Sensitivity of China’s ozone air quality to 2000-2050 global changes of climate and emissions

We use a global chemical transport model (GEOS-Chem) driven by the GISS GCM to investigate the effect on China’s ozone air quality from 2000-2050 global changes in climate and anthropogenic emissions of ozone precursors. The climate and emission effect in combination will increase afternoon mean surface ozone over China by an annual average of 8.7 ppbv, of which 65% is attributed to the projected increases in global (excluding China) anthropogenic emissions, 37% to Chinese emission increases, and a small negative contribution from climate change (-1.8%) which reduces ozone lifetime. Afternoon mean surface ozone over the Tibet Plateau is projected to increase by 10-15 ppbv in summer, attributed to increasing emissions from neighboring countries in addition to China, suggesting the crucial need for an effective trans-boundary pollution control policy to protect the fragile ecosystems and glaciers over this region. Over Central East China (CEC), a region of large population and intensive agriculture, the 2000-2050 global changes increase annual afternoon mean surface ozone by 9.0 ppbv, of which the Chinese emission change makes the largest contribution (49%), followed by global emission change (43%) and climate change (+7.9%). The change in Chinese anthropogenic emissions of nitrogen oxides (NOx) alone is responsible for 80% of the overall surface ozone increase resulting from the Chinese emission change of all ozone precursors, indicating that aggressive control of anthropogenic NOx emissions is the first priority for Chinese policy-makers to mitigate ozone pollution problems in the future. The climate change penalty projected over CEC is attributed to increasing biogenic emissions of volatile organic compounds (VOCs) as well as to changing meteorological factors such as reduced planetary boundary layers.