S1. Diurnal Cycle of Black Carbon and Mixing Layer HeightUrban ambient Black Carbon (BC) concentrations were determined from hourly data from 6 stations in Bogotá's Air Quality Monitoring Network.The BC is collected with Aethalometers model AE33.During the same period, Black Carbon data was collected at the Monserrate Sanctuary site as described in detail in the Methods section of the main manuscript.The daily mean profile for both datasets is shown in Figure S1.This analysis shows an overall similar diurnal profiles, with peak concentrations observed in the morning, likely associated to rush-hour traffic emissions.The mean ratio between ambient and background concentrations is 0.15.The similarity between both profiles, however, and the presence of a morning peak at the Monserrate site, suggests observations at the site are strongly impacted by urban emissions.