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| Titel |
Ozone deposition into a boreal forest over a decade of observations: evaluating deposition partitioning and driving variables |
| VerfasserIn |
Ü. Rannik, N. Altimir, I. Mammarella, J. Bäck, J. Rinne, T. M. Ruuskanen, P. Hari, T. Vesala, M. Kulmala  |
| 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 ; 12, no. 24 ; Nr. 12, no. 24 (2012-12-21), S.12165-12182 |
| Datensatznummer |
250011685
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| Publikation (Nr.) |
 copernicus.org/acp-12-12165-2012.pdf |
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| Zusammenfassung |
| This study scrutinizes a decade-long series of ozone deposition measurements
in a boreal forest in search for the signature and relevance of the
different deposition processes. The canopy-level ozone flux measurements
were analysed for deposition characteristics and partitioning into stomatal
and non-stomatal fractions, with the main focus on growing season day-time
data. Ten years of measurements enabled the analysis of ozone deposition
variation at different time-scales, including daily to inter-annual
variation as well as the dependence on environmental variables and
concentration of biogenic volatile organic compounds (BVOC-s). Stomatal
deposition was estimated by using multi-layer canopy dispersion and optimal
stomatal control modelling from simultaneous carbon dioxide and water vapour
flux measurements, non-stomatal was inferred as residual. Also, utilising
the big-leaf assumption stomatal conductance was inferred from water vapour
fluxes for dry canopy conditions. The total ozone deposition was highest
during the peak growing season (4 mm s−1) and lowest during winter
dormancy (1 mm s−1). During the course of the growing season the
fraction of the non-stomatal deposition of ozone was determined to vary from
26 to 44% during day time, increasing from the start of the season
until the end of the growing season. By using multi-variate analysis it was
determined that day-time total ozone deposition was mainly driven by
photosynthetic capacity of the canopy, vapour pressure deficit (VPD),
photosynthetically active radiation and monoterpene concentration. The
multi-variate linear model explained the high portion of ozone deposition
variance on daily average level (R2 = 0.79). The explanatory power of
the multi-variate model for ozone non-stomatal deposition was much lower
(R2 = 0.38). The set of common environmental variables and terpene
concentrations used in multivariate analysis were able to predict the
observed average seasonal variation in total and non-stomatal deposition but
failed to explain the inter-annual differences, suggesting that some still
unknown mechanisms might be involved in determining the inter-annual
variability. Model calculation was performed to evaluate the potential sink
strength of the chemical reactions of ozone with sesquiterpenes in the
canopy air space, which revealed that sesquiterpenes in typical amounts at
the site were unlikely to cause significant ozone loss in canopy air space.
The results clearly showed the importance of several non-stomatal removal
mechanisms. Unknown chemical compounds or processes correlating with
monoterpene concentrations, including potentially reactions at the surfaces,
contribute to non-stomatal sink term. |
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