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The dominant fraction of anthropogenic volatile organic compound (VOC) emissions shifted from transportation fuels to volatile chemical products (VCP) in Los Angeles (LA) in 2010. This shift in VOC composition raises the question about the importance of VCP emissions for ozone (O₃) formation. In this study, O₃chemistry during the CalNex 2010 was modeled using the Master Chemical Mechanism (MCM) version 3.3.1 and a detailed representation of VCP emissions based on measurements combined with inventory estimates. The model calculations indicate that VCP emissions contributed to 23% of the mean daily maximum 8‐hr average O₃(DMA8 O₃) during the O₃episodes. The simulated OH reactivity, including the contribution from VCP emissions, aligns with observations. Additionally, this framework was employed using four lumped mechanisms with simplified representations of emissions and chemistry. RACM2‐VCP showed the closest agreement with MCM, with a slight 4% increase in average DMA8 O₃(65 ± 13 ppb), whereas RACM2 (58 ± 13 ppb) and SAPRC07B (59 ± 14 ppb) exhibited slightly lower levels. CB6r2, however, recorded reduced concentrations (37 ± 10 ppb). Although emissions of O₃precursors have declined in LA since 2010, O₃levels have not decreased significantly. Model results ascribed this trend to the rapid reduction in NO_Xemissions. Moreover, given the impact of COVID‐19, an analysis of 2020 reveals a shift to a NO_X‐limited O₃formation regime in LA, thereby diminishing the influence of VCPs. This study provides new insights into the impact of VCP emissions on O₃pollution from an in‐depth photochemical perspective. 

Abstract. Recent studies have shown that surface ozone (O3)concentrations over central eastern China (CEC) have increased significantlyduring the past decade. We quantified the effects of changes inmeteorological conditions and O3 precursor emissions on surface O3levels over CEC between July 2003 and July 2015 using the GEOS-Chem model.The simulated monthly mean maximum daily 8 h average O3 concentration(MDA8 O3) in July increased by approximately 13.6 %, from 65.5±7.9 ppbv (2003) to 74.4±8.7 ppbv (2015), comparable to the observedresults. The change in meteorology led to an increase in MDA8 O3 of5.8±3.9 ppbv over the central part of CEC, in contrast to a decreaseof about -0.8±3.5 ppbv over the eastern part of the region. Incomparison, the MDA8 O3 over the central and eastern parts of CECincreased by 3.5±1.4 and 5.6±1.8 ppbv due to the increasedemissions. The increase in averaged O3 in the CEC region resulting fromthe emission increase (4.0±1.9 ppbv) was higher than that caused bymeteorological changes (3.1±4.9 ppbv) relative to the 2003 standardsimulation, while the regions with larger O3 increases showed a highersensitivity to meteorological conditions than to emission changes.Sensitivity tests indicate that increased levels of anthropogenic non-methanevolatile organic compounds (NMVOCs) dominate the O3 increase over theeastern part of CEC, and anthropogenic nitrogen oxides (NOx) mainly increaseMDA8 O3 over the central and western parts and decrease O3 in afew urban areas in the eastern part. Budget analysis showed that netphotochemical production and meteorological conditions (transport inparticular) are two important factors that influence O3 levels over theCEC. The results of this study suggest a need to further assess theeffectiveness of control strategies for O3 pollution in the context ofregional meteorology and anthropogenic emission changes.