Exploring the stratospheric source of ozone pollution over China during the 2016 Group of Twenty summit

Abstract

The 2016 Group of Twenty (G20) Hangzhou Summit was concurrently accompanied by extratropical cyclogenesis. To investigate whether the extratropical cyclone exerts any impact on the near surface ozone concentration, the Weather Research Forecast with Chemistry (WRF-Chem) model, with stratospheric passive tracers turned on, was used to simulate the air quality from August 24 to September 06, 2016. It turns out the WRF-Chem model generally performed well when compared to the observed data from a large number of air quality monitoring sites and satellite measurements. During the period, an occurrence of stratospheric intrusion was observed, associated with tropopause fold and curved upper-level jet in East Asia. A fairly large number of stratospheric passive tracers that had quite positive correlation with O3 concentrations were also found over the southeast China. Besides, observed ground surface anomaly of high O3 and the accompanied low CO as well as humidity further implied the downward transport of O3 from the stratosphere. These results suggest that stratospheric ozone intrusion acts as an additional source of the near surface tropospheric ozone concentration, which deteriorates the O3 pollution in China. This helps to explain the difficulty of O3 control during the campaign period of the G20, and provides some insights into stratosphere-to-troposphere transport of O3.