3D transport characteristics of ozone pollution affected by tropical cyclones over the Greater Bay Area, China: insights from a radar wind profiler network, surface observations, and model simulations

Abstract

Tropical cyclones (TC) exert a profound influence on the dynamics of ground-level ozone (O3) pollution in the Greater Bay Area (GBA) of China's Guangdong-Hong Kong-Macao. Although TC-related O3 transport processes are well recognized, their three-dimensional characteristics are still inadequately characterized. This study provides the first comprehensive observational analysis of O3 pollution transport mechanisms in the GBA under the influence of TC, integrating high-temporal-resolution wind profile measurements with hourly meteorological and air quality data and model simulations. The findings indicate that TC activity accounts for 39.9 % of O3 pollution episodes in the region, with pollutants advection from northern mainland areas to coastal cities. When TCs are located at a distance of approximately 1800–2000 km, horizontal transport mechanisms dominate (about 54.26 %), facilitating the conveyance of inland ozone to coastal regions. As the proximity of the TC decreases to within 1000–1700 km, the descending air currents intensify, driving ozone from coastal areas into the boundary layer and resulting in reduced O3 concentrations inland while they increase along the coast. In particular, when TCs approach Taiwan (less than 800 km, NE), increased vertical wind shear occurs about 34.25 % than before, with the contribution of vertical mixing also sharply rising by over 34.15 %. This is especially evident over coastal zones, where it facilitates the injection of free-atmosphere ozone into the boundary layer. This mechanism prolongs surface O3 pollution episodes. Our findings offer critical insights for O3 pollution mitigation strategies in the GBA and are of relevance for other globally significant bay regions susceptible to TC impacts, including Hangzhou Bay (China), Tokyo Bay (Japan), and the Bay of Bengal (India).