| dc.description.abstract | Ice and snow in the Central Andes contain significant amounts of light-absorbing particles such as black
carbon. The consequent accelerated melting of the cryosphere is not only a threat from a climate
perspective but also for water resources and snow-dependent species and activities, worsened by the
mega-drought affecting the region since the last decade. Given its proximity to the Andes, emissions
from the Metropolitan Area of Santiago, Chile, are believed to be among the main contributors to
deposition on glaciers. However, no evidence backs such an assertion, especially given the usually
subsident and stable conditions in wintertime, when the snowpack is at its maximum extent. Based on
high-resolution chemistry-transport modeling with WRF-CHIMERE, the present work shows that, for the
month of July 2015, up to 40% of black carbon dry deposition on snow or ice covered areas in the Central
Andes downwind from the Metropolitan area can be attributed to emissions from Santiago. Through the
analysis of aerosol tracers we determine (i) that the areas of the Metropolitan Area where emissions
matter most when it comes to export towards glaciers are located in Eastern Santiago near the foothills
of the Andes, (ii) the crucial role of the network of Andean valleys that channels pollutants up to remote
locations near glaciers, following gentle slopes. A direct corollary is that severe urban pollution, and
deposition of impurities on the Andes, are anti-correlated phenomena. Finally, a two-variable meteorological
index is developed that accounts for the dynamics of aerosol export towards the Andes, based
on the zonal wind speed over the urban area, and the vertical diffusion coefficient in the valleys close to
ice and snow covered terrain. Numerous large urban areas are found along the Andes so that the processes
studied here can shed light on similar investigations for other glaciers-dependent Andean regions. | |
