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| Titel |
Observations of reactive nitrogen oxide fluxes by eddy covariance above two midlatitude North American mixed hardwood forests |
| VerfasserIn |
J. A. Geddes, J. G. Murphy |
| 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. 6 ; Nr. 14, no. 6 (2014-03-21), S.2939-2957 |
| Datensatznummer |
250118520
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| Publikation (Nr.) |
 copernicus.org/acp-14-2939-2014.pdf |
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| Zusammenfassung |
| Significant knowledge gaps persist in the understanding of forest–atmosphere
exchange of reactive nitrogen oxides, partly due to a lack of direct
observations. Chemical transport models require representations of dry
deposition over a variety of land surface types, and the role of canopy
exchange of NOx (= NO + NO2) is highly uncertain.
Biosphere–atmosphere exchange of NOx and NOy
(= NOx + HNO3 + PANs + RONO2 + pNO3− + ...)
was measured by eddy covariance above a mixed hardwood forest in central
Ontario (Haliburton Forest and Wildlife Reserve, or HFWR), and a mixed
hardwood forest in northern lower Michigan (Program for Research on Oxidants:
Photochemistry, Emissions and Transport, or PROPHET) during the summers of
2011 and 2012 respectively. NOx and NOy mixing ratios
were measured by a custom-built two-channel analyser based on
chemiluminescence, with selective NO2 conversion via LED photolysis and
NOy conversion via a hot molybdenum converter. Consideration of
interferences from water vapour and O3, and random uncertainty of the
calculated fluxes are discussed. NOy flux observations were
predominantly of deposition at both locations. In general, the magnitude of
deposition scaled with NOy mixing ratios. Average midday
(12:00–16:00) deposition velocities at HFWR and PROPHET were
0.20 ± 0.25 and 0.67 ± 1.24 cm s−1 respectively. Average
nighttime (00:00–04:00) deposition velocities were
0.09 ± 0.25 cm s−1 and 0.08 ± 0.16 cm s−1
respectively. At HFWR, a period of highly polluted conditions
(NOy concentrations up to 18 ppb) showed distinctly different
flux characteristics than the rest of the campaign. Integrated daily average
NOy flux was −0.14 mg (N) m−2 day−1 and
−0.34 mg (N) m−2 day−1 (net deposition) at HFWR and PROPHET
respectively. Concurrent wet deposition measurements were used to estimate
the contributions of dry deposition to total reactive nitrogen oxide inputs,
found to be 22 and 40% at HFWR and PROPHET respectively. |
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