Significant increase of summertime ozone at Mount Tai in Central Eastern China

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 (NOx) 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 NOx alone, in the absence of VOC controls, is not sufficient to reduce regional O-3 levels in North China in a short period.