[Impact of Change in Meteorological Conditions on PM_2.5 Air Quality Improvement in Beijing-Tianjin-Hebei Region Using Process Analysis].

The air quality has significantly improved since the implementation of the Air Pollution Prevention and Control Action Plan in 2013. The effect of meteorological conditions on air quality improvement is complex, including affecting the emission, transport, diffusion, chemical transformation, and other processes of air pollutants. Based on the WRF-CMAQ model and process analysis （PA） tool, this study evaluates the impact of meteorological factor changes on the improvement of PM_2.5 concentration in the Beijing-Tianjin-Hebei Region from 2013 to 2020 and further analyzes the role of meteorological conditions on the diffusion, transport, and transformation of atmospheric pollutants. The results provided the technical support for improving air quality in China. The changed meteorological conditions resulted in the PM_2.5 concentration decreasing by 5.4 μg·m^-3 during the 2013-2017 period and increasing by 11.6 μg·m^-3 from 2017-2020. From 2013 to 2017, aerosol chemical processes, vertical transmission, and horizontal transmission processes were the main processes affecting the PM_2.5 improvement. Conversely, the change in meteorological conditions contributed little to the reduction of PM_2.5 level, which is mainly affected by aerosol chemical processes, horizontal transmission, and vertical transmission.