A global study of hygroscopicity-driven light-scattering enhancement in the context of other in situ aerosol optical properties

Titos, Gloria; Burgos, M.A.; Zieger, Paul; Alados-Arboledas, L.; Baltensperger, Urs; Jefferson, Anne; Sherman, James P.; Weingärtner, E.; Henzing, Bas; Luoma, Krista; O’Dowd, Colin; Wiedensohler, Alfred; Andrews, Elisabeth

doi:10.5194/acp-21-13031-2021

Cited by 9 publications

(7 citation statements)

References 84 publications

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“…It is interesting to find that the dust ARFETOA over East Asia is apparently higher than that over South Asia, which could be indicative of the different compositions of dust that lead to different absorbing capabilities. Comparatively, the U/I aerosols could be more influenced by the moisture conditions which are related to the hygroscopicity of U/I aerosols [67]. We could find noticeable differences in the ARFETOA of U/I aerosol between continental sites and coastal or marine sites.…”

Section: Aerosol Radiative Forcing and Radiative Forcing Efficiencies...mentioning

confidence: 86%

Aerosols over East and South Asia: Type Identification, Optical Properties, and Implications for Radiative Forcing

Liu

2022

Remote Sensing

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Identification of aerosol types has long been a difficult problem over East and South Asia due to various limitations. In this study, we use 2-dimensional (2-D) and multi-dimensional Mahalanobis distance (MD) clustering algorithms to identify aerosol characteristics based on the data from the Aerosol Robotic Network from March 1998 to February 2018 over the South and East Asian region (10°N~50°N, 70°E~135°E). The single scattering albedo (SSA), absorption Angstrom exponent (AAE), extinction Angstrom exponent (EAE), real index of refraction (RRI), and imaginary index of refraction (IRI) are utilized for classification of aerosols. Sub-regions with similar background conditions over East and South Asia are identified by hierarchical clustering algorithm to illustrate distinctive meteorological states in different areas. The East and South Asian aerosols are found to have distinct regional and seasonal features relating to the meteorological conditions, land cover, and industrial infrastructure. It is found that the proportions of dust aerosol are the highest in spring at the SACOL site and in summer at the sites near the Northern Indo-Gangetic Plain area. In spring, biomass-burning aerosols are dominant over the central Indo-China Peninsula area. The aerosol characteristics at coastal sites are also analyzed and compared with previous results. The 2-D clustering method is useful when limited aerosol parameters are available, but the results are highly dependent on the sets of parameters used for identification. Comparatively, the MD method, which considers multiple aerosol parameters, could provide more comprehensive classification of aerosol types. It is estimated that only about 50% of the data samples that are identifiable by the MD method could be classified by the 2-D methods, and a lot of undetermined data samples could be mis-classified by the 2-D methods. The aerosol radiative forcing (ARF) and the aerosol radiative forcing efficiency (ARFE) of various aerosol types at the top and the bottom of the atmosphere (TOA and BOA) are determined based on the MD aerosol classification. The dust aerosols are found to have the largest ARF at the TOA (−36 W/m2), followed by the urban/industrial aerosols and biomass-burning aerosols. The ARFE of biomass-burning aerosols at the BOA (−165 W/m2/AOD550nm) is the strongest among those of the other aerosol types. The comparison of the results by MD and 2-D methods shows that the differences in ARF and ARFE are generally within 10%. Our results indicate the importance of aerosol type classification in accurately attributing the radiative contributions of different aerosol components.

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Section: Aerosol Radiative Forcing and Radiative Forcing Efficiencies...mentioning

confidence: 86%

Aerosols over East and South Asia: Type Identification, Optical Properties, and Implications for Radiative Forcing

Liu

2022

Remote Sensing

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“…Previous studies found that the magnitude of the RFE increases with increasing b (Shen et al, 2018). Typical values of b for the atmospheric aerosol at 550 nm were from approximately 0.05 to 0.20 (Titos et al, 2021).…”

Section: Introductionmentioning

confidence: 92%

Measurement report: Rapid decline of aerosol absorption coefficient and aerosol optical property effects on radiative forcing in an urban area of Beijing from 2018 to 2021

Sun

Xia

et al. 2023

Atmos. Chem. Phys.

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Abstract. Reliable observations of aerosol optical properties are crucial for quantifying the radiative forcing of climate. The simultaneous measurements of aerosol optical properties at three wavelengths for PM1 and PM10 were conducted in urban Beijing from March 2018 to February 2022. The aerosol absorption coefficient (σab) at 550 nm of PM10 and PM1 decreased by 55.0 % and 53.5 % from 2018 to 2021. The significant reduction in σab may be related to reduced primary emissions caused by effective air pollution control measures. PM2.5 mass concentration decreased by 34.4 % from 2018 to 2021. Single scattering albedo (SSA) increased from 0.89±0.04 for PM10 (0.87±0.05 for PM1) in 2018 to 0.93±0.03 for PM10 (0.91±0.04 for PM1) in 2021. Increasing SSA and decreasing PM2.5 mass concentration suggest that the fraction of absorbing aerosols decreased with improved air quality due to pollution control measures being taken. The annual average submicron absorption ratio (Rab) increased from 86.1 % in 2018 to 89.2 % in 2021, suggesting that fine particles are the main contributors to total PM10 absorption and that the contribution of fine particles to absorption became more important. The absorption Ångström exponent (AAE) in winter decreased from 2018 to 2021, implying a decreasing contribution from brown carbon to light absorption, which may relate to the reduced emissions of biomass burning and coal combustion. During the study period, aerosol radiative forcing efficiency became more negative, mainly influenced by increasing SSA and was −27.0 and −26.2 W m−2 per aerosol optical depth (AOD) for PM10 and PM1 in 2021. Higher σab and PM2.5 mass concentrations were primarily distributed in clusters 4 and 5, transported from the south and the west of Beijing each year. σab and PM2.5 corresponding to clusters 4 and 5 decreased evidently from 2018 to 2021, which may result from the control of source emissions in surrounding regions of Beijing. The 4-year data presented in this study provide critical optical parameters for radiative forcing assessment within two size ranges and are helpful for evaluating the effectiveness of clean air action.

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“…As a result, nighttime AOD (0.45 ± 0.47) displayed larger mean values than during the day (0.40 ± 0.29). The large mean and standard deviation of nighttime AOD can be attributed to the nighttime formation of nitrate from the nocturnal processing of nitrogen oxides (H. Kim et al., 2018), a build‐up of pollutants due to stagnant atmospheric conditions within the nocturnal BL (Ma et al., 2017), and enhancement of aerosol extinction due to hygroscopic growth of aerosols (Eck et al., 2014; Titos et al., 2021; Ziemba et al., 2013).…”

Section: Temporal Variation Of Boundary Layer (Bl) and Free‐troposphe...mentioning

confidence: 99%

“…Uncertainties in aerosol optical property simulations of the model will affect the validation results of CTMs. Due to the large diversity in aerosol optical properties as a function of aerosol species (Kinne et al., 2006; Nemuc et al., 2013) and ambient relative humidity (RH; Pérez‐Ramírez et al., 2021; Titos et al., 2021), measurement‐based validation of the aerosol modules of CTMs is necessary (Hand & Malm, 2007; Saide et al., 2020).…”

Section: Introductionmentioning

confidence: 99%

Optical Properties of Boundary Layer Aerosols From High Spectral Resolution Lidar Measurements in a Polluted Urban Environment (Seoul, Korea)

et al. 2023

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Continuous measurements of aerosol extinction coefficient (σext) from the High Spectral Resolution Lidar (HSRL) in Seoul from 2016 to 2018 were used to investigate the diurnal variation of the aerosol optical depth (AOD). Nighttime AOD displayed a larger mean and standard deviation (0.45 ± 0.47) than daytime (0.40 ± 0.29). Hygroscopic growth of aerosols under humid conditions was a key factor in the relative enhancement of nighttime AOD. Taking advantage of the HSRL's vertically resolved measurements, the contribution of aerosols within the boundary layer (BL) and free troposphere (FT) to AOD and its temporal variation were investigated. Unlike the diurnal AOD variation, AOD within the BL (AODBL) showed similar diurnal variations with the mixing layer height (MLH), displaying lower nighttime values with a peak around 14–15 local standard time. However, the low correlation between MLH and AODBL (R2 = 0.06) implied that MLH was not the sole deterministic factor of AODBL. A larger AOD of FT aerosols (AODFT) was observed during spring due to frequent elevated dust layers. Using mean σext within the BL and surface PM10 concentrations, the mass extinction efficiency (MEE) of aerosols in Seoul was estimated. The PM10 MEE showed a mean of 5.40 g m−2 and displayed significant variability by PM2.5 to PM10 ratio, season, and ambient relative humidity. The uncertainty of estimated surface PM10 concentrations was minimized when the seasonality and humidity factor in MEE were taken into account (the normalized mean bias decreased from 10.6%, using a single MEE value, to 6.2%).

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A global study of hygroscopicity-driven light-scattering enhancement in the context of other in situ aerosol optical properties

Cited by 9 publications

References 84 publications

Aerosols over East and South Asia: Type Identification, Optical Properties, and Implications for Radiative Forcing

Aerosols over East and South Asia: Type Identification, Optical Properties, and Implications for Radiative Forcing

Measurement report: Rapid decline of aerosol absorption coefficient and aerosol optical property effects on radiative forcing in an urban area of Beijing from 2018 to 2021

Optical Properties of Boundary Layer Aerosols From High Spectral Resolution Lidar Measurements in a Polluted Urban Environment (Seoul, Korea)

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