Wildfire smoke demonstrates significant and predictable black carbon light absorption enhancements

Published: 14 March 2022| Version 1 | DOI: 10.17632/5g3khk2nj7.1
James Lee


Citation: James E. Lee, Kyle Gorkowski, Aaron Meyers, Katherine B. Benedict, Allison C. Aiken, and Manvendra K. Dubey, "Wildfire smoke demonstrates significant and predictable black carbon light absorption enhancements" (in prep). Corresponding Author: James E. Lee (jamesedlee@lanl.gov) Abstract: Black carbon (BC) is estimated to have the second largest anthropogenic radiative forcing in earth-systems models, but there is significant uncertainty in its impact due to complex mixing with organics. Laboratory-generated particles, uniform in BC size and quantity of coating material, show that co-mixed non-absorbing material enhances absorption by BC by a factor of 2-3.5. However, weak or no enhancements are often reported for field studies which implies a lower radiative impact of BC compared to how many models currently treat aerosols. To investigate real-world effects of BC-coatings, we analyzed twenty-four ambient wildfire smoke plumes that varied in geographic origin, fuel types, burn conditions, atmospheric age and transport. We conducted particle-by-particle analysis of BC mass and coating-thickness, capturing BC and BC-coating heterogeneity and allowing for unique determination of the population-integrated BC absorption. This data-driven approach successfully predicted the observed BC-absorption and absorption enhancements to better than 15% accuracy for smoke plumes transported through the lower troposphere, which stay relatively warm, and in the particle growth phase. We show that independent of fire conditions, fuels, and atmospherically-driven reactions (e.g., oxidation, photochemistry), fire emitted aerosol is well represented as spherical BC cores with concentric coatings. In contrast, estimates of BC absorption using bulk coating properties overestimated absorption by 20-50% due to assumptions of particle uniformity. Although particle-by-particle analysis is computationally prohibitive in some applications, we show that absorption enhancements in these plumes can be reliably estimated by the coating-to-BC volume ratio providing a suitable parameterization to implement in models. <Last Update 20220312> v0: Submitted for publication purposes



Los Alamos National Laboratory


Earth Sciences, Aerosol, Climate, Fire