title: Intense secondary aerosol formation due to strong atmospheric photochemical reactions in summer: observations at a rural site in eastern Yangtze River Delta of China.
abstract: High pollution episodes of PM2.5 and O3 were frequently observed at a rural site (N31.0935º, E120.978°) in eastern Yangtze River Delta (YRD) in summer. To study the impacts of photochemical reactions on secondary aerosol formation in this region, we performed real-time measurements of the mass concentration and composition of PM2.5, particle size distribution (13.6~736.5 nm), concentrations of gas pollutants including O3, SO2, NO2, CO, non-methane hydrocarbons (NMHC)), and nitrate radical in 2013. During the sampling period, the average concentration of PM2.5 was 76.1 (± 16.5) μg/m(3), in which secondary aerosol species including sulfate, nitrate, ammonium, and secondary organic aerosol (SOA) accounted for ~ 62%. Gas-phase oxidation of SO2 was mainly responsible for a fast increase of sulfate (at 1.70 μg/m(3)/h) in the morning. Photochemical production of nitric acid was intense during daytime, but particulate nitrate concentration was low in the afternoon due to high temperature. At night, nitrate was mainly formed through the hydrolysis of NO3 and/or N2O5. The correlations among NMHC, Ox (= O3 + NO2), and SOA suggested that a combination of high emission of hydrocarbons and active photochemical reactions led to the rapid formation of SOA. In addition, several new particle formation and fast growth events were observed despite high ambient aerosol loading. Since the onset of new particle events was accompanied by a rapid increase of H2SO4 and SOA, enhanced formation of sulfate and SOA driven by photochemical oxidation likely promoted the formation and growth of new particles. Together, our results demonstrated that strong atmospheric photochemical reactions enhanced secondary aerosols formation and led to the synchronous occurrence of high concentrations of PM2.5 and O3 in a regional scale. These findings are important for better understanding the air pollution in summer in YRD.
authors.affiliation: Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China; Shanghai Environmental Monitoring Center, Shanghai 200235, China.
authors.forename: Dongfang
authors.initials: D
authors.lastname: Wang
authors.affiliation: Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China; Fudan-Tyndall Center, Fudan University, Shanghai 200433, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Zhou
authors.affiliation: Shanghai Environmental Monitoring Center, Shanghai 200235, China. Electronic address: qingyanf@semc.gov.cn.
authors.forename: Qingyan
authors.initials: Q
authors.lastname: Fu
authors.affiliation: Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China; Shanghai Environmental Monitoring Center, Shanghai 200235, China.
authors.forename: Qianbiao
authors.initials: Q
authors.lastname: Zhao
authors.affiliation: Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China; Department of Environmental Toxicology, University of California, Davis, California 95616, United States. Electronic address: dkwzhang@ucdavis.edu.
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhang
authors.affiliation: Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China; Fudan-Tyndall Center, Fudan University, Shanghai 200433, China.
authors.forename: Jianmin
authors.initials: J
authors.lastname: Chen
authors.affiliation: Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Department of Environmental Science and Engineering, Fudan University, Shanghai 200433, China; Fudan-Tyndall Center, Fudan University, Shanghai 200433, China. Electronic address: yangxin@fudan.edu.cn.
authors.forename: Xin
authors.initials: X
authors.lastname: Yang
authors.affiliation: Shanghai Environmental Monitoring Center, Shanghai 200235, China.
authors.forename: Yusen
authors.initials: Y
authors.lastname: Duan
authors.affiliation: Shanghai Environmental Monitoring Center, Shanghai 200235, China.
authors.forename: Juan
authors.initials: J
authors.lastname: Li
mesh_terms: D000336:Aerosols / Q000032:analysis*; D000393:Air Pollutants / Q000032:analysis*; D002681:China; D004784:Environmental Monitoring; D010126:Ozone / Q000032:analysis*; D010316:Particle Size; D052638:Particulate Matter / Q000032:analysis*; D055668:Photochemical Processes; D012621:Seasons
chemical_list: D000336:Aerosols; D000393:Air Pollutants; D052638:Particulate Matter; D010126:Ozone
keywords: Gaseous Precursors; PM(2.5); Photochemical Oxidation; Secondary Aerosol Formation; Yangtze River Delta