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| Titel |
Observation and modelling of HOx radicals in a boreal forest |
| VerfasserIn |
K. Hens, A. Novelli, M. Martinez, J. Auld, R. Axinte, B. Bohn, H. Fischer, P. Keronen, D. Kubistin, A. C. Nölscher, R. Oswald, P. Paasonen, T. Petäjä, E. Regelin, R. Sander, V. Sinha, M. Sipilä, D. Taraborrelli, C. Tatum Ernest, J. Williams, J. Lelieveld  , H. Harder |
| 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 ; 14, no. 16 ; Nr. 14, no. 16 (2014-08-26), S.8723-8747 |
| Datensatznummer |
250118980
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| Publikation (Nr.) |
 copernicus.org/acp-14-8723-2014.pdf |
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| Zusammenfassung |
Measurements of OH and HO2 radicals were conducted in a pine-dominated forest in
southern Finland during the HUMPPA-COPEC-2010 (Hyytiälä United
Measurements of Photochemistry and Particles in Air –
Comprehensive Organic Precursor Emission and
Concentration study) field campaign in summer 2010. Simultaneous side-by-side
measurements of hydroxyl radicals were conducted with two instruments using chemical ionization
mass spectrometry (CIMS) and laser-induced fluorescence (LIF), indicating small systematic
disagreement, OHLIF / OHCIMS = (1.31 ± 0.14). Subsequently, the LIF instrument was moved to the top of a 20 m tower, just above the
canopy, to investigate the radical chemistry at the ecosystem–atmosphere interface. Comprehensive
measurements including observations of many volatile organic compounds (VOCs) and the total OH reactivity were conducted
and analysed using steady-state calculations as well as an observationally constrained box model.
Production rates of OH calculated from measured OH precursors are consistent with
those derived from the steady-state assumption and measured total OH loss under conditions
of moderate OH reactivity. The primary photolytic sources of OH contribute up to one-third to the total OH production. OH recycling, which occurs mainly by HO2
reacting with NO and O3, dominates the total hydroxyl radical production in this
boreal forest. Box model simulations agree with measurements for hydroxyl radicals
(OHmod. / OHobs. = 1.00 ± 0.16), while HO2 mixing ratios are
significantly under-predicted (HO2mod. / HO2obs. = 0.3 ± 0.2), and simulated
OH reactivity does not match the observed OH reactivity. The simultaneous
under-prediction of HO2 and OH reactivity in periods in which OH
concentrations were simulated realistically suggests that the missing OH reactivity is an
unaccounted-for source of HO2.
Detailed analysis of the HOx production, loss, and recycling pathways suggests that in
periods of high total OH reactivity there are additional recycling processes forming
OH directly, not via reaction of HO2 with NO or O3, or unaccounted-for primary HOx sources. Under conditions of moderate observed OH reactivity and high actinic flux, an additional RO2 source of approximately 1 × 106 molec cm−3 s−1 would be required to close the radical budget. Nevertheless,
a major fraction of the OH recycling occurs via the reaction of HO2 with NO
and O3 in this terpene-dominated environment. |
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