The Distribution Characteristics And Scavenging Efficiency Of Rainfall On Organic Carbon Aerosols For The Nanchang

Aerosol pollutants join into the atmosphere by emissions and atmosphericphysics chemical conversion, simultaneously removed from the atmosphere by wetand dry deposition and atmospheric transformation. Due to the growth of industrialsources, agricultural sources, domestic sources, transportation sources and otheranthropogenic sources, aerosol pollution is getting worse. Organic carbon aerosols(OC) is an important component of aerosols，it caused serious influence to humanhealth、solar radiation、photochemical reaction and ozone etc，it is an important factorin aerosol harm humans and the environment.This study collected rain samples on rainy days between May15，2013toJanuary11，2014，and collected the rainfall days TSP samples between October9，2013to November14，2013，by studying the OC，we can know that Concentrationdistribution characteristics of the OC、rain removal efficiency and the factorsaffecting the removal efficiency of rainfall. The main results were as follows：（1）The TSP and OC concentration distribution characteristics in theatmosphereThe daily average concentration of TSP and OC in rainy days in the summer,autumn and winter in Nanchang were96.82μg/m3、10.54μg/m3，126.74μg/m3、14.04μg/m3，135.16μg/m3、13.82μg/m3；The daily concentration of TSP and OC inno rain days in the summer in Nanchang were190.01μg/m3、32.42μg/m3；The meanconcentration at night were226.26μg/m3、39.39μg/m3；Daily average concentrationwere208.14μg/m3、35.91μg/m3，the Concentration of TSP and OC in no rain days inthe autumn is lower than the night during the day.The concentration of OC in no rain days in Nanchang is higher than the domesticcities such as Huangshi，Hangzhou，Dongying in Shandong province，Xiamen，Ningbo and so on.It is equal to Guangzhou，lower than Chongqing and Tianjin，8.6times that of Helsinki，Finland，1.2times that of Eddie’s bud in India. In Nanchang，in the autumn，the concentration of TSP in rainy days is the pecent of60.9thanconcentration of TSP in no rain days，the concentration of OC in rainy days is the pecent of39.1than concentration of TSP in no rain days,It is said that rain can cleanthe TSP and OC；In the rainy days in the autumn，OC is the pecent of11.98thanTSP，In the no rain days in the autumn，OC is the pecent of17.31than TSP，It is saidthat the effect of removal of OC is better than the effect of removing the TSP.In the rainy days，the concentration of TSP and OC is negative correlation，thegreater the rainfall，the lower concentration of TSP and OC. It shows that the greaterthe rainfall，the better removal efficiency of TSP and OC in the air.（2）Concentration distribution characteristics of OC in rain water samplesDaily average concentration of water-insoluble OC in the summer in Nanchangis267.27μg/L，which is Water soluble is1.10mg/L；Daily average concentration ofwater-insoluble OC in the autumn in Nanchang is487.16μg/L，which is Water solubleis0.72mg/L；Daily average concentration of water-insoluble OC in the winter inNanchang is624.07μg/L，which is Water soluble is0.65mg/L. The concentration ofWIOC in winter is the highest，and in summer is the lowest；On the other hand, Theconcentration of WSOC in summer is the highest，and in winter is the lowest.The correlation coefficient between the concentration of water-insoluble OC inrain water samples and rainfall is0.455，It shows negative correlation at the0.01level，The concentration of OC do not decreases with the increase of rainfall，Thereis a minimum of about200μg/L；There is a link among Get rid of Water soluble OCin rain water samples、content of the original water soluble OC in rain（Knot containswater-soluble OC when the cloud removed） and water-soluble OC content in theenvironment，so the water-soluble OC little correlation with rainfall.As the negatively correlated with the concentration of water-insoluble OC in rainwater samples and the pH of rain，lower the pH of rain，higher the concentration ofwater-insoluble OC，and the higher pollution degree of the rain；The organic acids inOC mainly formic acid，acetic acid and oxalic acid, all of them are soluble in water,there are some effects that compared with the sulfate and nitrate contribution to pH ofrain water is not obvious，there is no correlation between the concentration of watersoluble OC in rain water samples and the pH of rain，It shows that OC is not the mainfactors which affect rain acidity in Nanchang.Rain water electrical conductivity is only related to ion concentration，but water-insoluble OC does not dissolve in water which leads to its electricalconductivity do not contact；organic acid is part of the anion in water soluble OC inrain water samples，and the total concentrations of anion and cation determines theelectrical conductivity，so there is Positive correlation between the concentration ofwater soluble OC in rain water samples and the electrical conductivity of rain.（3）Rain removal efficiency of OC and the analysis of related factorsThe rain removal efficiency of OC in the summer，autumn and winter inNanchang were3.4%、0.80%、0.68%，rain removal efficiency of OC in the summeris much higher than that in the autumn and winter，the minimum rain removalefficiency of OC is the winter；The average rain removal efficiency of OC：Heavyrains>The heavy rain> moderate rain> light rain，rainfall and OC rainfall removalefficiency were positively correlated，and the correlation coefficient is0.64；Thecorrelation coefficient among the rain removal efficiency of OC、the pH of rain andand the electrical conductivity of rain is very small，so there is no correlationcoefficient among the rain removal efficiency of OC、the pH of rain and and theelectrical conductivity of rain；There is positive correlation between temperature andthe rain removal efficiency of OC，the correlation coefficient is0.55（It has significantcorrelation at the0.01level）；Air pressure and OC rainfall removal efficiency werenegative correlation，the correlation coefficient is-0.454，significance level is0.004；The wind speed and OC rainfall removal efficiency were positive correlation，thecorrelation coefficient is0.396，significance level is0.013；In this paper，analyzed thecorrelation between the humidity and the rain removal efficiency of OC in the29samples of the the humidity of75%~89%，it shows that they were positivecorrelation，the correlation coefficient is0.466，significance level is0.015；There isno correlation when the the humidity of below75%and90%~100%，it shows thathumidity is no correlation about the rain removal efficiency of OC.