Grantee Research Project Results
1999 Progress Report: The First Robust RO2 Analyzer for Urban Air
EPA Grant Number: R826176Title: The First Robust RO2 Analyzer for Urban Air
Investigators: Hard, Thomas M. , George, Linda A. , O'Brien, Robert J.
Institution: Portland State University
EPA Project Officer: Hahn, Intaek
Project Period: January 1, 1998 through December 31, 2000
Project Period Covered by this Report: January 1, 1999 through December 31,1999
Project Amount: $355,290
RFA: Exploratory Research - Environmental Chemistry (1997) RFA Text | Recipients Lists
Research Category: Water , Air , Safer Chemicals , Land and Waste Management
Objective:
Organic peroxy radicals (RO2) are important sources of both ozone and fine particulates in urban and regional air. Few direct measurements of urban total RO2 concentrations are available, because existing RO2 instruments are subject to major positive and negative interferences when used at the NO2 concentrations that prevail in urban air. These interferences arise from rapid chemical equilibrium between RO2, NO2, and peroxynitrates (RNO4). A total RO2 analyzer that is insensitive to ambient NO2 is urgently needed.
We are developing the first total RO2 analyzer that is free of NO2-related interferences at urban pollution levels. The analyzer employs the conversion of RO2 to hydroxyl radicals (OH), which are detected by fluorescence assay with gas expansion (FAGE). The conversion takes place at atmospheric temperature and pressure with a very short residence time, thus preventing formation or dissociation of peroxynitrates. Moreover, the high sensitivity of FAGE obviates the need for either preconcentration or chemical amplification. FAGE also distinguishes OH and HO2 (hydroperoxyl radical) from RO2.
The analyzer occupies one of the sampling channels of the FAGE instrument, used in the determination of atmospheric OH and HO2 for more than a decade. We propose to optimize the air-sampling configuration for response to a single RO2 species, generated by adaptation of an existing method, and to calibrate that response. We then propose to determine the response of the analyzer to each of the significant classes of atmospheric RO2 radicals, using individual species as before, and to test the analyzer for RNO4 interference. We feel it is important to characterize the analyzer thoroughly before taking it into the field. Next, we propose to determine total ambient RO2 in urban air at both downtown and downwind sites near Portland, Oregon, with simultaneous measurements of OH, HO2, ozone, NO, NO2, total nonmethane hydrocarbons, and ultraviolet radiation, yielding data suitable for atmospheric chemical modeling.
This work will yield a well-characterized total RO2 analyzer, whose response to individual RO2 species is known from direct, calibrated measurements. The RO2 analyzer will be suitable for use at any atmospheric NO2 level without interference from peroxynitrates, and thus, will be reliable in urban air. The work includes simultaneous, continuous ambient RO2, HO2, and OH determinations in urban air, with the supporting measurements needed for atmospheric chemical modeling.
Progress Summary:
By experimentation with atmospheric-pressure flowtubes and injectors, we have found an effective, efficient, and reproducible converter of HO2 and RO2 to OH, with negligible interference from thermal dissociation of peroxynitrates, using FAGE to detect the OH.
We have characterized this analyzer's responses to HO2 and to two RO2 species (ethylperoxyl radical EtO2 and methylperoxyl radical MeO2) as a function of the concentration of the added reagent, NO.
We have calibrated the analyzer's response to OH, HO2, EtO2, and MeO2.
The experimental data indicate no obstacles to our proposed method of measuring HO2 and total RO2 in the atmosphere with FAGE.
Future Activities:
We will measure the response of acetylperoxyl (MeCO3) radicals in the converter, as a function of added NO, with FAGE detecting the OH product. We will extend the existing instrument calibration, which now includes four radical species (OH, HO2, EtO2, MeO2), to the fifth species, MeCO3. When this characterization of instrument response is complete, we will apply it to the measurement of total RO2 in urban air.
Journal Articles on this Report : 1 Displayed | Download in RIS Format
| Other project views: | All 6 publications | 2 publications in selected types | All 2 journal articles |
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George LA, Hard TM, O'Brien RJ. Measurement of free radicals OH and HO2 in Los Angeles smog. Journal of Geophysical Research 1999;104(D9):11643-11655. |
R826176 (1999) R826176 (2000) R826176 (Final) R823319 (Final) |
Exit Exit |
Supplemental Keywords:
ambient air, tropospheric, urban, VOCs, oxidants, organics, intermediates, environmental chemistry, analytical, measurement methods., RFA, Air, Scientific Discipline, Toxics, Chemistry, particulate matter, Ecology, Environmental Chemistry, Engineering, Chemistry, & Physics, tropospheric ozone, VOCs, air toxics, organic peroxy radicals, peroxy radical analyzers, ultraviolet radiation, urban air, fine particulates, flourescence assay, fine particles, monitoring, particulates, particles, ozone, urban air , peroxynitrates, hydroxyl radical, ambient nitrogen dioxideProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.