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| Titel |
Contrasting atmospheric boundary layer chemistry of methylhydroperoxide (CH3OOH) and hydrogen peroxide (H2O2) above polar snow |
| VerfasserIn |
M. M. Frey, M. A. Hutterli, G. Chen, S. J. Sjostedt, J. F. Burkhart, D. K. Friel, R. C. Bales |
| 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 ; 9, no. 10 ; Nr. 9, no. 10 (2009-05-20), S.3261-3276 |
| Datensatznummer |
250007300
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| Publikation (Nr.) |
 copernicus.org/acp-9-3261-2009.pdf |
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| Zusammenfassung |
| Atmospheric hydroperoxides (ROOH) were measured at Summit, Greenland
(72.97° N, 38.77° W) in summer 2003 (SUM03) and spring 2004
(SUM04) and South Pole in December 2003 (SP03). The two dominant
hydroperoxides were H2O2 and CH3OOH (from here on MHP) with
average (±1σ) mixing ratios of 1448 (±688) pptv,
204 (±162) and 278 (±67) for H2O2 and 578 (±377) pptv,
139 (±101) pptv and 138 (±89) pptv for MHP, respectively. In
early spring, MHP dominated the ROOH budget and showed night time maxima and
daytime minima, out of phase with the diurnal cycle of H2O2, suggesting
that the organic peroxide is controlled by photochemistry, while H2O2
is largely influenced by temperature driven exchange between the atmosphere
and snow. Highly constrained photochemical box model runs yielded median
ratios between modeled and observed MHP of 52%, 148% and 3% for SUM03,
SUM04 and SP03, respectively. At Summit firn air measurements and model
calculations suggest a daytime sink of MHP in the upper snow pack, which
decreases in strength through the spring season into the summer. Up to 50%
of the estimated sink rates of
1–5×1011 molecules m−3 s−1 equivalent to
24–96 pptv h−1 can be explained by photolysis and reaction with the
OH radical in firn air and in the quasi-liquid layer on snow grains. Rapid
processing of MHP in surface snow is expected to contribute significantly to
a photochemical snow pack source of formaldehyde (CH2O). Conversely,
summer levels of MHP at South Pole are inconsistent with the prevailing high
NO concentrations, and cannot be explained currently by known photochemical
precursors or transport, thus suggesting a missing source. Simultaneous
measurements of H2O2, MHP and CH2O allow to constrain the NO
background today and potentially also in the past using ice cores, although
it seems less likely that MHP is preserved in firn and ice. |
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