scholarly journals Absorption properties of Mediterranean aerosols obtained from multi-year ground-based and satellite remote sensing observations

2013 ◽  
Vol 13 (4) ◽  
pp. 9267-9317 ◽  
Author(s):  
M. Mallet ◽  
O. Dubovik ◽  
P. Nabat ◽  
F. Dulac ◽  
R. Kahn ◽  
...  
Keyword(s):  
Carbonaceous Aerosols ◽  
Data Set ◽  
Angstrom Exponent ◽  
Aerosol Absorption ◽  
Ångström Exponent ◽  
Level 3 ◽  
The Mediterranean ◽  
Level 2 ◽  
East West ◽  
Ångstrom Exponent

Abstract. Aerosol absorption properties are of high importance to assess aerosol impact on regional climate. This study presents an analysis of aerosol absorption products obtained over the Mediterranean Basin or land stations in the region from multi-year ground-based AERONET and satellite observations with a focus on the Absorbing Aerosol Optical Depth (AAOD), Single Scattering Albedo (SSA) and their spectral dependence. The AAOD and Absorption Angström Exponent (AAE) data set is composed of daily averaged AERONET level 2 data from a~total of 22 Mediterranean stations having long time series, mainly under the influence of urban-industrial aerosols and/or soil dust. This data set covers the 17 yr period 1996–2012 with most data being from 2003–2011 (~89% of level-2 AAOD data). Since AERONET level-2 absorption products require a high aerosol load (AOD at 440 nm > 0.4), which is most often related to the presence of desert dust, we also consider level-1.5 SSA data, despite their higher uncertainty, and filter out data with an Angström exponent <1.0 in order to study absorption by carbonaceous aerosols. The SSA data set includes both AERONET level-2 and satellite level-3 products. Satellite-derived SSA data considered are monthly level 3 products mapped at the regional scale for the spring and summer seasons that exhibit the largest aerosol loads. The satellite SSA dataset includes the following products: (i) Multi-angle Imaging SpectroRadiometer (MISR) over 2000–2011, (ii) Ozone Monitoring Instrument (OMI) near-UV algorithm over 2004–2010, and (iii) MODerate resolution Imaging Spectroradiometer (MODIS) Deep-Blue algorithm over 2005–2011, derived only over land in dusty conditions. Sun-photometer observations show that values of AAOD at 440 nm vary between 0.024 ± 0.01 (resp. 0.040 ± 0.01) and 0.050 ± 0.01 (0.055 ± 0.01) for urban (dusty) sites. Analysis shows that the Mediterranean urban-industrial aerosols appear "moderately" absorbing with values of SSA close to ~0.94–0.95 ± 0.04 (at 440 nm) in most cases except over the large cities of Rome and Athens, where aerosol appears more absorbing (SSA ~0.89–0.90 ± 0.04). The aerosol Absorption Angström Exponent (AAE, estimated using 440 and 870 nm) is found to be larger than 1 for most sites over the Mediterranean, a manifestation of mineral dust (iron) and/or brown carbon producing the observed absorption. AERONET level-2 sun-photometer data indicate the existence of a moderate East–West gradient, with higher values over the eastern basin (AAEEast. = 1.39/AAEWest. = 1.33) due to the influence of desert dust. The North–South AAE gradient is more pronounced, especially over the western basin. Our additional analysis of AERONET level-1.5 data also shows that organic absorbing aerosols significantly affect some Mediterranean sites. These results indicate that current climate models treating organics as nonabsorbing over the Mediterranean certainly underestimate the warming effect due to carbonaceous aerosols. A~comparative analysis of the regional SSA variability has been attempted using satellite data. OMI and MODIS data show an absorbing zone (SSA ~0.90 at 470–500 nm) over Northeastern Africa that does not appear in the MISR retrievals. In contrast, MISR seems able to observe the East–West SSA gradient during summer, as also detected by AERONET. Also, the analysis of SSA provided by satellites indicates that the aerosol over the Mediterranean Sea appears less absorbing during spring (MAM) than summer (JJA).

scholarly journals Absorption properties of Mediterranean aerosols obtained from multi-year ground-based remote sensing observations

2013 ◽  
Vol 13 (18) ◽  
pp. 9195-9210 ◽  
Author(s):  
M. Mallet ◽  
O. Dubovik ◽  
P. Nabat ◽  
F. Dulac ◽  
R. Kahn ◽  
...  
Keyword(s):  
Climate Models ◽  
Carbonaceous Aerosols ◽  
Absorption Properties ◽  
Angstrom Exponent ◽  
Aerosol Absorption ◽  
Ångström Exponent ◽  
Sun Photometer ◽  
The Mediterranean ◽  
Level 2 ◽  
Ångstrom Exponent

Abstract. Aerosol absorption properties are of high importance to assess aerosol impact on regional climate. This study presents an analysis of aerosol absorption products obtained over the Mediterranean basin or land stations in the region from multi-year ground-based AERONET observations with a focus on the Absorbing Aerosol Optical Depth (AAOD), Single Scattering Albedo (SSA) and their spectral dependence. The AAOD and Absorption Angström Exponent (AAE) dataset is composed of daily averaged AERONET level 2 data from a total of 22 Mediterranean stations having long time series, mainly under the influence of urban-industrial aerosols and/or soil dust. This dataset covers the 17-yr period 1996–2012 with most data being from 2003–2011 (~89% of level-2 AAOD data). Since AERONET level-2 absorption products require a high aerosol load (AOD at 440 nm > 0.4), which is most often related to the presence of desert dust, we also consider level-1.5 SSA data, despite their higher uncertainty, and filter out data with an Angström exponent < 1.0 in order to study absorption by carbonaceous aerosols. The SSA dataset includes AERONET level-2 products. Sun-photometer observations show that values of AAOD at 440 nm vary between 0.024 ± 0.01 (resp. 0.040 ± 0.01) and 0.050 ± 0.01 (0.055 ± 0.01) for urban (dusty) sites. Analysis shows that the Mediterranean urban-industrial aerosols appear "moderately" absorbing with values of SSA close to ~0.94–0.95 ± 0.04 (at 440 nm) in most cases except over the large cities of Rome and Athens, where aerosol appears more absorbing (SSA ~0.89–0.90 ± 0.04). The aerosol Absorption Angström Exponent (AAE, estimated using 440 and 870 nm) is found to be larger than 1 for most sites over the Mediterranean, a manifestation of mineral dust (iron) and/or brown carbon producing the observed absorption. AERONET level-2 sun-photometer data indicate a possible East-West gradient, with higher values over the eastern basin (AAEEast = 1.39/AAEWest = 1.33). The North-South AAE gradient is more pronounced, especially over the western basin. Our additional analysis of AERONET level-1.5 data also shows that organic absorbing aerosols significantly affect some Mediterranean sites. These results indicate that current climate models treating organics as nonabsorbing over the Mediterranean certainly underestimate the warming effect due to carbonaceous aerosols.

scholarly journals Remote sensing of soot carbon – Part 2: Understanding the absorption Angstrom exponent

2015 ◽  
Vol 15 (15) ◽  
pp. 20911-20956 ◽  
Author(s):  
G. L. Schuster ◽  
O. Dubovik ◽  
A. Arola ◽  
T. F. Eck ◽  
B. N. Holben
Keyword(s):  
Refractive Index ◽  
Near Infrared ◽  
Carbonaceous Aerosols ◽  
Angstrom Exponent ◽  
Aerosol Absorption ◽  
Coarse Mode ◽  
Ångström Exponent ◽  
Soot Carbon ◽  
Definition Of ◽  
Ångstrom Exponent

Abstract. Recently, some authors have suggested that the absorption Angstrom exponent (AAE) can be used to deduce the component aerosol absorption optical depths (AAOD) of carbonaceous aerosols in the AERONET database. This "AAE approach" presumes that AAE &amp;ll; 1 for soot carbon, which contrasts the traditional small particle limit of AAE = 1 for soot carbon. Thus, we provide an overview of the AERONET retrieval, and investigate how the microphysics of carbonaceous aerosols can be interpreted in the AERONET AAE product. We find that AAE &amp;ll; 1 in the AERONET database requires large coarse mode fractions and/or imaginary refractive indices that increase with wavelength. Neither of these characteristics are consistent with the current definition of soot carbon, so we explore other possibilities for the cause of AAE &amp;ll; 1. We note that AAE is related to particle size, and that coarse mode particles have a smaller AAE than fine mode particles for a given aerosol mixture of species. We also note that the mineral goethite has an imaginary refractive index that increases with wavelength, is very common in dust regions, and can easily contribute to AAE &amp;ll; 1. We find that AAE &amp;ll; 1 can not be caused by soot carbon, unless soot carbon has an imaginary refractive index that increases with wavelength throughout the visible and near infrared spectrums. Finally, AAE is not a robust parameter for separating carbonaceous absorption from dust aerosol absorption in the AERONET database.

scholarly journals Remote sensing of soot carbon – Part 2: Understanding the absorption Ångström exponent

2016 ◽  
Vol 16 (3) ◽  
pp. 1587-1602 ◽  
Author(s):  
G. L. Schuster ◽  
O. Dubovik ◽  
A. Arola ◽  
T. F. Eck ◽  
B. N. Holben
Keyword(s):  
Refractive Index ◽  
Near Infrared ◽  
Carbonaceous Aerosols ◽  
Angstrom Exponent ◽  
Aerosol Absorption ◽  
Coarse Mode ◽  
Ångström Exponent ◽  
Soot Carbon ◽  
Definition Of ◽  
Ångstrom Exponent

Abstract. Recently, some authors have suggested that the absorption Ångström exponent (AAE) can be used to deduce the component aerosol absorption optical depths (AAODs) of carbonaceous aerosols in the AERONET database. This AAE approach presumes that AAE ≪ 1 for soot carbon, which contrasts the traditional small particle limit of AAE = 1 for soot carbon. Thus, we provide an overview of the AERONET retrieval, and we investigate how the microphysics of carbonaceous aerosols can be interpreted in the AERONET AAE product. We find that AAE ≪ 1 in the AERONET database requires large coarse mode fractions and/or imaginary refractive indices that increase with wavelength. Neither of these characteristics are consistent with the current definition of soot carbon, so we explore other possibilities for the cause of AAE ≪ 1. AAE is related to particle size, and coarse mode particles have a smaller AAE than fine mode particles for a given aerosol mixture of species. We also note that the mineral goethite has an imaginary refractive index that increases with wavelength, is very common in dust regions, and can easily contribute to AAE ≪ 1. We find that AAE ≪ 1 can not be caused by soot carbon, unless soot carbon has an imaginary refractive index that increases with wavelength throughout the visible and near-infrared spectrums. Finally, AAE is not a robust parameter for separating carbonaceous absorption from dust aerosol absorption in the AERONET database.

scholarly journals A Global Space-based Stratospheric Aerosol Climatology (Version 2.0): 1979–2018

2020 ◽  
Author(s):  
Mahesh Kovilakam ◽  
Larry Thomason ◽  
Nicholas Ernest ◽  
Landon Rieger ◽  
Adam Bourassa ◽  
...  
Keyword(s):  
Lower Stratosphere ◽  
Stratospheric Aerosol ◽  
Aerosol Extinction ◽  
Data Set ◽  
Angstrom Exponent ◽  
Global Space ◽  
Ångström Exponent ◽  
Version 2.0 ◽  
532 Nm ◽  
Ångstrom Exponent

Abstract. A robust stratospheric aerosol climate data record enables the depiction of the radiative forcing of this highly variable component of climate. Since stratospheric aerosol also plays a key role in the chemical processes leading to ozone depletion, stratosphere is one of the crucial parameters in understanding climate change in the past and potential changes in the future. As a part of Stratospheric-tropospheric Processes and their Role in Climate (SPARC) Stratospheric Sulfur and its Role in Climate (SSiRC) activity, the Global Space-based Stratospheric Aerosol Climatology (GloSSAC) was created (Thomason et al., 2018) to support the World Climate Research Programme (WCRP)’s Coupled Model Intercomparison Project Phase 6 (CMIP6) (Zanchettin et al., 2016). This data set is a follow-on to one created as a part of Stratosphere-Troposphere Process and their Role in Climate Project (SPARC)’s Assessment of Stratospheric Aerosol Properties (ASAP) activity(SPARC, 2006) and a data created for Chemistry-Climate Model Initiative (CCMI) in 2012 (Eyring and Lamarque, 2012). Herein, we discuss changes to the original release version including those as a part of v1.1 that was released in September 2018 that primarily corrects an error in the conversion of Cryogenic Limb Array Etalon Spectrometer (CLAES) data to Stratospheric Aerosol and Gas Experiment (SAGE) II wavelengths, and the new release, v2.0. Version 2.0 is focused on improving the post-SAGE II era (after 2005) with the goal to mitigate elevated aerosol extinction in the lower stratosphere at mid and high latitudes noted in v1.0 as noted in Thomason et al. (2018). Changes include the use of version 7.0 of Optical Spectrograph and InfraRed Imaging System(OSIRIS), the recently released Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) Lidar Level 3 Stratospheric Aerosol profile monthly product, and the new addition of SAGE III/ISS. Although, the version 7.0 OSIRIS data is substantially improved at its native wavelength of 750 nm, conversion to 525 nm using a constant Angstrom exponent often results in disagreements with SAGEII/ SAGE III/ISS overlap measurements. We, therefore use an observed relationship between OSIRIS extinction at 750 nm and SAGEII/SAGE III/ISS extinction at 525 nm to derive Altitude-Latitude based monthly climatology of Angstrom exponent to compute extinction at 525 nm, resulting in a better agreement between OSIRIS and SAGE measurements. We employ a similar approach to convert OSIRIS 750 nm extinction to 1020 nm extinction for the post-SAGEII period. Additionally, we incorporate the recently released standard CALIPSO stratospheric aerosol profile monthly product into GloSSAC with an improved conversion technique of 532 nm backscatter coefficient to extinction using an observed relationship between OSIRIS 525 nm extinction and CALIPSO 532 nm backscatter. We also investigate for any cloud contamination in OSIRIS/standard CALIPSO stratospheric aerosol product, which may have caused apparent enhancement in the aerosol extinction particularly in the lower stratosphere. SAGE III/ISS data is also incorporated in GloSSAC to extend the climatology to the present and to test the approach used to correct OSIRIS/CALIPSO data. The GloSSAC v2.0 netcdf file is accessible at https://doi.org/10.5067/glossac-l3-v2.0 (Thomason, 2020).

scholarly journals Stratospheric aerosol characteristics from space-borne observations: extinction coefficient and Ångström exponent

2018 ◽  
Author(s):  
Elizaveta Malinina ◽  
Alexei Rozanov ◽  
Landon Rieger ◽  
Adam Bourassa ◽  
Heinrich Bovensmann ◽  
...  
Keyword(s):  
Extinction Coefficient ◽  
Simple Relation ◽  
Stratospheric Aerosol ◽  
Accurate Information ◽  
Aerosol Extinction ◽  
Data Set ◽  
Extinction Coefficients ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Ångstrom Exponent

Abstract. Stratospheric aerosols are of a great importance to the scientific community, predominantly because of their role in climate, but also because accurate knowledge of aerosol characteristics is relevant for trace gases retrievals from remote sensing instruments. There are several data sets published which provide aerosol extinction coefficients in the stratosphere. However, for the instruments measuring in the limb viewing geometry, the use of this parameter is associated with uncertainties resulting from the need to assume an aerosol particle size distribution (PSD) within the retrieval process. These uncertainties can be mitigated if PSD information is retrieved. While occultation instruments provide more accurate information on the aerosol extinction coefficient, in this study, it was shown that limb instruments have better potential for the PSD retrieval, especially during the background aerosol loading periods. A data set containing PSD information was recently retrieved from SCIAMACHY limb measurements and provides two parameters of the log-normal PSD for the SCIAMACHY operational period (2002–2012). In this study, the data set is expanded by aerosol extinction coefficients and Ångström exponents calculated from the retrieved PSD parameters. Errors in the Ångström exponents and aerosol extinction coefficients are assessed using synthetic retrievals. For the extinction coefficient the resulting accuracy is within ±25 %, and for the Ångström exponent, it is better than 10 %. The recalculated SCIAMACHY aerosol extinction coefficients are compared to those from SAGE II. The differences between the instruments vary from 0 to 25 % depending on the wavelength. Ångström exponent comparison with SAGE II shows differences between 10 % at 31 km and 40 % at 18 km. Comparisons with SAGE II, however, suffer from the low amount of collocated profiles. Furthermore, the Ångström exponents obtained from the limb viewing instrument OSIRIS are used for the comparison. This comparison shows an average difference within 7 %. The time series of these differences do not show signatures of any remarkable events. Besides, the temporal behavior of the Ångström exponent in the tropics is analyzed using the SCIAMACHY data set. It is shown, that there is no simple relation between the Ångström exponent and the PSD because the same value of Ångström exponent can be obtained from an infinite number of combinations of the PSD parameters.

scholarly journals Relating aerosol absorption due to soot, organic carbon, and dust to emission sources determined from in-situ chemical measurements

2013 ◽  
Vol 13 (18) ◽  
pp. 9337-9350 ◽  
Author(s):  
A. Cazorla ◽  
R. Bahadur ◽  
K. J. Suski ◽  
J. F. Cahill ◽  
D. Chand ◽  
...  
Keyword(s):  
Optical Properties ◽  
Chemical Composition ◽  
Radiative Forcing ◽  
Wavelength Dependence ◽  
Optical Measurements ◽  
Carbonaceous Aerosols ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Ångstrom Exponent

Abstract. Estimating the aerosol contribution to the global or regional radiative forcing can take advantage of the relationship between the spectral aerosol optical properties and the size and chemical composition of aerosol. Long term global optical measurements from observational networks or satellites can be used in such studies. Using in-situ chemical mixing state measurements can help us to constrain the limitations of such estimates. In this study, the Absorption Ångström Exponent (AAE) and the Scattering Ångström Exponent (SAE) derived from 10 operational AERONET sites in California are combined for deducing chemical speciation based on wavelength dependence of the optical properties. In addition, in-situ optical properties and single particle chemical composition measured during three aircraft field campaigns in California between 2010 and 2011 are combined in order to validate the methodology used for the estimates of aerosol chemistry using spectral optical properties. Results from this study indicate a dominance of mixed types in the classification leading to an underestimation of the primary sources, however secondary sources are better classified. The distinction between carbonaceous aerosols from fossil fuel and biomass burning origins is not clear, since their optical properties are similar. On the other hand, knowledge of the aerosol sources in California from chemical studies help to identify other misclassification such as the dust contribution.

scholarly journals Can the Aerosol Absorption Ångström Exponent Represent Aerosol Color in the Atmosphere: A Numerical Study

Atmosphere ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 187
Author(s):  
Dapeng Zhao ◽  
Yan Yin ◽  
Chao Liu ◽  
Chunsong Lu ◽  
Xiaofeng Xu
Keyword(s):  
Numerical Study ◽  
Solar Spectrum ◽  
Transfer Model ◽  
Blue Color ◽  
Angstrom Exponent ◽  
Aerosol Absorption ◽  
Model Aerosol ◽  
Ångström Exponent ◽  
Human Eyes ◽  
Ångstrom Exponent

The aerosol absorption Ångström exponent (AAE) is widely used to indicate aerosol absorption spectrum variations and is an important parameter for characterizing aerosol optical absorption properties. This study discusses the relationship between aerosol AAEs and their colors numerically. By combining light scattering simulations, a two-stream radiative transfer model, and an RGB (Red, Green, and Blue) color model, aerosol colors that can be sensed by human eyes are numerically generated with both the solar spectrum and human eye response taken into account. Our results indicate that the responses of human eyes to visible light might be more significant than the incident spectrum in the simulation of aerosol color in the atmosphere. Using the improved numerical simulation algorithm, we obtain the color change of absorption aerosols with different AAEs. When the AAE value is small, the color of the aerosol is generally black and gray. When the AAE value increases to approximately 2 and the difference between the light transmittances at wavelengths of 400 nm and 730 nm is greater than 0.2, the aerosol will appear brown or yellow.

scholarly journals Relating aerosol absorption due to soot, organic carbon, and dust to emission sources determined from in-situ chemical measurements

2013 ◽  
Vol 13 (2) ◽  
pp. 3451-3483 ◽  
Author(s):  
A. Cazorla ◽  
R. Bahadur ◽  
K. J. Suski ◽  
J. F. Cahill ◽  
D. Chand ◽  
...  
Keyword(s):  
Optical Properties ◽  
Chemical Composition ◽  
Radiative Forcing ◽  
Optical Measurements ◽  
Carbonaceous Aerosols ◽  
Aerosol Composition ◽  
Angstrom Exponent ◽  
Ångström Exponent ◽  
Ångstrom Exponent

Abstract. Estimating the aerosol contribution to the global or regional radiative forcing can take advantage of the relationship between the spectral aerosol optical properties and the size and chemical composition of aerosol. Long term global optical measurements from observational networks or satellites can be used in such studies. Using in-situ chemical mixing state measurements can help us to constrain the limitations of such estimates. In this study, the Absorption Ångström Exponent (AAE) and the Scattering Ångström Exponent (SAE) derived from 10 operational AERONET sites in California are combined for deducing chemical speciation based on wavelength dependence of the optical properties. In addition, in-situ optical properties and single particle chemical composition measured during three aircraft field campaigns in California between 2010 and 2011 are combined in order to validate the methodology used for the estimates of aerosol composition using spectral optical properties. Results from this study indicate a dominance of mixed types in the classification leading to an underestimation of the primary sources, however secondary sources are better classified. The distinction between carbonaceous aerosols from fossil fuel and biomass burning origins is not clear, since their optical properties are similar. On the other hand, knowledge of the aerosol sources in California from chemical studies help to identify other misclassification such as the dust contribution.

scholarly journals Global evaluation of the Collection 5 MODIS dark-target aerosol products over land

2010 ◽  
Vol 10 (6) ◽  
pp. 14815-14873 ◽  
Author(s):  
R. C. Levy ◽  
L. A. Remer ◽  
R. G. Kleidman ◽  
S. Mattoo ◽  
C. Ichoku ◽  
...  
Keyword(s):  
Field Of View ◽  
Global Evaluation ◽  
Polar Orbit ◽  
Angstrom Exponent ◽  
The Earth ◽  
Modis Aod ◽  
Ångström Exponent ◽  
Level 2 ◽  
Ångstrom Exponent

Abstract. NASA's MODIS sensors have been observing the Earth from polar orbit, from Terra since early 2000 and from Aqua since mid 2002. We have applied a consistent retrieval and processing algorithm to both sensors to derive the Collection 5 (C005) dark-target aerosol products over land. Here, we co-locate the MODIS field of view aerosol retrievals with Level 2 AERONET sunphotometer measurements at over 300 sites, and find 85 000 matched pairs that represent mutually cloud-free conditions. From these collocations, we validate the total aerosol optical depth (AOD or τ) product, and define the expected error (EE) as ±(0.05+0.15τ). Since we find that >66% (one standard deviation) of MODIS AOD values compare to AERONET within EE, we can consider global AOD to be validated. However, MODIS does not compare as well to AERONET at particular sites and seasons. There are residual biases that are correlated with Ångstrom exponent, scattering angles, and scene reflectance conditions, resulting from assumptions about the aerosol optical properties and surface conditions that are not accurate everywhere. Although we conclude that the AOD over land is globally quantitative, MODIS-derived parameters of aerosol size over land (Ångström exponent, fine AOD) are not. When separating data into those derived from Terra versus those from Aqua, scatterplots to AERONET are nearly indistinguishable. However, while Aqua is stable, Terra shows a slight trend in its bias with respect to AERONET; overestimating (by ~0.005) before 2004, and underestimating by similar magnitude after. This suggests small, but significant calibration uncertainties of <2%, which could lead to spurious long-term aerosol trends.

scholarly journals The absorption Ångstrom exponent of black carbon with brown coatings: effects of aerosol microphysics and parameterization

2020 ◽  
Vol 20 (16) ◽  
pp. 9701-9711 ◽  
Author(s):  
Xiaolin Zhang ◽  
Mao Mao ◽  
Yan Yin ◽  
Shihao Tang
Keyword(s):  
Size Distribution ◽  
Black Carbon ◽  
Volume Fraction ◽  
Optical Parameter ◽  
Brown Carbon ◽  
Angstrom Exponent ◽  
Aerosol Absorption ◽  
Ångström Exponent ◽  
Bc Aerosols ◽  
Ångstrom Exponent

Abstract. The aerosol absorption Ångstrom exponent (AAE) is a crucial optical parameter for apportionment and characterization. Due to considerable inconsistences associated with observations, numerical research is a powerful means to give a better understanding of the AAE of aged black carbon (BC) aerosols. Numerical studies of the AAE of polydisperse BC aggregates with brown coatings using the exact multiple-sphere T-matrix method (MSTM) are performed. The objective of the study is to thoroughly assess the AAE of coated BC influenced by their observation-based detailed microphysics and then provide a new AAE parameterization for application. At odds with our expectations, more large-sized BC particles coated by thin brown carbon can have an AAE smaller than 1.0, indicating that BC aerosols internally mixing with brown carbon can even show lower AAE than pure BC particles. The AAE of BC with brown coatings is highly sensitive to the absorbing volume fraction of the coating, coated volume fraction of BC, shell ∕ core ratio, and particle size distribution with a wide variation, whereas the impacts of BC geometry and BC position within the coating are negligible. The AAE of BC with brown coatings can be larger than 3.0 if there are plenty of small-sized coated BC particles, heavy coating, or a large amount of brown carbon. However, the AAE of BC with non-absorbing coating appears to be weakly sensitive to particle microphysics with values around 1.0 (i.e., 0.7–1.4), suggesting the substantial role of the absorbing volume fraction of the coating in AAE determination. With more realistic BC geometries, our study also indicates that the occurrence of brown carbon may not be confidently determined unless AAE > 1.4. The currently popular core–shell Mie model reasonably approximates the AAE of fully coated BC by brown carbon, whereas it underestimates the AAE of partially coated or externally attached BC and underestimates more for a lower coated volume fraction of BC. In addition, we present a parameterization of the AAE of coated BC with a size distribution on the basis of numerical results, which can act as a guide for the AAE response to the absorbing volume fraction of the coating, coated volume fraction of BC, and shell ∕ core ratio. The proposed parameterization of coated BC AAE generates a decent prediction for moderate BC microphysics, whereas caution should be taken in applying it for extreme cases, such as externally attached coated BC morphology. Our findings could improve the understanding and application of the AAE of BC with brown coatings.

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