Observed dependence of surface ozone on increasing temperature in Shanghai, China

Eight-year measurements at urban (Xujiahui, XJH) and remote (Dongtan, DT) sites during time period 2010–2017 are employed to examine the surface ozone (O3)-temperature relationship in Shanghai, China. O3 pollution was getting worse in Shanghai, with daily maximum O3 concentrations increasing at a rate of 2.47 ppb yr−1 in urban site. The climate penalty (mO3-T), defined as the slope of O3 change with increasing temperature, exhibited largest values in summer. Summertime O3 increased faster as temperature increased, with mean rates of 6.65 and 13.68 ppb °C−1, respectively in XJH and DT above 30 °C. Sensitivity experiments indicate that the temperature dependence of biogenic volatile organic compounds (VOCs) emissions could be the main chemical driver of the high-temperature O3 response in summer, since the simulated mO3-T are most sensitive to changes of biogenic isoprene emissions. NOx emission reductions strengthened the high-temperature O3 response, with summer mean mO3-T values increasing from 1.52 ppb°C−1 during 2010–2012 to 2.97 ppb °C−1 during 2013–2017. As NOx emissions continue to decrease, the O3 production in urban Shanghai tend to become transitional and the dependence of mO3-T on the biogenic VOC emissions might be weakened. Model results suggest that anthropogenic VOC emission reductions would effectively relieve O3 pollution and reduce the sensitivity of O3 to increasing temperatures in urban Shanghai. Tailored emission reductions as well as scientific city planning strategies should be formulated to balance VOC/NOx ratios, so as to wrestle with the challenges for future O3 pollution under a warming climate.