Characterization Of Mass-size Distributions And Sources Of Chemical Compositions Of Fine Particles In The Yangtze River Delta(YRD) Area Of China

Atmospheric fine particles(PM1) have been the principal pollutant in China, which make an important impact on the decrease of visibility, climate change and health. Continuous four seasons of measurements were conducted in Lin’an regional background site of the Yangtze River Delta(YRD) using Q-AMS from July 2013 to May 2014. The seasonal characteristics of the main chemical compositions in PM1, including sulfate, nitrate, ammonium, organics and chloride, were observed. Annual averaged concentration of PM1 in YRD was 53 μg/m3 with the maximum seasonal average of 84 μg/m3 in winter followed by summer(55μg/m3), spring(48μg/m3) and fall(38μg/m3). Organics was the dominant chemical composition accounting about 47% of PM1. The classification of organics by PMF indicated SOA(Secondary Organic Aerosols) made ~65% contribution to organics around the four seasons. The proportions of BBOA(Biomass Burning Organic Aerosols) in fall and winter were around 9%, suggesting the influences of biomass burning. The analysis of acidity showed PM1 in spring and winter was acid while bulk neutralized in summer and fall. The peak sizes of all five chemical compositions in PM1 were largest in winter(~600 nm) with most aged aerosol in comparison with related fresh aerosol and minimum peak sizes of 400-500 nm in summer. The peak sizes of organics were largest among all chemical composition in PM1 while those of sulfate were smallest. Besides, the seasonal variations of sulfate concentration were not much significant due to constant sources of sulfate. The characteristics of PM1 changed most from clean condition to polluted condition in winter with the enhancement of mass concentration in the factor of 24 and double peak size. In contract, the difference of mass concentration of peak sizes between clean and polluted conditions in summer was minimum. However, the concentrations of PM1 in clean condition of summer were high as the result of the generation of much regional fresh aerosol. Besides of summer, nitrate increased significant during pollution period in other three seasons with much higher concentration than sulfate.Two persistent haze-fog episodes occurred in YRD during November and December of 2013. The mean concentration of PM1 was 212 μg/m3 in the heavy haze-fog period, which was about 10 times higher than that on clean days. The concentration of all chemical composition in PM1 increased heavily, especially for nitrate. The meteorological condition of weak regional exchange and the short-distance transport from Hangzhou Bay area were the principle reason for this haze-fog event. Drop in the height of the boundary layer and high relative humidity promoted aqueous reactions leading to the increase of sulfate and nitrate. The evident enhancement of BBOA caused by biomass burning and oxidation capacity of the atmosphere increased the concentration of LV-OOA(Low-Volatility Oxidized Organic Aerosols) during haze-fog event, which promoted the development of pollution.