AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Physical and Optical Aerosol Properties of Aged Biomass Burning Events at the Mt. Bachelor Observatory
JAMES LAING, Dan Jaffe, Jon Hee, University of Washington, Bothell, WA, USA
Abstract Number: 644 Working Group: Aerosols, Clouds, and Climate
Abstract The Mt. Bachelor Observatory (MBO) is located in central Oregon at 2.8 km asl and has been operational since 2004. In the summer of 2015 we investigated particle size distributions, PM1 mass concentration, and aerosol scattering (σscat) and absorption (σabs) coefficients and mass scattering efficiency at three wavelengths of 20 biomass burning (BB) plumes. During August, 51% of the month was influenced by biomass burning (defined as σscat > 20 Mm-1 and CO > 150 ppbv). The events were predominantly caused by regional BB smoke from fires in Northern California and South-West Oregon, as well as several events influenced by Siberian BB from intense forest fires around Lake Baikal.
Significant differences between Siberian events and Regional BB events were observed. Siberian events had higher absorption enhancement relative to PM1 (higher Δσabs/ΔPM1), CO (higher Δσabs/ΔCO), and aerosol scattering (lower single scattering albedo (ω)) compared to regional BB events. Transport from Siberia to the continental US via pyro-convection would typically be from intense, flaming combustion conditions which produce more black carbon (BC) compared to smoldering fires. The greater flaming combustion may account for the absorption enhancement. The Siberian events also had lower Absorption Ångström Exponent (AAE) values than the regional events, signifying either a lack of production of brown carbon (BrC) or the loss of BrC during transport to photo-bleaching, volatilization, and aerosol-phase reactions.
The geometric mean diameter (GMD) of the BB events size distributions ranged from 138 to 229 nm, and the geometric standard deviations (σg) ranged from 1.53-1.89. No clear distinction was observed between Siberian influenced and Regional BB event size distributions. GMD was determined to be well correlated with mass scattering efficiency (MSE), as well as σscat, and PM. A model from Sakamoto et al. (2016) based on fire characteristics was used to predict the GMD with reasonable accuracy.