| Atmospheric fine particles(PM2.5)can stay in the atmospheric environment for a long time and easily adsorb harmful heavy metals,organic matter,bacteria and viruses.It has important effects on environmental quality,atmospheric visibility and climate change.Nanchong and Dazhou,with a large population and a wide area,are the main urban agglomerations in Northeast Sichuan.To study the characteristics of mass concentration and chemical components of in PM2.5.5 in Nanchong and Dazhou and to analyze of the sources are of great significance in formulating regional pollution control strategies.The PM2.5.5 samples were collected by setting up environmental sampling points in Nanchong and Dazhou in 2017.The water-soluble ions,inorganic elements and carbon components were analyzed so as to obtain the concentration levels and seasonal variation characteristics of Nanchong and Dazhou PM2.5 and their chemical components in the key cities of northeast Sichuan.The main conclusions are as follows:?1?The annual average mass concentration of PM2.5 in Nanchong and Dazhou in 2017 was 48.4?g·m-3,54.3?g·m-3.It was 1.4 and 1.6 times of the secondary standard(35?g·m-3)specified in the standard?GB3095-2012?,respectively.The seasonal variation of mass concentration of PM2.5.5 in Nanchong was characterized by winter>spring>summer>autumn while that in Dazhou was characterized by winter>spring>autumn>summer.The atmospheric PM2.5concentration in Nanchong and Dazhou had obvious seasonal variation characteristics showing a trend of high pollution in winter and decreased in summer&autumn.The PM2.5.5 was greatly affected by meteorological factors and negatively correlated with temperature,wind speed and rainfall.?2?The concentration of total water-soluble ion of PM2.5.5 in Nanchong and Dazhou were 15.82?g·m-33 and 13.89?g·m-3.The sum of secondary inorganic ion average mass concentration werw 12.97?g·m-33 and 10.79?g·m-33 respectively.The seasonal variation of total water-soluble ions and secondary water-soluble ions were consistent which was winter>summer>spring>autumn.The water-soluble salt of PM2.5.5 in Nanchong was NH4NO3 and NH4HSO4 while that in Dazhou was NH4NO3 and?NH4?2SO4.The NO3-/SO42-values of Nanchong and Dazhou were less than 1 which meant it was greatly affected by the fixed source?coal burning etc.?.The sulfate and winter nitrate in PM2.5.5 were mainly derived from the secondary transformation.The PM2.5.5 of winter in Nanchong and Dazhou were both acidic and the other three seasons PM2.5.5 were alkaline.The annual average concentrations of inorganic elements of PM2.5.5 in Nanchong and Dazhou were 4.87?g·m-3 and 5.51?g·m-3,respectively.The seasonal variations in Nanchong were summer>autumn>spring>winter and that seasonal variations in Dazhou were winter>summer>spring>autumn.The average values of OC and EC in Nanchong were 10.29?g·m-3and 2.44?g·m-33 and the average values of OC and EC in Dazhou were 12.94?g·m-33 and 3.22?g·m-3.The annual averages of OC/EC in Nanchong and Dazhou were 4.22 and 4.01.Nanchong and Dazhou were jointly polluted by mixed sources of vehicle exhaust,coal and biomass combustion.There was a good correlation between OC and EC in each season in Nanchong and Dazhou.The correlation coefficient R2 was greater than 0.5 which meant OC and EC had a common source in PM2.5.The annual average ratio of OC/EC in both placed exceeded 2,indicating that there was secondary pollution in the atmosphere during the sampling period.Composition analysis showed that the water-soluble ions in PM2.5.5 were the most abundant chemical components in Nanchong and Dazhou,accounting for33.0%and 39.0%,respectively.The next were carbon components,which accounted for 26.0%and 30.0%of PM2.5.The proportion of inorganic elements in PM2.5 were smaller than water-soluble ions and carbon components.The mass concentration of water-soluble ions and carbon components in winter were the highest.The enrichment factor analysis showed that the EF value of the Mg,S,Cl,Cr,Co,Ni,Cu,Zn,Ba,Pb was much greater than 10,indicating that these elements were greatly affected by human sources.?3?Principal Component Analysis showed that the main sources of water-soluble ions in the atmospheric PM2.5.5 of Nanchong were coal combustion,secondary source and dust source.Inorganic elements mainly came from coal combustion,transportation sources,biomass combustion,industrial sources,and dust.Carbon source mainly came from vehicle exhaust,coal combustion and biomass combustion.Among the water-soluble ions in the atmosphere PM2.5.5 in Dazhou were coal combustion,secondary source and dust source.Inorganic elements mainly came from combustion sources,transportation sources,and dust sources.Carbon component mainly came motor vehicle exhaust,coal burning and biomass burning.According to the health risk assessment,the atmospheric PM2.5.5 in Nanchong and Dazhou may have a non-carcinogenic risk for children,and the non-carcinogenic risk of non-carcinogenic heavy metals for children is higher than that for adults.Mn has a higher non-carcinogenic risk for children,and Cr and Co have carcinogenic risk for adults and children. |
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