[Analysis of Ozone Pollution Spatio-temporal Evolution Characteristics and Identification of Its Long-term Variation Driving Factor over Hunan Province].

Despite the alleviation of particulate matter (PM), the ambient ozone (O) concentration is continuously increasing in Hunan province where the investigation of O pollution has been rarely reported. Accordingly, the spatio-temporal evolution of O pollution was first analyzed based on hourly air quality data observed by national monitoring stations from 2015 to 2020 over 14 cities in Hunan province. Afterwards, the combination of meteorological data from the European Center for Medium-range Weather Forecast (ECMWF) and the generalized additive model (GAM) was applied to investigate the driving factors of the O long-term trend during this period. The results presented obvious diurnal, monthly, and seasonal characteristics of O variations. High O concentrations occurred in May and September monthly, and the peak O season was autumn. Furthermore, the 90 percentile O increased at a rate of 4.7 μg·(m·a) temporally, and high O values mainly occurred in the north-eastern region spatially, in contrast to the low O values in the western region. The modeling results indicated that the increase in O was mainly ascribed to precursor emissions. Furthermore, meteorology promoted a rise in O with the impact magnitude of 1 μg·(m·a). Remarkably, meteorology accelerated the O increases in spring, summer, and the eastern region, whereas it restrained increases in autumn, winter, and the northwest. The effect of meteorology on PM was different from O during this period. Overall, this study highlighted the importance of meteorological impacts when regulating emission reduction measures for O abatement. It required greater effort regarding O mitigation to offset the side-effect from meteorology in meteorology-sensitive seasons and regions. Additionally, the regional corporation is indispensable to reduce O transportation from upwind.