Atmospheric Free Radical Measurements Related to Photochemical Oxidants in Urban AirEPA Grant Number: R823319
Title: Atmospheric Free Radical Measurements Related to Photochemical Oxidants in Urban Air
Investigators: Hard, Thomas M.
Current Investigators: Hard, Thomas M. , George, Linda A. , O'Brien, Robert J.
Institution: Portland State University
EPA Project Officer: Shapiro, Paul
Project Period: October 1, 1995 through September 30, 1997 (Extended to September 30, 1999)
Project Amount: $276,323
RFA: Exploratory Research - Chemistry and Physics of Air (1995) RFA Text | Recipients Lists
Research Category: Air Quality and Air Toxics , Air , Engineering and Environmental Chemistry
Polluted air chemistry leads to oxidant and acid production in the presence of sunlight, hydrocarbons, and oxides of sulfur and nitrogen. The indispensable agent of this transformation is HO, the hydroxyl free radical, which is generated by sunlight wherever traces of ozone, nitrous acid, or aldehydes are present. HO attacks hydrocarbons (from natural or human-made sources), and NOx transforms the intermediate products into larger concentrations of ozone and other oxidants, which are the undesirable irritants of urban smog. The hydroperoxyl radical, HO2, is closely linked with HO by photochemical reactions, and is an essential intermediate in ozone production, through its reaction with nitric oxide. Hydroxyl combines directly with nitrogen dioxide and sulfur dioxide to produce their corresponding acids which are the chief agents in acid precipitation.
Although extensive regions of the United States are in exceedance of the Federal Air Quality Standard for ozone, none approaches the Los Angeles area in the severity and duration of population exposure to this harmful pollutant. With support from the Office of Exploratory Research of the US EPA, the investigators have carried out the first direct measurements of HO and HO2 in the Los Angeles atmosphere. These measurements have been performed in concert with other research groups to provide the largest suite of supporting measurements yet obtained for the study of urban air photochemistry and the verification of oxidant control chemical models.
The investigators plan to continue these ambient radical concentration measurements in the Los Angeles atmosphere, this time in cooperation with a very much larger set of other atmospheric chemical and meterological measurements. The latter are made possible by a large study currently being planned by the California Air Resources Board and the South Coast Air Quality Management District for the summer of 1997. The purpose of these determinations is to provide experimental data on HO and HO2, in concert with other species, for use in testing models of urban and regional air photochemistry.