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| Titel |
OH reactivity measurements from Boreal tree species in a plant chamber |
| VerfasserIn |
Anke Nölscher, Thomas Custer, Vinayak Sinha, Astrid Kiendler-Scharr, Einhard Kleist, Ralf Tillmann, Jürgen Wildt, Jonathan Williams |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250036054
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| Zusammenfassung |
| Boreal forest covers a large area (ca. 15 million km2) comparable in size to the Tropical rain
forest (ca. 17 million km2). The vegetation in Boreal regions is typically conifer forest which
is known to emit significant amounts of biogenic volatile organic compounds (BVOCS), such
as monoterpenes, sesquiterpenes, methanol and acetone. Many of these organic chemicals
react rapidly with hydroxyl (OH) radicals to produce aerosols or secondary pollutants such as
ozone. The total effect of the emitted species on the OH radical can be determined by
measuring the total OH reactivity directly. Therefore a new measurement method was
recently devised (Sinha et al., 2008).
The Jülich plant atmosphere chamber (JPAC) at the Forschungszentrum-Jülich was used
to investigate the overall reactivity of emissions from several Boreal tree species
under controlled conditions in October 2009. Vegetation, temperature and light
intensities typical of the Hyytiälä measurement station in Finland were used in these
experiments and the levels of CO2, humidity and NOx were controlled. In addition to the
reactivity measurement, a gas chromatograph (GC), a proton transfer reaction mass
spectrometer (PTRMS) and a time-of-flight PTRMS (TOF-PTRMS) were used to quantify
individual organic chemicals emitted by the plants for comparison with the overall
reactivity.
Experiments were performed under three different conditions. 1) Lower temperatures
(T=20Ë C) resulted in low plant emissions with no diurnal variation. The total measured OH
reactivity ranged from below detection limit (3 sec-1) to 7 sec-1 during the day and
overnight rose to 8-13 sec-1. 2) Higher temperatures (T=35Ë C) produced higher emissions
of volatile organic compounds and a clear diurnal trend. Reactivity data matched well with
these results rising to 30-50 sec-1 by day and during the night sinking again to 8-13 sec-1. 3)
Finally a control experiment was performed without trees in the plant chamber. In this
experiment, reactivity showed no nocturnal or diurnal variation and measured values
remained below detection limit.
Significant fractions of the diurnal reactivity could be explained by the individual VOC
measurements; however, for all measured organic species we found higher emissions during
periods of illumination than during periods of darkness. Also subsequent laboratory tests
have eliminated interferences and influences of CO2 and water vapor concentrations as a
possible explanation. The elevated nighttime values can be attributed to the presence of the
plants and not to a chamber related artefact. The cause of the high nocturnal reactivity
remains unexplained. |
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