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| Titel |
Eddy covariance fluxes of acyl peroxy nitrates (PAN, PPN and MPAN) above a Ponderosa pine forest |
| VerfasserIn |
G. M. Wolfe, J. A. Thornton, R. L. N. Yatavelli, M. McKay, A. H. Goldstein, B. LaFranchi, K.-E. Min, R. C. Cohen |
| 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. 2 ; Nr. 9, no. 2 (2009-01-27), S.615-634 |
| Datensatznummer |
250006746
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| Publikation (Nr.) |
 copernicus.org/acp-9-615-2009.pdf |
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| Zusammenfassung |
| During the Biosphere Effects on
AeRosols and Photochemistry
EXperiment 2007 (BEARPEX-2007), we observed eddy covariance (EC) fluxes of
speciated acyl peroxy nitrates (APNs), including peroxyacetyl nitrate (PAN),
peroxypropionyl nitrate (PPN) and peroxymethacryloyl nitrate (MPAN), above a
Ponderosa pine forest in the western Sierra Nevada. All APN fluxes are net
downward during the day, with a median midday PAN exchange velocity of −0.3 cm s−1;
nighttime storage-corrected APN EC fluxes are smaller than
daytime fluxes but still downward. Analysis with a standard resistance model
shows that loss of PAN to the canopy is not controlled by turbulent or
molecular diffusion. Stomatal uptake can account for 25 to 50% of the
observed downward PAN flux. Vertical gradients in the PAN thermal
decomposition (TD) rate explain a similar fraction of the flux, suggesting
that a significant portion of the PAN flux into the forest results from
chemical processes in the canopy. The remaining "unidentified" portion of
the net PAN flux (~15%) is ascribed to deposition or reactive
uptake on non-stomatal surfaces (e.g. leaf cuticles or soil). Shifts in
temperature, moisture and ecosystem activity during the summer – fall
transition alter the relative contribution of stomatal uptake, non-stomatal
uptake and thermochemical gradients to the net PAN flux. Daytime PAN and
MPAN exchange velocities are a factor of 3 smaller than those of PPN during
the first two weeks of the measurement period, consistent with strong
intra-canopy chemical production of PAN and MPAN during this period.
Depositional loss of APNs can be 3–21% of the gross gas-phase TD loss
depending on temperature. As a source of nitrogen to the biosphere, PAN
deposition represents approximately 4–19% of that due to dry
deposition of nitric acid at this site. |
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