Exploration of O3-precursor relationship and observation-oriented O3 control strategies in a non-provincial capital city, southwestern China.

Abstract To investigate photochemical ozone (O3) formation and provide localized control strategies, an intensive sampling of O3 and its precursors (i.e. volatile organic compounds (VOCs) and nitrogen oxides (NOx = NO + NO2)) were conducted at an urban site in Leshan, Sichuan province during 4–13 August 2019. The mixing ratios of O3, total VOCs (TVOCs) and NOx were 40.0 ± 5.3, 22.5 ± 2.6 and 14.6 ± 3.8 ppbv, respectively (±95% confidence intervals). O3 and its precursors existed a well negative correlation, indicating intensive local O3 formation. To further explore the O3-precursors relationship and observation-oriented O3 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 O3 production was most sensitive to alkenes. Moreover, O3 isopleth diagram was drawn using the PBM-MCM simulation results and seven reduction scenarios were evaluated in Leshan. The reduction ratio of VOCs/NOx on 3:1 was proposed to be the best solution, which can be achieved effective reduction on local O3 formation. At last, since VOCs were the key precursors of O3 in Leshan, VOC sources and their potential contributions to O3 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 O3 formation, accounting for 30.9% and 18.3%, respectively, which should have high priorities on source reduction. This study provides scientific advices for future O3 pollution control strategies in Leshan, which can be extended to other cities.