Characteristics of surface ozone pollution and its correlations with meteorological factors: the case of Xiangtan

Based on ozone (O₃) monitoring data for Xiangtan and meteorological observation data for 2020-2022, we examined ozone pollution characteristics and the effects of meteorological factors on daily maximum 8-h average ozone (O_3-8h) concentrations in Xiangtan. Thus, we observed significant increases as well as notable seasonal variations in O_3-8h concentrations in Xiangtan during the period considered. The ozone and temperature change response slope (K_O3-T) indicated that local emissions had no significant effect on O_3-8h generation. Further, average O_3-8h concentration and maximum temperature (T_max) values showed a polynomial distribution. Specifically, at T_max < 27 °C, it increased almost linearly with increasing temperature, and at T_max between 27 and 37 °C, it showed an upward curvilinear trend as temperature increased, but at a much lower rate. Then, at T_max > 37 °C, it decreased with increasing temperature. With respect to relative humidity (RH), the average O_3-8h concentration primarily exceeded the standard value when RH varied in the range of 45-65%, which is the key humidity range for O₃ pollution, and the inflection point for the correlation curve between O_3-8h concentration and RH appeared at ~55%. Furthermore, at wind speeds (WSs) below 1.5 m∙s^-1, O_3-8h concentration increased rapidly, and at WSs in the 1.5-2 m∙s^-1 range, it increased at a much faster rate. However, at WSs > 2 m∙s^-1, it decreased slowly with increasing WS. O_3-8h concentration also showed the tendency to exceed the standard value when the dominant wind directions in Xiangtan were easterly or southeasterly.