HR: 1400h
AN: A23A-13    [Abstracts]
TI: Characterization of a Dilution Modulation CIMS-Based Method for Measuring Tropospheric Peroxy Radical Concentrations
AU: * Cantrell, C A
EM: cantrell@ucar.edu
AF: National Center for Atmospheric Research, 3450 Mitchell Lane, Boulder, CO 80301, United States
AU: Anderson, R S
EM: rsa@ucar.edu
AF: National Center for Atmospheric Research, 3450 Mitchell Lane, Boulder, CO 80301, United States
AB: Over the past few years, we have developed an improved method for quantification of peroxy radicals (HO₂ and HO₂+RO₂) using chemical ionization mass spectrometric detection, compared to our previous method (Edwards et al., 2003). This method was employed recently during the MIRAGE and INTEX-B campaigns in spring 2006. Our method involves operating the instrument inlet at two specific ratios of NO to O₂. At low [NO]/[O₂], HO₂ plus most RO₂ radicals are measured with high efficiency, while at high [NO]/[O₂], HO₂ is measured, but most RO₂ radicals are measured with low efficiency. This is due to the competition for reaction of alkoxy radicals (RO, produced when RO₂ radicals react with NO) between O₂ (usually to produce HO₂) and NO (to produce alkyl nitrites). We vary the [NO]/[O₂] ratio by diluting ambient air by half with either oxygen or nitrogen about, while at the same time changing reagent NO and SO₂ concentrations by a factor of ten. During our laboratory investigations, we examined the behavior of the instrument over a wide range of [NO]/[O₂] ratios. We have quantified the response to RO₂ radicals derived by reacting OH with various precursor hydrocarbons (methane, alkanes, alkenes, halocarbons, alcohols, aromatics and oxygenated species). The inlet chemistry converts ambient peroxy radicals to gas-phase sulfuric acid. We ionize the sulfuric acid by reaction with negatively charged nitrate reagent ions leading to production of bisulfate ions. We measure the abundances of reagent and product ions with mass spectrometry using quadrupole mass filtering and ion counting. Here, we described the results of the laboratory experiments we performed to characterize the behavior of the instrument. This characterization has led to detailed understanding that allows hydroperoxy and organic peroxy radical concentrations to be quantified aboard aircraft and on ground-based platforms. Edwards, G. D., C. A. Cantrell, S. Stephens, B. Hill, O. Goyea, R. E. Shetter, R. L. Mauldin, E. Kosciuch, D. J. Tanner, F. L. Eisele, Chemical ionization mass spectrometer instrument for measurement of Tropospheric HO2 and RO2, Analy. Chem. 75, 5317-5327, doi:10.1021/ac034402b, 2003.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0365 Troposphere: composition and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: 2007 Joint Assembly