Impacts of emission reduction and meteorological conditions on air quality improvement from 2016 to 2020 in the Northeast Plain, China

The Northeast Plain in China ranks among the top five regions that have been significantly impacted by haze pollution. To effectively control pollution, it is crucial to accurately assess the effects of emission reduction measures. In this study, we analyzed surveillance data and found substantial decreases (ranging from 19.0% to 50.1%) in average annual mass concentrations of key pollutants (such as CO, SO₂, NO₂, and PM_2.5) in the Northeast Plain from 2016 to 2020. To precisely determine the contributions of meteorological conditions and emission reductions to the improvement of air quality in the Northeast Plain, we conducted three scenario simulations. By comparing source emissions in December 2016 and 2020 using the WRF-Chem model (except for SO₂), we observed significant reductions of 21.3%, 8.8%, and 9.8% in mass concentrations of PM_2.5, NO₂, and CO, respectively, from 2016 to 2020. This highlights the essential role that meteorological conditions play in determining air quality in the Northeast Plain. Moreover, further reducing source emissions by 30% in December 2016 resulted in subsequent reductions of 25.3%, 29.0%, 4.5%, and 30.3% in mass concentrations of PM_2.5, SO₂, NO₂, and CO, respectively, under the same meteorological conditions. Notably, source emission reduction was effective for PM_2.5, SO₂, and CO, but not for NO₂. The improvement in air quality in the Northeast Plain from 2016 to 2020 can be attributed to the combined effects of improved meteorological conditions and reduced pollution sources.