Characteristics And Source Analysis Of Water-soluble Inorganic Ions And Non-polar Organic Compounds In PM_2.5 In Ya’an Yucheng City

In recent years,PM2 5(particulate matter with aerodynamic diameter less than 2.5μm)is the primary atmospheric pollutant for most areas in China.It was reported that PM2.5 not only decrease visibility and cause serious harm to human health,but also change the global climate.Therefore characterization and source apportionment of PM2 5 are important and could provide useful information for making effective strategies for air quality impovement.Total of 69 PM2.5 samples were collected during June 2013～May 2014 period in Ya’an Yucheng City.Water-soluble inorganic ions(WSIIs)and non-polar organic compounds in PM2 5 were analyzed.Combined with principal component analysis(PCA)and back trajectory model,source analysis of WSIIs were conducted.Using carbon preference index(CPI),plant wax index,and diagnostic ratio methods,source analysis of non-polar organic compounds were also investigated.The main results are as follows:(1)The annual concentration of PM2.5 in Ya’an Yucheng City was 61.34±29.95μg/m3,seasonal variation of PM2.5 mass concentrations were as follows:winter(88.18±36.32 μg/m3)>spring(63.39±26.13 μg/m3)>autumn(51.97±20.09 μg/m3)>summer(41.82±10.39 μg/m3).The annual average concentration of total WSIIs was 26.7±4.07 μg/m3,which accounted for 40.4±6.92%of PM2.5.During the Spring Festival,the concentration of total WSIIs reached up to 122.42 μg/m3 and 74.96 μg/m3 on New Year’s Eve and lunar New Year’s Day,respectively.This indicates that setting off fireworks during the Spring Festival could significantly increase the atmospheric pollutants.The conversion of SO2 to SO42-was mainly controlled by the heterogeneous oxidation processes.Based on the source anaylsis of WSIIs in PM2.5 using PCA,S042-,NO3-,NH4+,C1-and Ca2+ were identified as being from anthropogenic sources(including secondary pollution,vehicle emissions and construction fugitive dust);K+ and Na+ were classified as being from both natural(soil dust and sea salt)and anthropogenic sources(biomass burning and coal sources);Mg2+ was from natural source(soil dust).According to the back trajectory analysis,it was found that the WSIIs in PM2.5 in Ya’an were mainly affected by regional pollution in Sichuan basin and long-range transported air masses from west-southwest.(2)The annual concentration of total n-alkanes was 96.81±35.28 ng/m3.According to the values of CPI and plant wax index,it was found that the main source of n-alkanes during winter was anthropogenic,while during spring and summer the main source was biological,during autumn both sources were contributed.The annual concentration of total polycyclic aromatic hydrocarbons(ΣPAHs)was 27.47±6.56 ng/m3,and the order of PAHs with different benzene ring number were as follows:4 rings>2 rings>5 rings>3 rings>6 rings>7 rings,among which the PAHs with 4 rings had the highest concentration and accounted for 30.87%of the EPAHs.According to diagnostic ratio analysis,vehicle emissions and biomass burning were the main two sources of PAHs in Ya’an Yucheng City.Similarly,the concentration of ΣPAHs reached up to 97.53 ng/m3 and 33.67 ng/m3 on New Year’s Eve and lunar New Year’s Day,respectively,which indicates that setting off fireworks also had significant effect on PAHs level.Based on the evaluations of benzo[a]pyrene toxic equivalent and cancer risk,the results of health risk assessment for PAHs in PM2.5 were more optimistic,and the air quality is not bad in Ya’an Yucheng City.