Variations of Ozone Concentration with Its Impacts on Cities of Xizang

Under the harsh environmental conditions characterized by intense ultraviolet radiation and elevated ozone (O₃) background, the temporal dynamics of atmospheric O₃ concentrations and their associated environmental ramifications in the densely populated and emission-concentrated urban regions of the Tibetan Plateau have garnered considerable scientific interest. This comprehensive study meticulously compiles O₃ concentration data spanning 2015 to 2023 from 7 cities of Xizang, conducting rigorous trend analyses and employing a robust suite of 13 risk assessment indicators to gauge the implications for human health and ecological vegetation. It shows that O₃ concentrations of these cities demonstrate significant geographical variations, with the central city of Lhasa recording the highest O₃ mass concentration, while those in the southern cities of Shannan and Rikaze are relatively lower. O₃ concentrations of Nagqu, located in the north, are comparable to those of Lhasa and are significantly higher than those of Ali in the west, as well as those of Linzhi and Changdu in the east Plateau. O₃ concentrations of Changdu and Linzhi peak in June and March-April, respectively, while the other cities reach their peaks in May. Since 2015, interannual variations in O₃ concentrations of Ali, Nagqu, Lhasa, and Linzhi do not show statistically significant trends. In contrast, Shannan, Rikaze, and Changdu experience significant increases in concentration. Specifically, AMDA8_max and AMDA8_4th in Rikaze and Changdu increase significantly, whereas the other cities show decreasing trends. Similarly, both NDGT90 and NDGT70 exhibit comparable trends. SOMO35 indicator, which indicates human health risks, and AOT40 and W126 indicators, which are closely related to ecological vegetation and crop growth, show a high degree of consistency in their trends relative to diurnal O₃ concentration changes. In Lhasa, values of these indicators exceed safety thresholds, particularly during spring and summer, highlighting the combined effect of high background O₃ concentrations in the Plateau and intensified O₃ photochemical formation due to anthropogenic emissions, posing potential threats to human health and ecosystems. Although the current O₃-related risk indicators of Rikaze and Changdu have not yet reached critical levels, their significant upward trends should not be overlooked. With the continuous rise in anthropogenic pollutant emissions in the region, adverse effects of O₃ photochemical formation are anticipated to intensify. Therefore, there is an urgent need to enhance monitoring and assessment in these cities and to implement effective measures to mitigate or control O₃ pollution, thereby safeguarding regional environmental security and promoting sustainable development.