11 Apr 2022
11 Apr 2022
Status: this preprint is currently under review for the journal ACP.

Intensive aerosol properties of Boreal and regional biomass burning aerosol at Mt. Bachelor Observatory: Larger and BC-dominant particles transported from Siberian wildfires

Nathaniel May1, Noah Bernays1, Ryan Farley2, Qi Zhang2, and Daniel Jaffe1 Nathaniel May et al.
  • 1School of Science, Technology, Engineering, and Mathematics, University of Washington Bothell, WA 98011, USA
  • 2Department of Environmental Toxicology, University of California Davis, CA, 95616, USA

Abstract. We characterize the aerosol physical and optical properties of 13 transported biomass burning (BB) events. BB events included long-range influence from fires in Alaskan and Siberian Boreal Forests transported to MBO in the free troposphere (FT) over 8–14+ days and regional wildfires in Northern California and Southwestern Oregon transported to MBO in the boundary layer (BL) over 10 h to 3 days. Intensive aerosol optical properties and normalized enhancement ratios for BB events were derived from measured aerosol light scattering coefficients (σscat), aerosol light absorbing coefficients (σabs), fine particulate matter (PM1), and carbon monoxide (CO) measurements made from July to September 2019, with particle size distribution collected from August to September. The observations showed that the Siberian BB events had lower scattering Ångström exponent (SAE), higher mass scattering efficiency (MSE; Δσscat/ΔPM1), and a bimodal aerosol size distribution with a higher geometric mean diameter (Dg). We hypothesize that the larger particles and associated scattering properties were due to the transport of fine dust alongside smoke, in addition to contributions from condensation of secondary aerosol, coagulation of smaller particles, and aqueous phase processing during transport. Alaskan and Siberian Boreal Forest BB plumes were transported long distances in the FT and characterized by lower absorption Ångström exponent (AAE) values indicative of black carbon (BC) dominance in the radiative budget. Significantly elevated AAE values were only observed for BB events with <1 day transport, which suggests strong production of brown carbon (BrC) in these plumes but limited radiative forcing impacts outside of the immediate region.

Nathaniel May et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on acp-2022-167', Anonymous Referee #2, 06 Jun 2022
  • RC2: 'Comment on acp-2022-167', Anonymous Referee #3, 05 Jul 2022

Nathaniel May et al.

Nathaniel May et al.


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Short summary
In summer of 2019 at Mt. Bachelor Observatory, we observed smoke from wildfires with transport times ranging from less than a day up to two weeks. Aerosol absorption of multi-day transported smoke was dominated by black carbon, while smoke with shorter transport time had greater brown carbon absorption. Notably, Siberian smoke exhibited aerosol scattering and physical properties indicative of contributions from larger particles than typically observed in smoke.