10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Photochemical Aging of Light-Absorbing Biomass Burning Aerosol Selected by Volatility
ELIJAH SCHNITZLER, Rachel Hems, Jonathan Abbatt, University of Toronto, Toronto, Canada
Abstract Number: 1314 Working Group: Carbonaceous Aerosol
Abstract Brown carbon (BrC) aerosol from biomass burning (BB) has significant but poorly-constrained effects on climate. For example, absorption of solar radiation by BrC may increase downwind of a source if secondary chemistry produces more chromophores; in contrast, absorption may decrease if bleaching of primary chromophores predominates. Recently, the reactivity of ambient brown carbon, with respect to atmospheric aging, has been shown to decrease as the molecular size of the constituent chromophores increases. It is also known that the volatility of an organic aerosol component generally decreases as molecular size increases. Here, we investigate the photochemical aging of BrC generated from low-temperature BB of pine and selected by volatility using a thermo-denuder at a range of temperatures. Particles were generated by passing air through a heated (300 °C) flow tube containing pine. Subsequently, particles were passed through a diffusion dryer, a trace gas denuder containing activated carbon, and a thermo-denuder before being injected into a smog chamber, where they were exposed to OH radicals at a relative humidity of about 60%. Aerosol absorption and scattering coefficients were measured using a photo-acoustic spectrometer with an integrated reciprocal nephelometer. Based on the experimental single scattering albedo and particle size distributions, measured using a scanning mobility particle sizer, along with Mie theory calculations, the initial complex refractive indices of the treated particles were derived. Observed trends in the optical properties of the particles were compared to hypothetical trends that would be expected for the experimental size distributions and a constant refractive index. For each thermo-denuder temperature, deviations from the hypothetical trends provide insights into the dependence of BrC reactivity on the volatility of the constituent chromophores.