AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Investigation of Chemical and Physical Perturbations to Organic Aerosol Present in Biomass Burning Plumes over Prescribed Fires in South Carolina
ANDREW MAY, Taehyoung Lee, Gavin McMeeking, Sheryl K. Akagi, Amy P. Sullivan, Shawn P. Urbanski, Robert J. Yokelson, Sonia Kreidenweis, Colorado State University
Abstract Number: 140 Working Group: Biomass Burning Aerosol: From Emissions to Impacts
Abstract Prescribed fires are a land-management practice that may lessen the severity of wildfires. However, as they are planned in advance, they provide an opportunity to perform well-coordinated research to characterize emissions and investigate plume evolution with atmospheric transport. During Fall 2011, we performed online measurements of gas- and particle-phase compounds in biomass burning plumes from prescribed fires during research flights over South Carolina. Here, we focus on the evolution of the organic aerosol (OA) in the plumes using a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (AMS). These experiments were performed in two phases. First, the emissions were characterized at the source to quantify OA emission factors and emission ratios. We then followed the plume downwind, sampling in a quasi-Lagrangian manner, in order to evaluate potential secondary OA (SOA) formation. During each fire, the plume was rapidly diluted via mixing with cleaner background air. From our AMS data interpretation, we infer that we have little evidence of SOA formation in our sampled plumes during 1-3 hours of atmospheric transport as we do not observe a substantial change in OA elemental ratios or the production of AMS mass fragments indicative of SOA. We attribute this lack of chemical change to the short timescales over which we were able to observe the plume. Furthermore, applying a predictive model to estimate the quantity of SOA produced within the plume over the timescales of our sampling suggests that SOA may contribute up to ~20% of the total OA mass within our plumes, and thus, may be masked by the remaining primary OA. Finally, emission ratios and emission factors decreased with increasing sample age, suggesting that dilution-driven evaporation of the OA was the dominant transformation pathway for the OA in the smoke plumes; this behavior can be modeled reasonably well using a recently-developed laboratory parameterization.