Co-Occurrence of Surface O3, PM2.5 Pollution, and Tropical Cyclones in China

Extreme weather events are on the rise against the backdrop of climate change. Impact of tropical cyclone (TC) system, one of the extreme weather events, on air pollution remain poorly understood. A total of 103 recorded TCs (tropical storms and stronger) together with the surface air quality data collected from over 2000 observational sites in mainland China in 2014-2020 were utilized to examine the co-occurrence of TC with continental ozone (O-3) and fine particulate matters (PM2.5) pollution. TCs exhibit cleaning effects on PM2.5 within its coverage (typically similar to 650 km), but enhance the co-occurrence of O-3 and PM2.5 in an extended region. The co-occurrence frequencies are greater than 30% for any two co-occurring events, and similar to 8% for TC + PM2.5 + O-3. We observed superregional trans-boundary transportation of air pollutants driven by TC, led to ubiquitous spatial offsets and temporal lags of O-3, PM2.5 pollution and TC, which are often inconsistent with traditional mechanisms such as accelerated chemical reactions for O-3 formation. O-3 pollution tends to occur 1 similar to 2 days after PM2.5 pollution moved west. In contrast, PM2.5 pollution usually occur 4-12 hr following O-3 pollution within a day over most regions except the southeast of China. Such spatial and temporal offsets vary with the paths of TCs. Composite analysis shows that temperature, wind field and large pressure systems are the key factors for air pollution formation and transportation over TC periphery. Our results have implications for understanding the interactions between TCs and air pollution, particularly for coastal areas where there are recurring TCs.