HR: 1330h
AN: A32A-0110    [PDF]
TI: Investigation of Gas Phase Oxidation of Isoprene by OH Radicals in the Atmosphere Simulation Chamber SAPHIR
AU: Karl, M
EM: m.karl@fz-juelich.de
AF: Research Center Juelich ICG-II: Troposphere, Leo-Brand-Strasse, Juelich, 52425 Germany
AU: * Dorn, H
EM: h.p.dorn@fz-juelich.de
AF: Research Center Juelich ICG-II: Troposphere, Leo-Brand-Strasse, Juelich, 52425 Germany
AU: Holland, F
EM: f.holland@fz-juelich.de
AF: Research Center Juelich ICG-II: Troposphere, Leo-Brand-Strasse, Juelich, 52425 Germany
AU: Rupp, L
EM: l.rupp@fz-juelich.de
AF: Research Center Juelich ICG-II: Troposphere, Leo-Brand-Strasse, Juelich, 52425 Germany
AU: Schaub, A
EM: a.schaub@fz-juelich.de
AF: Research Center Juelich ICG-II: Troposphere, Leo-Brand-Strasse, Juelich, 52425 Germany
AU: Brauers, T
EM: th.brauers@fz-juelich.de
AF: Research Center Juelich ICG-II: Troposphere, Leo-Brand-Strasse, Juelich, 52425 Germany
AU: Wahner, A
EM: a.wahner@fz-juelich.de
AF: Research Center Juelich ICG-II: Troposphere, Leo-Brand-Strasse, Juelich, 52425 Germany
AB: Large emission rates from the biosphere and very high reactivity towards OH make isoprene particularly important in local and regional air chemistry. Concurrent measurements of isoprene and its primary oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) during the 2002 field campaign ECHO in Juelich, Germany, showed concentration ratios of MVK to MACR which could not be reproduced with current atmospheric reaction (box) models. We used the atmosphere simulation chamber SAPHIR at the Research Center Juelich to investigate the OH radical induced isoprene oxidation under nearly the same atmospheric conditions as they were encountered during the field campaign. Simultaneous measurements of isoprene, MVK, MACR, OH, HO$_2$, O$_3$, HCHO, NO, NO$_2$, and the photolysis frequencies of NO$_2$, O$_3$, and HCHO were used to constrain the model calculations. A photochemical model using a recently published updated degradation scheme for isoprene was applied to design and interpret the simulation chamber experiments. This new isoprene module is implemented into the Regional Atmospheric Chemistry Mechanism, RACM. We further upgraded this mechanism to explicitly treat the stable oxidation products MVK and MACR as individual species. The model analysis of the chamber experiments showed for the first time that the formation yields of MVK and MACR and therefore their ratio is strongly dependent on the NOx concentration due to the competition between the self-reaction of the primarily formed isoprene peroxy radicals and their reaction with NO. For very low NOx the ratio MVK/MACR is around 0.6 and rapidly increases to 1.5 for NOx above 100 ppt. We found a 30% higher yield of methacrolein compared to the literature (MCM V3), the yield of methyl vinyl ketone was confirmed. The rate coefficients of MVK and MACR with OH were found to be 20% lower as known so far (Atkinson 1986).
DE: 0317 Chemical kinetic and photochemical properties
DE: 0365 Troposphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting