Comparison of PM2.5 components and secondary formation during the heavily polluted period of two megacities in China.

This study assessed the regional differences of PM_2.5 (fine particulate matter) concentration and secondary components in China. Through chemical analysis (Thermal/Optical Carbon Analyzer and ion chromatography) and statistical tools (SPSS and Origin software), PM_2.5 samples' concentration and main components were estimated and compared in Tianjin and Guangzhou in December 2016. The average PM_2.5 mass concentration was 148 μg/m³ in Tianjin and 62 μg/m³ in Guangzhou, indicating heavy air pollution in both cities. Organic carbon constituted 15% of PM_2.5 in Tianjin, while that accounted for 25% in Guangzhou. The concentration of the secondary organic carbon accounted for 40% and 33% of organic carbon in Tianjin and Guangzhou, respectively. The ionic components in Tianjin made up 49% of PM_2.5, while those of Guangzhou were responsible for 36% locally. The sulfate oxidation ratio reached 0.41 in Tianjin and 0.53 in Guangzhou while the nitrate oxidation ratio was 0.23 and 0.14 in the two cities, respectively. These results indicated high secondary conversion rate in PM_2.5 pollution in both cities and suggested that PM_2.5 mass concentration could not fully reflect its environmental and health effects, and so more attentions should be paid to the effects of its components, especially secondary components. In addition, the results could provide a scientific basis for making policies concerning air pollution control and developing strategies of air quality improvement. [ABSTRACT FROM AUTHOR]