Chongqing Institute of Meteorological Sciences, Chongqing 401147, China; Heavy Rain and Drought-Flood Disasters in Plateau and Basin Key Laboratory of Sichuan Province, Chengdu 610072, China.
School of Atmospheric Sciences, Nanjing University, Nanjing 210023, China.
Sci Total Environ. 2022 Oct 10;842:156575. doi: 10.1016/j.scitotenv.2022.156575. Epub 2022 Jun 7.
Potential relationships among heavy air pollution, weather conditions, and meteorological effects are unclear and require further investigation, especially for areas with complex terrains, such as the Sichuan Basin (SCB), one of the most polluted regions in China. In this study, air pollution in the SCB was examined and 18 regional persistent heavy pollution events (RPHEs) were identified for the winters of 2014-2018. The average persistent period of the RPHEs was 8.89 days, and the number of affected cities was 17. Based on ground-based observations, CALIPSO satellite data, reanalysis data, and backward trajectory calculations, the synergistic effects of the thermodynamic structures, synoptic circulations and the radiative feedback of aerosols on the formation of RPHEs were revealed. The results can be summarized as follows: (1) An abnormal warming center, attributing to the warm southerly advection in the upper layer and the cold air dammed by the topography near the surface, always presented around 800-700 hPa to form a deep stable layer. (2) The diurnal variations in vertical motions triggered by the thermodynamic structures could regulate the pollution episodes. During the daytime, pollutants accumulated rapidly and thoroughly mixed under the control of sinking airflow from 800 hPa layer to the ground. At night, pollutants sometimes slowly diffused when weak ascending airflow appeared. (3) Forced by the stable layer and topography of the Tibetan Plateau, the local circulation was confined within SCB, resulting in the intensive mixing of local emissions and transport pollutants from other regions. This situation could be maintained for a long time with stable synoptic circulation in winter, leading to the formation of RPHEs. (4) The pollution episodes were featured with multi-layer pollutants above SCB according to the CALIPSO observations, including the local anthropogenic aerosols near the surface, dust aerosols originating from the Taklamakan Desert, and biomass burning aerosols from Southeast Asia. Solar absorption aerosols, including black carbon and dust above the region, could cause meteorological feedback, making the vertical layer more stable and enhancing the persistence and intensity of the pollution episodes. This study highlights the appreciable effects of synoptic circulations on the vertical thermodynamic structures of the atmosphere and air quality, and raises the understanding of the environmental and climate impacts of RPHEs in complex terrains.
大气重污染、天气条件和气象效应之间的潜在关系尚不清楚，需要进一步研究，特别是对于地形复杂的地区，如中国污染最严重的地区之一——四川盆地（SCB）。本研究对 SCB 的空气污染进行了考察，并确定了 2014-2018 年冬季的 18 次区域性持续重污染事件（RPHEs）。RPHE 的平均持续时间为 8.89 天，受影响的城市数量为 17 个。基于地面观测、CALIPSO 卫星数据、再分析数据和后向轨迹计算，揭示了热力学结构、天气环流和气溶胶辐射反馈对 RPHEs 形成的协同作用。结果可总结如下：（1）异常暖中心出现在 800-700 hPa 附近，这归因于上层暖南风和平流层下部的冷空气受阻于地形，形成深厚稳定层。（2）热力学结构引起的垂直运动日变化可调节污染事件。白天，在下沉气流的控制下，污染物迅速积累并充分混合，该气流来自 800 hPa 层至地面。夜间，当出现弱上升气流时，污染物有时会缓慢扩散。（3）受青藏高原稳定层和地形的限制，局地环流局限于 SCB 内，导致本地排放物与来自其他地区的传输污染物强烈混合。在冬季，稳定的天气环流可长时间维持这种情况，导致 RPHEs 的形成。（4）CALIPSO 观测结果表明，四川盆地上空存在多层污染物，包括局地人为气溶胶、来自塔克拉玛干沙漠的沙尘气溶胶以及来自东南亚的生物质燃烧气溶胶。太阳吸收气溶胶，包括该区域上方的黑碳和沙尘，可引起气象反馈，使垂直层更加稳定，增强污染事件的持续性和强度。本研究强调了天气环流对大气垂直热力学结构和空气质量的显著影响，提高了对复杂地形中 RPHEs 的环境和气候影响的认识。
