Light Exposure of Wood Smoke Aerosols: Link between Chemical Composition and Optical Properties

CAROLYN LIU-KANG, Anna Sokolova, Jonathan Abbatt, University of Toronto

     Abstract Number: 178
     Working Group: Aerosol Chemistry

Abstract
Increasing wildfire activity due to changing climate conditions has led to enhanced emissions of both gas-phase and particulate compounds from this source. Brown carbon (BrC) is a type of aerosol primarily emitted from biomass burning that has been shown to impact overall climate by its ability to absorb light in the ultraviolet and visible regions of the spectrum, potentially contributing to warming effects. However, due to its chemical complexity, as well as the range of atmospheric aging mechanisms affecting its composition and absorption properties, its effect on regional climate remains uncertain. Placing our focus on individual aging processes aids in understanding the overall picture of BrC aging during its time in the atmosphere.

Here, we investigated the effects of UV light exposure on the absorption capacity and chemical composition of BrC aerosols and the concomitant role played by other reactants in this aging process, such as molecular oxygen. In-lab generation of wood smoke aerosols from pine wood was conducted, with aging by photoreaction in both the aqueous, in-cloud, phase and particle state. Oxygen was removed from the reaction system, and the products were characterized by UV-Vis for the optical properties, high resolution mass spectrometry for the chemical composition, and electron paramagnetic resonance for radical formation. Results indicate that molecular oxygen plays an important role, partially in the form of singlet oxygen.