HR: 1340h
AN: A13C-0928    [Abstracts]
TI: Tropospheric Airborne and Ground-based Peroxy Radical Observations using Chemical Ionization Mass Spectroscopy
AU: * Cantrell, C A
EM: cantrell@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80303
AU: Anderson, R S
EM: rsa@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80303
AU: Mauldin, R L
EM: mauldin@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80303
AU: Kosciuch, E
EM: kosciuch@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80303
AU: Eisele, F L
EM: eisele@ucar.edu
AF: National Center for Atmospheric Research, 1850 Table Mesa Drive, Boulder, CO 80303
AB: We report on recent instrumental improvements to our Peroxy Radical Chemical Ionization Mass Spectrometer (PerCIMS) that allow us to nearly simultaneously measure HO₂ + RO₂ and HO₂ only. This is accomplished through a technique we call "oxygen dilution modulation", in which an air sample is diluted from 1:3 to 1:5 with either oxygen or nitrogen. At the same time, the NO and SO₂ reagent gases are also adjusted. Peroxy radicals are selectively converted to gas phase sulfuric acid molecules, which are chemi-ionized by reaction with gas phase nitrate ions, and quantified by mass spectroscopy. With oxygen dilution and low reagent concentrations, HO₂ and a large fraction of RO₂ (>90%) are measured, while with nitrogen dilution and higher reagent concentrations, HO₂ and a small fraction of RO₂ (<20%) are measured. An instrument with a single inlet can be rapidly switched between these two modes of operation (within 2 minutes), allowing better estimates of HO₂/RO₂ ratios for comparison with photochemical models. We will deploy this new instrument during the upcoming MIRAGE and INTEX-B missions in 2006.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0365 Troposphere: composition and chemistry
DE: 0394 Instruments and techniques
SC: Atmospheric Sciences [A]
MN: Fall Meeting 2005