Quantifying the anthropogenic and meteorological influences on summertime surface ozone in China over 2012–2017

Abstract

We applied the global 3-D chemical transport model GEOS-Chem to examine the anthropogenic and meteorological contributions in driving summertime (JJA) surface ozone (O3) trend in China during the Clean Air Action period 2012–2017. The model captures the observed spatial distribution of summertime O3 concentrations in China (R = 0.78) and reproduces the observed increasing trends in two most populated city clusters: North China Plain (NCP) and Yangtze River Delta (YRD). Trend of simulated maximum daily 8-h average (MDA8) O3 concentration is 0.58 ppbv yr−1 in NCP and 1.74 ppbv yr−1 in YRD in JJA 2012–2017. Sensitivity studies show that both changes in anthropogenic emissions and meteorology favored the MDA8 O3 increases in these two regions with respective contributions of 39% and 49% in NCP, and 13% and 84% in YRD. In NCP, the 49% meteorology impact includes a considerable contribution from natural emissions (19%). Changes in biogenic VOCs, soil NOx, and lightning NOx emissions are estimated to enhance MDA8 O3 in NCP with a rate of 0.14, 0.10, and 0.14 ppbv yr−1, respectively. In YRD, natural emissions made small contributions to the MDA8 O3 trend. Statistical analysis shows that higher temperatures and anomalous southerlies at 850 hPa in 2017 relative to 2012 are the two major meteorological drivers in NCP that favored the O3 increases, while weaker wind speed and lower relative humidity are those for YRD. We further examined the trend of fourth highest daily maximum 8-h average (4MDA8) O3 among a specific month that linked with extreme pollution episodes. Trends of simulated 4MDA8 O3 in NCP and YRD are 34–46% higher than those of MDA8 O3 and are found more meteorology-induced. Our results suggest an important role of meteorology in driving summertime O3 increases in China in recent years.