Source Apportionment and Secondary Transformation of Atmospheric Nonmethane Hydrocarbons in Chengdu, Southwest China

Nonmethane hydrocarbons (NMHCs) have an important influence on the formation of photochemical smog and secondary organic aerosols in the atmosphere. We investigated 55 NMHCs in Chengdu from 27 October 2016 to 30 September 2017 to identify their sources, pollution levels, and secondary transformation potential. The average concentration of NMHCs in Chengdu was 41.820.8ppbv. Meteorological conditions play a vital role in the formation and dispersion of NMHCs, PM2.5, and O-3. The photochemical conversion of NMHCs was inhibited by lower solar radiation, leading to low O-3 concentrations and high NMHC concentrations. Aromatics and alkenes played a leading role in the secondary transformation, accounting for 6016% and 2911% of the total secondary formation potential, respectively. The southwest air mass trajectory was the most significant transportation path affecting the NMHC concentration in Chengdu. The results of the positive matrix factorization model indicated that there were seasonal differences in the sources of NMHCs in Chengdu. Four major emission sources were identified, namely, vehicle exhaust, industrial, paint solvents, and biogenic sources. Vehicle exhaust emissions were the greatest contributor to NMHCs in Chengdu, accounting for approximately 45% of the NMHCs. Overall, toluene, m/p-xylene and ethylbenzene constitute a large fraction of the calculated ozone and secondary aerosol formation potential. Future studies should consider targeting these compounds when evaluating ozone and aerosol reduction strategies. However, in terms of total control of NMHC pollution, Chengdu should focus on effective control measures for traffic emissions. Plain Language Summary Nonmethane hydrocarbons (NMHCs) can enhance atmospheric oxidation, promote the formation of secondary pollutants, and affect air quality and human health in urban areas, as well as have an indirect effect on global climate change. The unique topographical factors, adverse meteorological conditions, and high pollution emissions make the levels, sources, and secondary transformation of NMHC pollution in Chengdu a vital and meaningful research topic. In this study, gas chromatography was used to conduct field observations of NMHCs in Chengdu from 27 October 2016 to 30 September 2017 with a 30-min time interval to establish a detailed analysis system for NMHCs. The analysis results showed that (1) aromatics and alkenes played a leading role in secondary transformation, (2) the trajectories from the southwest were the most important transport pathways influencing the concentrations of NMHCs in Chengdu, and (3) vehicle exhaust was the primary source of NMHCs in the Chengdu urban area. Through the above conclusions, we can formulate suitable pollution control measures in Chengdu. This work is of great significance to the improvement of air quality in Chengdu.