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

Abstract

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 PM_2.5 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 (PM_2.5 = 0~75 μg/m³, PM₁₀ = 0~150 μg/m³), and mainly NH₄⁺ and NO₃⁻ at Light-Medium levels (PM_2.5 = 75~150 μg/m³, PM₁₀ = 150~350 μg/m³). At Heavy levels (PM_2.5 = 150~250 μg/m³, PM₁₀ = 350~420 μg/m³), it is mainly SO₄²⁻ in PM_2.5, 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.