Significant increase of summertime ozone at Mount Tai in Central EasternChina

Abstract. Tropospheric ozone (O 3 ) is a trace gas playing important roles in atmospheric chemistry, air quality and climate change. In contrast to North America and Europe, long-term measurements of surface O 3 are very limited in China. We compile available O 3 observations at Mt. Tai – the highest mountain over the North China Plain – during 2003–2015 and analyze the decadal change of O 3 and its sources. A linear regression analysis shows that summertime O 3 measured at Mt. Tai has increased significantly by 1.7 ppbv yr −1 for June and 2.1 ppbv yr −1 for the July–August average. The observed increase is supported by a global chemistry-climate model hindcast (GFDL-AM3) with O 3 precursor emissions varying from year to year over 1980–2014. Analysis of satellite data indicates that the O 3 increase was mainly due to the increased emissions of O 3 precursors, in particular volatile organic compounds (VOCs). An important finding is that the emissions of nitrogen oxides (NO x ) have diminished since 2011, but the increase of VOCs appears to have enhanced the ozone production efficiency and contributed to the observed O 3 increase in central eastern China. We present evidence that controlling NO x alone, in the absence of VOC controls, is not sufficient to reduce regional O 3 levels in North China in a short period.