Optical and chemical analysis of absorption enhancement by mixed carbonaceous aerosols in the 2019 Woodbury, AZ fire plume

Published: 02-07-2020| Version 4 | DOI: 10.17632/j6c6trjvf3.4
James Lee,
Manvendra Dubey,
Allison Aiken


Citation: James E. Lee, Manvendra K. Dubey, Allison C. Aiken, Petr Chylek, Christian M. Carrico (2020) Optical and chemical analysis of absorption enhancement by mixed carbonaceous aerosols in the 2019 Woodbury, AZ fire plume, Journal of Geophysical Research: Atmospheres (2020). DOI:10.1029/2020JD032399 Corresponding Author: James E. Lee (jamesedlee@lanl.gov) Manvendra K. Dubey (Dubey@lanl.gov) Allison C. Aiken (acaiken@lanl.gov) Abstract: Biomass burning emits mixtures of light-absorbing aerosols (black and brown carbon, BC and BrC, respectively) and purely-scattering organic aerosol (OA) whose optical properties evolve with aging. BC, BrC and OA interactions are complex and dynamic resulting in large uncertainty in their radiative forcing. We report microphysical, optical and chemical measurements of multiple plumes from the Woodbury Fire (AZ, USA) observed at Los Alamos, NM after approximately 11-18 hour atmospheric transit time. We sampled an intact plume with little entrainment as well as periods of more diffuse plumes that had mixed more with background aerosols. Mass absorption cross-sections (MAC) are enhanced by a factor of 1.8-2.6 greater than bare-BC at 870 nm and correlate with the organic coating mass suggesting lensing by non-absorbing coatings following a core-shell morphology. We observed larger MAC enhancement factors of 2.7-6.7 at 450 nm that are larger than core-shell morphology can explain and are attributed to BrC. MAC of OA (MACOrg) at 450 nm is largest in intact plumes (0.7 to 1 m2/g) and drops significantly as plumes mix with background aerosols. Chemical analysis of OA-coatings and bulk OA show self-consistent values of fC2H4O2 (a tracer of levoglucosan-like species) and is used to diagnose plume aging/mixing. We report a strong correlation between fC2H4O2 and MACOrg(450 nm) that indicates that BrC in the Woodbury Fire is co-emitted with levoglucosan and that fC2H4O2 tracks BrC primary aerosol. Our process level finding should inform parameterizations of mixed BC, BrC and OA properties in wildfire plumes in climate models. <last updated 2020-06-28> -V3: update data following reviewers comments and re-analysis (2020-06-28) -V4: update contributors, citation, removed embargo (2020-07-02)