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.