Time Evolution of trace gasses, aerosols, and their optical properties in wildfire plumes sampled during the BBOP field campaign

Description

During the first phase of the Biomass Burn Operational Period (BBOP) field campaign, conducted in the Pacific Northwest, the DOE G-1 aircraft was used to follow the time evolution of wildfire smoke from near the point of emission to locations several hours downwind. In nine flights we made repeated transects of wildfire plumes at varying downwind distances and could thereby follow the plume’s time evolution. We observed an active photochemistry: rapid depletion of NOx and O3 concentrations up to 170 ppb. The peak concentration of biomass burning aerosols was 16,000 μg/m3. On average there was little change in dilution-normalized aerosol concentration during 2 – 4 hours of pseudo-Lagrangian sampling. This consistency seemingly hides a dynamic system in which primary aerosols are evaporating and secondary condensing. Particle size increases with downwind distance causing the particles to be more efficient scatters. Aerosol light scattering increases by up to a factor of two even though aerosol mass is nearly constant. Near-fire aerosol had a single scatter albedo (SSA) of 0.8 – 0.85. After 1 – 3 hours of aging, SSAs were typically 0.9 and above. For average surface and atmospheric conditions, the observed increases in SSA change plumes from having a small warming effect due to light absorption, to a cooling effect due to the scattering of sunlight upwards, back to space.