Analysis Of Characteristics And Formation During Haze Processes In Nanjing Northern Suburb

As an important industrial city of Yangtze River Delta,Nanjing has been one of the cities which suffered the heaviest haze.Due to the haze pollution of Nanjing has become more and more serious,this has bad influence on environmental quality and human health.To analysis the haze pollution in northern suburb of Nanjing systematically,we have been continuously observing PM2.5 from Dec.21,2015 to Apr.6,2016.The average mass concentration of PM2.5 was 120.53±56.56?g·m-3,suggesting the particle pollution was quite serious.The main water soluble ions content,carbon content,inorganic(metal)elements were measured.Three phase clustering of water soluble ions showed that the different precursor from different emission sources and the combination led to the discrepancies of distribution.OC and EC had a similar change trend.OC content was higher,while EC content was lower.OC/EC was more than 2.0,indicating the secondary reaction of SOC existed commonly.The results of source apportionment suggested that coal combustion and vehicle exhaust were the main sources.Moreover,a haze pollution(December 21,2015 to January 1,2016)have been selected as a case study.Besides,water soluble ions,carbon,metal elements and sulfur isotope of PM2.5 and S02 have been measured.In addition,the PM2 5 flux has been done through WRF-Chem model.It indicated that the average mass concentration of PM2.5 during the haze case was 144.67±54.12pg·m-3.The concentration of PM2.5 on 22 Dec had reached 233.43?g·m-3.The diameters of particulate matter were below 500nm,the peak value concentrated on 150nm,indicating there existed massive submicron particles.The results of source apportionment showed that the main emission sources were coal combustion and vehicle exhaust.The ?34S of sulfate in PM2.5 was closed to the ?34S of the sulfate which came from the direct emission of coal combustion,indicating coal combustion was the main sulfate source.Besides,the fractionation of sulfur isotope indicated that the concentrations of gaseous pollutant(such as NO2,SO2,O3)and RH were the main factors which could influence the heterogeneous reactions of S02.The PM2 5 flux on 22 Dec ranged from 200?g·m-2·s-1 to 250?g·m-2·s-1,the average wind speed was 1.35m·s-1.And there did not exist obvious circulation,the synoptic situation was relatively stable.Thus,the haze was mainly caused by the local accumulation of pollutant.There was no specific emission source found.Therefore,we speculated the color was caused by physical process and submicron particles.