[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 (O₃) concentration is continuously increasing in Hunan province where the investigation of O₃ pollution has been rarely reported. Accordingly, the spatio-temporal evolution of O₃ 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 O₃ long-term trend during this period. The results presented obvious diurnal, monthly, and seasonal characteristics of O₃ variations. High O₃ concentrations occurred in May and September monthly, and the peak O₃ season was autumn. Furthermore, the 90^th percentile O₃ increased at a rate of 4.7 μg·(m³·a)^-1 temporally, and high O₃ values mainly occurred in the north-eastern region spatially, in contrast to the low O₃ values in the western region. The modeling results indicated that the increase in O₃ was mainly ascribed to precursor emissions. Furthermore, meteorology promoted a rise in O₃ with the impact magnitude of 1 μg·(m³·a)^-1. Remarkably, meteorology accelerated the O₃ increases in spring, summer, and the eastern region, whereas it restrained increases in autumn, winter, and the northwest. The effect of meteorology on PM₁₀ was different from O₃ during this period. Overall, this study highlighted the importance of meteorological impacts when regulating emission reduction measures for O₃ abatement. It required greater effort regarding O₃ mitigation to offset the side-effect from meteorology in meteorology-sensitive seasons and regions. Additionally, the regional corporation is indispensable to reduce O₃ transportation from upwind.