged correlation analysis between in situ (surface and ozonesonde) measurements of ozone and satellite derived tropospheric BrO columns indicates that the ODEs are due to either local halogen-driven ozone loss or short-range (∼1 day) transport from nearby regions with ozone depletion. The effect of in situ ozone loss is also evident in the diurnal variation difference between low (10th and 25th percentiles) and higher percentiles of surface ozone concentrations at Alert, Canada. Aircraft observations indicate low-ozone air mass transported from adjacent high-BrO regions. Correlation analyses of ozone with potential temperature and time-lagged tropospheric BrO column show that the vertical extent of local ozone loss is surprisingly deep (1–2 km) at Resolute and Churchill, Canada. The unstable boundary layer during ODEs at Churchill could potentially provide a source of free-tropospheric BrO through convective transport and explain the significant negative correlation between free-tropospheric ozone and tropospheric BrO column at this site.
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Kuai, Le, Kevin W. Bowman, Kazuyuki Miyazaki, Makoto Deushi, Laura Revell, Eugene Rozanov, Fabien Paulot, et al. "Attribution of Chemistry-Climate Model Initiative (CCMI) ozone radiative flux bias from satellites." Atmospheric Chemistry and Physics 20, no. 1 (January 8, 2020): 281–301. http://dx.doi.org/10.5194/acp-20-281-2020.
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Abstract. The top-of-atmosphere (TOA) outgoing longwave flux over the 9.6 µm ozone band is a fundamental quantity for understanding chemistry–climate coupling. However, observed TOA fluxes are hard to estimate as they exhibit considerable variability in space and time that depend on the distributions of clouds, ozone (O3), water vapor (H2O), air temperature (Ta), and surface temperature (Ts). Benchmarking present-day fluxes and quantifying the relative influence of their drivers is the first step for estimating climate feedbacks from ozone radiative forcing and predicting radiative forcing evolution. To that end, we constructed observational instantaneous radiative kernels (IRKs) under clear-sky conditions, representing the sensitivities of the TOA flux in the 9.6 µm ozone band to the vertical distribution of geophysical variables, including O3, H2O, Ta, and Ts based upon the Aura Tropospheric Emission Spectrometer (TES) measurements. Applying these kernels to present-day simulations from the Chemistry-Climate Model Initiative (CCMI) project as compared to a 2006 reanalysis assimilating satellite observations, we show that the models have large differences in TOA flux, attributable to different geophysical variables. In particular, model simulations continue to diverge from observations in the tropics, as reported in previous studies of the Atmospheric Chemistry Climate Model Intercomparison Project (ACCMIP) simulations. The principal culprits are tropical middle and upper tropospheric ozone followed by tropical lower tropospheric H2O. Five models out of the eight studied here have TOA flux biases exceeding 100 mW m−2 attributable to tropospheric ozone bias. Another set of five models have flux biases over 50 mW m−2 due to H2O. On the other hand, Ta radiative bias is negligible in all models (no more than 30 mW m−2). We found that the atmospheric component (AM3) of the Geophysical Fluid Dynamics Laboratory (GFDL) general circulation model and Canadian Middle Atmosphere Model (CMAM) have the lowest TOA flux biases globally but are a result of cancellation of opposite biases due to different processes. Overall, the multi-model ensemble mean bias is -133±98 mW m−2, indicating that they are too atmospherically opaque due to trapping too much radiation in the atmosphere by overestimated tropical tropospheric O3 and H2O. Having too much O3 and H2O in the troposphere would have different impacts on the sensitivity of TOA flux to O3 and these competing effects add more uncertainties on the ozone radiative forcing. We find that the inter-model TOA outgoing longwave radiation (OLR) difference is well anti-correlated with their ozone band flux bias. This suggests that there is significant radiative compensation in the calculation of model outgoing longwave radiation.
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Roelofs, G. J., H. A. Scheeren, J. Heland, H. Ziereis, and J. Lelieveld. "A model study of ozone in the eastern Mediterranean free troposphere during MINOS (August 2001)." Atmospheric Chemistry and Physics 3, no. 4 (August 14, 2003): 1199–210. http://dx.doi.org/10.5194/acp-3-1199-2003.
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Abstract. A coupled tropospheric chemistry-climate model is used to analyze tropospheric ozone distributions observed during the MINOS campaign in the eastern Mediterranean region (August, 2001). Modeled ozone profiles are generally in good agreement with the observations. Our analysis shows that the atmospheric dynamics in the region are strongly influenced by the occurrence of an upper tropospheric anti-cyclone, associated with the Asian summer monsoon and centered over the Tibetan Plateau. The anti-cyclone affects the chemical composition of the upper troposphere, where ozone concentrations of about 50 ppbv were measured, through advection of boundary layer air from South-East Asia. A layer between 4-6 km thickness was present beneath, containing up to 120 ppbv of ozone with substantial contributions by transport from the stratosphere and through lightning NOx. Additionally, pollutant ozone from North America was mixed in. Ozone in the lower troposphere originated mainly from the European continent. The stratospheric influence may be overestimated due to too strong vertical diffusion associated with the relatively coarse vertical resolution. The estimated tropospheric ozone column over the eastern Mediterranean is ~50 DU in summer, to which ozone from recent stratospheric origin contributes about 30%, ozone from lightning 13%, and from South-East Asia, North America and Europe about 7%, 8% and 14%, respectively, adding to a long-term hemispheric background of 25% of the column.
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Emili, E., B. Barret, S. Massart, E. Le Flochmoen, A. Piacentini, L. El Amraoui, O. Pannekoucke, and D. Cariolle. "Combined assimilation of IASI and MLS observations to constrain tropospheric and stratospheric ozone in a global chemical transport model." Atmospheric Chemistry and Physics 14, no. 1 (January 8, 2014): 177–98. http://dx.doi.org/10.5194/acp-14-177-2014.
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Abstract. Accurate and temporally resolved fields of free-troposphere ozone are of major importance to quantify the intercontinental transport of pollution and the ozone radiative forcing. We consider a global chemical transport model (MOdèle de Chimie Atmosphérique à Grande Échelle, MOCAGE) in combination with a linear ozone chemistry scheme to examine the impact of assimilating observations from the Microwave Limb Sounder (MLS) and the Infrared Atmospheric Sounding Interferometer (IASI). The assimilation of the two instruments is performed by means of a variational algorithm (4D-VAR) and allows to constrain stratospheric and tropospheric ozone simultaneously. The analysis is first computed for the months of August and November 2008 and validated against ozonesonde measurements to verify the presence of observations and model biases. Furthermore, a longer analysis of 6 months (July–December 2008) showed that the combined assimilation of MLS and IASI is able to globally reduce the uncertainty (root mean square error, RMSE) of the modeled ozone columns from 30 to 15% in the upper troposphere/lower stratosphere (UTLS, 70–225 hPa). The assimilation of IASI tropospheric ozone observations (1000–225 hPa columns, TOC – tropospheric O3 column) decreases the RMSE of the model from 40 to 20% in the tropics (30° S–30° N), whereas it is not effective at higher latitudes. Results are confirmed by a comparison with additional ozone data sets like the Measurements of OZone and wAter vapour by aIrbus in-service airCraft (MOZAIC) data, the Ozone Monitoring Instrument (OMI) total ozone columns and several high-altitude surface measurements. Finally, the analysis is found to be insensitive to the assimilation parameters. We conclude that the combination of a simplified ozone chemistry scheme with frequent satellite observations is a valuable tool for the long-term analysis of stratospheric and free-tropospheric ozone.
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Abalos, Marta, Clara Orbe, Douglas E. Kinnison, David Plummer, Luke D. Oman, Patrick Jöckel, Olaf Morgenstern, et al. "Future trends in stratosphere-to-troposphere transport in CCMI models." Atmospheric Chemistry and Physics 20, no. 11 (June 11, 2020): 6883–901. http://dx.doi.org/10.5194/acp-20-6883-2020.
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Abstract. One of the key questions in the air quality and climate sciences is how tropospheric ozone concentrations will change in the future. This will depend on two factors: changes in stratosphere-to-troposphere transport (STT) and changes in tropospheric chemistry. Here we aim to identify robust changes in STT using simulations from the Chemistry Climate Model Initiative (CCMI) under a common climate change scenario (RCP6.0). We use two idealized stratospheric tracers to isolate changes in transport: stratospheric ozone (O3S), which is exactly like ozone but has no chemical sources in the troposphere, and st80, a passive tracer with fixed volume mixing ratio in the stratosphere. We find a robust increase in the tropospheric columns of these two tracers across the models. In particular, stratospheric ozone in the troposphere is projected to increase 10 %–16 % by the end of the 21st century in the RCP6.0 scenario. Future STT is enhanced in the subtropics due to the strengthening of the shallow branch of the Brewer–Dobson circulation (BDC) in the lower stratosphere and of the upper part of the Hadley cell in the upper troposphere. The acceleration of the deep branch of the BDC in the Northern Hemisphere (NH) and changes in eddy transport contribute to increased STT at high latitudes. These STT trends are caused by greenhouse gas (GHG) increases, while phasing out of ozone-depleting substances (ODS) does not lead to robust transport changes. Nevertheless, the decline of ODS increases the reservoir of ozone in the lower stratosphere, which results in enhanced STT of O3S at middle and high latitudes. A higher emission scenario (RCP8.5) produces stronger STT trends, with increases in tropospheric column O3S more than 3 times larger than those in the RCP6.0 scenario by the end of the 21st century.
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Jacob, D. "Heterogeneous chemistry and tropospheric ozone." Atmospheric Environment 34, no. 12-14 (2000): 2131–59. http://dx.doi.org/10.1016/s1352-2310(99)00462-8.
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Prados-Roman, C., C. A. Cuevas, R. P. Fernandez, D. E. Kinnison, J. F. Lamarque, and A. Saiz-Lopez. "A negative feedback between anthropogenic ozone pollution and enhanced ocean emissions of iodine." Atmospheric Chemistry and Physics Discussions 14, no. 15 (August 27, 2014): 21917–42. http://dx.doi.org/10.5194/acpd-14-21917-2014.
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Abstract. Naturally emitted from the oceans, iodine compounds efficiently destroy atmospheric ozone and reduce its positive radiative forcing effects in the troposphere. Emissions of inorganic iodine have been experimentally shown to depend on the deposition to the oceans of tropospheric ozone, whose concentrations have significantly increased since 1850 as a result of human activities. A chemistry-climate model is used herein to quantify the current ocean emissions of inorganic iodine and assess the impact that the anthropogenic increase of tropospheric ozone has had on the natural cycle of iodine in the marine environment since pre-industrial times. Our results indicate that the human-driven enhancement of tropospheric ozone has doubled the oceanic inorganic iodine emissions following the reaction of ozone with iodide at the sea surface. The consequent build-up of atmospheric iodine, with maximum enhancements of up to 70% with respect to preindustrial times in continental pollution outflow regions, has in turn accelerated the ozone chemical loss over the oceans with strong spatial patterns. We suggest that this ocean–atmosphere interaction represents a negative geochemical feedback loop by which current ocean emissions of iodine act as a natural buffer for ozone pollution and its radiative forcing in the global marine environment.
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Zeng, G., J. A. Pyle, and P. J. Young. "Impact of climate change on tropospheric ozone and its global budgets." Atmospheric Chemistry and Physics 8, no. 2 (January 29, 2008): 369–87. http://dx.doi.org/10.5194/acp-8-369-2008.
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Abstract. We present the chemistry-climate model UMCAM in which a relatively detailed tropospheric chemical module has been incorporated into the UK Met Office's Unified Model version 4.5. We obtain good agreements between the modelled ozone/nitrogen species and a range of observations including surface ozone measurements, ozone sonde data, and some aircraft campaigns. Four 2100 calculations assess model responses to projected changes of anthropogenic emissions (SRES A2), climate change (due to doubling CO2), and idealised climate change-associated changes in biogenic emissions (i.e. 50% increase of isoprene emission and doubling emissions of soil-NOx). The global tropospheric ozone burden increases significantly for all the 2100 A2 simulations, with the largest response caused by the increase of anthropogenic emissions. Climate change has diverse impacts on O3 and its budgets through changes in circulation and meteorological variables. Increased water vapour causes a substantial ozone reduction especially in the tropical lower troposphere (>10 ppbv reduction over the tropical ocean). On the other hand, an enhanced stratosphere-troposphere exchange of ozone, which increases by 80% due to doubling CO2, contributes to ozone increases in the extratropical free troposphere which subsequently propagate to the surface. Projected higher temperatures favour ozone chemical production and PAN decomposition which lead to high surface ozone levels in certain regions. Enhanced convection transports ozone precursors more rapidly out of the boundary layer resulting in an increase of ozone production in the free troposphere. Lightning-produced NOx increases by about 22% in the doubled CO2 climate and contributes to ozone production. The response to the increase of isoprene emissions shows that the change of ozone is largely determined by background NOx levels: high NOx environment increases ozone production; isoprene emitting regions with low NOx levels see local ozone decreases, and increase of ozone levels in the remote region due to the influence of PAN chemistry. The calculated ozone changes in response to a 50% increase of isoprene emissions are in the range of between −8 ppbv to 6 ppbv. Doubling soil-NOx emissions will increase tropospheric ozone considerably, with up to 5 ppbv in source regions.
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Lamarque, J. F., L. K. Emmons, P. G. Hess, D. E. Kinnison, S. Tilmes, F. Vitt, C. L. Heald, et al. "CAM-chem: description and evaluation of interactive atmospheric chemistry in the Community Earth System Model." Geoscientific Model Development 5, no. 2 (March 27, 2012): 369–411. http://dx.doi.org/10.5194/gmd-5-369-2012.
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Abstract. We discuss and evaluate the representation of atmospheric chemistry in the global Community Atmosphere Model (CAM) version 4, the atmospheric component of the Community Earth System Model (CESM). We present a variety of configurations for the representation of tropospheric and stratospheric chemistry, wet removal, and online and offline meteorology. Results from simulations illustrating these configurations are compared with surface, aircraft and satellite observations. Major biases include a negative bias in the high-latitude CO distribution, a positive bias in upper-tropospheric/lower-stratospheric ozone, and a positive bias in summertime surface ozone (over the United States and Europe). The tropospheric net chemical ozone production varies significantly between configurations, partly related to variations in stratosphere-troposphere exchange. Aerosol optical depth tends to be underestimated over most regions, while comparison with aerosol surface measurements over the United States indicate reasonable results for sulfate , especially in the online simulation. Other aerosol species exhibit significant biases. Overall, the model-data comparison indicates that the offline simulation driven by GEOS5 meteorological analyses provides the best simulation, possibly due in part to the increased vertical resolution (52 levels instead of 26 for online dynamics). The CAM-chem code as described in this paper, along with all the necessary datasets needed to perform the simulations described here, are available for download at www.cesm.ucar.edu.
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Zhang, Yuli, Mengchu Tao, Jinqiang Zhang, Yi Liu, Hongbin Chen, Zhaonan Cai, and Paul Konopka. "Long-term variations in ozone levels in the troposphere and lower stratosphere over Beijing: observations and model simulations." Atmospheric Chemistry and Physics 20, no. 21 (November 11, 2020): 13343–54. http://dx.doi.org/10.5194/acp-20-13343-2020.
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Abstract. Tropospheric ozone is both a major pollutant and a short-lived greenhouse gas and has therefore caused much concern in recent years. The ozone profile in the troposphere and lower stratosphere over Beijing has been observed since 2002 by ozonesondes developed by the Institute of Atmospheric Physics. Increasing concentrations of tropospheric ozone from 2002 to 2010 measured by these balloon-based observations have been reported previously. As more observations are now available, we used these data to analyse the long-term variability of ozone over Beijing during the whole period from 2002 to 2018. The ozonesondes measured increasing concentrations of ozone from 2002 to 2012 in both the troposphere and lower stratosphere. There was a sudden decrease in observed ozone between 2011 and 2012. After this decrease, the increasing trend in ozone concentrations slowed down, especially in the mid-troposphere, where the positive trend became neutral. We used the Chemical Lagrangian Model of the Stratosphere (CLaMS) to determine the influence of the transport of ozone from the stratosphere to the troposphere on the observed ozone profiles. CLaMS showed a weak increase in the contribution of stratospheric ozone before the decrease in 2011–2012 and a much more pronounced decrease after this time. Because there is no tropospheric chemistry in CLaMS, the sudden decrease simulated by CLaMS indicates that a smaller downward transport of ozone from the stratosphere after 2012 may explain a significant part of the observed decrease in ozone in the mid-troposphere and lower stratosphere. However, the influence of stratospheric ozone in the lower troposphere is negligible in CLaMS, and the hiatus in the positive trend after 2012 can be attributed to a reduction in ozone precursors as a result of stronger pollution control measures in Beijing.
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Gauss, M., G. Myhre, I. S. A. Isaksen, W. J. Collins, F. J. Dentener, K. Ellingsen, L. K. Gohar, et al. "Radiative forcing since preindustrial times due to ozone change in the troposphere and the lower stratosphere." Atmospheric Chemistry and Physics Discussions 5, no. 4 (August 10, 2005): 5751–807. http://dx.doi.org/10.5194/acpd-5-5751-2005.
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Abstract. Changes in atmospheric ozone have occurred since the preindustrial era as a result of increasing anthropogenic emissions. Within ACCENT, a European Network of Excellence, ozone changes between 1850 and 2000 are assessed for the troposphere and the lower stratosphere (up to 30 km) by a variety of seven chemistry-climate models and three chemical transport models. The modeled ozone changes are taken as input for detailed calculations of radiative forcing. When only changes in chemistry are considered (constant climate) the modeled global-mean tropospheric ozone column increase since preindustrial times ranges from 7.9 DU to 13.8 DU among the ten participating models, while the stratospheric column reduction lies between 14.1 DU and 47.9 DU in the models considering stratospheric chemistry. The resulting radiative forcing is strongly dependent on the location and altitude of the modeled ozone change and varies between 0.26 Wm−2 and 0.53 Wm−2 due to ozone change in the troposphere and −0.25 Wm−2 and +0.12 Wm−2 due to the stratospheric ozone change. Changes in ozone and other greenhouse gases since preindustrial times have altered climate. Six out of the ten participating models have performed an additional calculation taking into account both chemical and climate change. The isolated effect of climate change is an enhancement of the tropospheric ozone column increase in all models, ranging from 1% to 37%, while the stratospheric reduction becomes slightly less severe in most models. In the three climate-chemistry models with detailed tropospheric and stratospheric chemistry the inclusion of climate change increases the resulting radiative forcing due to tropospheric ozone change by up to 0.08 Wm−2, while the radiative forcing due to stratospheric ozone change is reduced by up to 0.14 Wm−2. Considering tropospheric and stratospheric change combined, the total ozone column change is negative while the resulting net radiative forcing is positive.
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Parrella, J. P., D. J. Jacob, Q. Liang, Y. Zhang, L. J. Mickley, B. Miller, M. J. Evans, et al. "Tropospheric bromine chemistry: implications for present and pre-industrial ozone and mercury." Atmospheric Chemistry and Physics Discussions 12, no. 4 (April 16, 2012): 9665–715. http://dx.doi.org/10.5194/acpd-12-9665-2012.
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Abstract. We present a new model for the global tropospheric chemistry of inorganic bromine (Bry) coupled to oxidant-aerosol chemistry in the GEOS-Chem chemical transport model (CTM). Sources of tropospheric Bry include debromination of sea-salt aerosol, photolysis and oxidation of short-lived bromocarbons, and transport from the stratosphere. Comparison to a GOME-2 satellite climatology of tropospheric BrO columns shows that the model can reproduce the observed increase of BrO with latitude, the northern mid-latitudes maximum in winter, and the Arctic maximum in spring. This successful simulation is contingent on the HOBr + HBr reaction taking place in aqueous aerosols and ice clouds. Bromine chemistry in the model decreases tropospheric ozone concentrations by <1−8 nmol mol−1 (6.5% globally), with the largest effects in the northern extratropics in spring. The global mean tropospheric OH concentration decreases by 4%. Inclusion of bromine chemistry improves the ability of global models (GEOS-Chem and p-TOMCAT) to simulate observed 19th-century ozone and its seasonality. Bromine effects on tropospheric ozone are comparable in the present-day and pre-industrial atmospheres so that estimates of anthropogenic radiative forcing are minimally affected. Br atom concentrations are 40% higher in the pre-industrial atmosphere due to lower ozone, which would decrease by a factor of 2 the atmospheric lifetime of elemental mercury against oxidation by Br. This suggests that historical anthropogenic mercury emissions may have mostly deposited to northern mid-latitudes, enriching the corresponding surface reservoirs. The persistent rise in background surface ozone at northern mid-latitudes during the past decades could possibly contribute to the observations of elevated mercury in subsurface waters of the North Atlantic.
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Xia, Lili, Peer J. Nowack, Simone Tilmes, and Alan Robock. "Impacts of stratospheric sulfate geoengineering on tropospheric ozone." Atmospheric Chemistry and Physics 17, no. 19 (October 9, 2017): 11913–28. http://dx.doi.org/10.5194/acp-17-11913-2017.
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Abstract. A range of solar radiation management (SRM) techniques has been proposed to counter anthropogenic climate change. Here, we examine the potential effects of stratospheric sulfate aerosols and solar insolation reduction on tropospheric ozone and ozone at Earth's surface. Ozone is a key air pollutant, which can produce respiratory diseases and crop damage. Using a version of the Community Earth System Model from the National Center for Atmospheric Research that includes comprehensive tropospheric and stratospheric chemistry, we model both stratospheric sulfur injection and solar irradiance reduction schemes, with the aim of achieving equal levels of surface cooling relative to the Representative Concentration Pathway 6.0 scenario. This allows us to compare the impacts of sulfate aerosols and solar dimming on atmospheric ozone concentrations. Despite nearly identical global mean surface temperatures for the two SRM approaches, solar insolation reduction increases global average surface ozone concentrations, while sulfate injection decreases it. A fundamental difference between the two geoengineering schemes is the importance of heterogeneous reactions in the photochemical ozone balance with larger stratospheric sulfate abundance, resulting in increased ozone depletion in mid- and high latitudes. This reduces the net transport of stratospheric ozone into the troposphere and thus is a key driver of the overall decrease in surface ozone. At the same time, the change in stratospheric ozone alters the tropospheric photochemical environment due to enhanced ultraviolet radiation. A shared factor among both SRM scenarios is decreased chemical ozone loss due to reduced tropospheric humidity. Under insolation reduction, this is the dominant factor giving rise to the global surface ozone increase. Regionally, both surface ozone increases and decreases are found for both scenarios; that is, SRM would affect regions of the world differently in terms of air pollution. In conclusion, surface ozone and tropospheric chemistry would likely be affected by SRM, but the overall effect is strongly dependent on the SRM scheme. Due to the health and economic impacts of surface ozone, all these impacts should be taken into account in evaluations of possible consequences of SRM.
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Haase, Sabine, Jaika Fricke, Tim Kruschke, Sebastian Wahl, and Katja Matthes. "Sensitivity of the Southern Hemisphere circumpolar jet response to Antarctic ozone depletion: prescribed versus interactive chemistry." Atmospheric Chemistry and Physics 20, no. 22 (November 20, 2020): 14043–61. http://dx.doi.org/10.5194/acp-20-14043-2020.
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Abstract. Southern Hemisphere lower-stratospheric ozone depletion has been shown to lead to a poleward shift of the tropospheric jet stream during austral summer, influencing surface atmosphere and ocean conditions, such as surface temperatures and sea ice extent. The characteristics of stratospheric and tropospheric responses to ozone depletion, however, differ among climate models depending on the representation of ozone in the models. The most appropriate way to represent ozone in a model is to calculate it interactively. However, due to computational costs, in particular for long-term coupled ocean–atmosphere model integrations, the more common way is to prescribe ozone from observations or calculated model fields. Here, we investigate the difference between an interactive and a specified chemistry version of the same atmospheric model in a fully coupled setup using a nine-member chemistry–climate model ensemble. In the specified chemistry version of the model the ozone fields are prescribed using the output from the interactive chemistry model version. We use daily resolved ozone fields in the specified chemistry simulations to achieve a very good comparability between the ozone forcing with and without interactive chemistry. We find that although the shortwave heating rate trend in response to ozone depletion is the same in the different chemistry settings, the interactive chemistry ensemble shows a stronger trend in polar cap stratospheric temperatures (by about 0.7 K decade−1) and circumpolar stratospheric zonal mean zonal winds (by about 1.6 m s−1 decade−1 as compared to the specified chemistry ensemble. This difference between interactive and specified chemistry in the stratospheric response to ozone depletion also affects the tropospheric response. However, an impact on the poleward shift of the tropospheric jet stream is not detected. We attribute part of the differences found in the experiments to the missing representation of feedbacks between chemistry and dynamics in the specified chemistry ensemble, which affect the dynamical heating rates, and part of it to the lack of spatial asymmetries in the prescribed ozone fields. This effect is investigated using a sensitivity ensemble that was forced by a three-dimensional instead of a two-dimensional ozone field. This study emphasizes the value of interactive chemistry for the representation of the Southern Hemisphere stratospheric-jet response to ozone depletion and infers that for periods with strong ozone variability (trends) the details of the ozone forcing could also have an influence on the representation of southern-hemispheric climate variability.
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Shindell, D. T., G. Faluvegi, N. Unger, E. Aguilar, G. A. Schmidt, D. M. Koch, S. E. Bauer, and R. L. Miller. "Simulations of preindustrial, present-day, and 2100 conditions in the NASA GISS composition and climate model G-PUCCINI." Atmospheric Chemistry and Physics 6, no. 12 (October 4, 2006): 4427–59. http://dx.doi.org/10.5194/acp-6-4427-2006.
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Abstract. A model of atmospheric composition and climate has been developed at the NASA Goddard Institute for Space Studies (GISS) that includes composition seamlessly from the surface to the lower mesosphere. The model is able to capture many features of the observed magnitude, distribution, and seasonal cycle of trace species. The simulation is especially realistic in the troposphere. In the stratosphere, high latitude regions show substantial biases during period when transport governs the distribution as meridional mixing is too rapid in this model version. In other regions, including the extrapolar tropopause region that dominates radiative forcing (RF) by ozone, stratospheric gases are generally well-simulated. The model's stratosphere-troposphere exchange (STE) agrees well with values inferred from observations for both the global mean flux and the ratio of Northern (NH) to Southern Hemisphere (SH) downward fluxes. Simulations of preindustrial (PI) to present-day (PD) changes show tropospheric ozone burden increases of 11% while the stratospheric burden decreases by 18%. The resulting tropopause RF values are −0.06 W/m2 from stratospheric ozone and 0.40 W/m2 from tropospheric ozone. Global mean mass-weighted OH decreases by 16% from the PI to the PD. STE of ozone also decreased substantially during this time, by 14%. Comparison of the PD with a simulation using 1979 pre-ozone hole conditions for the stratosphere shows a much larger downward flux of ozone into the troposphere in 1979, resulting in a substantially greater tropospheric ozone burden than that seen in the PD run. This implies that reduced STE due to stratospheric ozone depletion may have offset as much as 2/3 of the tropospheric ozone burden increase from PI to PD. However, the model overestimates the downward flux of ozone at high Southern latitudes, so this estimate is likely an upper limit. In the future, the tropospheric ozone burden increases by 101% in 2100 for the A2 scenario including both emissions and climate changes. The primary reason is enhanced STE, which increases by 124% (168% in the SH extratropics, and 114% in the NH extratropics). Climate plays a minimal role in the SH increases, but contributes 38% in the NH. Chemistry and dry deposition both change so as to reduce tropospheric ozone, partially in compensation for the enhanced STE, but the increased ozone influx dominates the burden changes. The net RF due to projected ozone changes is 0.8 W/m2 for A2. The influence of climate change alone is −0.2 W/m2, making it a substantial contributor to the net RF. The tropospheric oxidation capacity increases seven percent in the full A2 simulation, and 36% due to A2 climate change alone.
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Bowman, K. W., D. B. A. Jones, J. A. Logan, H. Worden, F. Boersma, R. Chang, S. Kulawik, G. Osterman, P. Hamer, and J. Worden. "The zonal structure of tropical O<sub>3</sub> and CO as observed by the Tropospheric Emission Spectrometer in November 2004 – Part 2: Impact of surface emissions on O<sub>3</sub> and its precursors." Atmospheric Chemistry and Physics 9, no. 11 (June 3, 2009): 3563–82. http://dx.doi.org/10.5194/acp-9-3563-2009.
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Abstract. The impact of surface emissions on the zonal structure of tropical tropospheric ozone and carbon monoxide is investigated for November 2004 using satellite observations, in-situ measurements, and chemical transport models in conjunction with inverse-estimated surface emissions.Vertical ozone profiles from the Tropospheric Emission Spectrometer (TES) and ozone sonde measurements from the Southern Hemisphere Additional Ozonesondes (SHADOZ) network show elevated concentrations of ozone over Indonesia and Australia (60–70 ppb) in the lower troposphere against the backdrop of the well-known zonal "wave-one" pattern with ozone concentrations of (70–80 ppb) centered over the Atlantic . Observational evidence from TES CO vertical profiles and Ozone Monitoring Instrument (OMI) NO2 columns point to regional surface emissions as an important contributor to the elevated ozone over Indonesia. This contribution is investigated with the GEOS-Chem chemistry and transport model using surface emission estimates derived from an optimal inverse model, which was constrained by TES and Measurements Of Pollution In The Troposphere (MOPITT) CO profiles (Jones et al., 2009). These a posteriori estimates, which were over a factor of 2 greater than climatological emissions, reduced differences between GEOS-Chem and TES ozone observations by 30–40% over Indonesia. The response of the free tropospheric chemical state to the changes in these emissions is investigated for ozone, CO, NOx, and PAN. Model simulations indicate that ozone over Indonesian/Australian is sensitive to regional changes in surface emissions of NOx but relatively insensitive to lightning NOx. Over sub-equatorial Africa and South America, free tropospheric NOx was reduced in response to increased surface emissions potentially muting ozone production.
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Wang, Xuan, Daniel J. Jacob, William Downs, Shuting Zhai, Lei Zhu, Viral Shah, Christopher D. Holmes, et al. "Global tropospheric halogen (Cl, Br, I) chemistry and its impact on oxidants." Atmospheric Chemistry and Physics 21, no. 18 (September 21, 2021): 13973–96. http://dx.doi.org/10.5194/acp-21-13973-2021.
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Abstract. We present an updated mechanism for tropospheric halogen (Cl + Br + I) chemistry in the GEOS-Chem global atmospheric chemical transport model and apply it to investigate halogen radical cycling and implications for tropospheric oxidants. Improved representation of HOBr heterogeneous chemistry and its pH dependence in our simulation leads to less efficient recycling and mobilization of bromine radicals and enables the model to include mechanistic sea salt aerosol debromination without generating excessive BrO. The resulting global mean tropospheric BrO mixing ratio is 0.19 ppt (parts per trillion), lower than previous versions of GEOS-Chem. Model BrO shows variable consistency and biases in comparison to surface and aircraft observations in marine air, which are often near or below the detection limit. The model underestimates the daytime measurements of Cl2 and BrCl from the ATom aircraft campaign over the Pacific and Atlantic, which if correct would imply a very large missing primary source of chlorine radicals. Model IO is highest in the marine boundary layer and uniform in the free troposphere, with a global mean tropospheric mixing ratio of 0.08 ppt, and shows consistency with surface and aircraft observations. The modeled global mean tropospheric concentration of Cl atoms is 630 cm−3, contributing 0.8 % of the global oxidation of methane, 14 % of ethane, 8 % of propane, and 7 % of higher alkanes. Halogen chemistry decreases the global tropospheric burden of ozone by 11 %, NOx by 6 %, and OH by 4 %. Most of the ozone decrease is driven by iodine-catalyzed loss. The resulting GEOS-Chem ozone simulation is unbiased in the Southern Hemisphere but too low in the Northern Hemisphere.
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Banerjee, Antara, Amanda C. Maycock, and John A. Pyle. "Chemical and climatic drivers of radiative forcing due to changes in stratospheric and tropospheric ozone over the 21st century." Atmospheric Chemistry and Physics 18, no. 4 (February 28, 2018): 2899–911. http://dx.doi.org/10.5194/acp-18-2899-2018.
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Abstract. The ozone radiative forcings (RFs) resulting from projected changes in climate, ozone-depleting substances (ODSs), non-methane ozone precursor emissions and methane between the years 2000 and 2100 are calculated using simulations from the UM-UKCA chemistry–climate model (UK Met Office's Unified Model containing the United Kingdom Chemistry and Aerosols sub-model). Projected measures to improve air-quality through reductions in non-methane tropospheric ozone precursor emissions present a co-benefit for climate, with a net global mean ozone RF of −0.09 W m−2. This is opposed by a positive ozone RF of 0.05 W m−2 due to future decreases in ODSs, which is driven by an increase in tropospheric ozone through stratosphere-to-troposphere transport of air containing higher ozone amounts. An increase in methane abundance by more than a factor of 2 (as projected by the RCP8.5 scenario) is found to drive an ozone RF of 0.18 W m−2, which would greatly outweigh the climate benefits of non-methane tropospheric ozone precursor reductions. A small fraction (∼ 15 %) of the ozone RF due to the projected increase in methane results from increases in stratospheric ozone. The sign of the ozone RF due to future changes in climate (including the radiative effects of greenhouse gases, sea surface temperatures and sea ice changes) is shown to be dependent on the greenhouse gas emissions pathway, with a positive RF (0.05 W m−2) for RCP4.5 and a negative RF (−0.07 W m−2) for the RCP8.5 scenario. This dependence arises mainly from differences in the contribution to RF from stratospheric ozone changes. Considering the increases in tropopause height under climate change causes only small differences (≤ |0.02| W m−2) for the stratospheric, tropospheric and whole-atmosphere RFs.
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Meul, Stefanie, Ulrike Langematz, Philipp Kröger, Sophie Oberländer-Hayn, and Patrick Jöckel. "Future changes in the stratosphere-to-troposphere ozone mass flux and the contribution from climate change and ozone recovery." Atmospheric Chemistry and Physics 18, no. 10 (June 1, 2018): 7721–38. http://dx.doi.org/10.5194/acp-18-7721-2018.
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Abstract. Using a state-of-the-art chemistry–climate model we investigate the future change in stratosphere–troposphere exchange (STE) of ozone, the drivers of this change, as well as the future distribution of stratospheric ozone in the troposphere. Supplementary to previous work, our focus is on changes on the monthly scale. The global mean annual influx of stratospheric ozone into the troposphere is projected to increase by 53 % between the years 2000 and 2100 under the RCP8.5 greenhouse gas scenario. The change in ozone mass flux (OMF) into the troposphere is positive throughout the year with maximal increase in the summer months of the respective hemispheres. In the Northern Hemisphere (NH) this summer maximum STE increase is a result of increasing greenhouse gas (GHG) concentrations, whilst in the Southern Hemisphere(SH) it is due to equal contributions from decreasing levels of ozone depleting substances (ODS) and increasing GHG concentrations. In the SH the GHG effect is dominating in the winter months. A large ODS-related ozone increase in the SH stratosphere leads to a change in the seasonal breathing term which results in a future decrease of the OMF into the troposphere in the SH in September and October. The resulting distributions of stratospheric ozone in the troposphere differ for the GHG and ODS changes due to the following: (a) ozone input occurs at different regions for GHG- (midlatitudes) and ODS-changes (high latitudes); and (b) stratospheric ozone is more efficiently mixed towards lower tropospheric levels in the case of ODS changes, whereas tropospheric ozone loss rates grow when GHG concentrations rise. The comparison between the moderate RCP6.0 and the extreme RCP8.5 emission scenarios reveals that the annual global OMF trend is smaller in the moderate scenario, but the resulting change in the contribution of ozone with stratospheric origin (O3s) to ozone in the troposphere is of comparable magnitude in both scenarios. This is due to the larger tropospheric ozone precursor emissions and hence ozone production in the RCP8.5 scenario.
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Young, P. J., A. T. Archibald, K. W. Bowman, J. F. Lamarque, V. Naik, D. S. Stevenson, S. Tilmes, et al. "Pre-industrial to end 21st century projections of tropospheric ozone from the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP)." Atmospheric Chemistry and Physics 13, no. 4 (February 21, 2013): 2063–90. http://dx.doi.org/10.5194/acp-13-2063-2013.
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Abstract. Present day tropospheric ozone and its changes between 1850 and 2100 are considered, analysing 15 global models that participated in the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP). The ensemble mean compares well against present day observations. The seasonal cycle correlates well, except for some locations in the tropical upper troposphere. Most (75 %) of the models are encompassed with a range of global mean tropospheric ozone column estimates from satellite data, but there is a suggestion of a high bias in the Northern Hemisphere and a low bias in the Southern Hemisphere, which could indicate deficiencies with the ozone precursor emissions. Compared to the present day ensemble mean tropospheric ozone burden of 337 ± 23 Tg, the ensemble mean burden for 1850 time slice is ~30% lower. Future changes were modelled using emissions and climate projections from four Representative Concentration Pathways (RCPs). Compared to 2000, the relative changes in the ensemble mean tropospheric ozone burden in 2030 (2100) for the different RCPs are: −4% (−16%) for RCP2.6, 2% (−7%) for RCP4.5, 1% (−9%) for RCP6.0, and 7% (18%) for RCP8.5. Model agreement on the magnitude of the change is greatest for larger changes. Reductions in most precursor emissions are common across the RCPs and drive ozone decreases in all but RCP8.5, where doubled methane and a 40–150% greater stratospheric influx (estimated from a subset of models) increase ozone. While models with a high ozone burden for the present day also have high ozone burdens for the other time slices, no model consistently predicts large or small ozone changes; i.e. the magnitudes of the burdens and burden changes do not appear to be related simply, and the models are sensitive to emissions and climate changes in different ways. Spatial patterns of ozone changes are well correlated across most models, but are notably different for models without time evolving stratospheric ozone concentrations. A unified approach to ozone budget specifications and a rigorous investigation of the factors that drive tropospheric ozone is recommended to help future studies attribute ozone changes and inter-model differences more clearly.
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Bowman, K. W., D. T. Shindell, H. M. Worden, J. F. Lamarque, P. J. Young, D. S. Stevenson, Z. Qu, et al. "Evaluation of ACCMIP outgoing longwave radiation from tropospheric ozone using TES satellite observations." Atmospheric Chemistry and Physics 13, no. 8 (April 18, 2013): 4057–72. http://dx.doi.org/10.5194/acp-13-4057-2013.
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Abstract. We use simultaneous observations of tropospheric ozone and outgoing longwave radiation (OLR) sensitivity to tropospheric ozone from the Tropospheric Emission Spectrometer (TES) to evaluate model tropospheric ozone and its effect on OLR simulated by a suite of chemistry-climate models that participated in the Atmospheric Chemistry and Climate Model Intercomparison Project (ACCMIP). The ensemble mean of ACCMIP models show a persistent but modest tropospheric ozone low bias (5–20 ppb) in the Southern Hemisphere (SH) and modest high bias (5–10 ppb) in the Northern Hemisphere (NH) relative to TES ozone for 2005–2010. These ozone biases have a significant impact on the OLR. Using TES instantaneous radiative kernels (IRK), we show that the ACCMIP ensemble mean tropospheric ozone low bias leads up to 120 mW m−2 OLR high bias locally but zonally compensating errors reduce the global OLR high bias to 39 ± 41 m Wm−2 relative to TES data. We show that there is a correlation (R2 = 0.59) between the magnitude of the ACCMIP OLR bias and the deviation of the ACCMIP preindustrial to present day (1750–2010) ozone radiative forcing (RF) from the ensemble ozone RF mean. However, this correlation is driven primarily by models whose absolute OLR bias from tropospheric ozone exceeds 100 m Wm−2. Removing these models leads to a mean ozone radiative forcing of 394 ± 42 m Wm−2. The mean is about the same and the standard deviation is about 30% lower than an ensemble ozone RF of 384 ± 60 m Wm−2 derived from 14 of the 16 ACCMIP models reported in a companion ACCMIP study. These results point towards a profitable direction of combining satellite observations and chemistry-climate model simulations to reduce uncertainty in ozone radiative forcing.
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Miles, G. M., R. Siddans, B. J. Kerridge, B. G. Latter, and N. A. D. Richards. "Tropospheric ozone and ozone profiles retrieved from GOME-2 and their validation." Atmospheric Measurement Techniques 8, no. 1 (January 22, 2015): 385–98. http://dx.doi.org/10.5194/amt-8-385-2015.
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Abstract. This paper describes and assesses the performance of the RAL (Rutherford Appleton Laboratory) ozone profile retrieval scheme for the Global Ozone Monitoring Experiment 2 (GOME-2) with a focus on tropospheric ozone. Developments to the scheme since its application to GOME-1 measurements are outlined. These include the approaches developed to account sufficiently for UV radiometric degradation in the Hartley band and for inadequacies in knowledge of instrumental parameters in the Huggins bands to achieve the high-precision spectral fit required to extract information on tropospheric ozone. The assessment includes a validation against ozonesondes (sondes) sampled worldwide over 2 years (2007–2008). Standard deviations of the ensemble with respect to the sondes are considerably lower for the retrieved profiles than for the a priori, with the exception of the lowest subcolumn. Once retrieval vertical smoothing (averaging kernels) has been applied to the sonde profiles there is a retrieval bias of 6% (1.5 DU) in the lower troposphere, with smaller biases in the subcolumns above. The bias in the troposphere varies with latitude. The retrieval underestimates lower tropospheric ozone in the Southern Hemisphere (SH) (15–20% or ~ 1–3 DU) and overestimates it in the Northern Hemisphere (NH) (10% or 2 DU). The ability of the retrieval to reflect the geographical distribution of lower tropospheric ozone, globally (rather than just ozonesonde launch sites) is demonstrated by comparison with the chemistry transport model TOMCAT. For a monthly mean of cloud-cleared GOME-2 pixels, a correlation of 0.66 is found between the retrieval and TOMCAT sampled accordingly, with a bias of 0.7 Dobson Units. GOME-2 estimates higher concentrations in NH pollution centres but lower ozone in the Southern Ocean and South Pacific, which is consistent with the comparison to ozonesondes.
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Miles, G. M., R. Siddans, B. J. Kerridge, B. G. Latter, and N. A. D. Richards. "Tropospheric ozone and ozone profiles retrieved from GOME-2 and their validation." Atmospheric Measurement Techniques Discussions 7, no. 7 (July 31, 2014): 7923–62. http://dx.doi.org/10.5194/amtd-7-7923-2014.
Full textAbstract:
Abstract. This paper describes and assesses the performance of the RAL (Rutherford Appleton Laboratory) ozone profile retrieval scheme for the Global Ozone Monitoring Experiment 2 (GOME-2) with a~focus on tropospheric ozone. Developments to the scheme since its application to GOME-1 measurements are outlined. These include the approaches developed to account sufficiently for UV radiometric degradation in the Hartley band and for inadequacies in knowledge of instrumental parameters in the Huggins bands to achieve the high precision spectral fit required to extract information on tropospheric ozone. The assessment includes a validation against ozonesondes (sondes) sampled worldwide over two years (2007–2008). Standard deviations of the ensemble with respect to the sondes are considerably lower for the retrieved profiles than for the a priori, with the exception of the lowest sub-column. Once retrieval vertical smoothing (averaging kernels) has been applied to the sonde profiles there is a retrieval bias of 6% (1.5 DU) in the lower troposphere, with smaller biases in the sub-columns above. The bias in the troposphere varies with latitude. The retrieval underestimates lower tropospheric ozone in the Southern Hemisphere (SH) (15–20% or ~ 1–3 DU) and overestimates it in the Northern Hemisphere (NH) (10% or 2 DU). The ability of the retrieval to represent the geographical distribution of lower tropospheric ozone, globally (rather than just ozonesonde launch sites) is demonstrated through agreement with the chemistry transport model TOMCAT. For a monthly mean of cloud-cleared GOME-2 pixels, a correlation of 0.66 is found between the retrieval and TOMCAT sampled accordingly, with a bias of 0.7 Dobson Units. GOME-2 estimates higher concentrations in NH pollution centres but lower ozone in the Southern Ocean and South Pacific, which is consistent with the comparison to ozonesondes.
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Folberth, G. A., D. A. Hauglustaine, J. Lathière, and F. Brocheton. "Interactive chemistry in the Laboratoire de Météorologie Dynamique general circulation model: model description and impact analysis of biogenic hydrocarbons on tropospheric chemistry." Atmospheric Chemistry and Physics 6, no. 8 (June 21, 2006): 2273–319. http://dx.doi.org/10.5194/acp-6-2273-2006.
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Abstract. We present a description and evaluation of LMDz-INCA, a global three-dimensional chemistry-climate model, pertaining to its recently developed NMHC version. In this substantially extended version of the model a comprehensive representation of the photochemistry of non-methane hydrocarbons (NMHC) and volatile organic compounds (VOC) from biogenic, anthropogenic, and biomass-burning sources has been included. The tropospheric annual mean methane (9.2 years) and methylchloroform (5.5 years) chemical lifetimes are well within the range of previous modelling studies and are in excellent agreement with estimates established by means of global observations. The model provides a reasonable simulation of the horizontal and vertical distribution and seasonal cycle of CO and key non-methane VOC, such as acetone, methanol, and formaldehyde as compared to observational data from several ground stations and aircraft campaigns. LMDz-INCA in the NMHC version reproduces tropospheric ozone concentrations fairly well throughout most of the troposphere. The model is applied in several sensitivity studies of the biosphere-atmosphere photochemical feedback. The impact of surface emissions of isoprene, acetone, and methanol is studied. These experiments show a substantial impact of isoprene on tropospheric ozone and carbon monoxide concentrations revealing an increase in surface O3 and CO levels of up to 30 ppbv and 60 ppbv, respectively. Isoprene also appears to significantly impact the global OH distribution resulting in a decrease of the global mean tropospheric OH concentration by approximately 0.7×105 molecules cm-3 or roughly 8% and an increase in the global mean tropospheric methane lifetime by approximately seven months. A global mean ozone net radiative forcing due to the isoprene induced increase in the tropospheric ozone burden of 0.09 W m-2 is found. The key role of isoprene photooxidation in the global tropospheric redistribution of NOx is demonstrated. LMDz-INCA calculates an increase of PAN surface mixing ratios ranging from 75 to 750 pptv and 10 to 250 pptv during northern hemispheric summer and winter, respectively. Acetone and methanol are found to play a significant role in the upper troposphere/lower stratosphere (UT/LS) budget of peroxy radicals. Calculations with LMDz-INCA show an increase in HOx concentrations region of 8 to 15% and 10 to 15% due to methanol and acetone biogenic surface emissions, respectively. The model has been used to estimate the global tropospheric CO budget. A global CO source of 3019 Tg CO yr-1 is estimated. This source divides into a primary source of 1533 Tg CO yr-1 and secondary source of 1489 Tg CO yr-1 deriving from VOC photooxidation. Global VOC-to-CO conversion efficiencies of 90% for methane and between 20 and 45% for individual VOC are calculated by LMDz-INCA.