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| Titel |
Detection of HO2 by laser-induced fluorescence: calibration and interferences from RO2 radicals |
| VerfasserIn |
H. Fuchs, B. Bohn, A. Hofzumahaus, F. Holland, K. D. Lu, S. Nehr, F. Rohrer, A. Wahner |
| 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. 6 ; Nr. 4, no. 6 (2011-06-28), S.1209-1225 |
| Datensatznummer |
250002018
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| Publikation (Nr.) |
 copernicus.org/amt-4-1209-2011.pdf |
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| Zusammenfassung |
| HO2 concentration measurements are widely accomplished by
chemical conversion of HO2 to OH including reaction
with NO and subsequent detection of OH by laser-induced
fluorescence. RO2 radicals can be converted to OH via
a similar radical reaction sequence including reaction with NO,
so that they are potential interferences for HO2
measurements. Here, the conversion efficiency of various RO2
species to HO2 is investigated. Experiments were conducted
with a radical source that produces OH and HO2 by water
photolysis at 185 nm, which is frequently used for calibration
of LIF instruments. The ratio of HO2 and the sum of OH
and HO2 concentrations provided by the radical source was
investigated and was found to be 0.50 ± 0.02. RO2 radicals
are produced by the reaction of various organic compounds with
OH in the radical source. Interferences via chemical conversion
from RO2 radicals produced by the reaction of OH with
methane and ethane (H-atom abstraction) are negligible consistent with
measurements in the past. However, RO2 radicals from OH
plus alkene- and aromatic-precursors including isoprene (mainly
OH-addition) are detected with a relative sensitivity larger
than 80 % with respect to that for HO2 for the configuration
of the instrument with which it was operated during field
campaigns. Also RO2 from OH plus methyl vinyl ketone
and methacrolein exhibit a relative detection sensitivity of
60 %. Thus, previous measurements of HO2 radical
concentrations with this instrument were biased in the presence of
high RO2 radical concentrations from isoprene, alkenes or
aromatics, but were not affected by interferences in remote clean
environment with no significant emissions of biogenic VOCs, when
the OH reactivity was dominated by small alkanes. By reducing
the NO concentration and/or the transport time between
NO addition and OH detection, interference from these
RO2 species are suppressed to values below 20 % relative to
the HO2 detection sensitivity. The HO2 conversion
efficiency is also smaller by a factor of four, but this is still
sufficient for atmospheric HO2 concentration measurements for
a wide range of conditions. |
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