Effects of aging on the smoke from a large forest fire

A smoke plume from a large wildfire in Oregon was sampled over a period of three days as it traveled more than 1000 km above the Pacific Ocean. ncreasing distance from the source, the dilution-normalized concentrations of particles in the nucleation mode (D < 0.2 μm) in the plume decreased rapidly and the average sizes of the particles in the accumulation mode (D=0.2−2.0 μm) and coarse-particle mode (D=2.0−5.4 μn) increased. The dilution-normalized optical scattering coefficient due to the particles in the smoke also decreased with increasing distance from the fire. Changes in the size distribution of the particles in the plume with distance downwind (age) are compared with numerical modeling results of particle coagulation and plume dilution and are found to be in reasonable agreement. rare field measurements of particle removal and modification rates in a dense, long-lived, plume are needed to help assess the role of biomass smokes as they relate to climate change. In the light of these measurements, it appears that the effects of particle coagulation in dense, persistent smokes may have been underestimated in some climate change calculations (e.g., nuclear winter) resulting in an overestimate of the smokeʹs impact.