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Aqueous Phase Reactions of Humic Like Substances (HULIS) Proxies with Photoproduced Reactive Oxygen Species (ROS)
ANTHONY CARRASQUILLO, Wyndom Chase, David Noeckel, Amelia Schaeffer, Allison Wong, Williams College
Abstract Number: 564
Working Group: Aerosol Chemistry
Abstract
Humic Like Substances (HULIS) have been identified as major light-absorbing components of aerosol formed from biomass burning events. This material is highly heterogenous, containing biopolymeric structures derived from the major components of cell walls (lignins, tannins, etc.). Aqueous phase reactions involving photolytically generated reactive oxygen species (ROS) within aerosol particles have the potential to degrade these structures, leading to the destruction of chromophores and in turn the alteration of their light-absorbing properties. While the major ROS previously identified in field studies include singlet oxygen (1O2), hydrogen peroxide (H2O2), superoxide (O2-), and organic radicals (RO), only the reaction of the hydroxyl radical (OH) with HULIS has received significant attention in the literature. Here we focus on the aqueous phase photochemical reactions of two HULIS proxies, gallic acid (GA) and egallic acid (EGA). Each proxy was irradiated with artificial sunlight in the presence of an ROS-specific photosensitizer to generate enhanced concentrations of each OH, 1O2, H2O2, RO, and O2- in bulk solutions. A relative-rates method was used to measure the concentration of ROS generated in each experiment, and to determine the rate constant for reaction with each proxy as a function of pH. Finally, we will present preliminary assignments for major products determined using GC-MS along with potential reaction mechanisms to provide new insight into the role of ROS in the degradation of atmospheric HULIS.