Spatiotemporal Characteristics And Driving Factors Of Ozone Precursors In Global Urban Agglomerations

With the rapid development of urbanization,cities are gradually strengthened their connection and forming a spatial compound with close links in economy,transportation and commuting,infrastructure,namely,urban agglomeration.Over the past few years,the number of urban agglomerations is booming,so it is necessary to analyze their impact on climate,ecosystem and air quality.As a secondary air pollutant,ozone is influenced by precursor concentration and ozone sensitivity.Existing studies have carried out a large number of analyses on ozone precursors,but there is inconsistency in comparing the concentrations of urban agglomerations with their background.In view of ozone sensitivity,previous studies generally regard the urban agglomerations as a whole,without considering the heterogeneity of ozone sensitivity Moreover,studies on heavy pollution events,mainly focus on its duration and frequency of occurrence,while ignoring the areas.In this context,this study proposed two indices of precursor pollution intensity index(Precursor Pollution Intensity,PPI)and chemical sensitivity ratio(Chemical Regime Coverage,CRC)to assess the pollution intensity and ozone sensitivity range of precursors in urban agglomerations,respectively.In addition,this study takes three Chinese urban agglomeration as study case and analyzes the relationship between the distribution of precursor hot spots and the urbanization process and meteorological conditions.Based on the analysis of 71 urban agglomerations in 2005-2016,the main conclusions are as follows:1)In 71 urban agglomerations,61 urban agglomerations exhibit higher precursor concentration than their surrounding background(PPI>0),indicating that urban agglomerations are sources of precursors;“source” and “non-pollution” non-pollution exhibit significant differences in latitude and ecological area(p<0.05),indicating that pollution signals are likely to be masked in low latitude and high forest cover regions;2)As urbanization levels and anthropogenic emissions rise,the pollution intensity and area of urban agglomerations increases(p<0.05);3)During 2005-2016,the PPI of urban agglomerations in developed regions decreases and CRC changes from VOClimited to NOx-limited,while the contrast change is observed in developed regions;4)the area of hot spots has significant seasonal changes,showing large winter area and small summer area;The area of hotspot has a significant correlation with temperature and planetary boundary layer height(p<0.05);5)the trend analysis results show that the NO2 hot spots in urban agglomerations will shift from high urbanization area to low urbanization area.The research in this paper provides new insights for future urban agglomeration development and satellite monitoring of ozone pollution.