Figure 2

Jinan map and location of air pollution monitoring stations. Map was performed using R software (version 3.2.2, https://mirrors.tuna.tsinghua.edu.cn/CRAN/). The packages of mapdata (https://cran.r-project.org/web/packages/mapdata/index.html), maps (https://cran.r-project.org/web/packages/maps/index.html) and ggmap (https://cran.r-project.org/web/packages/ggmap/) were applied.