[Contributions of Emissions Reduction and Regional Meteorological Conditions to Air Quality Improvement]

Regional meteorological conditions and emissions reduction are closely related to air quality. China has a monsoonal climate and regional meteorological conditions are significantly impacted by interannual climate variability. The objective of this study was to evaluate the contributions of meteorological conditions and emissions reduction to regional improvements in air quality. Trend analyses of key meteorological factors and air pollution for the Beijing-Tianjin-Hebei region, Chengdu-Chongqing region, Yangtze River Delta, and Pearl River Delta urban agglomeration areas were performed for the period from 2001 to 2018, and K-Nearest Neighbor (KNN) models were constructed for each calendar year. The analysis showed that approximately half of the years between 2001 and 2018 experienced abnormal global-scale climate conditions, i.e., El Niño and La Niña. Both emissions reduction and climate changes contributed to the improvement of air quality during the study period. The contribution of meteorological conditions to air quality improvement under abnormal climate conditions was 51% compared to 30% under normal climate conditions in the Beijing-Tianjin-Hebei region; for the Yangtze River Delta and Pearl River Delta regions, meteorological conditions contributed approximately 50% to the improvement of air quality under both abnormal and normal climate conditions. In addition, the contribution of emissions reduction to air quality improvement was higher in the study areas during 2015-2018 compared to 2001-2012. This indicates that emissions reduction has played an increasingly important role in air quality improvements largely due to the implementation of a variety of emission control measures. However, the contribution of meteorological conditions to air quality improvement cannot be ignored.