Investigating the causes of O3 pollution in the western rim of sichuan basin, southwestern China

The western rim of the Sichuan Basin (SCB), located between the Qinghai-Tibetan Plateau (QTP) and the Chengdu-Chongqing city cluster, is a mountainous region renowned for its rich biodiversity. Previous atmo-spheric modeling studies have revealed high O3 exposures for ecosystems in this region. To better understand the levels and causes of O3 pollution at different elevations, we conducted a year-long observation of air pollutants and meteorological conditions at the top and the base of Mount Emei. Results showed that O3 concentrations were higher at the top (Jinding: 3077 m) than at the foot (Leshan: 460 m), likely due to different O3 sources at the sites. O3 at Leshan was mainly generated by O3 photochemical production within the SCB. In contrast, O3 at Jinding was mainly transported from other regions and exhibited higher concentrations in the evening than in the daytime. Five major O3 transport pathways were identified for Jinding, including three in the QTP and its adjacent regions, one in the SCB, and one in the Yunnan-Guizhou Plateau. Furthermore, both sites can be affected by air pollutants from the spring biomass-burning in the southern and southeastern Asia. Although certain O3 exposure indices for ecosystem protection exceeded their empirical critical loads at both sites, others did not. In addition, our results revealed significant discrepancies between the observations and previous modeling results, which might be attributed to the complex topography and coarse horizontal resolution of the model. Further investigations are recommended to understand air pollution-ecosystem interactions in the western rim of the SCB.