time Dependence of Aerosols in Biomass Burn Plumes from Bbop

Friday, 19 December 2014: 10:20 AM
Lawrence I Kleinman1, Arthur J Sedlacek III1, Robert J Yokelson2, Timothy Bruce Onasch3, Kouji Adachi4, Peter R Buseck5, Duli Chand6, Sonya Collier7, Manvendra Krishna Dubey8, Fan Mei6, John E Shilling6, Stephen R. Springston1, Jian Wang1, Nicole L Wigder9 and Qi Zhang7, (1)Brookhaven National Lab, Upton, NY, United States, (2)Univ Montana, Missoula, MT, United States, (3)Aerodyne Research, Inc., Billerica, MA, United States, (4)Meteorological Research Institute, Ibaraki, Japan, (5)Arizona State University, Tempe, AZ, United States, (6)Pacific Northwest National Laboratory, Richland, WA, United States, (7)University of California Davis, Davis, CA, United States, (8)Los Alamos National Laboratory, Los Alamos, NM, United States, (9)University of Washington Seattle Campus, Seattle, WA, United States
The Biomass Burn Observation Project (BBOP) was conducted between the beginning of July, 2013 and the end of October, 2013. This period overlapped the wildland fire season in the Pacific Northwest from July to mid September, and in October, prescribed agricultural burns in the lower Mississippi River Valley. Urban plumes from 7 cities in the NW and SE U.S. provided a contrasting set of observations. An extended aircraft deployment using the DOE G-1 was made possible by the fortuitous citing of the planes home base within 2 hours flight time of regions with a high incidence of wildland fires. In this presentation we concentrate on wildland fires and the time development of aerosol concentration, size distributions, and optical and physical properties as a function of plume age. Our focus is on physical properties of organic aerosols, a category that often exceeded 95% of total aerosol mass. Other BBOP presentations will highlight carbonaceous particle chemical composition and morphology as revealed by an SP-AMS, an SP2, and electron microscopy. Flight patterns were designed so as to sample plumes as close to a fire as allowed by aviation rules, followed by one or two sets of three to six transects covering a transport time of two to four hours. Average values of aerosol parameters are calculated for each plume transect with CO used as an inert tracer to account for dilution. It is found that OA increases by ~ 50% to 100%, with much of the increase occurring within the first hour. There is a corresponding increase in scattering which causes single scattering albedo to increase. At 2 to 4 hours downwind, plumes have evolved to yield net cooling, an effect that is much more pronounced if one takes into account known artifacts in PSAP measurements or uses the photothermal interferometer (PTI) to measure light absorption. The fires sampled have a relatively narrow range of modified combustion efficiencies, but it is centered on 0.9, at which point there are emission changes associated with smoldering vs. flaming combustion. Oxidant and nitrate production is a prominent feature of some plumes but absent in others.