Comparison of NMHC measurements between 2010 and 2020 in Wuxi City, Yangtze River Delta region: Levels, compositions, sources, and impacts

Field observation analyses of volatile organic compounds (VOCs) have gained significant attention due to their potential explaining atmospheric temporal trends. This study measured non-methane hydrocarbons (NMHCs) in Wuxi City, located in the Yangtze River Delta (YRD) of China, in 2010 and 2020. The aim was to gain a better understanding of the ten-year change of VOCs in terms of their mixing ratios, sources, role in ozone, secondary organic aerosol (SOA) formation, and health risks. The average NMHC level 2020 was 20.67 ppbv, which indicated a 20% drop from 2010. A notable shift was observed in the chemical composition of NMHCs. The contribution of alkanes increased from 45% to 62% in 2020, while that of the aromatics decreased from 25% in 2010 to 21% in 2020. Ratio analysis and receptor modelling for 2010 and 2020 were used to identify the source changes of VOC species. The source apportionment model showed that the contribution of vehicle exhaust decreased from 34.5% to 20.9% from 2010 to 2020, and that of the solvent increased from 15.1% to 25.3%. The chemical reactivity results suggested that aromatics played significant roles in photochemical reactions in Wuxi City. The ozone formation potential (OFP) and SOA potential of VOCs also showed decreasing trends from 2010 to 2020. The total OFP of alkenes decreased by 34.0%, from 30.6 to 20.2 ppbvO₃/ppbv. The total non-carcinogenic risk value for the key VOC species was 0.034 in 2010 and 0.024 in 2020. Although the carcinogenic risks for benzene have decreased significantly, the value is still above the acceptable carcinogenic risk level. The results of this study demonstrate the effectiveness of air pollution control measures in Wuxi City and highlight the positive impacts on reducing secondary pollution and health risks in this region over one decade.