Atmospheric environment change in a summertime O3 pollution event over the North China Plain under the influence of recent-year anthropogenic emission reduction

The air pollutant emissions play a decisive role in the control of air quality. In recent years, the anthropogenic emission reduction measures have effectively reduced the PM_2.5 levels over China improving air quality in China. However, due to the complex physical and chemical processes in atmospheric environment, O₃ pollution events still occur frequently. To assess the impact of recent-year emission reduction of emissions on variations of summertime O₃ pollution in the North China Plain, this study conducted the simulations with the air quality model WRF-Chem by using China's Multiresolution Emission Inventory (MEIC) with 0.1° resolution in 2012 and 2019, and we understand the characteristics of summer O₃ pollution in the NCP under the scenario of anthropogenic emission reduction. The results show that the anthropogenic emissions of PM_2.5, PM₁₀, SO₂, CO, black carbon (BC), and organic carbon (OC) in the NCP region decreased significantly from 2012 to 2019, while the emissions of NMVOCs (non-methane volatile organic compounds) increased distinctly in urban areas, and NOx emissions decreased in urban and increased in rural, reflecting the uneven emission reduction of anthropogenic air pollutants in North China. The control of anthropogenic pollutant emissions induced an elevated concentrations of atmospheric oxidants (O₃ and multiple free radicals) in the NCP region, enhancing the atmospheric oxidation capacity, and then strengthening the chemical conversions of SO₂ and NOx to generate sulfate, nitrate, and other secondary particles. As a result, the proportion of secondary PM_2.5 in urban and rural areas markedly raised , especially during the O₃ pollution period, offsetting the reduction of primary PM_2.5 emissions. In addition, these emission reduction measures promote the transformation of O₃ generation mechanism in the NCP from VOC-control to NOx-control. This study reveals the complex effects of anthropogenic emission reduction altering the atmospheric physical and chemical processes on atmospheric environmental change.