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1
Morozova, A. L., and I. A. Mironova. "Aerosols over Continental Portugal (1978–1993): their sources and an impact on the regional climate." Atmospheric Chemistry and Physics Discussions 14, no. 22 (2014): 31009–38. http://dx.doi.org/10.5194/acpd-14-31009-2014.
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Abstract. Understanding of aerosol sources which affect climate is an important problem open in front of scientists as well as policymakers. The role of aerosols in local climate variability depends on a~balance between aerosol absorbing and scattering particles as well as on variability of environmental conditions. In this paper we investigate variability of aerosol content (both absorbing and scattering UV radiation) over Continental Portugal in dependence on aerosol sources (volcanic eruptions, dust events, wildfires and anthropogenic pollution). The effect of the aerosol on the climate is studied analyzing their contribution to variations of temperature, sunshine duration and precipitation over Portuguese regions. The present analysis is based on a developed modern multiple regression technique allowing us to build the statistical correlation models to determine both the main local aerosol sources and aerosol's influence on the climate of the Continental Portugal during 1978–1993 time period. The analysis allows us to conclude that the main sources driving the variations of the aerosol content over studied locations are wildfires, mineral dust intrusions and anthropogenic pollution. The relations between the aerosol content variations and the atmospheric parameters depend on the level of urbanization of the studied region, the type of aerosol and the season. The most significant finding is the decrease of the daily temperature (and diurnal temperature range) related to the decrease of sunshine duration observed during the summer periods of increased content of the absorbing aerosols in the atmosphere.
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Bréon, F. M. "Aerosol extinction to backscatter ratio derived from passive satellite measurements." Atmospheric Chemistry and Physics Discussions 13, no. 1 (2013): 2351–70. http://dx.doi.org/10.5194/acpd-13-2351-2013.
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Abstract. Spaceborne reflectance measurements from the POLDER instrument are used to study the specific directional signature close to the backscatter direction. The data analysis makes it possible to derive the extinction to backscatter ratio (EBR) which is the invert of the scattering phase function for an angle of 180° and is needed for a quantitative interpretation of lidar observations (active measurements). In addition, the multi-directional measurements are used to quantify the scattering phase function variations close to backscatter, which also provide some indication of the aerosol particle size and shape. The spatial distributions of both parameters show consistent patterns that are consistent with the aerosol type distributions. Pollution aerosols have an EBR close to 70, desert dust values are on the order of 50, while marine aerosol's is close to 25. The scattering phase function shows an increase with the scattering angle close to backscatter. The relative increase ∂lnP/∂ γ is close to 0.01 for dust and pollution type aerosols and 0.06 for marine type aerosols. These values are consistent with those retrieved from Mie simulations.
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Morozova, A. L., and I. A. Mironova. "Aerosols over continental Portugal (1978–1993): their sources and an impact on the regional climate." Atmospheric Chemistry and Physics 15, no. 11 (2015): 6407–18. http://dx.doi.org/10.5194/acp-15-6407-2015.
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Abstract. Understanding of aerosol sources that affect climate is an ongoing problem facing scientists as well as policymakers. The role of aerosols in local climate variability depends on a balance between light absorbing and scattering particles as well as on variability of environmental conditions. In this paper we investigate variability of aerosol content (both absorbing and scattering ultraviolet radiation) over continental Portugal in connection with aerosol sources (volcanic eruptions, dust events, wildfires and anthropogenic pollution). The effect of the aerosol on the climate is studied analyzing their contribution to variations of temperature, pressure, sunshine duration and precipitation over Portuguese regions. The present analysis is based on a developed modern multiple regression technique allowing us to build the statistical correlation models to determine both the main local aerosol sources and aerosol's influence on the climate of continental Portugal during 1978–1993. The analysis allows us to conclude that the main sources driving the variations of the aerosol content over studied locations are wildfires, mineral dust intrusions and anthropogenic pollution. The relations between the aerosol content variations and the atmospheric parameters depend on the level of urbanization of the studied region, the type of aerosol and the season. The most significant finding is the decrease of the daily maximum temperature (and diurnal temperature range) related to the decrease of sunshine duration observed during the summer periods of increased content of the absorbing aerosols in the atmosphere.
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Persad, Geeta G., David J. Paynter, Yi Ming, and V. Ramaswamy. "Competing Atmospheric and Surface-Driven Impacts of Absorbing Aerosols on the East Asian Summertime Climate." Journal of Climate 30, no. 22 (2017): 8929–49. http://dx.doi.org/10.1175/jcli-d-16-0860.1.
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East Asia has some of the largest concentrations of absorbing aerosols globally, and these, along with the region’s scattering aerosols, have both reduced the amount of solar radiation reaching Earth’s surface regionally (solar dimming) and increased shortwave absorption within the atmosphere, particularly during the peak months of the East Asian summer monsoon (EASM). This study analyzes how atmospheric absorption and surface solar dimming compete in driving the response of regional summertime climate to anthropogenic aerosols, which dominates, and why—issues of particular importance for predicting how East Asian climate will respond to projected changes in absorbing and scattering aerosol emissions in the future. These questions are probed in a state-of-the-art general circulation model using a combination of realistic and novel idealized aerosol perturbations that allow analysis of the relative influence of absorbing aerosols’ atmospheric and surface-driven impacts on regional circulation and climate. Results show that even purely absorption-driven dimming decreases EASM precipitation by cooling the land surface, counteracting climatological land–sea contrast and reducing ascending atmospheric motion and onshore winds, despite the associated positive top-of-the-atmosphere regional radiative forcing. Absorption-driven atmospheric heating does partially offset the precipitation and surface evaporation reduction from surface dimming, but the overall response to aerosol absorption more closely resembles the response to its surface dimming than to its atmospheric heating. These findings provide a novel decomposition of absorbing aerosol’s impacts on regional climate and demonstrate that the response cannot be expected to follow the sign of absorption’s top-of-the-atmosphere or even atmospheric radiative perturbation.
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Alston, Erica, and Irina Sokolik. "Assessment of Aerosol Radiative Forcing with 1-D Radiative Transfer Modeling in the U. S. South-East." Atmosphere 9, no. 7 (2018): 271. http://dx.doi.org/10.3390/atmos9070271.
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Aerosols and their radiative properties play an integral part in understanding Earth’s climate. It is becoming increasingly common to examine aerosol’s radiative impacts on a regional scale. The primary goal of this research is to explore the impacts of regional aerosol’s forcing at the surface and top-of-atmosphere (TOA) in the south-eastern U.S. by using a 1-D radiative transfer model. By using test cases that are representative of conditions common to this region, an estimate of aerosol forcing can be compared to other results. Speciation data and aerosol layer analysis provide the basis for the modeling. Results indicate that the region experiences TOA cooling year-round, where the winter has TOA forcings between −2.8 and −5 W/m2, and the summer has forcings between −5 and −15 W/m2 for typical atmospheric conditions. Surface level forcing efficiencies are greater than those estimated for the TOA for all cases considered i.e., urban and non-urban background conditions. One potential implication of this research is that regional aerosol mixtures have effects that are not well captured in global climate model estimates, which has implications for a warming climate where all radiative inputs are not well characterized, thus increasing the ambiguity in determining regional climate impacts.
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Choi, Wonei, Hyeongwoo Kang, Dongho Shin, and Hanlim Lee. "Satellite-Based Aerosol Classification for Capital Cities in Asia Using a Random Forest Model." Remote Sensing 13, no. 13 (2021): 2464. http://dx.doi.org/10.3390/rs13132464.
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Aerosol types in Asian capital cities were classified using a random forest (RF) satellite-based aerosol classification model during 2018–2020 in an investigation of the contributions of aerosol types, with or without Aerosol Robotic Network (AERONET) observations. In this study, we used the recently developed RF aerosol classification model to detect and classify aerosols into four types: pure dust, dust-dominated aerosols, strongly absorbing aerosols, and non-absorbing aerosols. Aerosol optical and microphysical properties for each aerosol type detected by the RF model were found to be reasonably consistent with those for typical aerosol types. In Asian capital cities, pollution-sourced aerosols, especially non-absorbing aerosols, were found to predominate, although Asian cities also tend to be seasonally affected by natural dust aerosols, particularly in East Asia (March–May) and South Asia (March–August). No specific seasonal effects on aerosol type were detected in Southeast Asia, where there was a predominance of non-absorbing aerosols. The aerosol types detected by the RF model were compared with those identified by other aerosol classification models. This study indicates that the satellite-based RF model may be used as an alternative in the absence of AERONET sites or observations.
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Chen, Qi-Xiang, Chun-Lin Huang, Yuan Yuan, Qian-Jun Mao, and He-Ping Tan. "Spatiotemporal Distribution of Major Aerosol Types over China Based on MODIS Products between 2008 and 2017." Atmosphere 11, no. 7 (2020): 703. http://dx.doi.org/10.3390/atmos11070703.
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Knowledge of aerosol-type distribution is critical to the evaluation of aerosol–climate effects. However, research on aerosol-type distribution covering all is limited. This study characterized the spatiotemporal distribution of major aerosol types over China by using MODerate resolution Imaging Spectroradiometer (MODIS) products from 2008 to 2017. Two aerosol-type classification methods were combined to achieve this goal. One was for relatively high aerosol load (AOD ≥ 0.2) using aerosol optical depth (AOD) and aerosol relative optical depth (AROD) and the other was for low aerosol load (AOD < 0.2) using land use and population density information, which assumed that aerosols are closely related to local emissions. Results showed that the dominant aerosol-type distribution has a distinct spatial and temporal pattern. In western China, background aerosols (mainly dust/desert dust and continent aerosol) dominate with a combined occurrence ratio over 70% and they have slight variations on seasonal scale. While in eastern China, the dominant aerosols show strong seasonal variations. Spatially, mixed aerosols dominate most parts of eastern China in spring due to the influence of long-range transported dust from Taklamakan and Gobi desert and urban/industry aerosols take place in summer due to strong photochemical reactions. Temporally, mixed and urban/industry aerosols co-dominate eastern China.
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Girado-Polo, Carlos, and Leonardo Gónima-Gónima. "Algoritmo teórico para la estimación de la radiación solar global para una atmósfera despejada." Revista de la Academia Colombiana de Ciencias Exactas, Físicas y Naturales 42, no. 162 (2018): 104. http://dx.doi.org/10.18257/raccefyn.610.
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En este trabajo se desarrolló un algoritmo para la estimación de la radiación solar global, para una atmósfera despejada, mediante el modelamiento de las ecuaciones teóricas de transferencia radiativa de onda corta (0,3 µm - 2,8 µm). Se determinaron las transmitancias espectrales de la radiación solar directa, debidas a la dispersión de Rayleigh y Mie. Mediante el software Propiedades Ópticas de Aerosoles y Nubes (Optical Properties of Aerosols and Clouds, OPAC) se calculó la Profundidad Óptica de los Aerosoles (Aerosol Optical Depth, AOD) para cuatro diferentes tipos de atmósferas, indispensable para la determinación del índice de turbidez de Ångström. Así mismo, se calcularon la transmitancias espectrales por absorción de la radiación solar directa, incluyendo aerosoles, vapor de agua, ozono y aire seco (mezcla de gases). El contenido de O3 se obtuvo de los datos diarios existentes en base de datos de la NASA. Para la componente difusa de la radiación solar, se dedujo una nueva expresión para el cálculo de la fracción de la radiación solar dispersada por los aerosoles hacia la superficie terrestre. La comparación estadística entre los resultados obtenidos con el algoritmo desarrollado, los datos medidos de la radiación global (estación Potsdam - Alemania) y los resultados de otros tres modelos radiativos, entre 2012 y 2014, muestra que el nuevo modelo permite calcular los valores horarios de la radiación solar global con suficiente precisión. © 2018. Acad. Colomb. Cienc. Ex. Fis. Nat.
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Li, Z., X. Zhao, R. Kahn, et al. "Uncertainties in satellite remote sensing of aerosols and impact on monitoring its long-term trend: a review and perspective." Annales Geophysicae 27, no. 7 (2009): 2755–70. http://dx.doi.org/10.5194/angeo-27-2755-2009.
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Abstract. As a result of increasing attention paid to aerosols in climate studies, numerous global satellite aerosol products have been generated. Aerosol parameters and underlining physical processes are now incorporated in many general circulation models (GCMs) in order to account for their direct and indirect effects on the earth's climate, through their interactions with the energy and water cycles. There exists, however, an outstanding problem that these satellite products have substantial discrepancies, that must be lowered substantially for narrowing the range of the estimates of aerosol's climate effects. In this paper, numerous key uncertain factors in the retrieval of aerosol optical depth (AOD) are articulated for some widely used and relatively long satellite aerosol products including the AVHRR, TOMS, MODIS, MISR, and SeaWiFS. We systematically review the algorithms developed for these sensors in terms of four key elements that influence the quality of passive satellite aerosol retrieval: calibration, cloud screening, classification of aerosol types, and surface effects. To gain further insights into these uncertain factors, the NOAA AVHRR data are employed to conduct various tests, which help estimate the ranges of uncertainties incurred by each of the factors. At the end, recommendations are made to cope with these issues and to produce a consistent and unified aerosol database of high quality for both environment monitoring and climate studies.
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Abd Jalal, Khairunnisa, Arnis Asmat, and Noordin Ahmad. "Retrievals of Aerosol Optical Depth and Angstrom Exponent for Identification of Aerosols at Kuching, Sarawak." Advanced Materials Research 518-523 (May 2012): 5734–37. http://dx.doi.org/10.4028/www.scientific.net/amr.518-523.5734.
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Anthropogenic and natural aerosols are important atmospheric constituents that significantly contribute to the Earth’s radiation budget but remain uncertainties due to the poor understanding of aerosol properties and its direct effects on scattering and absoprtion of solar radiation and the ability of aerosols to stay in atmosphere for a very short time. Different types of aerosols, representing biomass burning, urban or continental aerosols, maritime aerosols and dust particles will give different characterization and classification of aerosol properties. The data used in this study was obtained from Aerosol Robotic Network (AERONET).Two parameters were used for aerosol analysis which are Aerosol Optical Depth (AOD) at four wavelengths (440, 500, 675 and 870nm) and Angstrom exponent (α) derived from a multispectral log linear.
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Yakobi-Hancock, J. D., L. A. Ladino, R. H. Mason, et al. "Hygroscopicity of aerosol and its organic component at a coastal location." Atmospheric Chemistry and Physics Discussions 14, no. 9 (2014): 12525–53. http://dx.doi.org/10.5194/acpd-14-12525-2014.
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Abstract. As one aspect of the NETwork on Climate and Aerosols: Addressing Key Uncertainties in Remote Canadian Environments (NETCARE), measurements of the cloud condensation nucleation properties of 50 and 100 nm aerosol particles were conducted at Ucluelet on the west coast of Vancouver Island in August 2013. Additionally, the size-resolved chemical speciation of two particle size ranges (42–75 nm and 78–141nm) was inferred using a combination of ion chromatography and particle size distributions. Together, this information was used to estimate the hygroscopicity parameter of the organic species contained within the ambient aerosol particles (κorg). The overall hygroscopicity parameter of the aerosol (κambient) exhibited a wide variation, ranging from 0.14 to 1.08, with the highest values arising when the organic to sulfate ratio of the aerosol composition was lowest and when the winds were from the west, i.e. off the ocean. Correspondingly, the aerosol's two-day average chemical speciation also showed variation but was consistently dominated by its organic (60 to 86% by mass) and sulfate (10 to 34% by mass) components. With derived values of κorg from 0.3 to 0.5, it is illustrated that the organic component of marine-influenced aerosol can be viewed as quite hygroscopic, somewhat more than typical continental organics but not as much as soluble inorganic components.
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Yang, Hong, Jinhui Xu, Wai-Shing Wu, Chun Hong Wan, and Jian Zhen Yu. "Chemical Characterization of Water-Soluble Organic Aerosols at Jeju Island Collected During ACE-Asia." Environmental Chemistry 1, no. 1 (2004): 13. http://dx.doi.org/10.1071/en04006.
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Environmental Context. Atmospheric aerosols — particles suspended in the atmosphere — are responsible for many phenomena, including formation of cloud condensation nuclei and degradation of regional visibility. Water-soluble organic carbon (WSOC) components make up a significant fraction of the aerosols' carbon mass, and have consequently received increasing attention from researchers. The chemical composition of the WSOC fraction, and thus their sources and effects, are not well known. This study focusses on WSOC from samples collected in South Korea as part of ACE-Asia (Asia-Pacific Regional Aerosol Characterization Experiment), a large international collaboration including Asia, the USA, Europe and Australia. Abstract.During the Asia-Pacific Regional Aerosol Characterization Experiment (ACE-Asia) intensive field campaign, aerosol samples of less than 2.5 μm diameter were collected at Jeju Island, South Korea, for chemical characterization of the water-soluble organic carbon (WSOC) fraction. The WSOC fraction had an average mass concentration of roughly half of that of sulfate and accounted for about two-thirds of the organic carbon mass. Thirty individual water-soluble organic compounds, belonging to the classes of mono- and di-carboxylic acids, aliphatic amines, and amino acids, were identified, accounting for 14% of the WSOC on a carbon basis. Oxalic acid was the most abundant single component. An additional 3% of the WSOC was estimated to be monomeric carbohydrates. Thermal analysis of the aerosol’s water extracts indicated that a significant fraction (~50%) of WSOC was thermally recalcitrant, possibly consisting of polymeric materials.
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Chung, Chul E., Jung-Eun Chu, Yunha Lee, et al. "Global fine-mode aerosol radiative effect, as constrained by comprehensive observations." Atmospheric Chemistry and Physics 16, no. 13 (2016): 8071–80. http://dx.doi.org/10.5194/acp-16-8071-2016.
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Abstract. Aerosols directly affect the radiative balance of the Earth through the absorption and scattering of solar radiation. Although the contributions of absorption (heating) and scattering (cooling) of sunlight have proved difficult to quantify, the consensus is that anthropogenic aerosols cool the climate, partially offsetting the warming by rising greenhouse gas concentrations. Recent estimates of global direct anthropogenic aerosol radiative forcing (i.e., global radiative forcing due to aerosol–radiation interactions) are −0.35 ± 0.5 W m−2, and these estimates depend heavily on aerosol simulation. Here, we integrate a comprehensive suite of satellite and ground-based observations to constrain total aerosol optical depth (AOD), its fine-mode fraction, the vertical distribution of aerosols and clouds, and the collocation of clouds and overlying aerosols. We find that the direct fine-mode aerosol radiative effect is −0.46 W m−2 (−0.54 to −0.39 W m−2). Fine-mode aerosols include sea salt and dust aerosols, and we find that these natural aerosols result in a very large cooling (−0.44 to −0.26 W m−2) when constrained by observations. When the contribution of these natural aerosols is subtracted from the fine-mode radiative effect, the net becomes −0.11 (−0.28 to +0.05) W m−2. This net arises from total (natural + anthropogenic) carbonaceous, sulfate and nitrate aerosols, which suggests that global direct anthropogenic aerosol radiative forcing is less negative than −0.35 W m−2.
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Penning de Vries, M., S. Beirle, and T. Wagner. "UV aerosol indices from SCIAMACHY: introducing the SCattering Index (SCI)." Atmospheric Chemistry and Physics Discussions 9, no. 3 (2009): 13569–92. http://dx.doi.org/10.5194/acpd-9-13569-2009.
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Abstract. The Absorbing Aerosol Index (AAI) is a useful tool for detecting aerosols that absorb UV radiation – especially in cases where other aerosol retrievals fail, such as over bright surfaces (e.g. desert) and in the presence of clouds. The AAI does not, however, consider contributions from "scattering" (hardly absorbing) aerosols and clouds: they cause negative AAI values and are usually discarded. In this paper, we demonstrate the use of the AAI's negative counterpart, the SCattering Index (SCI) to detect "scattering" aerosols. Maps of seasonally averaged SCI show significantly enhanced values in summer in Southeast USA and Southeast Asia, pointing to high production of "scattering" aerosols (presumably mainly sulphate aerosols and organic aerosols) in this season. The application of a cloud filter makes the presence of "scattering" aerosols even more clear. In a comparison of AOT from AERONET and our Aerosol Indices from SCIAMACHY, good agreement was found for two AERONET stations in Southeast USA, and two stations in Africa. This fact confirms the suitability of SCI as a tool to detect "scattering" aerosols. The combination of the UV Aerosol Indices AAI and SCI provides the unique possibility to characterise absorbing properties of aerosols from space. Accurate knowledge about aerosol absorption is crucial for the correct determination of the contribution of aerosols to the radiative budget.
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Gharibzadeh, Maryam, Khan Alam, Yousefali Abedini, and Abbasali Aliakbari Bidokhti. "Classification of aerosols using multiple clustering techniques over Zanjan, Iran, during 2010-2014." E3S Web of Conferences 99 (2019): 02007. http://dx.doi.org/10.1051/e3sconf/20199902007.
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A more detailed study and identification of aerosol types can help to better understand the sources and effects of aerosols. In the present study, a number of optical properties of aerosols have been investigated seasonal for discrimination of aerosol types during 2010-2014 over Zanjan, Iran. Also using AERosol RObotic NETwork (AERONET) data, aerosol was classified by multiple clustering techniques. Both fine and coarse modes particles were seen in seasonal averaged of Aerosol Volume Size Distribution (AVSD). Single Scattering Albedo (SSA) variations indicate the presence of scattering aerosol like dust in the spring, summer and fall, and dominance of absorbing type aerosols in the winter. The maximum value of the phase function was observed in the summer and in small scattering angle which can be due to presence of coarse mode dust particles. The scatter plot of Aerosol Optical Depth (AOD) versus Angstrom Exponent (AE) is one of the most effective methods to find aerosol types. Extinction Angstrom exponent (EAE) versus SSA and EAE versus absorption Angstrom exponent (AAE) are other ways to classification of aerosol types. Graphs show abundance of dust in the spring, summer and fall in Zanjan's atmosphere. Also presence of urban/industrial aerosols is in all seasons, especially in the fall and winter. In addition mixed aerosols exist in all seasons. On the other hand, no biomass burning aerosols found in Zanjan's atmosphere.
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Yakobi-Hancock, J. D., L. A. Ladino, A. K. Bertram, et al. "CCN activity of size-selected aerosol at a Pacific coastal location." Atmospheric Chemistry and Physics 14, no. 22 (2014): 12307–17. http://dx.doi.org/10.5194/acp-14-12307-2014.
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Abstract. As one aspect of the NETwork on Climate and Aerosols: addressing key uncertainties in Remote Canadian Environments (NETCARE), measurements of the cloud condensation nucleation properties of 50 and 100 nm aerosol particles were conducted at Ucluelet on the west coast of Vancouver Island in August 2013. The overall hygroscopicity parameter of the aerosol (κambient) exhibited a wide variation, ranging from 0.14 ± 0.05 to 1.08 ± 0.40 (where the uncertainty represents the systematic error). The highest κ values arose when the organic-to-sulfate ratio of the aerosol was lowest and when winds arrived from the west after transport through the marine boundary layer. The average κambient during this time was 0.57 ± 0.16, where the uncertainty represents the standard deviation. At most other times, the air was predominantly influenced by both marine and continental emissions, which had lower average PM1 κambient values (max value, 0.41 ± 0.08). The two-day average aerosol ionic composition also showed variation, but was consistently acidic and dominated by ammonium (18–56% by mole) and sulfate (19–41% by mole), with only minor levels of sodium or chloride. Average κorg (hygroscopicity parameter for the aerosol's organic component) values were estimated using PM1 aerosol composition data and by assuming that the ratio of aerosol organic to sulfate mass is related directly to the composition of the size-selected particles.
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Chan, C. H., A. Y. S. Cheng, and A. Viseu. "A simplified empirical method for determination of aerosol hygroscopicity and composition." Atmospheric Chemistry and Physics Discussions 10, no. 10 (2010): 23627–56. http://dx.doi.org/10.5194/acpd-10-23627-2010.
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Abstract. Atmospheric aerosols have substantial influence on the Earth's radiation budget, visibility, cloud formation and precipitation. The aerosol hygroscopicity and the composition of aerosols are of vital importance for solar radiation budget calculation, cloud formation mechanism, and measurement of aerosol spatiotemporal distribution through remote sensing, such as Lidar, MODIS and sun/star photometer. In this paper, hourly averaged records of humidity, visibility and aerosol concentration, conducted in Macao, P.R.C. from 1 February 2006 to 31 December 2008 (LT), are used to estimate aerosol hygroscopicity and composition with a simplified empirical method. The result of monthly variation of aerosol hygroscopicity indicates the important role of aerosol composition on optical properties, which is in agreement with the previous study. This aerosol composition pattern is also consistent with the Asiatic Monsoon pattern and vicinity, such as Hong Kong. The monthly variation of aerosol hygroscopicity and composition also shows the necessity to consider such a factor for the aerosols monitoring by remote system and aerosols forcing simulated by climate model.
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Wang, J., Y. N. Lee, P. H. Daum, J. Jayne, and M. L. Alexander. "Effects of aerosol organics on cloud condensation nucleus (CCN) concentration and first indirect aerosol effect." Atmospheric Chemistry and Physics Discussions 8, no. 3 (2008): 9783–818. http://dx.doi.org/10.5194/acpd-8-9783-2008.
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Abstract. Aerosol microphysics, chemical composition, and CCN properties were measured on the Department of Energy Gulfstream-1 aircraft during the Marine Stratus/Stratocumulus Experiment (MASE) conducted over the coastal waters between Point Reyes National Seashore and Monterey Bay, California, in July 2005. Aerosols measured during MASE included free tropospheric aerosols, marine boundary layer aerosols, and aerosols with high organic concentration within a thin layer above the cloud. Closure analysis was carried out for all three types of aerosols by comparing the measured CCN concentrations at 0.22% supersaturation to those predicted based on size distribution and chemical composition using Köhler theory. The effect of aerosol organic species on predicted CCN concentration was examined using a single hygroscopicity parameterization. For aerosols with organics volume fraction up to 70%, such as the marine boundary layer and free troposphere aerosols, CCN concentration and the corresponding first indirect aerosol effect are insensitive to the properties of organics, and can be accurately predicted with a constant hygroscopicity for all organic species. This simplification can facilitate the prediction of indirect aerosol effects using physically-based parameterizations in large scale models. However, for the aerosols within the thin layers above clouds, organics contributed up to 90% of the total aerosol volume, and a detailed knowledge of organic hygroscopicity is required to accurately predict CCN concentrations. Derivations of organic properties in future closure studies, when aerosols are dominated by organic species, would help constrain the descriptions of organics and aerosol-cloud parameterizations in large scale models.
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Liao, Riwei, Wei Guo, Nan Zeng, et al. "Polarization Measurements and Evaluation Based on Multidimensional Polarization Indices Applied in Analyzing Atmospheric Particulates." Applied Sciences 11, no. 13 (2021): 5992. http://dx.doi.org/10.3390/app11135992.
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Online identification and characterization of suspended aerosols can provide a scientific basis for understanding aerosol transformations, quantitatively evaluating the impacts on air quality, public health, and the source apportionment of different atmospheric particulate matters. In this study, we confirm the validity of our developed high-throughput multi-angle polarized scattering vector detection of aerosols and multidimensional polarization scattering index systems. By observation of the mean values, variance, and Wilk’s Lambda of multidimensional polarization indices for different aerosol types, the polarization index shows unique characterization abilities for aerosol properties, and the optimal combination of polarization indices can always be found for a specific aerosol category with a high resolution and discrimination. Clearly, the multidimensional polarization indices of individual aerosols are more suitable for online and real-time aerosol identification and even help to explain the in situ microphysical characteristics of aerosols or evaluate the dynamic evolution of aerosols.
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Choi, Y., Y. S. Ghim, and B. N. Holben. "Identification of column-integrated dominant aerosols using the archive of AERONET data set." Atmospheric Chemistry and Physics Discussions 13, no. 10 (2013): 26627–56. http://dx.doi.org/10.5194/acpd-13-26627-2013.
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Abstract. Dominant aerosols were distinguished from level 2 inversion products for the Anmyon Aerosol Robotic Network (AERONET) site between 1999 and 2007. Secondary inorganic ions, black carbon (BC) and organic carbon (OC) were separated from fine mode aerosols, and mineral dust (MD), MD mixed with carbon, mixed coarse particles were separated from coarse mode aerosols. Four parameters (aerosol optical depth, single scattering albedo, absorption Angstrom exponent, and fine mode fraction) were used for this classification. Monthly variation of the occurrence rate of each aerosol type reveals that MD and MD mixed with carbon are frequent in spring. Although the fraction among dominant aerosols and occurrence rates of BC and OC tend to be high in cold season for heating, their contributions are variable but consistent due to various combustion sources. Secondary inorganic ions are most prevalent from June to August; the effective radius of these fine mode aerosols increases with water vapor content because of hygroscopic growth. To evaluate the validity of aerosol types identified, dominant aerosols at worldwide AERONET sites (Beijing, Mexico City, Goddard Space Flight Center, Mongu, Alta Floresta, Cape Verde), which have distinct source characteristics, were classified into the same aerosol types. The occurrence rate and fraction of the aerosol types at the selected sites confirm that the classification in this study is reasonable. However, mean optical properties of the aerosol types are generally influenced by the aerosol types with large fractions. The present work shows that the identification of dominant aerosols is effective even at a single site, provided that the archive of the data set is properly available.
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Peters, K., J. Quaas, and N. Bellouin. "Effects of absorbing aerosols in cloudy skies: a satellite study over the Atlantic Ocean." Atmospheric Chemistry and Physics Discussions 9, no. 5 (2009): 20853–80. http://dx.doi.org/10.5194/acpd-9-20853-2009.
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Abstract. Aerosol effects, direct as well as indirect, constitute one of the biggest sources of uncertainty when it comes to quantifying human forcing of climate change. Understanding these will thus increase the credibility of climate predictions. This study focuses on aerosol effects when absorbing aerosols reside in cloudy skies. In cloudfree conditions, aerosols usually exert a negative radiative forcing (RF) at the top of the atmosphere (TOA) due to their scattering properties. When located above clouds, absorbing aerosols can reduce the shortwave local planetary albedo α, resulting in an often significant local positive direct radiative forcing (DRF). A method for deriving the aerosol radiative effects of absorbing aerosols in cloudy situations from satellite retrievals is presented. Data of 2005 and 2006 from various sensors aboard satellites of the "A-Train" constellation, restricted to the tropical and subtropical Atlantic ocean, is used. A multiple linear regression is performed to identify the dependence of α in cloudy scenes on cloud liquid water path (LWP) and aerosol optical depth (AOD), using the OMI UV-Aerosolindex (UV-AI) as an indicator for absorbing aerosols. The results show an increase of α with increasing aerosol load, and a relative decrease of α with increasing amount of absorbing aerosols in cloudy scenes. This allows to derive the direct aerosol effect of absorbing aerosols above clouds, with the effect of aerosol absorption over clouds in the Atlantic contributing +0.08±1.2×10-3Wm-2 to the global TOA RF.
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Wang, J., Y. N. Lee, P. H. Daum, J. Jayne, and M. L. Alexander. "Effects of aerosol organics on cloud condensation nucleus (CCN) concentration and first indirect aerosol effect." Atmospheric Chemistry and Physics 8, no. 21 (2008): 6325–39. http://dx.doi.org/10.5194/acp-8-6325-2008.
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Abstract. Aerosol microphysics, chemical composition, and CCN properties were measured on the Department of Energy Gulfstream-1 aircraft during the Marine Stratus/Stratocumulus Experiment (MASE) conducted over the coastal waters between Point Reyes National Seashore and Monterey Bay, California, in July 2005. Aerosols measured during MASE included free tropospheric aerosols, marine boundary layer aerosols, and aerosols with high organic concentration within a thin layer above the cloud. Closure analysis was carried out for all three types of aerosols by comparing the measured CCN concentrations at ~0.2% supersaturation to those predicted based on size distribution and chemical composition using Köhler theory. The effect of aerosol organic species on predicted CCN concentration was examined using a single hygroscopicity parameterization. For aerosols with organics volume fraction up to 70%, such as the marine boundary layer and free troposphere aerosols, CCN concentration and the corresponding first indirect aerosol effect are insensitive to the properties of organics, and can be accurately predicted with a constant hygroscopicity for all organic species. This simplification can facilitate the prediction of indirect aerosol effects using physically-based parameterizations in large scale models. However, for the aerosols within the thin layers above clouds, organics contributed up to 90% of the total aerosol volume, and an accurate knowledge of the overall organic hygroscopicity is required to accurately predict CCN concentrations. Derivations of organic properties in future closure studies, when aerosols are dominated by organic species, would help constrain the descriptions of organics and aerosol-cloud parameterizations in large scale models.
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Rahav, Eyal, Natalia Belkin, Adina Paytan, and Barak Herut. "The Relationship between Air-Mass Trajectories and the Abundance of Dust-Borne Prokaryotes at the SE Mediterranean Sea." Atmosphere 10, no. 5 (2019): 280. http://dx.doi.org/10.3390/atmos10050280.
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Airborne prokaryotes are transported along with dust/aerosols, yet very little attention is given to their temporal variability above the oceans and the factors that govern their abundance. We analyzed the abundance of autotrophic (cyanobacteria) and heterotopic airborne microbes in 34 sampling events between 2015–2018 at a coastal site in the SE Mediterranean Sea. We show that airborne autotrophic (0.2–7.6 cells × 103 m−3) and heterotrophic (0.2–30.6 cells × 103 m−3) abundances were affected by the origin and air mass trajectory, and the concentration of dust/aerosols in the air, while seasonality was not coherent. The averaged ratio between heterotrophic and autotrophic prokaryotes in marine-dominated trajectories was ~1.7 ± 0.6, significantly lower than for terrestrial routes (6.8 ± 6.1). Airborne prokaryotic abundances were linearly and positively correlated to the concentrations of total aerosol, while negatively correlated with the aerosol’s anthropogenic fraction (using Pb/Al or Cu/Al ratios as proxies). While aerosols may play a major role in dispersing terrestrial and marine airborne microbes in the SE Mediterranean Sea, the mechanisms involved in the dispersal and diversity of airborne microorganisms remain to be studied and should include standardization in collection and analysis protocols.
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Kristiansen, N. I., A. Stohl, D. J. L. Olivié, et al. "Evaluation of observed and modelled aerosol lifetimes using radioactive tracers of opportunity and an ensemble of 19 global models." Atmospheric Chemistry and Physics Discussions 15, no. 17 (2015): 24513–85. http://dx.doi.org/10.5194/acpd-15-24513-2015.
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Abstract. Aerosols have important impacts on air quality and climate, but the processes affecting their removal from the atmosphere are not fully understood and are poorly constrained by observations. This makes modelled aerosol lifetimes uncertain. In this study, we make use of an observational constraint on aerosol lifetimes provided by radionuclide measurements and investigate the causes of differences within a set of global models. During the Fukushima Dai-Ichi nuclear power plant accident of March 2011, the radioactive isotopes cesium-137 (137Cs) and xenon-133 (133Xe) were released in large quantities. Cesium attached to particles in the ambient air, approximately according to their available aerosol surface area. 137Cs size distribution measurements taken close to the power plant suggested that accumulation-mode (AM) sulphate aerosols were the main carriers for the cesium. Hence, 137Cs can be used as a proxy tracer for the AM sulphate aerosol's fate in the atmosphere. In contrast, the noble gas 133Xe behaves almost like a passive transport tracer. Global surface measurements of the two radioactive isotopes taken over several months after the release allow the derivation of a lifetime of the carrier aerosol. We compare this to the lifetimes simulated by 19 different atmospheric transport models initialized with identical emissions of 137Cs that were assigned to an aerosol tracer with each model's default properties of AM sulphate, and 133Xe emissions that were assigned to a passive tracer. We investigate to what extent the modelled sulphate tracer can reproduce the measurements, especially with respect to the observed loss of aerosol mass with time. Modelled 37Cs and 133Xe concentrations sampled at the same location and times as station measurements allow a direct comparison between measured and modelled aerosol lifetime. The e-folding lifetime τe, calculated from station measurement data taken between two and nine weeks after the start of the emissions, is 14.3 days (95 % confidence interval 13.1–15.7 days). The equivalent modelled τe lifetimes have a large spread, varying between 4.8 and 26.7 days with a model median of 9.4 ± 2.3 days, indicating too fast removal in most models. Because sufficient measurement data were only available from about two weeks after the release, the estimated lifetimes apply to aerosols that have undergone long-range transport, i.e. not for freshly emitted aerosol. However, modelled instantaneous lifetimes show that the initial removal in the first two weeks was quicker (lifetimes between 1–5 days) due to the emissions occurring at low altitudes and co-location of the fresh plume with strong precipitation. Deviations between measured and modelled aerosol lifetimes are largest for the northernmost stations and at later time periods, suggesting that models do not transport enough of the aerosol towards the Arctic. The models underestimate passive tracer (133Xe) concentrations in the Arctic as well but to a smaller extent than for the aerosol (137Cs) tracer. This indicates that in addition to too fast aerosol removal in the models, errors in simulated atmospheric transport towards the Arctic in most models also contribute to the Arctic aerosol underestimates.
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Kristiansen, N. I., A. Stohl, D. J. L. Olivié, et al. "Evaluation of observed and modelled aerosol lifetimes using radioactive tracers of opportunity and an ensemble of 19 global models." Atmospheric Chemistry and Physics 16, no. 5 (2016): 3525–61. http://dx.doi.org/10.5194/acp-16-3525-2016.
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Abstract. Aerosols have important impacts on air quality and climate, but the processes affecting their removal from the atmosphere are not fully understood and are poorly constrained by observations. This makes modelled aerosol lifetimes uncertain. In this study, we make use of an observational constraint on aerosol lifetimes provided by radionuclide measurements and investigate the causes of differences within a set of global models. During the Fukushima Dai-Ichi nuclear power plant accident of March 2011, the radioactive isotopes cesium-137 (137Cs) and xenon-133 (133Xe) were released in large quantities. Cesium attached to particles in the ambient air, approximately according to their available aerosol surface area. 137Cs size distribution measurements taken close to the power plant suggested that accumulation-mode (AM) sulfate aerosols were the main carriers of cesium. Hence, 137Cs can be used as a proxy tracer for the AM sulfate aerosol's fate in the atmosphere. In contrast, the noble gas 133Xe behaves almost like a passive transport tracer. Global surface measurements of the two radioactive isotopes taken over several months after the release allow the derivation of a lifetime of the carrier aerosol. We compare this to the lifetimes simulated by 19 different atmospheric transport models initialized with identical emissions of 137Cs that were assigned to an aerosol tracer with each model's default properties of AM sulfate, and 133Xe emissions that were assigned to a passive tracer. We investigate to what extent the modelled sulfate tracer can reproduce the measurements, especially with respect to the observed loss of aerosol mass with time. Modelled 137Cs and 133Xe concentrations sampled at the same location and times as station measurements allow a direct comparison between measured and modelled aerosol lifetime. The e-folding lifetime τe, calculated from station measurement data taken between 2 and 9 weeks after the start of the emissions, is 14.3 days (95 % confidence interval 13.1–15.7 days). The equivalent modelled τe lifetimes have a large spread, varying between 4.8 and 26.7 days with a model median of 9.4 ± 2.3 days, indicating too fast a removal in most models. Because sufficient measurement data were only available from about 2 weeks after the release, the estimated lifetimes apply to aerosols that have undergone long-range transport, i.e. not for freshly emitted aerosol. However, modelled instantaneous lifetimes show that the initial removal in the first 2 weeks was quicker (lifetimes between 1 and 5 days) due to the emissions occurring at low altitudes and co-location of the fresh plume with strong precipitation. Deviations between measured and modelled aerosol lifetimes are largest for the northernmost stations and at later time periods, suggesting that models do not transport enough of the aerosol towards the Arctic. The models underestimate passive tracer (133Xe) concentrations in the Arctic as well but to a smaller extent than for the aerosol (137Cs) tracer. This indicates that in addition to too fast an aerosol removal in the models, errors in simulated atmospheric transport towards the Arctic in most models also contribute to the underestimation of the Arctic aerosol concentrations.
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Penning de Vries, M. J. M., S. Beirle, and T. Wagner. "UV Aerosol Indices from SCIAMACHY: introducing the SCattering Index (SCI)." Atmospheric Chemistry and Physics 9, no. 24 (2009): 9555–67. http://dx.doi.org/10.5194/acp-9-9555-2009.
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Abstract. The Absorbing Aerosol Index (AAI) is a useful tool for detecting aerosols that absorb UV radiation – especially in cases where other aerosol retrievals fail, such as over bright surfaces (e.g. desert) and in the presence of clouds. The AAI does not, however, consider contributions from scattering (hardly absorbing) aerosols and clouds: they cause negative AAI values and are usually disregarded. In this paper, we demonstrate the use of the AAI's negative counterpart, the SCattering Index (SCI) to detect scattering aerosols. Consideration of the full UV Aerosol Index scale is of importance if the Aerosol Index is to be used for the quantification of aerosol absorption in the future. Maps of seasonally averaged SCI show significantly enhanced values in summer in Southeast USA and Southeast Asia, pointing to a high production of scattering aerosols (presumably mainly sulphate aerosols and secondary organic aerosols) in this season. The application of a cloud filter makes the presence of scattering aerosols even more clear. Radiative transfer calculations were performed to investigate the sensitivity of AAI and SCI to cloud parameters, and it is demonstrated that clouds cause significant SCI, in some special cases even small AAI values. The results from cloud modelling imply that cloud effects need to be taken into account when AAI and SCI are used in a quantitative manner. The paper concludes with a comparison of aerosol parameters from AERONET and our Aerosol Indices (AAI and SCI) from SCIAMACHY, where reasonable agreement was found for six AERONET stations in Southeast USA, Southeast Asia, and Africa. These findings corroborate the suitability of SCI as a tool to detect scattering aerosols.
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Fadnavis, S., K. Semeniuk, L. Pozzoli, M. G. Schultz, S. D. Ghude, and S. Das. "Transport of aerosol pollution in the UTLS during Asian summer monsoon as simulated by ECHAM5-HAMMOZ model." Atmospheric Chemistry and Physics Discussions 12, no. 11 (2012): 30081–117. http://dx.doi.org/10.5194/acpd-12-30081-2012.
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Abstract. An eight member ensemble of ECHAM5-HAMMOZ simulations for the year 2003 is analyzed to study the transport of aerosols in the Upper Troposphere and Lower Stratosphere (UTLS) during the Asian Summer Monsoon (ASM). Simulations show persistent maxima in black carbon, organic carbon, sulfate, and mineral dust aerosols within the anticyclone in the UTLS throughout the ASM (period from July to September) when convective activity over the Indian subcontinent is highest. Model simulations indicate boundary layer aerosol pollution as the source of this UTLS aerosol layer and identify ASM convection as the dominant transport process. Evidence of ASM transport of aerosols into the stratosphere is observed in HALogen Occultation Experiment (HALOE) and Stratospheric Aerosol and Gas Experiment (SAGE) II aerosol extinction. The impact of aerosols in the UTLS region is analyzed by evaluating the differences between simulations with (CTRL) and without aerosol (HAM-off) loading. The transport of anthropogenic aerosols in the UTLS increases cloud ice, water vapour and temperature, indicating that aerosols play an important role in enhancement of cloud ice in the Upper-Troposphere (UT). Aerosol induced circulation changes include a weakening of the main branch of the Hadley circulation and increased vertical transport around the southern flank of the Himalayas and reduction in monsoon precipitation over the India region.
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Giannakaki, E., D. S. Balis, V. Amiridis, and C. Zerefos. "Optical properties of different aerosol types: seven years of combined Raman- elastic backscatter lidar measurements in Thessaloniki, Greece." Atmospheric Measurement Techniques Discussions 2, no. 6 (2009): 3027–54. http://dx.doi.org/10.5194/amtd-2-3027-2009.
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Abstract. We present our combined Raman/elastic backscatter lidar observations which were carried out at the EARLINET station of Thessaloniki, Greece, during the period 2001–2007. The largest optical depths are observed for Saharan dust and smoke aerosol loads. For "local" and "continental polluted" aerosols the measurements indicate moderate aerosol loads. However, measurements associated with the "local" path show lower values of free tropospheric contribution (37% versus 46% for "continental polluted") and thus, enhanced aerosol load within the Planetary Boundary Layer. The lowest value of aerosol optical depth is observed for "continental clean" aerosols. The largest lidar ratios, of the order of 70 sr are found for biomass burning aerosols. A significant and distinct correlation between lidar ratio and backscatter related Ångström exponent values was estimated for well defined aerosol categories, which provides a statistical measure of the lidar ratio's dependency on aerosol-size, which is a useful tool for elastic lidar systems. Scatter plot between lidar ratio values and Ångström exponent values for "local" and "continental polluted" aerosols does not show a significant correlation, with a large variation in both parameters possibly due to variable absorption characteristics of these aerosols. Finally for "clean continental" aerosols we found constantly low lidar ratios almost independent of size.
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Jeong, Gill-Ran. "Weather Effects of Aerosols in the Global Forecast Model." Atmosphere 11, no. 8 (2020): 850. http://dx.doi.org/10.3390/atmos11080850.
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The weather effects of aerosol types were investigated using well-posed aerosol climatology through the aerosol sensitivity test of thermodynamic and hydrometeor fields, and the weather forecast performances in July of 2017. The largest aerosol direct radiative forcing (ADRF) in July was due to dust aerosols at the surface and atmosphere, and sulfate at the top of the atmosphere (TOA), respectively. The ADRF of total aerosols had unilateral tendencies in thermodynamic and hydrometeor fields. The contribution of individual aerosols was linearly additive to those of total aerosols in the heat fluxes, heating rates, humidity, and convective precipitation. However, no such linearity existed in temperature, geopotential height, cloud liquid or ice contents, and large-scale precipitation. Dust was the most influential forcing agent in July among five aerosol types due to the largest light-absorption capacity. Such unilateral tendencies of total aerosols and a part of the linearity of individual aerosols were exerted on the weather systems. The verification of medium-range forecasts showed that aerosols alleviated the overestimation of surface shortwave (SW) downward fluxes, the negative biases of temperature and geopotential heights at TOA and surface, and the underestimation in light and moderate precipitation. In contrast, they enhanced warm biases at the mid-atmosphere and underestimation in heavy precipitations, particularly negative biases in the intertropical convergence zone (ITCZ). Weather forecast scores including current aerosol information were improved in geopotential height (GPH) of the northern hemisphere (NH); however, they got worse in the temperature and the upper atmosphere GPH of the southern hemisphere (SH), which was mostly due to black carbon (BC) aerosols in the tropical regions. The missing mechanisms such as aerosol–cloud interactions, better aerosol spectral optical properties including mixing states and aging, and the near-real-time (NRT) based aerosol loading data are worthwhile to be tried in the near future for fixing the intrinsic underestimation of precipitation in ITCZ and surface radiative fluxes in the desert and biomass burning area.
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Benedetti, Angela, and Frédéric Vitart. "Can the Direct Effect of Aerosols Improve Subseasonal Predictability?" Monthly Weather Review 146, no. 10 (2018): 3481–98. http://dx.doi.org/10.1175/mwr-d-17-0282.1.
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Abstract The fact that aerosols are important players in Earth’s radiation balance is well accepted by the scientific community. Several studies have shown the importance of characterizing aerosols in order to constrain surface radiative fluxes and temperature in climate runs. In numerical weather prediction, however, there has not been definite proof that interactive aerosol schemes are needed to improve the forecast. Climatologies are instead used that allow for computational efficiency and reasonable accuracy. At the monthly to subseasonal range, it is still worth investigating whether aerosol variability could afford some predictability, considering that it is likely that persisting aerosol biases might manifest themselves more over time scales of weeks to months and create a nonnegligible forcing. This paper explores this hypothesis using the ECMWF’s Ensemble Prediction System for subseasonal prediction with interactive prognostic aerosols. Four experiments are conducted with the aim of comparing the monthly prediction by the default system, which uses aerosol climatologies, with the prediction using radiatively interactive aerosols. Only the direct aerosol effect is considered. Twelve years of reforecasts with 50 ensemble members are analyzed on the monthly scale. Results indicate that the interactive aerosols have the capability of improving the subseasonal prediction at the monthly scales for the spring/summer season. It is hypothesized that this is due to the aerosol variability connected to the different phases of the Madden–Julian oscillation, particularly that of dust and carbonaceous aerosols. The degree of improvement depends crucially on the aerosol initialization. More work is required to fully assess the potential of interactive aerosols to increase predictability at the subseasonal scales.
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Croft, B., J. R. Pierce, R. V. Martin, C. Hoose, and U. Lohmann. "Uncertainty associated with convective wet removal of entrained aerosols in a global climate model." Atmospheric Chemistry and Physics 12, no. 22 (2012): 10725–48. http://dx.doi.org/10.5194/acp-12-10725-2012.
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Abstract. The uncertainties associated with the wet removal of aerosols entrained above convective cloud bases are investigated in a global aerosol-climate model (ECHAM5-HAM) under a set of limiting assumptions for the wet removal of the entrained aerosols. The limiting assumptions for the wet removal of entrained aerosols are negligible scavenging and vigorous scavenging (either through activation, with size-dependent impaction scavenging, or with the prescribed fractions of the standard model). To facilitate this process-based study, an explicit representation of cloud-droplet-borne and ice-crystal-borne aerosol mass and number, for the purpose of wet removal, is introduced into the ECHAM5-HAM model. This replaces and is compared with the prescribed cloud-droplet-borne and ice-crystal-borne aerosol fraction scavenging scheme of the standard model. A 20% to 35% uncertainty in simulated global, annual mean aerosol mass burdens and optical depth (AOD) is attributed to different assumptions for the wet removal of aerosols entrained above convective cloud bases. Assumptions about the removal of aerosols entrained above convective cloud bases control modeled upper tropospheric aerosol concentrations by as much as one order of magnitude. Simulated aerosols entrained above convective cloud bases contribute 20% to 50% of modeled global, annual mean aerosol mass convective wet deposition (about 5% to 10% of the total dry and wet deposition), depending on the aerosol species, when including wet scavenging of those entrained aerosols (either by activation, size-dependent impaction, or with the prescribed fraction scheme). Among the simulations, the prescribed fraction and size-dependent impaction schemes yield the largest global, annual mean aerosol mass convective wet deposition (by about two-fold). However, the prescribed fraction scheme has more vigorous convective mixed-phase wet removal (by two to five-fold relative to the size-dependent impaction scheme) since nearly all entrained accumulation and coarse mode aerosols are assumed to be cloud-droplet borne or ice-crystal borne, and evaporation due to the Bergeron-Findeisen process is neglected. The simulated convective wet scavenging of entrained accumulation and coarse mode aerosols has feedbacks on new particle formation and the number of Aitken mode aerosols, which control stratiform and convective cloud droplet number concentrations and yield precipitation changes in the ECHAM5-HAM model. However, the geographic distribution of aerosol annual mean convective wet deposition change in the model is driven by changes to the assumptions regarding the scavenging of aerosols entrained above cloud bases rather than by precipitation changes, except for sea salt deposition in the tropics. Uncertainty in the seasonal, regional cycles of AOD due to assumptions about entrained aerosol wet scavenging is similar in magnitude to the estimated error in the AOD retrievals. The uncertainty in aerosol concentrations, burdens, and AOD attributed to different assumptions for the wet scavenging of aerosols entrained above convective cloud bases in a global model motivates the ongoing need to better understand and model the activation and impaction processes that aerosols undergo after entrainment into convective updrafts.
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Cerully, K. M., A. Bougiatioti, J. R. Hite, et al. "On the link between hygroscopicity, volatility, and oxidation state of ambient and water-soluble aerosols in the southeastern United States." Atmospheric Chemistry and Physics 15, no. 15 (2015): 8679–94. http://dx.doi.org/10.5194/acp-15-8679-2015.
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Abstract. The formation of secondary organic aerosols (SOAs) combined with the partitioning of semivolatile organic components can impact numerous aerosol properties including cloud condensation nuclei (CCN) activity, hygroscopicity, and volatility. During the summer 2013 Southern Oxidant and Aerosol Study (SOAS) field campaign in a rural site in the southeastern United States, a suite of instruments including a CCN counter, a thermodenuder (TD), and a high-resolution time-of-flight aerosol mass spectrometer (AMS) were used to measure CCN activity, aerosol volatility, composition, and oxidation state. Particles were either sampled directly from ambient or through a particle-into-liquid sampler (PILS), allowing the investigation of the water-soluble aerosol component. Ambient aerosols exhibited size-dependent composition with larger particles being more hygroscopic. The hygroscopicity of thermally denuded aerosols was similar between ambient and PILS-generated aerosols and showed limited dependence on volatilization. Results of AMS three-factor positive matrix factorization (PMF) analysis for the PILS-generated aerosols showed that the most hygroscopic components are most likely the most and the least volatile features of the aerosols. No clear relationship was found between organic hygroscopicity and the oxygen-to-carbon ratio; in fact, isoprene-derived organic aerosols (isoprene-OAs) were found to be the most hygroscopic factor, while at the same time being the least oxidized and likely most volatile of all PMF factors. Considering the diurnal variation of each PMF factor and its associated hygroscopicity, isoprene-OA and more-oxidized oxygenated organic aerosols are the prime contributors to hygroscopicity and co-vary with less-oxidized oxygenated organic aerosols in a way that induces the observed diurnal invariance in total organic hygroscopicity. Biomass burning organic aerosols contributed little to aerosol hygroscopicity, which is expected since there was little biomass burning activity during the sampling period examined.
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Li, G., N. Bei, X. Tie, and L. T. Molina. "Aerosol effects on the photochemistry in Mexico City during MCMA-2006/MILAGRO campaign." Atmospheric Chemistry and Physics Discussions 11, no. 3 (2011): 8625–64. http://dx.doi.org/10.5194/acpd-11-8625-2011.
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Abstract. In the present study, the impact of aerosols on the photochemistry in Mexico City is evaluated using the WRF-CHEM model for the period from 24 to 29 March during the MCMA-2006/MILAGRO campaign. An aerosol radiative module has been developed with detailed consideration of aerosol size, composition, and mixture. The module has been coupled into the WRF-CHEM model to calculate the aerosol optical properties, including optical depth, single scattering albedo, and asymmetry factor. Calculated aerosol optical properties are in good agreement with the surface observations and aircraft and satellite measurements during daytime. In general, the photolysis rates are reduced due to the absorption by carbonaceous aerosols, particularly in the early morning and late afternoon with a long aerosol optical path. However, with the growth of aerosol particles and the decrease of the solar zenith angle around noontime, aerosols can slightly enhance photolysis rates when ultraviolet (UV) radiation scattering dominates UV absorption by aerosols. The changes in photolysis rates due to aerosols lead to about 2–17% surface ozone reduction during daytime in the urban area in Mexico City, resulting in a decrease of OH level by about 9%, as well as a decrease in the daytime concentrations of nitrate and secondary organic aerosols by 5–6% on average. In addition, the rapid aging of black carbon aerosols and the enhanced absorption of UV radiation by organic aerosols contribute substantially to the reduction of photolysis rates, resulting in a further decrease of other chemical species.
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Li, G., N. Bei, X. Tie, and L. T. Molina. "Aerosol effects on the photochemistry in Mexico City during MCMA-2006/MILAGRO campaign." Atmospheric Chemistry and Physics 11, no. 11 (2011): 5169–82. http://dx.doi.org/10.5194/acp-11-5169-2011.
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Abstract. In the present study, the impact of aerosols on the photochemistry in Mexico City is evaluated using the WRF-CHEM model for the period from 24 to 29 March during the MCMA-2006/MILAGRO campaign. An aerosol radiative module has been developed with detailed consideration of aerosol size, composition, and mixing. The module has been coupled into the WRF-CHEM model to calculate the aerosol optical properties, including optical depth, single scattering albedo, and asymmetry factor. Calculated aerosol optical properties are in good agreement with the surface observations and aircraft and satellite measurements during daytime. In general, the photolysis rates are reduced due to the absorption by carbonaceous aerosols, particularly in the early morning and late afternoon hours with a long aerosol optical path. However, with the growth of aerosol particles and the decrease of the solar zenith angle around noontime, aerosols can slightly enhance photolysis rates when ultraviolet (UV) radiation scattering dominates UV absorption by aerosols at the lower-most model layer. The changes in photolysis rates due to aerosols lead to about 2–17 % surface ozone reduction during daytime in the urban area in Mexico City with generally larger reductions during early morning hours near the city center, resulting in a decrease of OH level by about 9 %, as well as a decrease in the daytime concentrations of nitrate and secondary organic aerosols by 5–6 % on average. In addition, the rapid aging of black carbon aerosols and the enhanced absorption of UV radiation by organic aerosols contribute substantially to the reduction of photolysis rates.
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Giannakaki, E., D. S. Balis, V. Amiridis, and C. Zerefos. "Optical properties of different aerosol types: seven years of combined Raman-elastic backscatter lidar measurements in Thessaloniki, Greece." Atmospheric Measurement Techniques 3, no. 3 (2010): 569–78. http://dx.doi.org/10.5194/amt-3-569-2010.
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Abstract. We present our combined Raman/elastic backscatter lidar observations which were carried out at the EARLINET station of Thessaloniki, Greece, during the period 2001–2007. The largest optical depths are observed for Saharan dust and smoke aerosol particles. For local and continental polluted aerosols the measurements indicate high aerosol loads. However, measurements associated with the local path indicate enhanced aerosol load within the Planetary Boundary Layer. The lowest value of aerosol optical depth is observed for continental aerosols, from West directions with less free tropospheric contribution. The largest lidar ratios, of the order of 70 sr, are found for biomass burning aerosols. A significant and distinct correlation between lidar ratio and backscatter related Ångström exponent values were estimated for different aerosol categories. Scatter plot between lidar ratio values and Ångström exponent values for local and continental polluted aerosols does not show a significant correlation, with a large variation in both parameters possibly due to variable absorption characteristics of these aerosols. Finally for continental aerosols with west and northwest directions that follow downward movement when arriving at our site constantly low lidar ratios almost independent of size are found.
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Pedrós, R., J. L. Gómez-Amo, C. R. Marcos, et al. "AEROgui: A Graphical User Interface for the Optical Properties of Aerosols." Bulletin of the American Meteorological Society 95, no. 12 (2014): 1863–71. http://dx.doi.org/10.1175/bams-d-13-00162.1.
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Atmospheric aerosols have an uncertain effect on climate and serious impacts on human health. The uncertainty in the aerosols' role on climate has several sources. First, aerosols have great spatial and temporal variability. The spatial variability arises from the fact that aerosols emitted in a certain place can travel thousands of kilometers, swept by the winds to modify the destination region's climate. The spatial variability also means that aerosols are inhomogeneously distributed in the vertical direction, which can lead to a differential effect on the energy balance depending on the aerosols' altitude. On the other hand, aerosols experience physical and chemical transformations in the time they spend in the atmosphere, commonly known as aging, which modifies its optical properties. These factors make necessary the use of two approaches for the study of the aerosol impact on climate: global aerosol models and satellite- and ground-based measurements. The disagreement between the estimates of the two approaches is the main cause of the climate uncertainty. One way to reduce climate uncertainty is to create new tools to simulate more realistic aerosol scenarios. We present a graphical user interface to obtain aerosol optical properties: extinction, scattering, and absorption coefficients; single-scattering albedo; asymmetry parameter; and aerosol optical depth. The tool can be used to obtain the optical properties of the external and internal mixture of several aerosol components. Interface outputs have successfully been compared to a black carbon plume and to aging mineral dust.
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Grythe, Henrik, Nina I. Kristiansen, Christine D. Groot Zwaaftink, et al. "A new aerosol wet removal scheme for the Lagrangian particle model FLEXPART v10." Geoscientific Model Development 10, no. 4 (2017): 1447–66. http://dx.doi.org/10.5194/gmd-10-1447-2017.
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Abstract. A new, more physically based wet removal scheme for aerosols has been implemented in the Lagrangian particle dispersion model FLEXPART. It uses three-dimensional cloud water fields from the European Centre for Medium-Range Weather Forecasts (ECMWF) to determine cloud extent and distinguishes between in-cloud and below-cloud scavenging. The new in-cloud nucleation scavenging depends on cloud water phase (liquid, ice or mixed-phase), based on the aerosol's prescribed efficiency to serve as ice crystal nuclei and liquid water nuclei, respectively. The impaction scavenging scheme now parameterizes below-cloud removal as a function of aerosol particle size and precipitation type (snow or rain) and intensity.Sensitivity tests with the new scavenging scheme and comparisons with observational data were conducted for three distinct types of primary aerosols, which pose different challenges for modeling wet scavenging due to their differences in solubility, volatility and size distribution: (1) 137Cs released during the Fukushima nuclear accident attached mainly to highly soluble sulphate aerosol particles, (2) black carbon (BC) aerosol particles, and (3) mineral dust. Calculated e-folding lifetimes of accumulation mode aerosols for these three aerosol types were 11.7, 16.0, and 31.6 days respectively, when well mixed in the atmosphere. These are longer lifetimes than those obtained by the previous removal schem, and, for mineral dust in particular, primarily result from very slow in-cloud removal, which globally is the primary removal mechanism for these accumulation mode particles.Calculated e-folding lifetimes in FLEXPART also have a strong size dependence, with the longest lifetimes found for the accumulation-mode aerosols. For example, for dust particles emitted at the surface the lifetimes were 13.8 days for particles with 1 µm diameter and a few hours for 10 µm particles. A strong size dependence in below-cloud scavenging, combined with increased dry removal, is the primary reason for the shorter lifetimes of the larger particles. The most frequent removal is in-cloud scavenging (85 % of all scavenging events) but it occurs primarily in the free troposphere, while below-cloud removal is more frequent below 1000 m (52 % of all events) and can be important for the initial fate of species emitted at the surface, such as those examined here.For assumed realistic in-cloud removal efficiencies, both BC and sulphate have a slight overestimation of observed atmospheric concentrations (a factor of 1.6 and 1.2 respectively). However, this overestimation is largest close to the sources and thus appears more related to overestimated emissions rather than underestimated removal. The new aerosol wet removal scheme of FLEXPART incorporates more realistic information about clouds and aerosol properties and it compares better with both observed lifetimes and concentration than the old scheme.
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Park, Soon-Ung, and Jeong Hoon Cho. "Air Quality in East Asia during the heavy haze event period of 10 to 15 January 2013." International Journal of Energy and Environment 15 (March 24, 2021): 1–9. http://dx.doi.org/10.46300/91012.2021.15.1.
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A prolonged heavy haze event that has caused for the Environmental Protection Bureau (EPB) in Beijing to take emergency measures for the protection of the public health and the reduction of air pollution damages in China has been analyzed with the use of the Aerosol modeling System (AMS) to identify causes of this event. It is found that the heavy haze event is associated with high aerosols and water droplets concentrations. These high aerosol concentrations are mainly composed of anthropogenic aerosols, especially secondary inorganic aerosols formed by gas-to-particle conversion of gaseous pollutants in the eastern part of China whereas those in the northeastern parts of China are composed of the mixture of the anthropogenic aerosols and the Asian dust aerosol originated from the dust source regions of northern China and Mongolia. These high aerosol concentrations are found to be subsequently transported to the downwind regions of the Korean Peninsula and Japan causing a prolonged haze event there. It is also found that the Asian dust aerosol originated from northern China and Mongolia and the anthropogenic aerosols produced by chemical reactions of pollutants in the high emissions region of eastern China can cause significantly adverse environmental impacts in the whole Asian region by increased atmospheric aerosol loadings that may cause respiration diseases and visibility reduction and by excess deposition of aerosols causing adverse impacts on terrestrial and marine eco-systems.
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Fadnavis, S., K. Semeniuk, L. Pozzoli, et al. "Transport of aerosols into the UTLS and their impact on the Asian monsoon region as seen in a global model simulation." Atmospheric Chemistry and Physics 13, no. 17 (2013): 8771–86. http://dx.doi.org/10.5194/acp-13-8771-2013.
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Abstract. An eight-member ensemble of ECHAM5-HAMMOZ simulations for a boreal summer season is analysed to study the transport of aerosols in the upper troposphere and lower stratosphere (UTLS) during the Asian summer monsoon (ASM). The simulations show persistent maxima in black carbon, organic carbon, sulfate, and mineral dust aerosols within the anticyclone in the UTLS throughout the ASM (period from July to September), when convective activity over the Indian subcontinent is highest, indicating that boundary layer aerosol pollution is the source of this UTLS aerosol layer. The simulations identify deep convection and the associated heat-driven circulation over the southern flanks of the Himalayas as the dominant transport pathway of aerosols and water vapour into the tropical tropopause layer (TTL). Comparison of model simulations with and without aerosols indicates that anthropogenic aerosols are central to the formation of this transport pathway. Aerosols act to increase cloud ice, water vapour, and temperature in the model UTLS. Evidence of ASM transport of aerosols into the stratosphere is also found, in agreement with aerosol extinction measurements from the Halogen Occultation Experiment (HALOE) and Stratospheric Aerosol and Gas Experiment (SAGE) II. As suggested by the observations, aerosols are transported into the Southern Hemisphere around the tropical tropopause by large-scale mixing processes. Aerosol-induced circulation changes also include a weakening of the main branch of the Hadley circulation and a reduction of monsoon precipitation over India.
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Muhlbauer, Andreas, and Ulrike Lohmann. "Sensitivity Studies of Aerosol–Cloud Interactions in Mixed-Phase Orographic Precipitation." Journal of the Atmospheric Sciences 66, no. 9 (2009): 2517–38. http://dx.doi.org/10.1175/2009jas3001.1.
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Abstract Anthropogenic aerosols serve as a source of both cloud condensation nuclei (CCN) and ice nuclei (IN) and affect microphysical properties of clouds. Increasing aerosol number concentration is assumed to retard the cloud droplet coalescence and the riming process in mixed-phase orographic clouds, thereby decreasing orographic precipitation. In this study, idealized 3D simulations are conducted to investigate aerosol–cloud interactions in mixed-phase orographic clouds and the possible impact of anthropogenic and natural aerosols on orographic precipitation. Two different types of aerosol anomalies are considered: naturally occurring mineral dust and anthropogenic black carbon. In the simulations with a dust aerosol anomaly, the dust aerosols serve as efficient ice nuclei in the contact mode, leading to an early initiation of the ice phase in the orographic cloud. As a consequence, the riming rates in the cloud are increased, leading to increased precipitation efficiency and enhancement of orographic precipitation. The simulations with an anthropogenic aerosol anomaly suggest that the mixing state of the aerosols plays a crucial role because coating and mixing may cause the aerosols to initiate freezing in the less efficient immersion mode rather than by contact nucleation. It is found that externally mixed black carbon aerosols increase riming in orographic clouds and enhance orographic precipitation. In contrast, internally mixed black carbon aerosols decrease the riming rates, leading in turn to a decrease in orographic precipitation.
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Adler, G., J. M. Flores, A. Abo Riziq, S. Borrmann, and Y. Rudich. "Chemical, physical, and optical evolution of biomass burning aerosols: a case study." Atmospheric Chemistry and Physics Discussions 10, no. 10 (2010): 24371–407. http://dx.doi.org/10.5194/acpd-10-24371-2010.
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Abstract. In-situ chemical composition measurements of ambient aerosols have been used for characterizing the evolution of submicron aerosols from a large anthropogenic biomass burning (BB) event in Israel. A high resolution Time of Flight Aerosol Mass Spectrometer (Hi-RES-TOF-AMS) was used to follow the chemical evolution of BB aerosols during a night-long, extensive nationwide wood burning event and during the following day. While extensive BB is not common in this region, burning of agricultural waste is a common practice. The aging process of the BB aerosols was followed through their chemical, physical and optical properties. Mass spectrometric analysis of the aerosol organic component showed that aerosol aging is characterized by shifting from less oxidized fresh BB aerosols to more oxidized aerosols. Evidence for aerosol aging during the day following the BB event was indicated by an increase in the organic mass, its oxidation state, the total aerosol concentration, and a shift in the modal particle diameter. The effective broadband refractive index (EBRI) was derived using a white light optical particle counter (WELAS). The average EBRI for a mixed population of aerosols dominated by open fires was m=1.53(±0.03)+0.07i(±0.03), during the smoldering phase of the fires we found the EBRI to be m=1.54(±0.01)+0.04i(±0.01) compared to m=1.49(±0.01)+0.02i(±0.01) of the aged aerosols during the following day. This change indicates a decrease in the overall aerosol absorption and scattering. Elevated levels of particulate Polycyclic Aromatic Hydrocarbons (PAHs) were detected during the entire event, which suggest possible implications for human health during such extensive event.
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Adler, G., J. M. Flores, A. Abo Riziq, S. Borrmann, and Y. Rudich. "Chemical, physical, and optical evolution of biomass burning aerosols: a case study." Atmospheric Chemistry and Physics 11, no. 4 (2011): 1491–503. http://dx.doi.org/10.5194/acp-11-1491-2011.
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Abstract. In-situ chemical composition measurements of ambient aerosols have been used for characterizing the evolution of submicron aerosols from a large anthropogenic biomass burning (BB) event in Israel. A high resolution Time of Flight Aerosol Mass Spectrometer (HR-RES-TOF-AMS) was used to follow the chemical evolution of BB aerosols during a night-long, extensive nationwide wood burning event and during the following day. While these types of extensive BB events are not common in this region, burning of agricultural waste is a common practice. The aging process of the BB aerosols was followed through their chemical, physical and optical properties. Mass spectrometric analysis of the aerosol organic component showed that aerosol aging is characterized by shifting from less oxidized fresh BB aerosols to more oxidized aerosols. Evidence for aerosol aging during the day following the BB event was indicated by an increase in the organic mass, its oxidation state, the total aerosol concentration, and a shift in the modal particle diameter. The effective broadband refractive index (EBRI) was derived using a white light optical particle counter (WELAS). The average EBRI for a mixed population of aerosols dominated by open fires was m = 1.53(±0.03) + 0.07i(±0.03), during the smoldering phase of the fires we found the EBRI to be m = 1.54(±0.01) + 0.04i(±0.01) compared to m = 1.49(±0.01) + 0.02i(±0.01) of the aged aerosols during the following day. This change indicates a decrease in the overall aerosol absorption and scattering. Elevated levels of particulate Polycyclic Aromatic Hydrocarbons (PAHs) were detected during the entire event, which suggest possible implications for human health during such extensive event.
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Li, Meng, Hang Su, Guo Li, Nan Ma, Ulrich Pöschl, and Yafang Cheng. "Relative importance of gas uptake on aerosol and ground surfaces characterized by equivalent uptake coefficients." Atmospheric Chemistry and Physics 19, no. 16 (2019): 10981–1011. http://dx.doi.org/10.5194/acp-19-10981-2019.
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Abstract. Quantifying the relative importance of gas uptake on the ground and aerosol surfaces helps to determine which processes should be included in atmospheric chemistry models. Gas uptake by aerosols is often characterized by an effective uptake coefficient (γeff), whereas gas uptake on the ground is usually described by a deposition velocity (Vd). For efficient comparison, we introduce an equivalent uptake coefficient (γeqv) at which the uptake flux of aerosols would equal that on the ground surface. If γeff is similar to or larger than γeqv, aerosol uptake is important and should be included in atmospheric models. In this study, we compare uptake fluxes in the planetary boundary layer (PBL) for different reactive trace gases (O3, NO2, SO2, N2O5, HNO3 and H2O2), aerosol types (mineral dust, soot, organic aerosol and sea salt aerosol), environments (urban areas, agricultural land, the Amazon forest and water bodies), seasons and mixing heights. For all investigated gases, γeqv ranges from magnitudes of 10−6–10−4 in polluted urban environments to 10−4–10−1 under pristine forest conditions. In urban areas, aerosol uptake is relevant for all species (γeff≥γeqv) and should be considered in models. On the contrary, contributions of aerosol uptakes in the Amazon forest are minor compared with the dry deposition. The phase state of aerosols could be one of the crucial factors influencing the uptake rates. Current models tend to underestimate the O3 uptake on liquid organic aerosols which can be important, especially over regions with γeff≥γeqv. H2O2 uptakes on a variety of aerosols are yet to be measured under laboratory conditions and evaluated. Given the fact that most models have considered the uptakes of these species on the ground surface, we suggest also considering the following processes in atmospheric models: N2O5 uptake by all types of aerosols, HNO3 and SO2 uptake by mineral dust and sea salt aerosols, H2O2 uptake by mineral dust, NO2 uptakes by sea salt aerosols and O3 uptake by liquid organic aerosols.
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Bossolasco, Adriana, Fabrice Jegou, Pasquale Sellitto, Gwenaël Berthet, Corinna Kloss, and Bernard Legras. "Global modeling studies of composition and decadal trends of the Asian Tropopause Aerosol Layer." Atmospheric Chemistry and Physics 21, no. 4 (2021): 2745–64. http://dx.doi.org/10.5194/acp-21-2745-2021.
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Abstract. The Asian summer monsoon (ASM) traps convectively lifted boundary layer pollutants inside its upper-tropospheric lower-stratospheric Asian monsoon anticyclone (AMA). It is associated with a seasonal and spatially confined enhanced aerosol layer, called the Asian Tropopause Aerosol Layer (ATAL). Due to the dynamical variability of the AMA, the dearth of in situ observations in this region, the complexity of the emission sources and of transport pathways, knowledge of the ATAL properties in terms of aerosol budget, chemical composition, as well as its variability and temporal trend is still largely uncertain. In this work, we use the Community Earth System Model (CESM 1.2 version) based on the coupling of the Community Atmosphere Model (CAM5) and the MAM7 (Modal Aerosol Model) aerosol module to simulate the composition of the ATAL and its decadal trends. Our simulations cover a long-term period of 16 years from 2000 to 2015. We identify a typical “double-peak” vertical profile of aerosols for the ATAL. We attribute the upper peak (around 100 hPa, predominant during early ATAL, e.g., in June) to dry aerosols, possibly from nucleation processes, and the lower peak (around 250 hPa, predominant for a well-developed and late ATAL, e.g., in July and August) to cloud-borne aerosols associated with convective clouds. We find that mineral dust (present in both peaks) is the dominant aerosol by mass in the ATAL, showing a large interannual variability but no long-term trend, due to its natural variability. The results between 120 and 80 hPa (dry aerosol peak) suggest that for aerosols other than dust the ATAL is composed of around 40 % of sulfate, 30 % of secondary and 15 % of primary organic aerosols, 14 % of ammonium aerosols and less than 3 % of black carbon. Nitrate aerosols are not considered in MAM7. The analysis of the anthropogenic and biomass burning aerosols shows a positive trend for all aerosols simulated by CESM-MAM7.
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Renard, J. B., S. N. Tripathi, M. Michael, et al. "In situ detection of electrified aerosols in the upper troposphere and stratosphere." Atmospheric Chemistry and Physics 13, no. 22 (2013): 11187–94. http://dx.doi.org/10.5194/acp-13-11187-2013.
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Abstract. Electrified aerosols have been observed in the lower troposphere and in the mesosphere, but have never been detected in the stratosphere and upper troposphere. We present measurements of aerosols obtained during a balloon flight to an altitude of ~ 24 km. The measurements were performed with an improved version of the Stratospheric and Tropospheric Aerosol Counter (STAC) aerosol counter dedicated to the search for charged aerosols. It is found that most of the aerosols are charged in the upper troposphere for altitudes below 10 km and in the stratosphere for altitudes above 20 km. Conversely, the aerosols seem to be uncharged between 10 km and 20 km. Model calculations are used to quantify the electrification of the aerosols with a stratospheric aerosol-ion model. The percentages of charged aerosols obtained with model calculations are in excellent agreement with the observations below 10 km and above 20 km. However, the model cannot reproduce the absence of electrification found in the lower stratosphere, as the processes leading to neutralisation in this altitude range are unknown. The presence of sporadic transient layers of electrified aerosol in the upper troposphere and in the stratosphere could have significant implications for sprite formation.
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Nabat, Pierre, Samuel Somot, Christophe Cassou, et al. "Modulation of radiative aerosols effects by atmospheric circulation over the Euro-Mediterranean region." Atmospheric Chemistry and Physics 20, no. 14 (2020): 8315–49. http://dx.doi.org/10.5194/acp-20-8315-2020.
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Abstract. The present work aims at better understanding regional climate–aerosol interactions by studying the relationships between aerosols and synoptic atmospheric circulation over the Euro-Mediterranean region. Two 40-year simulations (1979–2018) have been carried out with version 6.3 of the Centre National de Recherches Météorologiques (National Centre for Meteorological Research) – Aire Limitée Adaptation dynamique Développement InterNational (CNRM-ALADIN) regional climate model, one using interactive aerosols and the other one without any aerosol. The simulation with aerosols has been evaluated in terms of different climate and aerosol parameters. This evaluation shows a good agreement between the model and observations, significant improvements compared to the previous model version and consequently the relevance of using this model for the study of climate–aerosol interactions over this region. A first attempt to explain the climate variability of aerosols is based on the use of the North Atlantic Oscillation (NAO) index. The latter explains a significant part of the interannual variability, notably in winter for the export of dust aerosols over the Atlantic Ocean and the eastern Mediterranean, and in summer for the positive anomalies of anthropogenic aerosols over western Europe. This index is however not sufficient to fully understand the variations of aerosols in this region, notably at daily scale. The use of “weather regimes”, namely persisting meteorological patterns, stable at synoptic scale for a few days, provides a relevant description of atmospheric circulation, which drives the emission, transport and deposition of aerosols. The four weather regimes usually defined in this area in winter and in summer bring significant information to answer this question. The blocking and NAO+ regimes are largely favourable to strong aerosol effects on shortwave surface radiation and near-surface temperature, either because of higher aerosol loads or because of weaker cloud fraction, which reinforces the direct aerosol effect. Inversely, the NAO− and Atlantic Ridge regimes are unfavourable to aerosol radiative effects, because of weaker aerosol concentrations and increased cloud cover. This study thus puts forward the strong dependence of aerosol loads on the synoptic circulation from interannual to daily scales and, as a consequence, the important modulation of the aerosol effects on shortwave surface radiation and near-surface temperature by atmospheric circulation. The role of cloud cover is essential in this modulation as shown by the use of weather regimes.
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Ekman, A. M. L., A. Engström, and A. Söderberg. "Aerosol effects on deep convective clouds: impact of changes in aerosol size distribution and aerosol activation parameterization." Atmospheric Chemistry and Physics Discussions 10, no. 3 (2010): 6341–74. http://dx.doi.org/10.5194/acpd-10-6341-2010.
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Abstract. A cloud-resolving model including explicit aerosol physics and chemistry is used to study the impact of aerosols on deep convective strength. More specifically, by conducting six sensitivity series we examine how the complexity of the aerosol model, the size of the aerosols and the aerosol activation parameterization influence the aerosol-induced deep convective cloud sensitivity. Only aerosol effects on liquid droplet formation are considered. We find that an increased aerosol concentration generally results in stronger convection, which for the simulated case is in agreement with the conceptual model presented by Rosenfeld et al. (2008). However, there are two sensitivity series that do not display a monotonic increase in updraft velocity with increasing aerosol concentration. These exceptions illustrate the need to: 1) account for changes in evaporation processes and subsequent cooling when assessing aerosol effects on deep convective strength, 2) better understand graupel impaction scavenging of aerosols which may limit the number of CCN at a critical stage of cloud development and thereby dampen the convection, 3) increase our knowledge of aerosol recycling due to evaporation of cloud droplets. Furthermore, we find a significant difference in the aerosol-induced deep convective cloud sensitivity when using different complexities of the aerosol model and different aerosol activation parameterizations. For the simulated case, a 100% increase in aerosol concentration results in a difference in average updraft between the various sensitivity series which is as large as the average updraft increase itself. The model simulations also show that the change in graupel and rain formation is not necessarily directly proportional to the change in updraft velocity. For example, several of the sensitivity series display a decrease of the rain amount at the lowest model level with increasing updraft velocity. Finally, an increased number of aerosols in the Aitken mode (here defined by 23 nm≤d≤100.0 nm) may result in a larger impact on the convective strength compared to an increased number of aerosols in the accumulation mode (here defined by 100 nm≤d≤900.0 nm). When accumulation mode aerosols are activated and grow at the beginning of the cloud cycle, the supersaturation near the cloud base is lowered which to some extent limits further aerosol activation.
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Croft, B., R. V. Martin, W. R. Leaitch, et al. "Processes controlling the seasonal cycle of Arctic aerosol number and size distributions." Atmospheric Chemistry and Physics Discussions 15, no. 20 (2015): 29079–124. http://dx.doi.org/10.5194/acpd-15-29079-2015.
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Abstract. Measurements at high-Arctic sites show a strong seasonal cycle in aerosol number and size. The number of aerosols with diameters larger than 20 nm exhibits a maximum in late spring associated with a dominant accumulation mode (0.1 to 1 μm in diameter), and a second maximum in the summer associated with a dominant Aitken mode (10 to 100 nm in diameter). Seasonal-mean aerosol effective diameter ranges from about 180 nm in summer to 260 nm in winter. This study interprets these seasonal cycles with the GEOS-Chem-TOMAS global aerosol microphysics model. We find improved agreement with in-situ measurements of aerosol size at both Alert, Nunavut, and Mt. Zeppelin, Svalbard following model developments that: (1) increase the efficiency of wet scavenging in the Arctic summer and (2) represent coagulation between interstitial aerosols and aerosols activated to form cloud droplets. Our simulations indicate that the dominant summertime Aitken mode is associated with increased efficiency of wet removal, which limits the number of larger aerosols and promotes local new-particle formation. We also find an important role of interstitial coagulation in clouds in the Arctic, which limits the number of Aitken-mode aerosols in the non-summer seasons when direct wet removal of these aerosols is inefficient. Total aerosol number reaches a minimum in October at both Alert and Mt. Zeppelin. Our simulations indicate that this October minimum can be explained by diminishing local new-particle formation, limited transport of pollution from lower latitudes, and efficient wet removal. We recommend that the key processes of aerosol wet removal, interstitial coagulation and new-particle formation be carefully considered in size-resolved aerosol simulations of the Arctic. Uncertainties about these processes, which strongly control the seasonal cycle of aerosol number and size, limit confidence in estimates of aerosol radiative effects on the Arctic climate.
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Ahn, Jeonghyeon, Guiying Rao, and Eric Vejerano. "Partitioning of 1,2-dichlorobenzene onto organic and inorganic aerosols." Environmental Chemistry 18, no. 2 (2021): 61. http://dx.doi.org/10.1071/en21016.
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Environmental contextContaminants adsorbed in aerosols are transported and deposited effectively to the respiratory system compared to their vapours. Measuring the extremely low concentration of highly volatile contaminants contained in aerosols is challenging; hence assessing their adverse effects on environmental and human health is less understood. The measured concentrations of these contaminants are similar to less volatile chemicals sampled from diverse environmental aerosols, suggesting that their contribution cannot be neglected. AbstractVolatile organic compounds (VOCs) are not expected to partition onto aerosols because of their high vapour pressure. Studies on gas–aerosol partitioning of VOCs have been limited because of the challenge in discriminating the small mass fraction of the VOCs in the aerosol relative to that in the gas phase. Here, we developed a bench-scale system to investigate the partitioning of a surrogate VOC, 1,2-dichlorobenzene (1,2-DCB), into inorganic and organic aerosols under different relative humidities (RHs) and temperatures. The partitioning coefficient (Kip) of 1,2-DCB into succinic acid (SA) aerosol was ~10× higher than those into ammonium sulfate (Am Sulf) aerosol. These Kip corresponded to 0.23–3.27 pg 1,2-DCB µg−1 of SA aerosol and 0.02–3.82 pg 1,2-DCB µg−1 of Am Sulf aerosol for RH levels of 5–95%. Sorption of 1,2-DCB onto Am Sulf aerosol followed the classic relationship between Kip and RH, whereas that onto SA did not. For Am Sulf aerosols, RH levels exceeding 50% have a negligible effect on partitioning, in which the extremely low amount of 1,2-DCB partitioned into the aerosol via dissolution. The octanol–air partition (KOA) model predicted the Kip of 1,2-DCB for SA aerosol better than the saturated vapour pressure partition (Pi0) model, whereas the Pi0 model predicted Kip better than the KOA model only when absorptive partitioning was considered.
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Croft, B., J. R. Pierce, R. V. Martin, C. Hoose, and U. Lohmann. "Strong sensitivity of aerosol concentrations to convective wet scavenging parameterizations in a global model." Atmospheric Chemistry and Physics Discussions 12, no. 1 (2012): 1687–732. http://dx.doi.org/10.5194/acpd-12-1687-2012.
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Abstract. This study examines the influences of assumptions in convective wet scavenging parameterizations on global climate model simulations of aerosol concentrations and wet deposition. To facilitate this study, an explicit representation of the uptake of aerosol mass and number into convective cloud droplets and ice crystals by the processes of activation, collisions, freezing and evaporation is introduced into the ECHAM5-HAM model. This development replaces the prescribed aerosol cloud-droplet-borne/ice-crystal-borne fractions of the standard model. Relative to the standard model, the more consistent treatment between convective aerosol-cloud microphysical processes yields a reduction of aerosol wet removal in mixed liquid and ice phase convective clouds by at least a factor of two, and the global, annual mean aerosol burdens are increased by at least 20%. Two limiting cases regarding the wet scavenging of entrained aerosols are considered. In the first case, aerosols entering convective clouds at their bases are the only aerosols that are scavenged into cloud droplets, and are susceptible to removal by convective precipitation formation. In the second case, aerosols that are entrained into the cloud above the cloud base layer can activate, can collide with existing cloud droplets and ice crystals, and can subsequently be removed by precipitation formation. The limiting case that allows aerosols entrained above cloud base to become cloud-droplet-borne and ice-crystal-borne reduces the annual and global mean aerosol burdens by 30% relative to the other limiting case, and yields the closest agreement with global aerosol optical depth retrievals, and black carbon vertical profiles from aircraft campaigns (changes of about one order of magntiude in the upper troposphere). Predicted convective cloud droplet number concentrations are doubled in the tropical middle troposphere when aerosols entrained above cloud base are allowed to activate. These results show that aerosol concentrations and wet deposition predicted in a global model are strongly sensitive to the assumptions made regarding the wet scavenging of aerosols in convective clouds.