Chen et al. / J Zhejiang Univ-Sci A (Appl Phys & Eng) 2018 19(1):45-59 45 Effect of relative humidity on non-refractory submicron aerosol evolution during summertime in Hangzhou, China *# Ling-hong CHEN †1 , Biao LV 1 , Xian-jue ZHENG 2 , Kang-wei LI 1 , Jian-dong SHEN 2 , Kai-ji BAO 1 , Xue-cheng WU 1 , Cheng-hang ZHENG 1 , Fang YING 2 , Xiang GAO 1 , Ke-fa CEN 1 1 State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou 310027, China 2 Hangzhou Environmental Monitoring Center Station, Hangzhou 310007, China † E-mail: chenlh@zju.edu.cn Received May 24, 2017; Revision accepted Dec. 10, 2017; Crosschecked Dec. 15, 2017 Abstract: Relative humidity (RH) has a significant and complex effect on aerosols because of the aqueous phase process and gas-particle partition. The mass concentration and size distribution of organic aerosols, sulfate, nitrate, ammonium, and chloride were measured using high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS). These measurements were rec-orded from Aug. 5 to Sept. 23, 2016 in Binjiang District, Hangzhou, China, during which period more than 78% of the readings showed an RH over 60%, while the average temperature was 26 °C. Correlation analysis was applied to inorganic aerosol meas-urements while positive matrix factorization (PMF) was applied for source apportionment of organic aerosols (OA). The pattern of fixation of ammonium in aerosols changed as the RH increased, suggesting that RH enhances nitrate participation in particles, while sulfate is scavenged by droplets. All species of non-refractory submicron particles (NR-PM 1 ) showed an increase in their peak size as the RH increased. Primary OA (POA) continuously accumulated as the RH increased. When RH<60%, oxygenated OA (OOA) increased with increasing RH because of oxidation; semi-volatile OOA (SV-OOA) had a higher mass concentration during the daytime than at nighttime, indicating that the aqueous phase process and photochemistry synergistically affect the formation of oxygenated SV-OOA. When RH>60%, there was a relatively slow decrease in OOA, dominated by the wet removal effect rather than oxidation. The degree of oxidation of OA decreased as RH increased; this can be explained by most of the OOA with higher hygroscopicity being removed as droplets. Key words: Relative humidity (RH); Aerosol composition; Size distribution; Wet removal; Aqueous-phase https://doi.org/10.1631/jzus.A1700567 CLC number: TV5 1 Introduction Atmospheric aerosols markedly affect the radia-tive balance in the Earth’s atmosphere and play a central role in climate (Solomon, 2007; Tong et al., 2015, 2016a, 2016b, 2017). They also have a signif-icant impact on human health (Davidson et al., 2005). Submicron particles (PM 1 , aerodynamic diameter less than 1 μm) have a greater effect on the environment and human health because of their longer lifetime and smaller gravity settlement effect and a greater effect since they penetrate deeper into the lungs. Aerosols contain organic and inorganic compounds, and or-ganic aerosols (OA) play a major role in fine particles (Kanakidou et al., 2005; Zhang et al., 2007a). Organic aerosols can be divided into primary organic aerosol (POA) and secondary organic aerosol (SOA). POA is direct outputs from pollutant sources such as vehicles and plants, while SOA is formed by nucleation, Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering) ISSN 1673-565X (Print); ISSN 1862-1775 (Online) www.jzus.zju.edu.cn; www.springerlink.com E-mail: jzus@zju.edu.cn * Project supported by the Project of Hangzhou G20 Environmental Protection (No. 2016-004), the Project of Hangzhou Technology (No. 20160533B85), the Public Project of Ministry of Environmental Protection (No. 201409008-4), the National Basic Research Program of China (No. 2015CB251501), the Program of Introducing Talents of Discipline to University (No. B08026), and the Innovative Research Groups of the National Natural Science Foundation of China (No. 51621005) # Electronic supplementary materials: The online version of this article (https://doi.org/10.1631/jzus.A1700567) contains supplementary materials, which are available to authorized users ORCID: Ling-hong CHEN, https://orcid.org/0000-0002-8171-4632© Zhejiang University and Springer-Verlag GmbH Germany, part of Springer Nature 2018 万方数据
