Research Of The Chemical Composition Characteristics Of PM_2.5 In Wanzhou City In Summer And Winter

In recent years, atmospheric particulate matter, especially fine particles PM2.5have seriously impacted the environment and human health. Researches indicated that the average annual concentration of PM2.5in Beijing, Guangzhou, Chongqing, Lanzhou etcetera was much higher than that in foreign cities. As the largest industrial city in Southwest of China, Chongqing has become one of the cities with serious air pollution along with economic development and energy consumption increase. Currently, the researches about PM2.5in Chongqing focused on main city, including the concentration levels, pollution characteristics and chemical composition. Wanzhou City is the hinterland of the Three Gorges reservoir and the second largest city of Chongqing, with important geographical and economic status, to date, the study of particulate matter is still blank.This study took Chongqing Three Gorges College as a sample spot to collect PM2.5from the atmosphere during July1-July30,2013and November22-December22,2013, then analyzes the concentration features of OC and EC, water-soluble cations K+、Na+、Ca2+、Mg2+、NH4+water-soluble anions F-、Cl、SO42-、NO3-、NO2-,and heavy metal elements Pb、Cu、Nk、Cr、Cd in PM2.5, and then applied the enrichment factor method to make a preliminary judgment on their sources. The results of this research are useful to understand the chemical composition of PM2.5in Wanzhou District and provide a scientific basis for the prevention and control of air particles pollution. The main conclusions are as follows:(1) The seasonal changes in chemical components of PM2.5were obvious, the concentration of water-soluble cationic, anionic, carbon-containing components and heavy metals in this study in winter were higher than in summer. Throughout the sampling period, the percentage of water-soluble anionic in PM2.s was the highest, followed by the carbon and water-soluble cationic and the secondary inorganic aerosols was the mainly components of the water-soluble ions.(2) During the sampling period, the concentration of OC and EC in PM2.5were significantly related, so it was predicated that they may have the same sources of pollution, and the correlation between carbon components and K+was also related, that mean it’s sources were related to the biomass burning. The ratio of OC/EC in PM2.5was greater than2, indicating the presence of secondary organic carbon. (3) By analyzing the correlation between SO42-and NO3-and their precursors and meteorological factors, we speculated that SO42-was mainly generated by photochemical reactions, and NO3-was mainly produced in the liquid phase chemical reactions. The ratio of [NO3-]/[SO42-] was less than1,described that the stationary sources of Wanzhou District was greater than mobile sources in the contribution of water-soluble components of PM2.5. Comparing the estimating and actual concentrations of NH4+, we find it mainly existed in the form of (NH4)2SO4and NH4NO3in PM2.5. The NR values were greater than1. which mean PM2.5was alkaline in the sampling time.(4) The highest concentration of heavy metals in PM2.5of Wanzhou was Pb. The correlation between each of the heavy metals shown that, Cu, Ni and Cr, Pb and Cd, have the same sources respectively. The EF values of heavy metals were greater than10by enrichment factor analysis, indicating that they were mainly from man-made pollution, and Pb was worst affected by human pollution.