ANALYSIS OF CARBON COMPONENTS IN PM2. 5 DURING LATE SUMMER AND EARLY AUTUMN OF XI’AN CITY

An on-line monitoring of OC，EC in PM2. 5 was done by OC/EC online analyzer from 1st to 30th September，2012 in Xi'an． O3 and UV were also monitored and analyzed． The results showed that the daily average concentration of PM2. 5 ， OC，EC，O3 was 85. 22，19. 50，7. 18 and 56. 69 μg /m3 ，respectively． The daily change rules of PM2. 5 ，OC and EC were present“bimodal”distribution，and the daily changes of OC and EC were both smaller than PM2. 5 ． Furthermore，OC had a larger fluctuation range than EC，while the relative correlation of them was high ( Ｒ2 = 0. 72899 ) ． TCA was the main component of PM2. 5 and could occupy 47. 85% ． The majority composition of TCA was OM，and the concentrations of SOC in the OM could be up to 54. 76% ． SOC and O3 showed a high correlation，which indicated that the organic photochemical reactions were relatively heavy during the study period in Xi' an． The proportions of SOC in PM2. 5 were highest during 10: 00am to 7: 00pm in a day，and did a increasing trend，The changes of TCA in the PM2. 5 were present“W shape” bimodal distribution．