Characteristics of ambient volatile organic compounds during spring O pollution episode in Chengdu, China.

Surface ozone (O) has become a critical pollutant impeding air quality improvement in many Chinese megacities. Chengdu is a megacity located in Sichuan Basin in southwest China, where O pollution occurs frequently in both spring and summer. In order to understand the elevated O during spring in Chengdu, we conducted sampling campaign at three sites during O pollution episodes in April. Volatile organic compounds (VOCs) compositions at each site were similar, and oxygenated VOCs (OVOCs) concentrations accounted for the highest proportion (35%-45%), followed by alkanes, alkens (including acetylene), halohydrocarbons, and aromatics. The sensitivity of O to its precursors was analyzed using an observation based box model. The relative incremental reactivity of OVOCs was larger than other precursors, suggesting that they also played the dominant role in O formation. Furthermore, the positive matrix factorization model was used to identify the dominant emission sources and to evaluate their contribution to VOCs in the city. The main sources of VOCs in spring were from combustion (27.75%), industrial manufacturing (24.17%), vehicle exhaust (20.35%), and solvent utilization (18.35%). Discussions on VOCs and NO reduction schemes suggested that Chengdu was typical in the VOC-limited regime, and VOC emission reduction would help to prevent and control O. The analysis of emission reduction scenarios based on VOCs sources showed that the emission reduction ratio of VOCs to NO needs to reach more than 3 in order to achieve O prevention. Emission reduction from vehicular exhaust source and solvent utilization source may be more effective.