由于气象和前兆的非线性影响,在北京大城市的不同地区,臭氧(O3)趋势对排放变化的响应非常复杂。根据对35个空气质量站点的长期现场观测(四类,即,城市,交通,北部郊区和南部郊区站点)和卫星数据,O3的时空变异性,气态前体,在2013年至2020年的温暖季节,通过多种指标探索了O3-VOCs-NOx敏感性。此外,气象和排放对O3的贡献是通过基于机器学习的去风化方法分开的。年平均MDA8O3和O3分别增加3.7和2.9μg/m3/年,分别,交通点最高,北郊最低,Ox(O3+NO2)含量为0.2μg/m3/yr,南郊最高,尽管NO2强烈下降,HCHO略有下降。然而,白天O3和Ox的增量呈现一定程度的下降趋势。此外,NOx减排通过较少的NO滴定削弱了O3的损失,这推动了城市-郊区O3和Ox的差异缩小。由于市区和北郊的HCHO的NO2下降幅度较大,北京和北郊VOCs限制制度的范围波动逐渐转变为过渡或NOx限制制度。与直接观察到的趋势相比,去风化O3的增长率较低,这归因于2017年之后O3生成的有利气象条件,尤其是在6月(污染最严重的月份);而除南部郊区外,去风化的Ox有所下降。总的来说,清洁空气行动有效地降低了城市和北部郊区的大气氧化能力,北京上空局部光化学生产减弱,抑制北郊O3变质。加强VOCs控制,保持NOx减排,尤其是在六月,将对扭转北京O3增长趋势至关重要。
Due to the nonlinear impacts of meteorology and precursors, the response of ozone (O3) trends to emission changes is very complex over different regions in megacity Beijing. Based on long-term in-situ observations at 35 air quality sites (four categories, i.e., urban, traffic, northern suburban and southern suburban sites) and satellite data, spatiotemporal variability of O3, gaseous precursors, and O3-VOCs-NOx sensitivity were explored through multiple metrics during the warm season from 2013 to 2020. Additionally, the contribution of meteorology and emissions to O3 was separated by a machine-learning-based de-weathered method. The annual averaged MDA8 O3 and O3 increased by 3.7 and 2.9 μg/m3/yr, respectively, with the highest at traffic sites and the lowest in northern suburb, and the rate of Ox (O3 + NO2) was 0.2 μg/m3/yr with the highest in southern suburb, although NO2 declined strongly and HCHO decreased slightly. However, the increment of O3 and Ox in the daytime exhibited decreasing trends to some extent. Additionally, NOx abatements weakened O3 loss through less NO titration, which drove narrowing differences in urban-suburban O3 and Ox. Due to larger decrease of NO2 in urban region and HCHO in northern suburb, the extent of VOCs-limited regime fluctuated over Beijing and northern suburb gradually shifted to transition or NOx-limited regime. Compared with the directly observed trends, the increasing rate of de-weathered O3 was lower, which was attributed to favorable meteorological conditions for O3 generation after 2017, especially in June (the most polluted month); whereas the de-weathered Ox declined except in southern suburb. Overall, clean air actions were effective in reducing the atmospheric oxidation capacity in urban and northern suburban regions, weakening local photochemical production over Beijing and suppressing O3 deterioration in northern suburb. Strengthening VOCs control and keeping NOx abatement, especially in June, will be vital to reverse O3 increase trend in Beijing.