PSM-DID-based analysis of the impact of creating national hygienic cities on the environmental levels of 231 prefecture-level cities in China

Objective To analyze the impact of creating national hygienic cities on the environmental levels of prefecture-level cities in China.

Methods This study included 104 hygienic cities in China during the period of 2007—2019, and selected 127 cities as the control group by combining propensity score matching (PSM) and difference-in-difference (DID) to analyze the impact of creating hygienic activities on the environmental level of prefecture-level cities in China. The following environmental indicators were analyzed: the rate of harmless treatment of domestic waste, the rate of wastewater treatment in sewage treatment plants, the amount of wastewater discharges, the amount of smoke and dust emissions, and the rate of green coverage. The following factors were adjusted: the level of economic development, population density, the level of technological innovation, the degree of industrialization, average annual temperature, average annual relative humidity, average annual sunshine duration, average annual wind speed, and average annual air pressure. Placebo tests were conducted by assuming policies 3, 4, and 5 years in advance and randomizing the treatment and control groups.

Results Creating hygienic cities resulted in significant increases in the waste treatment rate (11.8%, P=0.038), wastewater treatment rate (8.1%, P=0.035), and municipal green coverage rate (16.5%, P=0.016), as well as decreases in wastewater discharges (9.5%, P=0.049).

Conclusion Creating national hygienic cities significantly increases the waste treatment rate, wastewater treatment rate, and municipal green coverage rate of China's prefecture-level cities.