| Based on the analysis of the spatial-temporal distribution characteristics of PM2.5concentration in 1436 environmental monitoring sites in China during 2015-2018,this paper selected 11 representative cities?i.e.Beijing,Shijiazhuang,Shanghai,Nanjing,Hangzhou,Guangzhou,Shenzhen,Chongqing,Chengdu,Wuhan and Xi'an?from 6 main city clusters?i.e.Jingjinji Megalopolis,Yangtze River Delta Megalopolis,Guangdong-Hong Kong-Macao Greater Bay Area,Chengyu Megalopolis,Middle Yangtze River Valley Megalopolis and Guanzhong Plain Megalopolis?as research areas.The observation sites were categorized into urban,suburban and rural to investigate urban-rural differences in PM2.5 concentrations by calculating the proportion of construction land type area and the information entropy of land use.Furthermore,emission,transmission and diffusion rules were revealed through correlation analysis of PM2.5 concentration and PM2.5 emission rate.The results showed that:?1?There are obvious regional and seasonal differences in the distribution of PM2.5 concentration in China and the overall PM2.5 concentration showed a downward trend from 2015 to 2018?51.72?g/m3,48.36?g/m3,45.80?g/m3,39.83?g/m3?;?2?The urban-rural differences in PM2.5 concentrations were relatively similar in the cities from the same city cluster.In Jingjinji Megalopolis and Yangtze River Delta Megalopolis,the PM2.5concentrations were highest in urban sites,7.8%?9.7%and 11.3%?16.9%higher,respectively,than in suburban sites and rural sites.However,in Guangdong-Hong Kong-Macao Greater Bay Area and the inland city clusters?i.e.,Chengyu Megalopolis,Middle Yangtze River Valley Megalopolis and Guanzhong Plain Megalopolis?,the PM2.5 concentrations were highest in the suburban sites,2.6%?11.2%higher than in the urban sites and 16.7%?26.5%higher than in the rural sites;?3?The diurnal variation patterns of PM2.5 were relatively similar in the cities from the same city cluster,and they were also similar among the urban,suburban and rural areas in a specific city.Moreover,different diurnal variation patterns of urban-rural PM2.5 concentration differences were observed in different cities.For example,the diurnal variation of urban-rural PM2.5 concentration difference was unimodal in Shanghai but bimodal in Hangzhou.The maximum of urban-rural PM2.5 concentration difference occurred during the daytime in Guangzhou but during the nighttime in Shenzhen;?4?There were differences in PM2.5 emission rates in 11 representative cities and the regular performance was urban area>suburb>rural area.In addition,transportation and diffusion of PM2.5 were dissimilar in the cities from the same city cluster,and they were also dissimilar among the urban,suburban and rural areas in a specific city.Further,distribution of PM2.5 concentration in the urban,suburban and rural areas was under the combined effects of PM2.5 emission,transportation and diffusion. |
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