[Identification of Impacts from Meteorology and Local and Transported Photochemical Generation on Ozone Trends in...

Ozone (O₃) pollution in Hunan province has become the most important factor among the six common conventional pollutants (i.e., NO₂, SO₂, CO, O₃, PM₁₀, and PM_2.5) in the atmospheric environment. Further investigation has indicated that the relevant studies of O₃ are insufficient. Therefore, it is essential to clarify the key driving factors of O₃ variations for government regulators. In this study, a combined method consisting of a generalized additive model (GAM), empirical orthogonal function (EOF), and absolute principal component scores (APCs) model was employed to identify and quantify the impacts of meteorology and local photochemical generation (local) and that transported from outside (nonlocal) on O₃ variations from 2018-2020. Simultaneously, the driving factors of O₃ annual values from 2018 to 2019 and from 2019 to 2020 in Changsha were analyzed. The results showed that O₃ episodes were commonly caused by meteorology when the relative contribution from precursors was high, on the short-term time scale. Overall, on the temporal scale, meteorology and local were the driving factors for the increasing annual O₃ from 2018 to 2019. Additionally, the contribution from meteorology, local, and nonlocal decreased from 2019 to 2020, leading to a lower level of O₃ concentration in 2020. Geographically, the east, north, and south of Changsha were mainly affected by meteorology, local, and nonlocal, respectively. Throughout the three years, nonlocal exhibited a sustained decreasing trend, whereas the tendencies from meteorology and local varied by year and geography. Local contribution in the north of Changsha increased from 2018 to 2019, which was likely attributed to the increasing biogenic volatile organic compound emission (BVOCs), and it became lower in the south owing to the strengthened consumption by NO. Impacts from meteorology on O₃ in all sites were enhanced from 2018 to 2019. By contrast, local contribution decreased in the north and increased in the south with the decline in BVOC and NO emissions from 2019 to 2020, when the meteorological impacts on O₃ in the whole area became weak.