Strong light scattering of highly oxygenated organic aerosols impacts significantly on visibility degradation

• Published in: Atmospheric chemistry and physics 2022-06, Vol.22 (11), p.7713-7726
• Main Authors: Liu, Li, Kuang, Ye, Zhai, Miaomiao, Xue, Biao, He, Yao, Tao, Jun, Luo, Biao, Xu, Wanyun, Tao, Jiangchuan, Yin, Changqin, Li, Fei, Xu, Hanbing, Deng, Tao, Deng, Xuejiao, Tan, Haobo, Shao, Min
• Format: Article
• Language: English
• Subjects: Aerosol scattering; Aerosols; Ammonium; Ammonium compounds; Ammonium nitrate; Analysis; Atmospheric aerosols; Atmospheric models; Chemical speciation; Components; Degradation; Efficiency; Hydrophobicity; Hygroscopicity; Identification; Light scattering; Mass; Nephelometers; Nitrates; Oxygenation; Parameters; Physical properties; Regression models; Relative humidity; Scattering coefficient; Secondary aerosols; Solar radiation; Speciation; Uptake; Visibility; Water uptake; Winter
• ISSN: 1680-7324; 1680-7316; 1680-7324
• DOI: 10.5194/acp-22-7713-2022

Secondary organic aerosols (SOAs) account for a large fraction of atmospheric aerosol mass and play significant roles in visibility impairment by scattering solar radiation. However, comprehensive evaluations of SOA scattering abilities under ambient relative humidity (RH) conditions on the basis of field measurements are still lacking due to the difficulty of simultaneously direct quantifications of SOA scattering efficiency in dry state and SOA water uptake abilities. In this study, field measurements of aerosol chemical and physical properties were conducted in winter in Guangzhou (lasting about 3 months) using a humidified nephelometer system and aerosol chemical speciation monitor. A modified multilinear regression model was proposed to retrieve dry-state mass scattering efficiencies (MSEs, defined as scattering coefficient per unit aerosol mass) of aerosol components. The more oxidized oxygenated organic aerosol (MOOA) with an O/C ratio of 1.17 was identified as the most efficient light scattering aerosol component. On average, 34 % mass contribution of MOOA to total submicron organic aerosol mass contributed 51 % of dry-state organic aerosol scattering. The overall organic aerosol hygroscopicity parameter κOA was quantified directly through hygroscopicity closure, and hygroscopicity parameters of SOA components were further retrieved using a multilinear regression model by assuming hydrophobic properties of primary organic aerosols. The highest water uptake ability of MOOA among organic aerosol factors was revealed with κMOOA reaching 0.23, thus further enhancing the fractional contribution of MOOA in ambient organic aerosol scattering. In particular, the scattering abilities of MOOA were found to be even higher than those of ammonium nitrate under RH of