Exploration of O-precursor relationship and observation-oriented O control strategies in a non-provincial capital city, southwestern China.

To investigate photochemical ozone (O) formation and provide localized control strategies, an intensive sampling of O and its precursors (i.e. volatile organic compounds (VOCs) and nitrogen oxides (NO = NO + NO)) were conducted at an urban site in Leshan, Sichuan province during 4-13 August 2019. The mixing ratios of O, total VOCs (TVOCs) and NO were 40.0 ± 5.3, 22.5 ± 2.6 and 14.6 ± 3.8 ppbv, respectively (±95% confidence intervals). O and its precursors existed a well negative correlation, indicating intensive local O formation. To further explore the O-precursors relationship and observation-oriented O control strategies, a photochemical box model coupled with master chemical mechanism (PBM-MCM) was adapted. The relative incremental reactivity (RIR) calculated by model results showed that Leshan was in the VOCs-limited and O production was most sensitive to alkenes. Moreover, O isopleth diagram was drawn using the PBM-MCM simulation results and seven reduction scenarios were evaluated in Leshan. The reduction ratio of VOCs/NO on 3:1 was proposed to be the best solution, which can be achieved effective reduction on local O formation. At last, since VOCs were the key precursors of O in Leshan, VOC sources and their potential contributions to O formation were investigated by using the positive matrix factorization (PMF) model. Seven sources were identified, and traffic related emissions (including vehicle exhaust and gasoline evaporation, 29.9%) and fixed combustion (27.7%) had the large contribution to ambient VOCs. Among anthropogenic sources, fixed combustion and solvent usage in painting were the large contributors to O formation, accounting for 30.9% and 18.3%, respectively, which should have high priorities on source reduction. This study provides scientific advices for future O pollution control strategies in Leshan, which can be extended to other cities.