Temporal and spatial variation relationship and influence factors on surface urban heat island and ozone pollution in the Yangtze River Delta, China

Urbanization has led to an obvious urban heat island (UHI) effect in the Yangtze River Delta (YRD), China. The ozone (O3) pollution in the YRD is getting worse. The UHI effect is a key factor that affects the O3 level. Understanding the influences of the UHI effect on O3 concentrations is necessary for improving air quality. In this study, the temporal and spatial relationship between UHI and O3 in the YRD during 2015 was investigated. The influence factors of UHI effect and O3 are both natural and artificial. Multi-source remote sensing data, which include land cover, land surface temperature (LST), Normalization Difference Vegetation Index (NDVI), and digital elevation model (DEM) data, were used to extract surface landscape elements. The results showed that: (1) the average hourly O3 concentration was 61.83 μg/m3 (30.92 ppb), the highest value was 105.32 μg/m3 (52.66 ppb) at 15:00 and the O3 peak was 82.50 μg/m3 (41.25 ppb) in September. The O3 concentrations and temperature have a similar variation trend both in diurnal and monthly. The O3 concentrations in coastal stations are higher than those inland. (2) The average daytime UHI intensity was 1.24 °C, and the daytime O3 concentration was 80.66 μg/m3 (40.33 ppb). There is a positive relationship between UHI and O3 in the YRD. The relationship in the central developed cities is higher than that in the northern and southern cities. (3) The related factors influencing UHI and O3 include surface landscape, topography and population. The LST and NDVI are most important among these factors. (4) Due to various geographical backgrounds, the UHI intensities and O3 concentrations show obvious spatial differences. This study provides a reference with which to better understand the relationship among UHI, O3 and related factors. Furthermore, the issues of atmospheric and energy transmission in this region deserve further study.