Impact of Extreme Meteorological Events on Ozone in the Pearl River Delta, China

Along with rapid economic development in the Pearl River Delta (PRD) region of China for the past two decades, ozone (O-3) pollution has deteriorated significantly. Extreme meteorological events (EMEs), including heat wave (HW), atmospheric stagnation (AS), and temperature inversion (TI), exert significant impacts on O-3. Base on observational O-3 data and meteorological reanalysis data, we analyze the impact of EMEs on O-3 during O-3 season of April-October in 2006-2017 over the PRD. Statistical analysis indicates significant but spatially heterogeneous sensitivities of O-3 to EMEs. AS poses the largest impact on O-3 concentration over the PRD, resulting in 58% increase compared with normal days, while the increases by HW and TI are 28% and 14%, respectively. O-3 pollution events are largely initiated by HW and AS which favor formation and build-up of O-3, while O-3 pollution events are maintained mostly by persistent AS and TI. HW poses higher impacts on northern and eastern PRD, while AS impacts more on central and western PRD. The effect of AS on O-3 concentration is similar as 10 K temperature increase during non-AS days, while the effect of AS and TI on O-3 exceedance is comparable with 6 K temperature increase during non-EMEs condition. O-3 concentrations under different synoptic patterns are largely associated with the occurrence of AS, and Siberian high and the approaching of a tropical cyclone are the dominant synoptic patterns for EMEs impact on O-3 and largely determines the long-term increasing trend of O-3 concentration over the PRD. This study highlights the importance of establishing a location-specific O-3 control strategy targeting on normal conditions and O-3 pollution events separately. This study also provides scientific support to use EMEs forecast as an indicator to implement contingency O-3 control in advance so as to maximize peak O-3 reduction over the PRD.