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| Titel |
Ozone, OH and NO3 sink terms at a coniferous forest site in Central Germany: Role of biogenic VOCs |
| VerfasserIn |
B. Bonn, S. Bourtsoukidis, W. Haunold, R. Sitals, S. Jacobi |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250068075
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| Zusammenfassung |
| Oxidation capacities of ecosystems are important to facilitate an ecosystem feedback on
oxidation stress and in order to survive. We have conducted seasonal ambient measurements
of a series of biogenic VOCs using a plant enclosure technique and determined the ambient
levels of ozone, NOx as well as basic meteorological parameters at a managed spruce forest
site in Central Germany (Mt. Kleiner Feldberg). The site is 810 m a.s.l. and faces distinct
anthropogenic contributions from the Rhine-Main-area including the airport and major traffic
routes in from the southeast. The opposite direction is moderately polluted and can be
classified as Central German background condition. Since atmospheric chemistry and
pollutants become very important especially for this site, which is the most polluted one in
Germany with respect to ozone we approximated the sink terms for the atmospheric oxidation
agents of interest at this site, i.e ozone, OH and NO3 using the measurements and
box model steady state calculations for intermediate species not measured directly
between the first of April and the start of November 2011. BVOC measurements were
obtained with PTR-MS every 36 s and averaged for 30 min intervals afterwards
to facilitate the inclusion of the monitoring data of the Hessian Agency for the
Environment and Geology (HLUG) in Wiesbaden, Germany: temperature, humidity, global
radiation, ozone and NOx. Analysis was performed with Matlab (Mathworks Inc.)
and included the gas-phase chemistry set-up described by the Master Chemical
Mechanism (MCM, v3, [1]). This resulted in the following outcome for sinks of
oxidants:
Ozone: Significant contributions were found for mono- and sesquiterpenes as well as for
NOx. The individual contributions vary notably with the time of the day and the year and the
emission strength of biogenic VOCs. Especially for the early season in April sesquiterpene
reactions dominated the sink by up to 80% during nighttime, while NOx reactions dominated
the sink terms during daytime. The contributions of monoterpene and isoprene reactions
strengthened towards the summer period, while sesquiterpene reactions slowed
down.
Hydroxyl radical: The picture becomes much more complex for OH. Besides the reaction
with nitrogen dioxide, isoprene and monoterpenes were key destructing agents of OH with
estimated contributions of about 50-60%, increasing towards the summertime. Contributions
of their oxidation products to the total sink of OH are supposed to be less than 20% but
showing more intense during summer and less towards cooler periods. Sesquiterpene
OH-reactions only contributed to 10% with a maximum of about 20% at the early
April.
Nitrate radical: NO3 displayed a mixture of the sinks of OH and ozone. The
dominant destruction takes place via NOx-reactions (about 50%) and the remainder
primarily via monoterpene (36±20%), sesquiterpene (11±8%) and isoprene (2±1%)
OH-reactions.
From our observations at this particular site it is apparent that the spruce forest provides a
quite efficient variety of pathways to compensate oxidation stress. This is essentially
displayed in the variation of emission pattern of different compound classes with different
reactivity for the three major oxidation agents. One needs to be aware of the fact that the sink
is highly variable in space, too. Therefore we conclude: In order to understand and describe
the oxidation tolerance of a certain ecosystem one needs to detect at least the reactive
hydrocarbons.
[1] Jenkin, M.E., Shallcross, D. E., and Harvey, J. N.: Development and application of a
possible mechanism for the generation of cis-pinic acid form the ozonolysis of α- and
β-pinene. Atmos.Environ., 34, 2837–2850, 2000. |
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