LAUSR

Abstract This study detected the spatial variations in the surface O3 concentrations along the urban-suburban-rural-background land use gradient and strived to identify the driving factors of these spatial differences. The average O3 concentrations exhibited an increasing gradient from urban cores to background areas with values of 43.5 μg/m3 in urban areas, 50.1 μg/m3 in the green regions of urban areas, 50.6 μg/m3 in suburban towns, 53.9 μg/m3 in rural areas, and 69.1 μg/m3 at background sites. The differences in the annual O3 concentrations between urban and background areas were strongly negatively correlated with the differences in NO2 and PM10 (particulate matter 10 μm or less in diameter) across China. Moreover, the monthly O3 differences between urban and background sites were generally large when the O3 concentration at the background site was at a high level. At the hourly scale, the O3 differences were larger during the night than during the day, and the O3 differences were significantly negatively correlated with the differences in the NO2 and PM10 concentrations but positively correlated with those in the CO and SO2 concentrations. In particular, SO2 had a positive effect on the O3 concentration when SO2 was at a high level. These results provide a scientific basis for enacting policies to control O3 pollution.