Effects of hygroscopicity on aerosol optical properties and direct radiative forcing in Beijing: Based on two-year observations

Can Xia; Junying Sun; Xinyao Hu; Xiaojing Shen; Yangmei Zhang; Sinan Zhang; Jialing Wang; Quan Liu; Jiayuan Lu; Shuo Liu; Xiaoye Zhang

doi:10.1016/j.scitotenv.2022.159233

Effects of hygroscopicity on aerosol optical properties and direct radiative forcing in Beijing: Based on two-year observations

Sci Total Environ. 2023 Jan 20;857(Pt 1):159233. doi: 10.1016/j.scitotenv.2022.159233. Epub 2022 Oct 6.

Authors

Can Xia¹, Junying Sun², Xinyao Hu³, Xiaojing Shen⁴, Yangmei Zhang⁴, Sinan Zhang⁴, Jialing Wang⁴, Quan Liu⁴, Jiayuan Lu⁴, Shuo Liu⁴, Xiaoye Zhang⁴

Affiliations

¹ School of Atmospheric Physics, Nanjing University of Information Science & Technology, Nanjing 210044, China; State Key Laboratory of Severe Weather & Key Laboratory of Atmospheric Chemistry of CMA, Chinese Academy of Meteorological Sciences, Beijing 100081, China.
² State Key Laboratory of Severe Weather & Key Laboratory of Atmospheric Chemistry of CMA, Chinese Academy of Meteorological Sciences, Beijing 100081, China. Electronic address: jysun@cma.gov.cn.
³ State Key Laboratory of Severe Weather & Key Laboratory of Atmospheric Chemistry of CMA, Chinese Academy of Meteorological Sciences, Beijing 100081, China; University of Chinese Academy of Sciences, Beijing 100049, China.
⁴ State Key Laboratory of Severe Weather & Key Laboratory of Atmospheric Chemistry of CMA, Chinese Academy of Meteorological Sciences, Beijing 100081, China.

PMID: 36208762
DOI: 10.1016/j.scitotenv.2022.159233

Abstract

The influence of relative humidity on aerosol properties and the direct radiative forcing of PM₁₀ and PM₁ were investigated in Beijing from January 2018 to December 2019. The annual mean scattering hygroscopic growth factor at RH = 80 % [f(80 %)] of PM₁₀ and PM₁ were 1.60 ± 0.24 and 1.58 ± 0.22, respectively. The variation of aerosol hygroscopic growth factors of PM₁₀ and PM₁ aerosols was similar, which is mainly due to the fact that aerosol scattering in Beijing is dominated by fine particles. The seasonal mean f(80 %) of PM₁₀ from spring to winter were 1.66 ± 0.23, 1.71 ± 0.25, 1.51 ± 0.20, 1.49 ± 0.16, respectively, which were higher in spring and summer, and lower in autumn and winter. The diurnal variation of f(80 %) was relatively higher from 12:00 to 18:00, which could be related to the formation of secondary aerosols by photochemical reactions. f(80 %) shows a strong positive relationship with both the scattering Angström exponent (SAE) and the single scattering albedo (ω₀) under dry conditions; therefore, the scattering hygroscopic growth factor could be estimated using these two parameters. The upscatter fraction (β) and single scattering albedo, which are the key aerosol optical properties for the calculation of direct radiative forcing, are also RH-dependent. As RH increases, the upscatter fraction (backscatter fraction) decreases and ω₀ increases. The aerosol radiative forcing at RH 80 % was 1.48 times as that in the dry state. The sensitivity experiment showed that the variation in the scattering coefficient with relative humidity had the greatest influence on radiation forcing, followed by β and ω₀. The seasonal variation of ΔF(80 %)/ΔF(dry) coincides with that of the aerosol hygroscopic growth factor. Our study suggests that understanding the influence of relative humidity on aerosol properties and direct radiative forcing is important for accurately estimating the radiative forcing of aerosols.

Keywords: Aerosol direct radiative forcing; Backscatter fraction; Scattering Angström exponent; Scattering hygroscopic growth factor; Single scattering albedo.

MeSH terms

Aerosols / analysis
Beijing
Seasons
Wettability*

Substances

Aerosols