AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
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Photooxidation Reactions of Polycyclic Aromatic Hydrocarbons in the Presence of Environmentally Relevant Metals
JOHN HAYNES, Keith Miller, Brian Majestic, University of Denver
Abstract Number: 407 Working Group: Aerosol Chemistry
Abstract This study focuses on the interaction between polycyclic aromatic hydrocarbons (PAH) and soil-derived metals. PAH are introduced to the atmosphere through a variety of natural and anthropogenic sources. They are considered persistent pollutants and therefore undergo long range transport. Long term exposure to PAH have been implicated with pulmonary and cardiovascular diseases, with some considered carcinogenic. The extended atmospheric lifetimes of PAH lend themselves to longer exposure times to sunlight and oxidizing pollutants, potentially producing other branched and oxidized PAH (oxPAH) products such as benzo-e-pyrene and naphthol, which are more toxic than their parent compounds. Metals commonly found in atmospheric environments may serve as catalysts or direct oxidizing agents in the presence of sunlight to promote the production of oxPAH by donating electrons to surrounding molecules analogous to complexation reactions. Additionally, soluble metals may use ultraviolet radiation as a catalyst in an electron transfer interaction with water molecules to produce hydroxyl radicals, mimicking a Fenton-like reaction. Hydroxyl radicals are highly reactive oxidation agents and may initiate several oxidizing pathways, including proximal PAH resulting in the production of oxPAH.
The production of oxidized organic compounds due to metal assisted reactions is monitored by HPLC, while they are identified by LCMS. Reaction conditions use varying light exposure, metal concentration, and duration. Initial PAH data include many new HPLC peaks during and following light exposure periods, which indicate the production of several species of oxPAH. Increasing absorbances at specific retention times throughout the reaction demonstrate the evolution of explicit reaction pathways toward predictable products. Combining the formation of products from specific PAH species with photo-reactions conducted against individual major soil components including iron, aluminum and silica allows for the determination of specific reaction mechanisms. This will offer a comparison of each compound and its contribution to these genres of reactions.