School of Meteorology

Laboratory Studies of Hydrocarbon Oxidation Mechanisms under Atmospheric Conditions

Dr. John Orlando

Senior Scientist & Deputy Director, Atmospheric Chemistry Division, National Center for Atmospheric Research

23 September 2014, 4:00 PM

National Weather Center, Room 1313
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

The Earth’s lower atmosphere contains an array of hydrocarbon compounds of all shapes, sizes and functionalities. Emissions from natural sources provide the major source of hydrocarbons on a global scale, but emissions from human activity are also significant in and near populated areas. Collectively, these hydrocarbon species can be thought of as the ‘fuel’ that drives much of the chemistry of the troposphere. As such, their oxidative chemistry generates so-called “secondary pollutants” such as ozone, organic acids, and secondary organic aerosols, with significant impacts on air quality and human health, the oxidative capacity of the atmosphere and the Earth’s climate system.
Understanding the intricacies of the atmospheric behavior of the variety of organic species present in the atmosphere can, at first glance, appear a daunting task. However, the atmospheric oxidation of essentially all hydrocarbons (with general formula RH) follows a familiar pattern, involving the successive formation and reaction of an alkyl radical (R•), a peroxy radical (ROO•), and an alkoxy (RO•) radical. While this general pattern is well established, it is also the case that, for each individual species, differences in the structure and energetics of the radicals involved impacts the rates and branching to the relevant processes, and hence determines the eventual environmental impact of that species.
In this presentation, an overview of the basic atmospheric hydrocarbon oxidation process will first be presented. Data from our laboratory will then be used to illustrate the basic reaction pathways, with a focus on recent findings related to the behavior of organic peroxy radicals.

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