Abstract With Tibetan Plateau higher than 4 km to the west, the location of Sichuan Basin is unique all around the world and provides a good platform to study air pollution in the urban agglomerations over the complex terrain. To fill in the blanks on vertical distributions of PM1 (the particles smaller than 1 μm) and carbonaceous aerosols within the basin, by means of high topographic relief, PM1 were off-line sampled during 20 January to 2 February 2018 at eight sites with increasing altitudes from the basin to southeastern margins of the Tibetan Plateau. The regional potential sources for each site were revealed by HYbrid-Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model and concentration-weighted trajectory (CWT) method. The lowest carbonaceous aerosol levels occurred at Lixian, while the highest OC (organic carbon) (EC, elemental carbon) was at Hongyuan (the altitude of 3500 m) (Ande, a rural site) due to more primary emissions. The pollutants inside the basin can be transported the altitudes from 2 km to 3 km by vertical dispersion, but they cannot be dispersed to higher altitudes. The vertical stratification of the pollutants was obvious and easily formed “high-low-high” pattern from Sichuan Basin to southeastern Tibetan Plateau, especially during highly polluted episodes. The regional potential sources significantly varied as the increased altitudes. Regional pollution was significant inside the basin. The sources at the altitudes from 2 km to 3 km originated from southeastern margins of the Plateau and surrounding cities, while those at higher altitudes were transported from southeastern margins of the Plateau. The impact of basic meteorological variables (temperature, wind speed and vapor pressure) on carbonaceous aerosols was opposite between the basin and Plateau sites. This study was essential to understanding formation mechanisms of severe pollution episodes and thus to making control measures for the urban agglomerations inside the mountainous terrain.

中文翻译：

---

四川盆地西部冬季碳质气溶胶垂直廓线及关键影响因素

摘要 四川盆地西部海拔4km以上的青藏高原，地理位置在全球独一无二，为研究复杂地形城市群空气污染提供了良好的平台。为填补盆地内PM1（小于1 μm的颗粒）和碳质气溶胶垂直分布的空白，通过高地形起伏，于2018年1月20日至2月2日在8个地点离线采样PM1，并增加了从盆地到青藏高原东南缘的海拔高度。通过混合单粒子拉格朗日综合轨迹（HYSPLIT）模型和浓度加权轨迹（CWT）方法揭示了每个站点的区域潜在来源。最低的含碳气溶胶水平发生在澧县，而最高的 OC（有机碳）（EC，元素碳）在宏源（海拔 3500 m）（安德，农村地区）由于更多的初级排放。流域内的污染物可以通过垂直扩散的方式向2km～3km的高度输送，但不能向更高的高度扩散。从四川盆地到青藏高原东南部，污染物的垂直分层明显，容易形成“高-低-高”格局，尤其是在高污染时期。区域潜在来源随着海拔高度的增加而显着变化。流域内区域污染显着。海拔2~3km的源来自高原东南缘及周边城市，高海拔的源来自高原东南缘。基本气象变量（温度、风速和蒸气压）对碳质气溶胶的影响在盆地和高原站点之间是相反的。这项研究对于了解严重污染事件的形成机制，从而对山区内的城市群制定控制措施至关重要。