State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry (LAPC), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China; Collaborative Innovation Centre on Forecast and Evaluation of Meteorological Disasters, School of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing 210044, China.
Collaborative Innovation Centre on Forecast and Evaluation of Meteorological Disasters, School of Atmospheric Physics, Nanjing University of Information Science and Technology, Nanjing 210044, China.
Sci Total Environ. 2019 Jun 15;669:493-504. doi: 10.1016/j.scitotenv.2019.03.097. Epub 2019 Mar 12.
The Urban Boundary layer (UBL) structure plays an important role in the accumulation of air pollutants in cities. To understand how the near-surface UBL structure affects air pollutants, we analyzed 40-day vertical observations collected at a 325-m meteorology tower in Beijing from 1 December 2016 to 9 January 2017. The occurrences of heavy pollution episodes (HPEs) in the study period were closely associated with weak wind speed (WS), high temperature, high relative humidity, weak fraction velocity (u) and weak turbulence kinetic energy (TKE) in near-surface UBL. In particular, the thickness and intensity of the temperature inversions were enhanced during all HPEs at nighttime. In addition, the PM concentration at the ground was significantly negative/positive correlation with vertical dynamic factors (e.g., WS, u and TKE)/temperature inversion in the near-surface UBL. Diurnal variations in the vertical WS, potential temperature (θ), u and TKE were less evident on the 23 polluted days than those on the 14 clean days; specifically, there were larger differences in the WS and θ between polluted and clean days at higher levels. Note that the varying quantitative relationships between the observed PM concentration and UBL dynamic factors during the daytime were much more significant than those at nighttime at all vertical levels. Compared with the WS, u and TKE, the PM concentration showed a much more sensitive change with u (WS) during the daytime (at nighttime).
城市边界层（UBL）结构在城市空气污染物的积累中起着重要作用。为了了解近地表 UBL 结构如何影响空气污染物，我们分析了 2016 年 12 月 1 日至 2017 年 1 月 9 日期间在北京 325 米气象塔采集的 40 天垂直观测数据。研究期间，重度污染事件（HPEs）的发生与弱风速（WS）、高温、高相对湿度、近地表 UBL 中弱分速（u）和弱湍流动能（TKE）密切相关。特别是，所有夜间 HPE 期间，温度逆增的厚度和强度都增强了。此外，地面 PM 浓度与近地表 UBL 中的垂直动力因子（如 WS、u 和 TKE）/温度逆增呈显著负/正相关。在污染日（23 天），垂直 WS、位温（θ）、u 和 TKE 的日变化比清洁日（14 天）不明显；特别是，在较高的水平上，污染日和清洁日之间的 WS 和 θ 差异更大。请注意，在白天，观测到的 PM 浓度与 UBL 动力因子之间的关系变化幅度明显大于夜间所有垂直层次。与 WS、u 和 TKE 相比，PM 浓度在白天（夜间）随 u（WS）的变化更为敏感。
