Transboundary transport of biomass burning aerosols and photochemical pollution in the Orinoco River Basin

Abstract

The “Llanos” is a complex savanna ecosystem that occupies most of the Orinoco River Basin, from the Colombian Andes foothills almost to the Orinoco River Delta at the Atlantic Ocean in Venezuela. It undergoes periodic, human-induced and natural biomass burning during the dry season, which is shorter in Colombia. Northeast trade winds that prevail during the dry season can transport biomass burning plumes from Venezuela to Colombia, even during the Colombian Llanos wet season. Our analysis is based on ambient air measurements at two middle size Colombian Llanos cities located 266 km apart, during April–May 2015, right after the end of the dry season in Colombia, but when there was still high fire activity in Venezuela. Observed 24-h averaged PM10 concentrations in the two cities were unexpectedly high (up to 112 μg/m3), particularly when considering their relatively small size, and low industrial and road traffic activity, and their trends were very similar, which indicates a common remote source. Ozone enhancements of up to ∼94 ppbv (7-day average) were also observed. A reasonably good correlation was found between PM10 and a proxy of fire emissions within footprints calculated using the Stochastic Time-Inverted Lagrangian Transport model. There is currently no permanent air quality surveillance system in the Colombian Llanos. Our findings imply that such a system should be established and incorporate near real-time, synoptic scale biomass burning remote sensing information.