Significant Photoproduction of Singlet Oxygen from Aqueous Extracts of Biomass-Burning Aerosol
DANIEL BONOMO, Ryan Sullivan, Carnegie Mellon University
Abstract Number: 574
Working Group: Aerosol Chemistry
Abstract
Biomass-burning aerosol (BBA) is the gases and particles produced by the incineration of living and dead vegetation. The aqueous aerosol phase can contain a large amount of dissolved organic matter. This chromophoric organic carbon has a dynamic atmospheric lifecycle where more brown carbon is produced as the smoke plume evolves, and then becomes lost, presumably due to oxidation and photo-bleaching. Due to their large quantities of brown carbon, biomass-burning aerosols can generate oxidants through photosensitization, including the reactive oxygen species singlet oxygen (1O2). By generating 1O2, chromophoric biomass-burning aerosol can contribute to the pool of aerosol-phase reactants, the oxidation of atmospheric contaminants, as well as its own photo-bleaching of brown carbon.
Our research group quantified these contributions by measuring the quantum yield of 1O2 in the dissolved organic matter (DOM) aqueous fraction extracted from authentic biomass-burning aerosol collected from flaming-phase combustion of different fuels. The production of 1O2 by these aqueous extracts during exposure to UVA light was measured by loss of the molecular probe furfuryl alcohol. The steady-state concentration and quantum yield of 1O2 were determined for BBA from different fuels with and without chamber aging.
The results show that aqueous extracts of BBA produce significant amounts of 1O2 during UVA illumination. Quantum yields of 1O2 ranged between 1.2-3.4%, with different 1O2 yields from biomass-burning aerosol of different fuels. Steady-state concentrations of 1O2 were on the order of 10-13 M, similar to aquatic dissolved organic matter, a major source of 1O2 in the aquatic environment. 1O2 production was also observed to change during UVA exposure, indicating that photo-induced changes to biomass-burning aerosol can alter its photosensitization properties, and drive its own photo-bleaching. These results suggest that photosensitization of brown carbon from biomass-burning is an important source of aerosol-phase oxidants and contributes to the dynamic lifecycle of brown carbon.