区域气象条件和减排对空气质量改善的贡献评估

区域气象条件和减排与空气质量的变化关系密切.区域污染天气的发生不只受人为排放的影响，其与气象条件也密切有关.我国地处全球的主要季风气候区，大气环流具有明显的季风气候变化特征，区域气象条件受年际气候变化影响显著.研究通过分析不同气候条件下京津冀地区、成渝地区、长三角和珠三角城市群2001~2018年主要气象要素及其污染天气的变化趋势，利用KNN大数据挖掘算法量化分析区域气象条件和减排对大气污染的贡献率.结果表明，2001~2018年间全球气候变化异常频繁，厄尔尼诺/拉尼娜非正常气候占比近一半.减排与气候变化均对空气质量的改善起促进作用.在非正常气候条件下，气象对空气质量改善的贡献更为明显.例如，非正常气候时京津冀地区气象条件对空气质量改善的贡献约为51%，而正常气候时约为30%.对于长三角和珠三角城市群，其气象条件在非正常气候时的贡献达到了50%左右，几乎与减排贡献相当.此外，各区域2015~2018年的减排贡献均高于2001~2012年的平均水平，表明随着我国实施大气污染物排放控制措施力度的增大，减排对空气质量改善的贡献显著.但气象条件对空气质量改善的贡献仍不容忽视，区域减排控制仍然任重而道远.

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.