Chemical Composition Characteristics And Source Apportionment Of Atmospheric PM_2.5 In Xiamen City

The PM_2.5 samples were synchronously collected in urban and suburban areas of Xiamen City during summer and winter months to investigate the characteristics and sources of chemical composition in atmospheric PM_2.5. The main conclusions of the research were summarized as follow:Xiamen showed a lighter pollution level with the comparative lower concentrations of PM_2.5 comparing with previous studies. The level of PM_2.5 pollution in winter was significantly higher than that in summer, and suburban area was slightly more serious than urban area. The chemical composition of atmospheric PM_2.5 in Xiamen was in a relatively low level comparing with the research of other cities in China.The SOC/OC ratios in this study were more than 31.75%, suggesting that the secondary OC pollution in Xiamen was serious. The correlations between OC and EC showed that EC might mainly come from primary emission sources, such as fossil fuel and biomass incomplete combustion. OC was mainly influenced by the effects of fossil fuel burning and secondary pollution. In addition, sources of cooking and biomass burning had great contribution to urban areas.The study found SO₄^2-, NO₃^-, NH₄⁺（SNA） were the major components of water-soluble ions in PM_2.5, suggesting that the level of secondary ions was relatively high. Ion balance relationship showed anions in PM_2.5 were relative loss in summer,whereas in winter. Ion fitting equation and SNA triangular diagram showed that（NH₄）₂SO₄ and NH₄NO₃ were the main forms of ions, but there were some differences between summer and winter. The ratio of NO₃^-/SO₄^2- and principal component analysis indicated that the water-soluble ions in PM_2.5 of Xiamen City mainly came from coal combustion, traffic emission and biomass burning.Enrichment factors analysis showed that the heavy metals in PM_2.5 were enriched in different degrees. And the order of enrichment factor of 8 heavy metals was: Cd>Cu>Zn>Ni, Pb>Cr, V>Co. Carcinogenic risk showed Cr had a certain carcinogenic risk, which would cause harm to human body through respiratorypathway. In addition, adult males were at the highest non-carcinogenic risk, followed by adult females. Correlation analysis, principal component analysis and cluster analysis showed that V, Cr, Ni, Cu and Zn were mainly from industrial pollution sources. Pb and Cd mainly come from coal and traffic emissions. Co was mainly influenced by natural sources. Lead isotope tracing method further confirmed the effect of Pb was mainly affected by coal combustion, traffic emissions and natural sources, and the contribution rates were 48.86 %, 26.62% and 24.52 %, respectively.Lead and strontium isotope tracing showed main sources of lead, strontium and related elements were mainly from anthropogenic sources（coal and traffic emissions）.Therefore, the sources of atmospheric PM_2.5 in Xiamen City were coal combustion, traffic emissions, biomass burning, cooking sources, industrial sources,natural sources and secondary pollution. Temporal and spatial characteristics showed that the natural sources was relatively large when in winter months, while coal combustion when in summer months; And sources of cooking and biomass burning had great contribution to urban areas, the suburban areas were seriously affected by natural sources.