Toward clean air in developing countries: A comparative analysis of PM_2.5 trajectories under emission-reduction policies in China and India

Over the past decade, China and India have faced severe challenges from PM_2.5 pollution, leading to the implementation of major air quality policies. However, the effectiveness of these policies remains debated, partly due to differences in monitoring and data comparability. To address this issue, this study uses harmonized PM_2.5 observations from the U.S. Embassy monitoring networks for three Chinese cities (Beijing, Shanghai, Guangzhou) and three Indian cities (Delhi, Mumbai, Chennai), spanning periods before and after China's Blue Sky Action Plan Phase II (2018) and India's National Clean Air Program (2019). Using a covariate-adjusted sharp Regression Discontinuity Design (RDD) that controls for meteorological variability and COVID-19 disruptions, we estimate the causal treatment effects of policy implementation on weekly PM_2.5. Long-term RDD estimates (2014–2023) indicate sustained reductions in Beijing (−18.71 μg/m³, SE = 7.47), with more modest changes elsewhere, including Delhi (−11.69 μg/m³, SE = 9.04). Our findings reveal significant policy impacts in China, with cities such as Beijing, Shanghai, and Guangzhou achieving reductions of 35.75 μg/m³ (47.85%), 13.72 μg/m³ (34.55%), and 16.38 μg/m³ (34.95%), relative to the 2014 baseline. In contrast, Indian cities saw more modest improvements, with Mumbai showing a reduction of only 16.25 μg/m³ (−27.84%). At the same time, Delhi and Chennai experienced minimal or even slight increases in PM_2.5 levels. Overall, these conclusions indicate that China's centrally enforced, multi-sectoral policy framework achieved more durable PM_2.5 reductions than India's decentralized and city-action-plan model, underscoring the importance of binding targets, enforcement capacity, and coordinated implementation for developing countries seeking sustained air-quality improvements.