Evaluating emissions and meteorological contributions to air quality trends in northern China based on measurements at a regional background station†

The contributions of meteorology and emissions to air pollutant trends are critical for air quality management, but they have not been fully analyzed, especially in the background area of northern China. Here, we used a machine learning technique to quantify the impacts of meteorological conditions and emissions on PM_2.5, NO₂, SO₂, O₃, and CO pollution during 2013–2021 and evaluated their contributions to Clean Air Action policies. The annual effect of the meteorology on PM_2.5, NO₂, SO₂, and CO levels was dominated by the meteorological conditions during the cold season, while that of the O₃ level largely depended on the meteorological conditions during the warm season. Meteorology-driven anomalies contributed −14.8 to 10.3%, −8.5 to 7.3%, −11 to 7.1%, −7.9 to 6.0%, and −7.4 to 7.3% to the annual mean concentrations of PM_2.5, NO₂, SO₂, O₃, and CO during the study period, respectively. The Clean Air Actions have led to a major improvement in the air quality at regional scale, with the reduction of 1.7 μg m⁻³ year⁻¹, 0.2 μg m⁻³ year⁻¹, 1.5 μg m⁻³ year⁻¹, 0.7 μg m⁻³ year⁻¹, and 0.03 mg m⁻³ year⁻¹ for PM_2.5, NO₂, SO₂, O₃, and CO at background area, respectively, after meteorological correction. Although emissions dominated the long-term variations in pollutants, the meteorological conditions obviously played a positive role during the action periods for pollutants except for O₃. Considering the notable effects of the meteorological conditions on air pollution and the interreaction between pollutants, a more comprehensive control strategy should be considered on a broader regional scale.