Evaluating the Sustainability Impact of Ship Emission Control Area Policies on Air Quality in Inland Yangtze River Cities and Underdeveloped Hainan Coastal Cities

Ship emissions represent a significant challenge to environmental sustainability and public health. The widely implemented Emission Control Area (ECA) policy aims to mitigate these emissions; however, existing research often overlooks inland and underdeveloped coastal regions. This study evaluates the impact of China’s Domestic Emissions Control Area (DECA) policy on SO2 and PM2.5 air concentrations in three inland cities along the Yangtze River and three underdeveloped coastal cities since its inception in 2018. Employing regression discontinuity (RD) and difference-in-differences (DID) methodologies, this analysis seeks to provide a comprehensive understanding of the DECA’s effects on air quality and its implications for sustainability in these areas. This study revealed that DECA policies resulted in significant improvements in both SO2 and PM2.5 concentrations, contributing directly to environmental sustainability and potential public health co-benefits in inland urban areas as well as underdeveloped coastal cities. In the case of inland cities, the daily average concentrations of SO2 in Yichang and Taicang decreased by 5.3% and 18.9%, respectively, while the average daily concentrations of PM2.5 saw reductions of 21.9% and 13.9%, respectively. Among the underdeveloped coastal cities, the average daily concentration of SO2 in Haikou, Danzhou, and Sanya declined by 1.6%, 20.2%, and 21.2%, respectively; additionally, the average daily concentrations of PM2.5 in Danzhou and Sanya decreased by 13.8% and 9.5%, respectively. The effectiveness of this policy exhibited geographical variation within inland cities and was influenced by urban development indicators in coastal areas. These findings not only underscore the success of the DECA policy in enhancing air quality but also highlight its role in advancing sustainable development goals. They provide essential evidence for formulating effective and sustainable emissions control strategies applicable to similar inland regions and underdeveloped coastal settings worldwide.