HR: 08:30h
AN: A21A-03    [PDF]
TI: Photochemistry in a Mixed Deciduous Forest: First Results of the Measurements of Isoprene and its Oxidation Products During two Years of the ECHO Project
AU: * Schaub, A
EM: a.schaub@fz-juelich.de
AF: Forschungszentrum Juelich, Institut fuer Chemie und Dynamik der Geosphaere, Institut II: Troposphaere, Leo-Brandt-Strasse, Juelich, 52425 Germany
AU: Komenda, M
AF: Forschungszentrum Juelich, Institut fuer Chemie und Dynamik der Geosphaere, Institut II: Troposphaere, Leo-Brandt-Strasse, Juelich, 52425 Germany
AU: Koppmann, R
AF: Forschungszentrum Juelich, Institut fuer Chemie und Dynamik der Geosphaere, Institut II: Troposphaere, Leo-Brandt-Strasse, Juelich, 52425 Germany
AB: Isoprene contributes significantly to the regional tropospheric ozone formation. Forest stands are the largest sources of isoprene in the troposphere. During the last years various field studies have been carried out to measure isoprene and its oxidation products at rural sites. However, the interaction between photochemistry within the forest canopy and exchange processes with the PBL are not yet fully understood. One aim of the ECHO project (Emission and chemical transformation of biogenic volatile organic compounds) is to investigate to what extent the photochemistry within the canopy influences the net emission of isoprene and secondary products from the forest stand into the PBL. Here we present measurements of the mixing ratios of isoprene and its oxidation products methacrolein (MACR) and methy vinyl ketone (MVK) obtained in a mixed deciduous forest during the vegetation periods in 2002 and 2003. The measurements were carried out at a tower between 2 m and 36 m at different heights above ground. On the same tower comprehensive measurements of other trace gases (nitrogen oxides, ozone, free radicals, CO, PAN, HONO, and anthropogenic VOC), as well as photolysis frequencies and meteorological parameters were conducted in order to get insight into the influence of ambient trace gas levels and transport processes on the oxidation of isoprene and its oxidation products. During daytime mixing ratios of isoprene varied between 400 ppt at low ambient temperature levels and 5.8 ppb on hot and sunny days. During the night isoprene mixing ratios dropped to typical values of about 30 ppt. In June and July 2002 the ratio of MVK/MACR often was less than 1 which is in contrast to the product yield ratio found in other field and laboratory experiments. In 2003 the ratio changed from values of less than 1 in June to values up to 1.8 in August. This observation indicates that the oxidation of isoprene may be influenced by factors previously not considered. Based on these observations simulation experiments were carried out in the atmosphere simulation chamber SAPHIR (see contribution by M. Karl et al.). Together with the extensive measurements of mixing ratios of other trace gases, free radicals, photolysis frequencies, and meteorological parameters, the combination of field and simulation experiments allows to investigate the isoprene oxidation within a forest canopy at different ambient conditions.
UR: http://www.fz-juelich.de/icg/icg-ii/echo
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0315 Biosphere/atmosphere interactions
DE: 0322 Constituent sources and sinks
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting