CHARACTERISTICS AND INFLUENCING FACTORS OF THE NEAR-GROUND OZONE CONCENTRATIONS IN CHANGSHA, A TYPICAL CITY IN CENTRAL AND SOUTHERN CHINA.

This study aimed to preliminarily explore the distribution characteristics of the ozone (O₃) pollution period in 2021 in Changsha, which is a typical city in central and southern China, and the differences in reasons for ozone and other pollutions were also investigated. The study was based on the hourly environmental monitoring and meteorological data in 2021 provided by the Ecological Environment Monitoring Center and Meteorological Observatory of Hunan Province. The effects of topography, precursors, meteorological conditions, and other factors on the O3 concentration were analyzed. The results showed that the overall air quality of 14 environmental monitoring stations in Changsha in 2021 was less affected by sulfur dioxide, nitrogen dioxide (NO₂), and carbon monoxide, and principally affected by particulate matter and O₃. Among the 14 environmental monitoring stations, the duration of pollution due to O₃ was in the range of 0-29 days, with a maximum concentration of 252 µg/m³; the daily O₃ concentrations were in the range of 29-94 µg/m³, showing "unimodal" trends in general; and the monthly average O3-8 h (the daily maximum 8-h O3 concentrations) concentrations were in the range of 44-149 µg/m³, showing "bimodal" trends in general. Generally speaking, compared with the provincial control sites, the ozone concentration of the national control sites was higher, and the urban areas were higher than the suburbs. The O₃ concentrations were ranked in the following order: summer > autumn > spring > winter, and the urban area was affected to a larger extent by the emission. The concentrations of O₃ and NO₂ varied in opposite trends. The O₃ concentration exhibited a typical "inverted U-shaped" profile, while that of NO₂ substantially exhibited a "U-shaped" profile. The O3 concentration was significantly positively correlated with the daily average wind speed and ambient temperature but negatively correlated with the wind direction, wind pressure, and humidity. The following conditions promoted the generation of O3 in Changsha: ambient temperature of around 30°C, relative humidity of around 50%, and wind speed of 0.5-2.0 m/s. These findings are beneficial for the scientific prediction, warning, and control of O₃ pollution in the central and southern regions of China. [ABSTRACT FROM AUTHOR]