Impact of the Urban Heat Island Effect on Ozone Pollution in Chengdu City, China

With the advancement of urbanization, the urban heat island effect and ozone pollution have become hot issues in urban research. The urban heat island effect can impact ozone conversion, but its mechanism of action is unclear. In this study, the effects of the urban heat island effect on ozone concentration in Chengdu City, China, were investigated by comparing the ozone concentration under different heat island levels with ozone data from March 2020 to February 2021 and the temperature and wind field data of ERA5-Land during the same period. The results showed that: 1) regarding the distribution characteristics, the ozone concentration in Chengdu presented a 'high in summer and low in winter' distribution. The ozone concentration in summer (189.54 µg/m3) was nearly twice that in winter (91.99 µg/m3), and the ozone diurnal variation presented a 'single peak and single valley' distribution, with a peak at 16:00. 2) For the characteristics of the heat island effect, the heat island intensity in Chengdu was obviously higher in spring than in other seasons, and the diurnal variation showed a 'single peak and single valley' distribution, with the peak and trough values appearing at 9:00 and 17:00, respectively. Spatially, the eastern part of Chengdu was a heat island, while the western and northwestern parts were mostly cold island. 3) The correlation analysis between heat island intensity and ozone concentration showed a significant positive correlation but with a 7–8 h time lag. Ambient air temperature was not the main factor affecting ozone concentration. The heat island effect impacts the ozone concentration in two ways: changing the local heat budget to promote ozone generation and forming local urban wind, which promotes ozone diffusion or accumulation and forms different areas of low and high ozone values.