Attribution of air quality benefits to clean winter heating polices in China: combining machine learning with causal inference

Heating is a major source of air pollution. To improve air quality, a range of clean heating polices were implemented in China over the past decade. Here, we evaluated the impacts of winter heating and clean heating polices on air quality in China using a novel, observation-based causal inference approach. During 2015-2021, winter heating causally increased annual PM_2.5, daily maximum 8-h average O_3, and SO₂ by 4.6, 2.5, and 2.3 μg m^-3, respectively. From 2015 to 2021, the impacts of winter heating on PM_2.5 in Beijing and surrounding cities (i.e., "2 + 26" cities) decreased by 5.9 μg m^-3 (41.3%), whereas that in other northern cities only decreased by 1.2 μg m^-3 (12.9%). This demonstrates the effectiveness of stricter clean heating policies on PM_2.5 in "2 + 26" cities. Overall, clean heating policies caused the annual PM_2.5 in mainland China to reduce by 1.9 μg m^-3 from 2015 to 2021, potentially avoiding 23,556 premature deaths in 2021.