Abstract: Weather classification is the basis for research ground-level ozone (O₃) pollution potential and the key technical support for atmospheric environmental management in summer. The principal component analysis in T-mode (PCT), an objective synoptic classication method, was applied to identify the synoptic types in Changsha based on the ERA-interim reanalysis data, the O₃ hourly monitoring data, and conventional meteorological observations during 2016 to 2018. The sealevel pressure field in Changsha was objectively divided into six weather patterns:uniform pressure type (T1), bottom of high pressure type (T2), edge of high pressure type (T3), west side of high pressure type (T4), rear of high pressure type (T5) and two high pressure shear type (T6). A further analysis of O₃ over-standard rates under different weather types indicate that T1, T4, and T6 are ozone-polluted weather types, with corresponding O₃ over-standard rates of 20.39%, 8.59% and 8.40%, respectively. Under the control of ozone-polluted weather type, the meteorological conditions were manifested as high radiation, high temperature and low relative humidity, which were conducive to the photochemical production of local O₃. At the same time, the O₃ pollution in Changsha was not only originated from the photochemical generation of local O₃, but also closely related to the transport effect of O₃ and its precursors from the northwest cities.

Key words: O₃ pollution, objective synoptic weather classification, PCT, meteorological condition, Changsha