Modeling the Effects of Climate Change on Surface Ozone during Summer in the Yangtze River Delta Region, China

Future climate change can impact ozone concentrations by changing regional meteorological factors related to ozone (O₃) pollution. To better understand the variations of meteorological factors and their effects on O₃ formation processes under future climate conditions, we model the present and the future meteorology and air quality in summer over the Yangtze River Delta (YRD) region by using the Weather Research and Forecasting Model with Chemistry module (WRF/Chem), which is driven by the outputs of Community Climate System Model version 4 (CCSM4). The simulations predict that solar radiation, 2-m air temperature, and wind speed increase in the daytime over most of the YRD region. Absolute humidity and precipitation increase in the north and decrease in the south, while the planetary boundary layer height (PBLH) has an opposite change pattern displaying a decrease in the north and an increase in the south. The southerly wind will be strengthened in the daytime. At night, the change patterns of the meteorological factors are similar to the daytime but with small variations. Meanwhile, O₃ and its precursors all increase in the north and decrease in the south. The increases of NO_x, volatile organic compounds (VOC), and CO are related with the decreases of PBLH and the input effect of stronger southerly wind, while the decreases are attributed to the output effect of the stronger southerly wind. During the daytime, the increase of surface O₃ in the north is dominated by the chemical processes related with the increases of solar radiation, air temperature, and O₃ precursors. The decrease of surface O₃ in the south is mainly caused by the transport process changing with the strengthened southerly wind. At night, the surface O₃ changing the amplitude is less than the daytime. The less O₃ variations at night can be attributed to an O₃ titration reaction with NO, the changes in NO_x concentrations, and the increases of nocturnal PBLH. With the aid of H₂O₂/HNO₃, O₃ formation in the YRD region is found to be easily affected by NO_x in the future. The findings can help to understand the changing trend of O₃ in the YRD region and can propose reasonable pollution control policies.