Ion Chemistry Characteristics Of Atmospheric Particulate Matter And Precipitation In Shanghai

In recent years,the haze problem has intensified in many big cities.In 2013,China suffered the worst in history haze weather.Severe haze weather lasted for a week or soin early December 2013 in Shanghai.Haze is wide-field presentation of all kinds of suspended particles in the atmosphere.The pollutants in the air can be cleared through wet subsidence.Rainfall can condense and stick suspended particles in the airat a certain extent,and it is one of the most effective andrapid process of atmospheric pollutants removed.In order to comprehensively and system atically analyze the chemical feature of the atmospheric wet deposition in Shanghai,with water soluble ion in atmospheric particulate matter and precipitation as main line.In this study,we collected the samples of PM2.5,PM 10 and size-fractionated atmospheric particles samples from April to September in 2015 in Xuhui campus of Shanghai normal university institute of tourism 6th floor roof(about 25 meters high).Rainwater samples were analyzed for pH,EC,major cations(Na+,NH4+,K+,Ca2+ and Mg2+)and anions(F-,CH3COO-,HCOO-,BrO3-,Cl-,NO2-,Br-,NO3-,SO42-,C2O42-and PO43-).Atmospheric particulates samples were analyzed from the same indicator but pH and EC.Based on the laboratory analyzing and statistic illustration,this work has systematically studied the composi-tion,size distribution,and sources of those aerosols,with emphasis on the water-soluble ions to explore the scouring effect of precipitation of atmospheric particulate matter in the ion.Research data show that the average value of pH in precipitation samples is 5.88,the acid rain accounts for about 43%of the total number of precipitation,the average value of conductivity is 27.8μs/cm and remains in a relatively flatstate.Precipitation samples conductivitypositive correlateto total ion concentration and water soluble ions has a larger effect on the conductivity.Total concentration of five kinds cationic in rainfall samples range between 28.7 to 651.5 μeq/L.Total concentration of eleven kinds anions in rainfall samples range between 46.2 to 314.7 μeq/L.In PM2.5,the concentration of ions range from 9.17 to 65.36μg/m3.In the16 set samples of PM1O,ion concentration range from11.54 to 88.45μg/m3.In different sample,the composition of the ion and the order is not the same.The quality ratio of NO3-and SO4-is 0.73 in PM2.5 and 1.39 in PM10,shows that moving source(exhaust of motor vehicle)contribute more to the nitrogen and sulfur of PM 10 and fixed source(coal emissions)contribute bigger in PM2.5.In size-fractionated atmospheric particles samples,water-soluble ions are mainly concentrated in particles which size is greater than 9.0 μm and between 0.7～1.1μm.The quality ratio between NO3-and SO42-is different in different size particles,the ratio of greater than 1 focused on the particle of which size is range from 3.3 to 4.7 μm.This shows that this range particle is affected by mobile.Through correlation analysis,it found that the NH4+ between SO42-and NO3-has significant correlation in precipitation,PM2.5 and PMlO.Human activity is the main source of SO42-and NO3-in settlement of atmospheric dry and wet in Shanghai by the analysis of contribution of different source.Most of the ions in PM2.5 and PM 10 are evidently eliminated by the flushing action of precipitation especially Ca2+.Precipitation has a clear effect to the ions of NO2-,F-,BrO3-,Ca2+,HCOO-,Cl-,K+,N03-,SO42-,Mg2+,Br-,and the formation rate of BrO3-,F-,HCOO-,Ca2+,NO3-,Mg2+and Br-is higher than or equal to 100%after rain in PM10.But in size-fractionated atmospheric particlessamples the concentration of some ions during the rainis greater than before the rain,so the flushing action is not obvious.