Impact of planetary boundary layer structure on the formation and evolution of air-pollution episodes in Shenyang, Northeast China
Impact of planetary boundary layer structure on the formation and evolution of air-pollution episodes in Shenyang, Northeast China
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行星边界层结构对沉阳大气污染事件形成和演化的影响
DOI：
10.1016/j.atmosenv.2019.116850
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发表时间：
2019-10-01
影响因子：
5
通讯作者：
Zhao, Ziqi
中科院分区：
文献类型：
--
作者：
Li, Xiaolan;Hu, Xiao-Ming;Zhao, Ziqi
在秋冬频繁发生大气污染事件的中国东北地区，由于缺乏观测资料，行星边界层（PBL）结构对大气污染的影响尚不清楚。本文利用气象探测资料和激光雷达反演的气溶胶消光系数廓线，分析了2016年东北省会城市沈阳市秋冬4次大气污染事件中PBL结构与大气污染的关系。我们还使用天气研究与预报化学模型（WRF-Chem）进行了示踪模拟，以展示大气污染物在PBL中的输送和垂直混合。结果表明，在11月26日12时至27日7时的第一次大气污染事件（EP1）中，由于地表辐射冷却强烈，气温急剧下降，形成了一个稳定、湿润的浅层（< 400 m），并在夜间保持不变。稳定的分层和停滞的风对EP1地表污染物浓度的增加有贡献。12月2日13:00-23:00 LT强地表电位逆温和晚高峰时段局地排放增强导致EP2形成。观测和模拟结果表明，EP2之后，大量污染物通过夜间偏南低空急流从华北平原输送到沈阳。这些污染物在夜间被困在残留层中，在日出后由于对流湍流的作用混合到地面，形成了EP3（12月3日06:00-23:00 LT）。EP4（12月4日03:00-14:00 LT）发生在靠近的低压槽前方辐合区。低风速（< 6 m s(-1)）和高相对湿度（> 80%）加剧了近地面空气质量的恶化。
The impact of the planetary boundary layer (PBL) structure on air pollution in Northeast China, where frequently experiences air pollution episodes in autumn and winter, is not well understood due to a lack of observations. In this study, four pollution episodes during autumn and winter of 2016 at Shenyang, a provincial capital city in Northeast China, were examined to investigate the linkage between the PBL structure and air pollution using meteorological sounding data and LiDAR-retrieved profiles of aerosol extinction coefficients. We also conducted a tracer simulation using the Weather Research and Forecasting model with Chemistry (WRF-Chem) to demonstrate the transport and vertical mixing of air pollutants in the PBL. The results indicated that a stable, moist and shallow surface layer (< 400 m) formed and remained at night due to strong surface radiative cooling after a steep decline of temperature during the first air-pollution episode (EP1, from 12:00 Local Time (LT) on November 26 to 07:00 LT on November 27). Stable stratification and stagnant winds contributed to the increase of surface pollutant concentrations in EP1. Strong surface potential temperature inversion and enhanced local emissions during evening rush hour resulted in the formation of EP2 (13:00-23:00 LT on December 2). Observations and modelling results revealed that large amount of pollutants were transported by the southerly nocturnal low-level jets from the North China Plain to Shenyang after EP2. These pollutants were trapped in the residue layer at night and then mixed to the surface after sunrise due to convective turbulence, leading to the formation of EP3 (06:00-23:00 LT on December 3). EP4 (03:00-14:00 LT on December 4) occurred in the convergence zone ahead of an approaching trough. Low wind speed (< 6 m s(-1)) and high relative humidity (> 80%) in the PBL enhanced the deterioration of air quality near the surface.