Black and Brown Carbon Optical Characterization in the El Paso – Ciudad Juarez Airshed

Pamela I Lara, University of Texas at El Paso


Black (EBC) and Brown (BrC) Carbon are ubiquitous constituents of atmospheric particulate matter that affect people’s health, disrupt ecosystems, and modulate local and global climate. Tracking the local deposition and sources of these aerosol particles is essential to better understanding their multidimensional environmental impact. The main goal of the current study is to measure the absorption coefficient (Babs) of particles within the Planetary Boundary Layer (PBL) of the El Paso (US)–Ciudad Juárez (Mexico) airshed and assess the contribution of black and brown carbon particles to the total optical absorption. Measurements were taken during winter (January, 2022), spring (May, 2022), and a summer-wildfire (August-September, 2021)- season to evaluate the optical properties of BC and non-volatile and low-volatile BrC. The summer-wildfire season presented the greatest variation in the Babs from the background values due to EBC and BrC rich smoke plumes arriving to this region from the US West seasonal wildfires. The winter season presented a variation from the background Babs in the late evening hours (3:00 PM to midnight) due to an increase of biofuel burning for heating driven by lower temperatures. The spring season presented variations according to the background Babs common to the region, as follows. It was found that the international bridges’ vehicular traffic, characterized by hours of waiting time to cross back and forth between both cities, supplemented by other local anthropogenic activities, such as brick kiln emissions in Ciudad Juarez, have created a background of air pollution in this region. These pollutants include carbon monoxide, sulfur dioxide, nitrogen and nitric oxides, coarse and fine particulate matter dominated by BC and BrC. The absorption coefficients due to EBC and BrC of this background constitute what we have called a baseline EBC and BrC. Aided by two photoacoustic Extinctiometers (PAX), operating at 405 nm and 870 nm wavelengths, connected to a 340°C thermal denuder to remove non-refractory organics, the particles absorption characteristics were documented and evaluated to identify the impact of long-range transported emissions, from western wildfires, to the local occurrences during summer, as well as the winter and spring EBC and BrC Babs behavior. The Single Scattering Albedo and the Absorption Ångstrom exponent were calculated for the three seasons. Of notice was a decrease in the Ångstrom Absorption exponent during the wildfire event days (eighteen events recorded) due to the aging process. The High-Resolution Rapid Refresh Smoke model, HRRR, and the Hybrid Single-Particle Lagrangian Integrated Trajectory model, HYSPLIT, were used to estimate the sources of the particles during the summer-wildfire season.

Subject Area

Environmental science|Atmospheric sciences|Environmental Studies|Atmospheric Chemistry

Recommended Citation

Lara, Pamela I, "Black and Brown Carbon Optical Characterization in the El Paso – Ciudad Juarez Airshed" (2022). ETD Collection for University of Texas, El Paso. AAI29999694.