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Volume 18, issue 19
Atmos. Chem. Phys., 18, 14079-14094, 2018
https://doi.org/10.5194/acp-18-14079-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
Atmos. Chem. Phys., 18, 14079-14094, 2018
https://doi.org/10.5194/acp-18-14079-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 04 Oct 2018

Research article | 04 Oct 2018

Mixing state and particle hygroscopicity of organic-dominated aerosols over the Pearl River Delta region in China

Juan Hong1,2,3,4, Hanbing Xu5, Haobo Tan6, Changqing Yin6, Liqing Hao7, Fei Li6, Mingfu Cai8, Xuejiao Deng6, Nan Wang6, Hang Su1,3, Yafang Cheng1,3, Lin Wang4, Tuukka Petäjä2, and Veli-Matti Kerminen2 Juan Hong et al.
  • 1Institute for Environmental and Climate Research, Jinan University, Guangzhou, Guangdong 511443, China
  • 2Department of Physics, University of Helsinki, P.O. Box 64, Helsinki 00014, Finland
  • 3Multiphase Chemistry Department, Max Planck Institute for Chemistry, Mainz 55128, Germany
  • 4Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Department of Environmental Science & Engineering, Fudan University, 220 Handan Road, Shanghai 200433, China
  • 5Experimental Teaching Center, Sun Yat-Sen University, Guangzhou 510275, China
  • 6Institute of Tropical and Marine Meteorology/Guangdong Provincial Key Laboratory of Regional Numerical Weather Prediction, CMA, Guangzhou 510640, China
  • 7Department of Applied Physics, University of Eastern Finland, Kuopio 70211, Finland
  • 8School of Atmospheric Sciences, Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, and Institute of Earth Climate and Environment System, Sun Yat-sen University, Guangzhou, Guangdong 510275, China

Abstract. Simultaneous measurements of aerosol hygroscopicity and particle-phase chemical composition were performed at a suburban site over the Pearl River Delta region in the late summer of 2016 using a self-assembled hygroscopic tandem differential mobility analyzer (HTDMA) and an Aerodyne quadruple aerosol chemical speciation monitor (ACSM), respectively. The hygroscopic growth factor (HGF) of the Aitken mode (30nm, 60nm) and accumulation mode (100nm, 145nm) particles were obtained under 90% relative humidity (RH). An external mixture was observed for particles of every size during this study, with a dominant mode of more-hygroscopic (MH) particles, as aged aerosols dominated due to the anthropogenic influence. The HGF of less-hygroscopic (LH) mode particles increased, while their number fractions decreased during the daytime due to a reduced degree of external mixing that probably resulted from the condensation of gaseous species. These LH mode particles in the early morning or late afternoon could be possibly dominated by carbonaceous material emitted from local automobile exhaust during rush hours. During polluted days with air masses flowing mainly from the coastal areas, the chemical composition of aerosols had a clear diurnal variation and a strong correlation with the mean HGF. Closure analysis was carried out between the HTDMA-measured HGF and the ACSM-derived hygroscopicity using various approximations for the hygroscopic growth factor of organic compounds (HGForg). Considering the assumptions regarding the differences in the mass fraction of each component between PM1 and 145nm particles, the hygroscopicity-composition closure was achieved using an HGForg of 1.26 for the organic material in the 145nm particles and a simple linear relationship between the HGForg and the oxidation level inferred from the O : C ratio of the organic material was suggested. Compared with the results from other environments, HGForg obtained from our measurements appeared to be less sensitive to the variation of its oxidation level, which is, however, similar to the observations in the urban atmosphere of other megacities in China. This finding suggests that the anthropogenic precursors or the photooxidation mechanisms might differ significantly between the suburban and urban atmosphere in China and those in other background environments. This may lead to different characteristics of the oxidation products in secondary organic aerosols (SOA) and therefore to a different relationship between the HGForg and its O : C ratio.

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In this manuscript, we provide the results of the hygroscopicity of a more anthropogenically influenced aerosol in a suburban site in China. Organic material in the current type of aerosols showed moderate hygroscopicity, and it appeared to be less sensitive towards the variation of its oxidation level, which suggests different characteristics of the oxidation products in secondary organic aerosols (SOA) under the suburban/urban atmosphere in China when compared to other background environments.
In this manuscript, we provide the results of the hygroscopicity of a more anthropogenically...
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