Investigating the mechanism of typhoon tracks on ozone pollution episodes in Guangdong, China

Abstract. Ozone (O3) pollution has emerged as one of the core challenges in atmospheric environmental governance in China, particularly in Guangdong Province. As a crucial weather system during East Asian summers, typhoons exert profound influences on O3 formation, accumulation, and transboundary transport through variations in their tracks and intensities. This study examined 237 historical typhoons approaching or making landfall in China between 2013–2023 classifying them into three distinct trajectory types using k-means clustering: westward-moving typhoons (Type 1), Distant northward-recurving typhoons (Type 2) and Proximal northward-recurving typhoons (Type 3). By integrating ground-based observations, reanalysis data, and WRF-CMAQ model simulations, the mechanisms through which typhoon tracks affect ozone pollution in Guangdong Province were investigated. The results demonstrate that for Guangdong Province, proximal northward-recurving typhoons induce more extreme meteorological conditions compared to westward-moving and distant northward-moving typhoons. The analysis of consecutive northward-moving typhoons' impact on ozone pollution in Guangdong Province reveals that surface photochemical reactions served as the dominant factor, while vertical downward transport of upper-level ozone acted as a secondary contributor. Nevertheless, the long-range vertical transport induced by typhoons cannot be neglected. During this event, vertical transport contributed up to 39.9 ppbv to near-surface (100 m) ozone concentrations, with cross-boundary-layer transport accounting for up to 16 % of boundary layer ozone concentrations, demonstrating that typhoon-induced vertical transport significantly enhances boundary layer ozone levels and consequently worsens surface pollution. Additionally, analysis of the backward trajectories and 3-dimensional ozone concentration fields of 237 typhoons indicates that northward-moving typhoons significantly enhance the downward transport of ozone, consequently increasing the ozone concentration at the central point of Guangdong Province by 2.5–14.0 ppbv (Type 2) and 0.3–14.5 ppbv (Type 3) within the 250–900 hPa layer.