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Aerosol Size Distribution Changes in Biomass Burning Plumes: The Competing Roles of Coagulation and OA Condensation/Evaporation
NICOLE JUNE, Anna Hodshire, Elizabeth Wiggins, Richard Moore, Edward Winstead, Claire Robinson, Kenneth Thornhill, Kevin Sanchez, Demetrios Pagonis, Hongyu Guo, Pedro Campuzano-Jost, Jose-Luis Jimenez, Matthew Coggon, Sonia Kreidenweis, Shantanu Jathar, Jeffrey R. Pierce, Colorado State University
Abstract Number: 417
Working Group: Wildfire Aerosols
Abstract
The evolution of organic aerosols and aerosol size distributions within smoke plumes are uncertain due to the variability in rates of coagulation and OA condensation/evaporation across different smoke plumes and potentially in different locations of a single plume. We use aircraft data from the western US portion of FIREX-AQ campaign to evaluate differences in aerosol size distribution evolution (growing by 10s to over 100 nm in several hours) under different concentrations and amounts of dilution. We estimated the role of coagulation using model simulations and the role of OA condensation/evaporation using the observed time evolution of the observed total organic aerosol (OA) mass. We find that coagulation alone can explain a majority of the diameter growth in concentrated portions of the smoke plumes (i.e., when the initial ΔOA concentrations were >1000 μg m-3) and even overestimates the observed growth in some cases. In concentrated smoke plumes, there is observed OA evaporation, which helps reduce the over estimation of growth due to coagulation alone. In dilute portions of plumes (i.e., ΔOA < 100 μg m-3), coagulation alone tends to underestimate the observed aerosol growth. On the other hand, the ΔOA enhancement ratios tend to increase with age in the dilute portions of smoke plumes, implying that there is net condensational growth of these particles, and we infer that condensation plays a larger role than coagulation in particle growth in dilute smoke regions. In some smoke plumes, the combined growth from coagulation and OA changes still results in an overprediction in the concentrated portions yet an underestimation in dilute portions, may indicate that turbulent mixing between the percentile groups is important. Overall, we conclude that coagulation dominates growth in concentrated plumes, while OA condensation dominates in dilute plumes, and we discuss potential reasons for this.