OH radical-initiated oxidation of organic compounds in atmospheric water phases: part 1. Reactions of peroxyl radicals derived from 2-butoxyethanol in water

The aim of this series of two publications is to characterise important rad ical reactions of organic molecules in atmospheric water phases, such as cl oud, fog, and rain droplets, or on wetted aerosols. In this first study the reactions occurring in a mixed peroxyl radical system generated from the O H radical attack on a model compound, 2-butoxyethanol, in oxygenated aqueou s solution are investigated in the absence of trace compounds typically fou nd in such natural waters. Using gamma-radiation emitted from a Co-60 sourc e, We have produced steady-state concentrations of O-2(-)/HO2- and OH radic als comparable to those predicted for daytime conditions in cloud or fog dr oplets. The reactions of the peroxyl radicals derived from 2-butoxyethanol (C4H9OCH2CH2OH) in oxygenated aqueous solution have been investigated by me asuring detailed product distributions resulting from the oxidation process . The observed and quantified products are mainly esters, ketones, aldehyde s and hydroperoxides and accounted for 83% of the removal of 2-butoxyethano l (expressed as a carbon balance). A mechanism for the formation of the rea ction products is proposed. It includes the OH attack at four carbon center s of the molecule producing carbon centered radicals, the formation of pero xyl radicals by addition of oxygen to these radicals, the decay of the pero xyl radicals in a reaction system of six different peroxyl radicals and sup eroxide via bimolecular and unimolecular reactions and the reactions of int ermediary produced oxyl radicals. (C) 2000 Elsevier Science Ltd. All rights reserved.