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| Titel |
Contrasting winter and summer VOC mixing ratios at a forest site in the Western Mediterranean Basin: the effect of local biogenic emissions |
| VerfasserIn |
R. Seco, J. Peñuelas, I. Filella, J. Llusià, R. Molowny-Horas, S. Schallhart, A. Metzger, M. Müller, A. Hansel |
| 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 ; 11, no. 24 ; Nr. 11, no. 24 (2011-12-21), S.13161-13179 |
| Datensatznummer |
250010296
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| Publikation (Nr.) |
 copernicus.org/acp-11-13161-2011.pdf |
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| Zusammenfassung |
Atmospheric volatile organic compounds (VOCs) are involved in ozone and
aerosol generation, thus having implications for air quality and climate.
VOCs and their emissions by vegetation also have important ecological roles
as they can protect plants from stresses and act as communication cues
between plants and between plants and animals. In spite of these key
environmental and biological roles, the reports on seasonal and daily VOC
mixing ratios in the literature for Mediterranean natural environments are
scarce.
We conducted seasonal (winter and summer) measurements of VOC mixing ratios
in an elevated (720 m a.s.l.) holm oak Mediterranean forest site near the
metropolitan area of Barcelona (NE Iberian Peninsula). Methanol was the most
abundant compound among all the VOCs measured in both seasons. While
aromatic VOCs showed almost no seasonal variability, short-chain oxygenated
VOCs presented higher mixing ratios in summer, presumably due to greater
emission by vegetation and increased photochemistry, both enhanced by the
high temperatures and solar radiation in summer. Isoprenoid VOCs showed the
biggest seasonal change in mixing ratios: they increased by one order of
magnitude in summer, as a result of the vegetation's greater physiological
activity and emission rates. The maximum diurnal concentrations of ozone
increased in summer too, most likely due to more intense photochemical
activity and the higher levels of VOCs in the air.
The daily variation of VOC mixing ratios was mainly governed by the wind
regime of the mountain, as the majority of the VOC species analyzed followed
a very similar diel cycle. Mountain and sea breezes that develop after
sunrise advect polluted air masses to the mountain. These polluted air
masses had previously passed over the urban and industrial areas surrounding
the Barcelona metropolitan area, where they were enriched in NOx and in
VOCs of biotic and abiotic origin. Moreover, these polluted air masses
receive additional biogenic VOCs emitted in the local valley by the
vegetation, thus enhancing O3 formation in this forested site. The only
VOC species that showed a somewhat different daily pattern were monoterpenes
because of their local biogenic emission. Isoprene also followed in part the
daily pattern of monoterpenes, but only in summer when its biotic sources
were stronger. The increase by one order of magnitude in the concentrations
of these volatile isoprenoids highlights the importance of local biogenic
summer emissions in these Mediterranean forested areas which also receive
polluted air masses from nearby or distant anthropic sources. |
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