HR: 09:15h
AN: A21A-06    [PDF]
TI: Fluxes of Primary and Secondary Biogenic Volatile Organic Compounds (BVOC) During the BEWA Field Experiments
AU: * Steinbrecher, R
EM: rainer.steinbrecher@imk.fzk.de
AF: Institute for Meteorology and Climate Research (IMK-IFU), Forschungszentrum Karlsruhe GmbH, Kreuzeckbahnstr. 19, Garmisch-Partenkirch, D-82467 Germany
AU: Rappengl\"{u}ck, B
EM: bernhard.rappenglueck@imk.fzk.de
AF: Institute for Meteorology and Climate Research (IMK-IFU), Forschungszentrum Karlsruhe GmbH, Kreuzeckbahnstr. 19, Garmisch-Partenkirch, D-82467 Germany
AU: Steigner, D
EM: dominik.steigner@imk.fzk.de
AF: Institute for Meteorology and Climate Research (IMK-IFU), Forschungszentrum Karlsruhe GmbH, Kreuzeckbahnstr. 19, Garmisch-Partenkirch, D-82467 Germany
AU: Hansel, A
EM: armin.hansel@uibk.ac.at
AF: Institute of Ion Physics, Leopold-Franzens-University, Technikerstr. 25, Innsbruck, A-6020 Austria
AU: Graus, M
EM: martin.graus@uibk.ac.at
AF: Institute of Ion Physics, Leopold-Franzens-University, Technikerstr. 25, Innsbruck, A-6020 Austria
AU: Lindinger, C
EM: christian.lindinger@uibk.ac.at
AF: Institute of Ion Physics, Leopold-Franzens-University, Technikerstr. 25, Innsbruck, A-6020 Austria
AB: Biogenic volatile organic compounds (BVOCs) play a crucial role in the formation of photo-oxidants and particles through the diverse BVOC degradation pathways. Yet, current estimations about temporal and spatial BVOC emissions, including the specific BVOC mix are rather vague. This paper reports results from the determination of BVOC net emission rates that were obtained within the frame of the BEWA field experiments at the Waldstein site in the Fichtelgebirge in 2001 and 2002, an extended forest site that is largely dominated by Norway spruce (Picea abies [L.] Karst.). Stand fluxes of volatile organic compounds were determined with Proton Transfer Reaction Mass Spectrometry (PTR-MS) coupled to a Relaxed-Eddy-Accumulation (REA) system. The PTR-MS is capable to measure simultaneously a variety of organic trace gases, including oxygenated compounds. Air samples were taken at the top of a meteorological tower at the height of 32 m a.g.l. close to the Gill Sonic anemometer that controlled the REA-sampling. A critical value when using the REA approach is the Businger-Oncley parameter b. For this canopy type a b value of 0.39 (threshold velocity wo = 0.6) was determined. The PTR-MS data show clear diurnal variations of ambient air mixing ratios of isoprene and monoterpenes, but also of oxygenated VOC such as methanol, carbonyls, methylvinylketone (MVK) and methacrolein (MAC). Canopy fluxes of isoprene reached up to 7 nmol m$^{-2}$ s$^{-1}$ during daytime. The fluxes of the sum of monoterpenes were in the same range. MVK and MAC are products from isoprene oxidation. The BEWA data confirm this relationship and reveal a better correlation of MVK+MAC with isoprene (r$^{2}$=0.78) than with the sum of monoterpenes (r$^{2}$=0.30). In our study MVK+MAC fluxes were about 30% lower than isoprene fluxes. Both observations indicate active photochemical degradation of isoprene in this area. Actealdehyde and acetone are typical intermediate compounds in the photochemical degradation of both anthropogenic and biogenic VOCs. However, they may also be emitted directly. Growing evidence shows that beside anthropogenic significant biogenic sources exist for both compounds. The results of the BEWA campaign reveal only a poor correlation between acetaldehyde and acetone (r$^{2}$=0.02) indicating different origins of both species. The observations show that acetone deposition prevails suggesting that biogenic sources of acetone play a minor role, at least at this site. Acetaldehyde fluxes usually better agree with isoprene fluxes (r$^{2}$=0.55). However, they correlate best with MVK+MAC fluxes (r$^{2}$=0.81). This is an indication that acetaldehyde is primarily produced in photochemical degradation processes of VOC. Methanol canopy fluxes reached 22 nmol m$^{-2}$ s$^{-1}$ and daytime methanol mixing ratios were up to 15 ppbv and were comparable with previously reported values. The methanol mixing ratios are consistent with its relatively long atmospheric life time of approximately 16 days making advection an important issue. However, twig enclosure measurements during the summer 2002 intensive field experiment at the Waldstein site did not reveal significant direct methanol emissions.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0315 Biosphere/atmosphere interactions
DE: 0322 Constituent sources and sinks
DE: 0365 Troposphere--composition and chemistry
DE: 0368 Troposphere--constituent transport and chemistry
SC: Atmospheric Sciences [A]
MN: 2003 Fall Meeting