京津冀及周边地区“2+26”城市空气质量特征及其影响因素

京津冀及周边地区“2+26”城市为京津冀大气污染传输通道城市，也是我国空气污染最严重的区域之一.针对京津冀及周边地区“2+26”城市，利用中国环境监测总站公布的PM_2.5、PM₁₀、SO₂、NO₂、O₃和CO数据，对2013—2019年京津冀及周边地区“2+26”城市大气污染特征进行分析，并探讨影响其空气质量变化的因素.研究表明:①2013—2019年京津冀及周边地区“2+26”城市空气质量总体向好，2019年ρ（PM_2.5）、ρ（PM₁₀）、ρ（SO₂）、ρ（CO）和ρ（NO₂）比2013年分别下降了50%、41%、79%、49%和20%，ρ（O₃-8 h-90per）（臭氧日最大8 h平均值第90百分位数）比2013年升高了21%.②2013—2019年京津冀及周边地区“2+26”城市重污染天数持续减少，2019年比2013年下降67%，严重污染天数下降尤为明显，降幅达90%.优良天数比例虽然增加，但2016年以后基本稳定在50%左右，没有持续增加的趋势.③ρ（PM₁₀）、ρ（SO₂）、ρ（NO₂）和ρ（CO）的最大值均出现在1月，ρ（O₃-8 h）（臭氧日最大8 h平均值）的最大值出现在6月.ρ（PM_2.5）越高，PM_2.5/PM₁₀和SO₂/NO₂越大，表明二次污染源和燃煤源的贡献越大.④就空间分布而言，ρ（PM_2.5）和ρ（PM₁₀）高值区主要集中在区域中南部太行山脉山前的平原地区，低值区主要集中在区域北部.⑤地理位置、气象条件、产业结构、能耗消耗以及减排政策是影响2013—2019年京津冀及周边地区“2+26”城市空气质量变化的重要因素.研究显示，随着大气污染防治减排措施实施的力度逐渐加大，政策影响已成为京津冀及周边地区“2+26”城市空气质量持续改善的最重要手段. 

Characteristics and Influencing Factors of Urban Air Quality in Beijing-Tianjin-Hebei and Its Surrounding Areas ('2+26' Cities)

The '2+26' cities in Beijing-Tianjin-Hebei and its surrounding areas are the transmission channels of air pollution in the Beijing-Tianjin-Hebei areas and also one of the most serious air pollution cities in China. The PM_2.5, PM₁₀, SO₂, NO₂, O₃ and CO data from 2013 to 2019 released by China National Environmental Monitoring Centre (CNEMC) were selected in this paper to describe the characteristics of air pollution of '2+26' cities, and the factors influencing urban air quality were discussed. The results showed that the air quality of '2+26' cities generally tended to improve as the concentration of PM_2.5, PM₁₀, SO₂, CO and NO₂ decreased by 50%, 41%, 79%, 49% and 20%, respectively, in 2019 compared with 2013. However, the 90th percentile of the daily maximum 8-hour average ozone concentration (O₃-8 h-90per) increased by 21%. From 2013 to 2019, the number of heavy pollution days in the '2+26' cities continued to decrease, and it decreased by 67% in 2019 compared with 2013. The number of serious pollution days decreased by 90%. Although the proportion of excellent days had increased, it had basically stabilized at about 50% after 2016, and there was no continuous increasing trend. The highest concentrations of PM_2.5, PM₁₀, SO₂, NO₂ and CO all appeared in January, while the highest concentration of 8-hour average ozone concentration (O₃-8 h) appeared in June. The higher the PM_2.5 concentration, the higher the ratios of PM_2.5/PM₁₀ and SO₂/NO₂, and the greater the contribution of secondary pollution sources and coal-fired sources to PM_2.5. In terms of spatial distribution, the areas with high PM_2.5 and PM₁₀ were mainly concentrated in the plains in front of the Taihang Mountains, and the low concentration areas were mainly concentrated in the north of the Beijing-Tianjin-Hebei areas. Geographical location, meteorological conditions, industrial structure, energy consumption intensity and emission reduction policies were important factors affecting the air quality of '2+26' cities from 2013 to 2019. With the strengthening implementations of air pollution prevention and control measures, the emission reduction policies have become the most important measure to the air quality improvement in '2+26' cities in the Beijing-Tianjin-Hebei and its surrounding areas.