Sulfur Isotope Compositons Of PM_2.5during Different Weather Conditions In Nanjing Northern Suburb

Nanjing industrial coal combustion was simulated in our laboratory under different combustion conditions.In order to analyze the composition of coal and sulfur isotope fractionation,and explore the influencing factors of coal sulfur isotope fractionation,the coal of sulfur isotopic compositions in Nanjing region might provide an insight into source apportionment of atmospheric PM2.5.Atmospheric SO2 and PM2.5 samples for chemical and isotopic analysis were collected in Nanjing northern suburb during the second session of the Youth Olympic Games(July 6-September 20,2014)and haze days in Winter(December 21,2015-January 1,2016).The concentration,temporal variations,sulfur isotope compositions of SO2 and PM2.5,as well as their relationships between changes in meteorological conditions were studied in these two periods,which were traced the sources of sulfate in aerosol and the transformation mechanism of SO2 to secondary sulfate.The main conclusions are as follows:sulfur content of the coal is not an important factor affecting the sulfur isotopes.However,differences of sulfur isotopes in coal and the formation of sulfate-reducing bacteria and high temperature are closely related.Under different combustion conditions,the temperature,the type of coal combustion and oxidation rates have a significant impact on sulfur isotope fractionation.The potential sources of coal and exhaust emissions,and the lower value ?34S sulfur source(biological sulfur)affected atlospheric PM2.5 during the second session of the Youth Olympic Games.However,coal burning,vehicle exhaust and road dust were the main sulfur source of atmospheric PM2.5 in the haze days.Combining with the Backward air trajectory and MODIS fire spot photos,thereby excluding the long-distance source of straw burning for PM2.5 in these two periods.The ?34S value of atmospheric SO2 was found lower than that of sulfate aerosol in Nanjing northern suburb,indicating an obvious isotope fractionation during the SO2 oxidation process.The sulfur isotopic fractionation factor ?c was intermediate between that expected from homogeneous and heterogeneous oxidation pathways,suggesting that both processes can be important for SO2 to form secondary sulfate.However,the dominant reaction is different in different seasons.The homogeneous oxidation reactions are more important in the production of sulfate aerosol during the Youth Olympic Games.The mechanism of transformation for SO2 to sulfate aerosol is also controlled by homogeneous oxidation in haze days,it is suggested that SO2 is converted to sulfate during the oxidation reaction influenced by the relative humidity.