Characteristics of Particulate Matter at Different Pollution Levels in Chengdu, Southwest of China

Air pollution is becoming increasingly serious along with social and economic development in the southwest of China. The distribution characteristics of particle matter (PM) were studied in Chengdu from 2016 to 2017, and the changes of PM bearing water-soluble ions and heavy metals and the distribution of secondary ions were analyzed during the haze episode. The results showed that at different pollution levels, heavy metals were more likely to be enriched in fine particles and may be used as a tracer of primary pollution sources. The water-soluble ions in PM2.5 were mainly Sulfate-Nitrate-Ammonium (SNA) accounting for 43.02%, 24.23%, 23.50%, respectively. SO42-, NO3-, NH4+ in PM10 accounted for 34.56%, 27.43%, 19.18%, respectively. It was mainly SO42- in PM at Clean levels (PM2.5 = 0-75 mu g/m(3), PM10 = 0 similar to 150 mu g/m(3)), and mainly NH4+ and NO3- at Light-Medium levels (PM2.5 = 75-150 mu g/m(3), PM10 =150 similar to 350 mu g/m(3)). At Heavy levels (PM2.5 = 150 similar to 250 mu g/m(3), PM10 = 350 similar to 420 mu g/m(3)), it is mainly SO42- in PM2.5, and mainly NH4+ and NO3- in PM10. The contribution of mobile sources to the formation of haze in the study area was significant. SNA had significant contributions to the PM during the haze episode, and more attention should be paid to them in order to improve air quality.