Measured and modeled humidification factors of fresh smoke particles from biomass burning: role of inorganic constituents

摘要

During the 2006 FLAME study (ire aboratory tissoula xperiment), laboratory burns of biomass fuelswere performed to investigate the physico-chemical, optical, and hygroscopicproperties of fresh biomass smoke. As part of the experiment, twonephelometers simultaneously measured dry and humidified light scatteringcoefficients ( and , respectively) in order toexplore the role of relative humidity (RH) on the optical properties ofbiomass smoke aerosols. Results from burns of several biomass fuels from thewest and southeast United States showed large variability in thehumidification factor ((RH)=/). Values of (RH) atRH=80–85% ranged from 0.99 to 1.81 depending on fuel type. Weincorporated measured chemical composition and size distribution data tomodel the smoke hygroscopic growth to investigate the role of inorganiccompounds on water uptake for these aerosols. By assuming only inorganicconstituents were hygroscopic, we were able to model the water uptake withinexperimental uncertainty, suggesting that inorganic species were responsiblefor most of the hygroscopic growth. In addition, humidification factors at80–85% RH increased for smoke with increasing inorganic salt to carbonratios. Particle morphology as observed from scanning electron microscopyrevealed that samples of hygroscopic particles contained soot chains eitherinternally or externally mixed with inorganic potassium salts, while samplesof weak to non-hygroscopic particles were dominated by soot and organicconstituents. This study provides further understanding of the compoundsresponsible for water uptake by young biomass smoke, and is important foraccurately assessing the role of smoke in climate change studies andvisibility regulatory efforts.