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The heaviest aerosol pollution day in the historical record of the Yangtze River Delta occurred on 19 January 2007, in which the daily concentration of PM10 reached 512μgm−3 in Shanghai, 463μgm−3 in Suzhou, 354μgm−3 in Hangzhou, and 282μgm−3 in Nanjing. The hourly concentrations of PM2.5 and PM10 reached peak values of 466 and 744μgm−3, respectively, in Shanghai. With visibility <0.6km, the regional haze covered nearly the entire Yangtze River Delta. High ratios of PM2.5/PM10 (61%), SO2/PM10 (0.38) and NO2/PM10 (0.24) were observed. The unusual stagnant dispersion conditions before a cold front played the predominant role in this high pollution episode, with relative humidity (RH) of 88%, both surface and upper-level inversions, as well as low wind speed (<1ms−1). The sulfur oxidation rate (SOR) reached 0.67 and the nitrogen oxidation rate (NOR) reached 0.61, signifying that formation of sulfate and nitrate contributed significantly to the high secondary aerosol concentration of PM2.5. The enrichment factors of As, Cd, and Pb reached 4058, 6971, and 3972, which were 4.45–6.68 times higher than those on good/moderate days. It was demonstrated that emissions from anthropogenic sources, especially stationary sources such as power plants, industrial boilers, and furnaces, were the major contributors to the heaviest aerosol pollution in the delta. More attention should be paid to the increases in emissions and the higher occurrence of haze days that have accompanied the rapid development of the economy in the Yangtze River Delta. [Copyright &y& Elsevier]

High pollution episodes of PM 2.5 and O 3 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 PM 2.5 , particle size distribution (13.6 ~ 736.5 nm), concentrations of gas pollutants including O 3 , SO 2 , NO 2 , CO, non-methane hydrocarbons (NMHC)), and nitrate radical in 2013. During the sampling period, the average concentration of PM 2.5 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 SO 2 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 NO 3 and/or N 2 O 5 . The correlations among NMHC, O x (= O 3 + NO 2 ), 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 H 2 SO 4 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 PM 2.5 and O 3 in a regional scale. These findings are important for better understanding the air pollution in summer in YRD. [ABSTRACT FROM AUTHOR]

Joint field observations were conducted from October to November in 2011 to observe haze pollution in the Yangtze River Delta (YRD), China. Samples of particulate matter with diameter less than 2.5 μm (PM 2.5 ) and less than 10 μm (PM 10 ), gaseous pollutants and meteorology data were collected in five cities – Shanghai, Suzhou, Nanjing, Ningbo and Hangzhou – in the YRD. The chemical composition of PM 2.5 was analyzed and the light extinction resulting from each chemical species was calculated using the IMPROVE algorithm. A typical heavy haze episode was selected and the chemical mass balance (CMB) model was applied to identify the sources of PM 2.5 . The average PM 2.5 and PM 10 mass concentrations during the haze episode were 100 ± 24 μg/m 3 and 164 ± 19 μg/m 3 , respectively; visibility decreased to 1 km. Organic matter (OM), sulfate, nitrate, and ammonium were the dominant components of PM 2.5 , accounting for 33%, 19%, 17% and 11% of PM 2.5 mass, respectively. Sulfate, OM and nitrate had the highest impact on light extinction, contributing 30%, 28% and 19%, respectively. The source apportionment indicate that PM 2.5 is primarily from secondary pollutants and primary emissions from vehicles and biomass burning. A polluted air mass from north Jiangsu Province and stagnant meteorology further aggravated the haze pollution. The five cities had similar characteristics and pollution sources. [ABSTRACT FROM AUTHOR]