Long-term Brown Carbon and Smoke Tracer Observations in Bogotá, Colombia: Association to Medium-Range Transport of Biomass Burning Plumes

Abstract

Abstract. Light-absorbing aerosols emitted during open biomass burning (BB) events such as wildfires and agricultural burns have a strong impact on the Earth’s radiation budget through both direct and indirect effects. Additionally, BB aerosols and gas-phase emissions can substantially reduce air quality at local, regional, and global scales, negatively affecting human health. South America is one of largest contributors to BB emissions globally. After Amazonia, the BB emissions from the wildfires and agricultural burns in the grassland plains of Northern South America (NSA) are the most significant in the region. However, few studies have analyzed the potential impact of NSA BB emissions on regional air quality. Recent evidence suggests that seasonal variations in air quality in several major cities in NSA could be associated with open biomass burning emissions, but it is still uncertain to what those sources impact air quality in the region. In this work, we report on 3 years of continuous equivalent Black Carbon (eBC) and Brown Carbon (BrC) observations at a hill-top site located upwind of the city of Bogotá and we demonstrate its association with MODIS detected fires in a 3000 km × 2000 km domain. Off-line PM2.5 filter samples collected during three field campaigns were analyzed to quantify water-soluble organic carbon (WSOC), organic and elemental carbon (OC/EC), and biomass burning tracers such as levoglucosan, galactosan, and potassium. MODIS Active Fire Data and HYSPLIT back-trajectories were used to identify potential biomass burning plumes transported to the city. We analyzed the relationship between BrC, WSOC, water-soluble potassium, and levoglucosan to identify signals of regional transport of BB aerosols. Our results confirm that regional biomass burning transport from wildfires occurs annually during the months of January and April. The seasonality of eBC followed closely that of PM2.5 at the city air quality stations, however, the observed seasonality of BrC is distinctly different to that of eBC and strongly associated to regional fire counts. The strong correlation between BrC and regional fire counts was observed both at daily, weekly, and monthly time-scales. WSOC at the measurement site was observed to increase linearly with levoglucosan during high BB periods, and to remain constant at ∼ 2.5 µgC m−3 during the low BB activity seasons. Our findings show, for the first time in this region, that aged BB plumes can regularly reach densely populated areas in the Central Andes of Northern South America. A source footprint analysis involving BrC observations, back-trajectories, and remotely sensed fire activity shows that the eastern savannas in NSA are the main BB source region for the domain analyzed.

Air quality variations in Northern South America during the COVID-19 lockdown

“…The comparison between the days of high and low fire activity ( Table 4 ) shows that the increase in background concentrations associated with BB was as high as 20 μg/m 3 of PM 10 in Bogotá and 19 μg/m 3 of PM 10 in Medellín. The impact of BB on air quality has been identified in previous studies, especially in the first quarter of the year ( Mendez-Espinosa et al, 2019 ; Hernandez et al, 2019 ; Rincón-Riveros et al, 2020 ).…”

The Negative Impact of Biomass Burning and the Orinoco Low-Level Jet on the Air Quality of the Orinoco River Basin

“…The impacts of BB on air quality has been evaluated in several South American countries such as Colombia (Mendez-Espinosa et al, 2019;Hernandez et al, 2019;Rincón-Riveros et al, 2020),…”