Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, 230031, China.
Key Laboratory of Environmental Optics and Technology, Anhui Institute of Optics and Fine Mechanics, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, 230031, China; Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, 361021, China; Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China, Hefei, 230026, China; Key Laboratory of Precision Scientific Instrumentation of Anhui Higher Education Institutes, University of Science and Technology of China, Hefei, 230026, China.
Environ Pollut. 2022 Nov 1;312:119988. doi: 10.1016/j.envpol.2022.119988. Epub 2022 Aug 24.
The influence of regional transport on aerosol pollution has been explored in previous studies based on numerical simulation or surface observation. Nevertheless, owing to inhomogeneous vertical distribution of air pollutants, vertical observations should be conducted for a comprehensive understanding of regional transport. Here we obtained the vertical profiles of aerosol and its precursors using ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) at the Nancheng site in suburban Beijing on the southwest transport pathway of the Beijing-Tianjin-Hebei (BTH) region, China, and then estimated the vertical profiles of transport fluxes in the southwest-northeast direction. The maximum net transport fluxes per unit cross-sectional area, calculated as pollutant concentration multiply by wind speed, of aerosol extinction coefficient (AEC), NO, SO and HCHO were 0.98 km m s, 24, 14 and 8.0 μg m s from southwest to northeast, which occurred in the 200-300 m, 100-200 m, 500-600 m and 500-600 m layers, respectively, due to much higher pollutant concentrations during southwest transport than during northeast transport in these layers. The average net column transport fluxes were 1200 km m s, 38, 26 and 15 mg m s from southwest to northeast for AEC, NO, SO and HCHO, respectively, in which the fluxes in the surface layer (0-100 m) accounted for only 2.3%-4.2%. Evaluation only based on surface observation would underestimate the influence of the transport from southwest cities to Beijing. Northeast or weak southwest transports dominated in clean conditions with PM <75 μg m and intense southwest transport dominated in polluted conditions with PM >75 μg m. Southwest transport through the middle boundary layer was a trigger factor for aerosol pollution events in urban Beijing, because it not only directly bringing air pollutants, but also induced an inverse structure of aerosols, which resulted in stronger atmospheric stability and aggravated air pollution in urban Beijing.
先前的研究基于数值模拟或地面观测探讨了区域传输对气溶胶污染的影响。然而，由于空气污染物的垂直分布不均匀，为了全面了解区域传输，应该进行垂直观测。在这里，我们使用基于地面的多轴差分光学吸收光谱法（MAX-DOAS）在北京市郊南城站点获得了气溶胶及其前体的垂直廓线，该站点位于中国京津冀地区的西南传输路径上，然后估计了西南-东北方向的传输通量的垂直廓线。以污染物浓度乘以风速计算的气溶胶消光系数（AEC）、NO、SO 和 HCHO 的单位横截面面积的最大净传输通量分别为 0.98km m s、24、14 和 8.0μg m s，从西南向东北，分别出现在 200-300m、100-200m、500-600m 和 500-600m 层，这是由于这些层中西南传输期间的污染物浓度远高于东北传输期间的污染物浓度。AEC、NO、SO 和 HCHO 的平均净柱传输通量分别为从西南向东北的 1200km m s、38、26 和 15mg m s，其中表层（0-100m）的通量仅占 2.3%-4.2%。仅基于地面观测进行评估会低估来自西南城市向北京传输的影响。在 PM<75μg m 的清洁条件下，东北或弱西南传输占主导地位，在 PM>75μg m 的污染条件下，强烈的西南传输占主导地位。西南传输穿过中层边界层是北京市区气溶胶污染事件的触发因素，因为它不仅直接带来空气污染物，还导致气溶胶出现反结构，从而导致更强的大气稳定性，并加剧了北京市区的空气污染。
