2.3. Data acquisition and processingSocial and economic data were mainly from each city’s Sta-tistical Yearbook, China City Statistical Yearbook, China EnergyStatistical Yearbook, China Statistical Yearbook, and StatisticalCommuniqué on Economic and Social Development. Environ-mental data were obtained from the published literature, eachcity’s Statistical Yearbook, and China Statistical Yearbook on Envi-ronment (the data sources of each indicator were listed in theAppendix). For missing values, we used the first order regression tofill the gaps within a series based on closest available data points(Emerson et al., 2012).