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| Titel |
Measurements of tropospheric HO2 and RO2 by oxygen dilution modulation and chemical ionization mass spectrometry |
| VerfasserIn |
R. S. Hornbrook, J. H. Crawford, G. D. Edwards, O. Goyea, R. L. Mauldin III, J. S. Olson, C. A. Cantrell |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1867-1381
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Measurement Techniques ; 4, no. 4 ; Nr. 4, no. 4 (2011-04-14), S.735-756 |
| Datensatznummer |
250001931
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| Publikation (Nr.) |
 copernicus.org/amt-4-735-2011.pdf |
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| Zusammenfassung |
| An improved method for the measurement of hydroperoxy radicals (HO2)
and organic peroxy radicals (RO2, where R is any organic group) has
been developed that combines two previous chemical conversion/chemical
ionization mass spectrometry (CIMS) peroxy radical measurement techniques.
Applicable to both ground-based and aircraft platforms, the method provides
good separation between HO2 and RO2, and frequent measurement
capability with observations of both HO2 and HO2 + RO2
amounts each minute. These improvements allow for analyses of measured [HO2]/[HO2 + RO2]
ratios on timescales relevant to tropospheric photochemistry.
By varying both [NO] and [O2] simultaneously in the chemical conversion
region of the PeRCIMS (Peroxy Radical CIMS) inlet, the method exploits the
changing conversion efficiency of RO2 to HO2 under different inlet
[NO]/[O2] to selectively observe either primarily HO2 or the sum
of HO2 and RO2. Two modes of operation have been established for
ambient measurements: in the first half of the minute, RO2 radicals are
measured at close to 100% efficiency along with HO2 radicals (low
[NO]/[O2] = 2.53 × 10−5) and in the second half of the
minute, HO2 is detected while the majority of ambient RO2 radicals
are measured with low efficiency, approximately 15% (high
[NO]/[O2] = 6.80 × 10−4). The method has been tested extensively in the
laboratory under various conditions and for a variety of organic peroxy
radicals relevant to the atmosphere and the results of these tests are
presented. The modified PeRCIMS instrument has been deployed successfully
using the new measurement technique on a number of aircraft campaigns,
including on the NSF/NCAR C-130 during the MIRAGE-Mex and NASA INTEX-B field
campaigns in the spring of 2006. A brief comparison of the peroxy radical
measurements during these campaigns to a photochemical box model indicates
good agreement under tropospheric conditions where NOx (NO + NO2)
concentrations are lower than 0.5 ppbV (parts per billion by volume). |
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