Regional Transport of Biomass Burning Aerosols in Northern South America and Its Contribution to PM2.5 in Colombian Cities

Fine particulate matter (PM2.5) concentration in Colombian cities often exceeds local limits, and customarily exceeds WHO guideline concentrations. Because of the high degree of urbanization in the country, the focus in air quality studies has been on the contributions of local sources, mainly mobile and industrial, to the urban environment. Therefore regional sources such as open biomass burning, and long-range transport of mineral dust have often been neglected. Recent works, however, have compiled evidence suggesting a strong correlation between the number of fires in Northern South America (NSA) and deteriorated ambient air quality in some Colombian cities. In this work, we assess the contribution of open biomass burning events to particulate matter (PM) in urban environment using an atmospheric regional chemical transport model (WRF-Chem). The model was configured in a parent domain of 3200 km (121 x 121 x 40) and two higher-resolution nested domains. The horizontal resolution of each domain is 27, 9, and 3km respectively. Anthropogenic emissions for the domain were extracted from EDGAR v4.3.1 and were merged with a local emission inventory for the city of Bogotá. Biogenic emissions from MEGAN were also included in the simulations. The contribution from biomass burning to PM in Colombian cities was evaluated through a sensitivity analysis in which two scenarios, FIRE and NOFIRE, were constructed. In these scenarios fire emissions from the FINN inventory are turned on and off respectively. Model performance was evaluated by comparing simulation results against in-situ observations from air quality networks, remote sensing data, and speciated PM2.5 from measurements campaigns. Results indicate an increment on PM2.5 concentration over Bogotá when biomass burning emissions are included in the simulation. This increment is shown to be mainly driven by Secondary Organic Aerosols (SOA) suggesting that POA from biomass burning emissions is not a significant contributor to fine particulate in Bogotá. This is likely due to the high gas-phase SOA precursors emitted from open biomass burning and the typical three days of aging endured by the fresh biomass burning plumes before reaching the city