Air pollution in the central zone of Chile (30°S to 37°S) not only is a public health concern, but also threatens water resources and climate, in connection with the export and deposition of black carbon (BC) from urban centers onto the glaciers of the Andes Cordillera. Despite the stakes, little is know about the magnitude of this deposition flux, the underlying export mechanisms, and the consequent radiative impact. This work explores how seasonal changes in BC emissions and atmospheric circulation dynamics affect deposition rates on glaciers of the central Chilean Andes. Incidentally, a first-ever high-resolution map of BC deposition on glaciers of the region is obtained.

Chemistry-transport simulations at high resolution on a domain covering central Chile are performed with WRF-CHIMERE for one summer month and one winter month to derive BC deposition rate on glaciers. A sensitivity analysis to emissions from Santiago city is also included. They are complemented with reanalysis data from ERA5 and observations from local networks to extend the relevance of the study to climatological time scales.

The simulations reveal BC deposition fluxes on glaciers 4 times larger in winter than in summer, in relation with stronger emissions from wood burning for residential heating. In the direct vicinity of Santiago however, the seasonality is less pronounced despite much lower emissions in summer. Reanalysis and local observation data connect this phenomenon to a higher export potential in summer months when mountain-valley circulation is stronger and coupled with a consistent westerly synoptic forcing coming from the Pacific ocean, which is not found in winter. The monthly accumulated BC deposition fluxes obtained with WRF-CHIMERE are comparable to what is found in the literature for glaciers of the Tibetan Plateau, thereby pointing to a radiative impact possibly underestimated for central Chilean glaciers.