Chemical Composition And Optical Properties Of Surface Atmospheric Particles In Shanghai

As main atmospheric pollutants that affect urban air quality in China, atmospheric particulate matters can bring important effects on urban visibility, global climate, and human health. As PM2.5 can enter human respiratory system and even penetrate through lung cells into the blood circulation, it brings worse harms to human health. PM2.5 has become the study issue and chief pollutant for rigorous control in the world, especially in the developed countries. PM2.5 was incorporated in the National Standard (GB3015-2012) in 2012, which will be conducted since 2016. This study can objectively reflect the PM2.5 polluted situations of developed cities represented by Shanghai, and provide scientific evidences for controlling atmospheric fine particulate matters in this city.This study focuses on the atmospheric particles of Shanghai, including the distribution characteristic of PM2.5 concentration, and the chemical composition and optical properties of particulate matters. Source analysis is conducted using the factor analysis method and the back-trajectory method.Major conclusions of this study as follow:(1) The daily average concentration of PM2.5 during the sampling period was 40.3μg/m3, exceeding the standard of the National Standard (GB3015-2012). This indicated a slightly pollution. Pollution was most serious in winter and mildest in summer with daily average concentration of 50.2μg/m3 and 27.2μg/m3, respectively. The average concentration of the study period exceeded the standard of National Standard (GB3015-2012) except summer.(2) SO42- accounted for the highest proportion (24.75%) among detected chemical compositions, following by OM (24.62%) and NO3-(11.53%) in autumn. However, OM accounted for the highest proportion (20.10%) among detected chemical compositions, following by SO42-(18.78%) and NO3-(16.85%) in winter, which revealed the different pollution situation among these two seasons. Eight water-soluble ions were important parts of PM2.5, accounting for about a half in mass of PM2.5.(3) The mean extinction, scattering and absorption coefficients and SSA in 2012 spring were 122.28 Mm-1、88.67 Mm-1、33.61 Mm-1 and 0.727, respectively. A low value of SSA denoted that aerosol particles in Shanghai contained a large fraction of absorbing material such as black carbon. The average scattering Angstrom exponent (αs (450/700)) was 1.68, indicating a predominance of fine particles. The Angstrom exponent also exhibited higher values in the afternoon, possibly correlated with the formation of secondary fine particles. A higher concentration of nitrate and ammonium in night time and the increase of SSA at night demonstrated the existence of some nighttime chemistry process.(4) A good correlation with correlation coefficient of 0.942 was found in scattering coefficients measured and calculated by the revised IMPROVE formula. The slope (1.092) was very close to 1, demonstrating that this revised IMPROVE formula can reflect the atmospheric scattering coefficient in Shanghai. Ammonium sulfate had the largest contribution to scattering coefficient accounting for 43%, following by ammonium nitrate (38%) and OM (16%).(5) The main contributor of PM2.5 was anthropogenic sources such as the emissions of fossil-fuel, biomass burning, and so on. The ocean source accounted for a smaller part. The proportion distributions of pollutants in autumn and spring was different. The analysis results of airmass back-trajectory confirmed the conclusion above.