“…There is no unified standard for the measurement of environmental pollution in the existing literature. Some studies adopt comprehensive and indirect environmental pollution index such as Environmental Performance Index to measure the level of environmental pollution [12], but most previous studies adopt specific environmental pollution index, such as emissions of carbon dioxide (CO 2 ), sulfur dioxide (SO 2 ) and nitrous oxide (NO X ) [53,54]. As for China, some studies choose carbon dioxide or sulfur dioxide as the indicator of environmental pollution [55,56,57], while others choose one or several pollutants of three industrial wastes (waste gas, waste water and solid waste) [1,58,59].…”