Do ship emission control areas in China reduce sulfur dioxide concentrations in local air? A study on causal effect using the difference-in-difference model

As a global factory and trade power, China has paid a high ecological price. Heavy shipping traffic is observed around the nation's most highly populated areas, including the Yangtze River Delta (YRD), Pearl River Delta (PRD), and Bohai Rim (BR) regions. Among the various shipping pollutants, sulfur dioxide (SO2) has received increased attention because of its significant adverse health effects. China delimited three emission-control areas...