Impacts of meteorology and emissions on summertime surface ozone increases over central eastern China between 2003 and 2015

Recent studies have shown that surface ozone (O-3) concentrations over central eastern China (CEC) have increased significantly during the past decade. We quantified the effects of changes in meteorological conditions and O-3 precursor emissions on surface O-3 levels over CEC between July 2003 and July 2015 using the GEOS-Chem model. The simulated monthly mean maximum daily 8 h average O-3 concentration (MDA8 O-3) in July increased by approximately 13.6 %, from 65.5 +/- 7.9 ppbv (2003) to 74.4 +/- 8.7 ppbv (2015), comparable to the observed results. The change in meteorology led to an increase in MDA8 O-3 of 5.8 +/- 3.9 ppbv over the central part of CEC, in contrast to a decrease of about 0.8 +/- 3.5 ppbv over the eastern part of the region. In comparison, the MDA8 O-3 over the central and eastern parts of CEC increased by 3.5 +/- 1.4 and 5.6 +/- 1.8 ppbv due to the increased emissions. The increase in averaged O-3 in the CEC region resulting from the emission increase (4.0 +/- 1.9 ppbv) was higher than that caused by meteorological changes (3.1 +/- 4.9 ppbv) relative to the 2003 standard simulation, while the regions with larger O-3 increases showed a higher sensitivity to meteorological conditions than to emission changes. Sensitivity tests indicate that increased levels of anthropogenic non-methane volatile organic compounds (NMVOCs) dominate the O-3 increase over the eastern part of CEC, and anthropogenic nitrogen oxides (NO x) mainly increase MDA8 O-3 over the central and western parts and decrease O-3 in a few urban areas in the eastern part. Budget analysis showed that net photochemical production and meteorological conditions (transport in particular) are two important factors that influence O-3 levels over the CEC. The results of this study suggest a need to further assess the effectiveness of control strategies for O-3 pollution in the context of regional meteorology and anthropogenic emission changes.