Department of Geophysics, Universidad de Chile, Santiago, Chile.
Laboratoire de Météorologie Dynamique, IPSL, École Polytechnique, Institut Polytechnique de Paris, ENS, Université PSL, Sorbonne Université, CNRS, Palaiseau, France.
Environ Pollut. 2021 Dec 15;291:118124. doi: 10.1016/j.envpol.2021.118124. Epub 2021 Sep 9.
Black carbon transport from the Santiago Metropolitan Area, Chile, up to the adjacent Andes Cordillera and its glaciers is of major concern. Its deposition accelerates the melting of the snowpack, which could lead to stress on water supply in addition to climate feedback. A proposed pathway for this transport is the channelling through the network of canyons that connect the urban basin to the elevated summits, as suggested by modelling studies, although no observations have validated this hypothesis so far. In this work, atmospheric measurements from a dedicated field campaign conducted in winter 2015, under severe urban pollution conditions, in Santiago and the Maipo canyon, southeast of Santiago, are analysed. Wind (speed and direction) and particulate matter concentrations measured at the surface and along vertical profiles, demonstrate intrusions of thick layers (up to 600 m above ground) of urban black carbon deep into the canyon on several occasions. Transport of PM down-valley occurs mostly through shallow layers at the surface except in connection with deep valley intrusions, when a secondary layer in altitude with return flow (down-valley) at night is observed. The transported particulate matter is mostly from the vicinity of the entrance to the canyon and uncorrelated to concentrations observed in downtown Santiago. Reanalyses data show that for 10% of the wintertime days, deep intrusions into the Maipo canyon are prevented by easterly winds advecting air pollutants away from the Andes. Also, in 23% of the cases, intrusions proceed towards a secondary north-eastward branch of the Maipo canyon, leaving 67% of the cases with favourable conditions for deep penetrations into the main Maipo canyon. Reanalyses show that the wind directions associated to the 33% anomalous cases are related to thick cloud cover and/or the development of coastal lows.
智利圣地亚哥大都市区的黑碳物质输送到相邻的安第斯山脉及其冰川，这引起了人们的极大关注。其沉降作用加速了积雪的融化，除了气候反馈之外，这可能会给供水带来压力。研究模型表明，这些物质的输送途径可能是通过连接城市盆地和高海拔山顶的峡谷网络进行输送，尽管到目前为止还没有观察到可以验证这一假设的证据。在这项工作中，分析了 2015 年冬季在圣地亚哥和圣地亚哥东南部迈波峡谷进行的专门实地考察期间的大气测量结果，当时城市污染严重。在地表和垂直剖面测量的风速和风向以及颗粒物浓度表明，在几次情况下，城市黑碳的厚层（地面以上高达 600 米）都被强烈地输送到峡谷深处。山谷下风方向的颗粒物输送主要通过浅层输送，除非与深谷入侵有关，此时夜间会观察到在海拔高度上的二次层和回流（下风方向）。输送的颗粒物主要来自峡谷入口附近，与圣地亚哥市中心观测到的浓度无关。再分析数据表明，在冬季的 10%的日子里，东风将污染物从安第斯山脉吹离，从而阻止了深入侵迈波峡谷。此外，在 23%的情况下，入侵会朝着迈波峡谷的东北次支推进，只有 67%的情况下有利于黑碳物质深入主迈波峡谷。再分析表明，与 33%异常情况相关的风向与厚云层覆盖和/或沿海低压的发展有关。
