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| Titel |
Contributions of primary and secondary biogenic VOC tototal OH reactivity during the CABINEX (Community Atmosphere-Biosphere INteractions Experiments)-09 field campaign |
| VerfasserIn |
S. Kim, A. Guenther, T. Karl, J. Greenberg |
| 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. 16 ; Nr. 11, no. 16 (2011-08-24), S.8613-8623 |
| Datensatznummer |
250010025
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| Publikation (Nr.) |
 copernicus.org/acp-11-8613-2011.pdf |
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| Zusammenfassung |
| We present OH reactivity measurements using the comparative reactivity
method with a branch enclosure technique for four different tree species
(red oak, white pine, beech and red maple) in the UMBS PROPHET tower
footprint during the Community Atmosphere Biosphere INteraction EXperiment
(CABINEX) field campaign in July of 2009. Proton Transfer Reaction-Mass
Spectrometry (PTR-MS) was sequentially used as a detector for OH reactivity
and BVOC concentrations including isoprene and monoterpenes (MT) for
enclosure air. Therefore, the measurement dataset contains both measured and
calculated OH reactivity from well-known BVOC. The results indicate that
isoprene and MT, and in one case a sesquiterpene, can account for the
measured OH reactivity. Significant discrepancy between measured OH
reactivity and calculated OH reactivity from isoprene and MT is found for
the red maple enclosure dataset but it can be reconciled by adding
reactivity from emission of a sesquiterpene, α-farnesene, detected
by GC-MS. This leads us to conclude that no significant unknown BVOC
emission contributed to ambient OH reactivity from these trees at least
during the study period. However, this conclusion should be followed up by
more comprehensive side-by-side intercomparison between measured and
calculated OH reactivity and laboratory experiments with controlled
temperature and light environments to verify effects of those essential
parameters towards unknown/unmeasured reactive BVOC emissions. This conclusion leads us to explore the contribution towards ambient OH reactivity
(the dominant OH sink in this ecosystem) oxidation products such as
hydroxyacetone, glyoxal, methylglyoxal and C4 and C5-hydroxycarbonyl using
recently published isoprene oxidation mechanisms (Mainz Isoprene Mechanism
II and Leuven Isoprene Mechanism). Evaluation of conventionally unmeasured
first generation oxidation products of isoprene and their possible
contribution to ambient missing OH reactivity indicates that the ratio of OH
reactivity from unmeasured products over OH reactivity from MVK + MACR is
strongly dependent on NO concentrations. The unmeasured oxidation products
can contribute ~7.2 % (8.8 % from LIM and 5.6 % by MIM 2
when NO = 100 pptv) of the isoprene contribution towards total ambient OH
reactivity. This amount can explain ~8.0 % (9.7 % from LIM and
6.2 % from MIM 2) of missing OH reactivity, reported by Di Carlo et al. (2004)
at the same site. Further study on the contribution from further
generation of unmeasured oxidation products is needed to constrain
tropospheric photochemical reactivity of BVOC that have important
implications for both photochemical ozone and secondary organic aerosol
formation. |
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