A quantitative analysis of the driving factors affecting seasonal variation of aerosol pH in Guangzhou, China

Shiguo Jia; Weihua Chen; Qi Zhang; Padmaja Krishnan; Jingying Mao; Buqing Zhong; Minjuan Huang; Qi Fan; Jinpu Zhang; Ming Chang; Liming Yang; Xuemei Wang

doi:10.1016/j.scitotenv.2020.138228

A quantitative analysis of the driving factors affecting seasonal variation of aerosol pH in Guangzhou, China

Sci Total Environ. 2020 Jul 10:725:138228. doi: 10.1016/j.scitotenv.2020.138228. Epub 2020 Mar 31.

Authors

Shiguo Jia¹, Weihua Chen², Qi Zhang³, Padmaja Krishnan⁴, Jingying Mao², Buqing Zhong², Minjuan Huang¹, Qi Fan³, Jinpu Zhang⁵, Ming Chang², Liming Yang⁶, Xuemei Wang⁷

Affiliations

¹ School of Atmospheric Sciences, Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, Sun Yat-sen University, Guangzhou 510275, PR China; Guangdong Provincial Field Observation and Research Station for Climate Environment and Air Quality Change in the Pearl River Estuary, Guangzhou 510275, PR China.
² Guangdong-Hongkong-Macau Joint Laboratory of Collaborative Innovation for Environmental Quality, Institute for Environmental and Climate Research, Jinan University, Guangzhou 510632, PR China.
³ School of Atmospheric Sciences, Guangdong Province Key Laboratory for Climate Change and Natural Disaster Studies, Sun Yat-sen University, Guangzhou 510275, PR China.
⁴ Department of Civil & Environmental Engineering, National University of Singapore, 1 Engineering Drive 2, Singapore 117576, Singapore.
⁵ Guangdong Environmental Monitoring Center, Guangzhou 510308, PR China.
⁶ Department of Chemical and Biomolecular Engineering, National University of Singapore, 117576, Singapore. Electronic address: cheylm@nus.edu.sg.
⁷ Guangdong-Hongkong-Macau Joint Laboratory of Collaborative Innovation for Environmental Quality, Institute for Environmental and Climate Research, Jinan University, Guangzhou 510632, PR China. Electronic address: eciwxm@jnu.edu.cn.

PMID: 32302828
DOI: 10.1016/j.scitotenv.2020.138228

Abstract

Aerosol acidity is of great interest due to its effects on atmospheric chemical processes and impact on human health; however, the driving factors of aerosol acidity have only been scarcely investigated. This study characterized the aerosol acidity during the wet and dry seasons in Guangzhou, China, and systematically analyzed the seasonal variation and the corresponding driving factors of aerosol acidity followed by the discussion of their impact on gas-aerosol partitioning of NH₃ and HNO₃. It was demonstrated that the pH of PM_2.5 was 0.08 unit lower (more acidic) during wet season than during the dry season and the aerosol acidity varied less in South China than that in North China. Additionally, our results showed that the meteorological parameters including temperature and relative humidity have larger effect on aerosol pH variation than chemical species. Particularly, the lower temperature during dry season had the positive influence (0.38 pH unit) on aerosol pH compared to the wet season; however, the negative effect due to relative humidity (RH) and chemical species resulted in a smaller seasonal variation of aerosol pH between these two seasons. The sensitivity analysis showed that the increase of temperature has negative impact (reducing pH) on aerosol pH with an almost linear relationship, while RH and chemical species represented a two-phase linear and nonlinear effect, respectively. Finally, the calculation of gas-aerosol partitioning indicated that the temperature had the largest influence on the seasonal variation of gas-aerosol partitioning for both HNO₃ and NH₃ followed by liquid water content and non-ideality, while aerosol acidity imposed the lowest impact, which suggests that all the parameters including meteorological and chemical species should be comprehensively evaluated to devise a PM_2.5 control strategy.

Keywords: Aerosol acidity; Driving factors; Seasonal variation.