The Effect of Particle Phase State on Multiphase Hydroxyl Radical (OH) Oxidation Kinetics and Products of Biomass Burning Aerosol

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Biomass burning aerosols (BBA) are ubiquitous throughout the global atmosphere. BBA source strength is believed to be of similar magnitude to the fossil fuel burning aerosols. Biomass burning plumes can affect the atmosphere on local to global scales, and BBAs can have a significant impact on visibility, and on the radiative forcing due to the direct scattering and absorption of radiation. By altering the properties of clouds, BBA also exert indirect effects on the radiation balance. Organic aerosols, representing a major mass fraction of the submicron size fraction, are implicated in human health effects. During atmospheric transport, organic aerosol particles are chemically transformed due to reactions with trace oxidizing species such as the hydroxyl radical (OH), resulting in chemical aging and ultimately cleansing of the atmosphere. The chemical aging of BBA particles by reactive trace gas species is not well understood, and so far investigations have been limited mostly to room temperature and dry conditions, although most of the atmosphere exhibits oxidizing conditions at lower temperatures and wider variations in relative humidity. Ambient environmental parameters, which induce altered viscosity or even phase changes, are responsible for altered chemical reactivity in BBA, and may in turn be responsible for altering the kinetics of many of these chemical transformations. A series of laboratory based investigations, using proxy and surrogate compounds under controlled conditions, are to be carried out in order to further describe the chemical transformations taking place during the formation, dispersal and aging of natural, biomass burning aerosols