CAS: Autoxidation of Oxygenated Volatile Chemical Products in the Atmosphere

California Institute Of Technology, Pasadena CA

Investigators

Abstract

With support from the Environmental Chemical Sciences Program in the Division of Chemistry, Drs. Paul Wennberg, Brian Stoltz, and John Crounse at the California Institute of Technology will study atmospheric reactions of volatile chemical products (VCPs). VCPs are oxygen-containing hydrocarbons (such as glycol ethers and esters) that are common solvents used in a array of products, including paints, cleaning agents and liquid soaps, herbicides, hydraulic fracturing fluids, and dyes for fabrics. When they are used, large quantities of these compounds vaporize and become a major, if not the dominant, contributor to the photochemistry producing ozone and small particles (aerosols) that contribute to poor air quality in many cities. The importance of VCPs is also growing because of decreasing vehicle emissions. Accurate knowledge of how much ozone and aerosols are produced is important to understand air quality. Ozone is broadly toxic to plants and animals, including humans because it causes inflammation of the lungs and bronchia. Aerosols make the air hazy, reduce visibility and are associated with respiratory and other illnesses. Through a collaboration with the University of Copenhagen and the U.S. Environmental Protection Agency (EPA), modeling studies will be carried on the oxidative chemistry of VCPs to learn how they contribute to the formation of ozone and particles in air. In addition to training of students, the team will engage in outreach both at their campus and at local schools, addressing air quality as a topic of high interest to the community. A major uncertainty in understanding the impacts of VCPs on air quality is whether their oxidation results in formation of low volatility compounds. In particular, radical autoxidation may be active in their degradation. Autoxidation via H-shift reactions of organic peroxy radicals can rapidly produce highly oxygenated organic compounds from much more volatile precursors. These highly oxygenated compounds have a much lower vapor pressure and condense to form aerosol. This laboratory and computational investigation will examine the hypothesis that the ether moiety, common in many oxygenated VCPs, enhances the rate of these H-shifts making autoxidation an essential part of accurately describing their atmospheric degradation and thus their impact on air pollution. In this project, the investigators will study the rates of these oxidative reactions for a diverse set of organic substrates that include those that dominate the emissions of oxygenated VCPs to the atmosphere. There are potentially important long range scientific implications of this work for the understanding of the genesis of oxidized organics in the atmosphere, while at the same time mapping out mechanism and product distribution for a wide spectrum of relevant volatile organic compounds. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.