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| Titel |
Concentrations of OH and HO2 radicals during NAMBLEX: measurements and steady state analysis |
| VerfasserIn |
S. C. Smith, J. D. Lee, W. J. Bloss, G. P. Johnson, T. Ingham, D. E. Heard |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 6, no. 5 ; Nr. 6, no. 5 (2006-05-04), S.1435-1453 |
| Datensatznummer |
250003738
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| Publikation (Nr.) |
 copernicus.org/acp-6-1435-2006.pdf |
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| Zusammenfassung |
| OH and HO2 concentrations were measured simultaneously at
the Mace Head Atmospheric Research Station in the summer of 2002
during the NAMBLEX (North Atlantic Marine Boundary Layer EXperiment)
field campaign. OH was measured by laser-induced fluorescence
employing the FAGE (Fluorescence Assay by Gas Expansion) technique,
with a mean daytime detection limit of 2.7×105 molecule cm−3
(5 min acquisition period; signal-to-noise
ratio = 1). HO2 was detected as OH following its chemical
conversion through addition of NO, with a mean detection limit of
4.4×106 molecule cm−3. The diurnal variation of OH was
measured on 24 days, and that of HO2 on 17 days. The local
solar noon OH concentrations ranged between (3–8)×106 molecule
cm−3, with a 24 h mean concentration of
9.1×105 molecule cm−3. The local solar noon
HO2 concentrations were (0.9–2.1)×108 molecule
cm−3 (3.5–8.2 pptv), with a 24 h mean concentration of 4.2×107 molecule
cm−3 (1.6 pptv). HO2 radicals in the
range (2–3)×107 molecule cm−3 were observed at
night. During NAMBLEX, a comprehensive suite of supporting
measurements enabled a detailed study of the behaviour of HOx
radicals under primarily clean marine conditions. Steady state expressions are used to calculate OH and
HO2 concentrations and to evaluate the effect of different
free-radical sources and sinks. The diurnally averaged calculated to
measured OH ratio was 1.04±0.36, but the ratio displays a
distinct diurnal variation, being less than 1 during the early
morning and late afternoon/evening, and greater than 1 in the middle
of the day. For HO2 there was an overprediction, with the
agreement between calculated and measured concentrations improved by
including reaction with measured IO and BrO radicals and uptake to
aerosols. Increasing the concentration of IO radicals included in
the calculations to above that measured by a DOAS instrument with an
absorption path located mainly over the ocean, reflecting the domination
of the inter-tidal region as an iodine source at Mace Head, led to
further improvement. The results are compared with previous
measurements at Mace Head, and elsewhere in the remote marine
boundary layer. |
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