Biogenic hydrocarbons are known to act as important precursors in tropospheric photochemical ozone formation. Large uncertainties exist about the composition of the mix of volatile organic compounds emitted by various plant species, and the respective emission rates. A screening study of important woody and crop plants revealed that the portion of isoprene emitting species within deciduous tree species is small. But in contrast to the general assumption, all investigated deciduous tree species emitted traces of monoterpenes. As expected, oaks are strong isoprene emitters, however, some Mediterranean oak species emitted no detectable amounts. Isoprene emission is strongly dependent on temperature and insolation. Wheat and rape seed plants emitted only traces of isoprenoids. The emission and deposition behavior of wheat plants, as far as C2 to C9 hydrocarbons (NMHCs), formaldehyde, and acetaldehyde are concerned, was studied both in the field (BIATEX experimental site, Manndorf, Bavaria) and in the laboratory. Ambient temperature appears to control the fluxes of ethane, ethene, propane and propene, whereas acetaldehyde emission by wheat plants as well as by Norway spruce is controlled by light. Gradient measurements of NMHCs over a grassland area in the Rhine valley (TRACT Erlenhof 17, Brühl, Germany) showed that meadows have a negligible impact on ambient air mixing ratios of NMHCs. Over a spruce canopy (BIATEX experimental site Schachtenau Bayerischer Wald National Park, Germany) the twelve most abundant non-terpenoid NMHC exhibited no distinct diurnal cycle, and only small differences in mixing ratios were detected between the heights 31 and 51 m indicating that the influence of the canopy on the abundance of the non-terpenoid NMHCs present in the air above the canopy was small. Aldehyde mixing ratios above a spruce canopy, however, may significantly be influenced either by direct emission of aldehydes from spruce or by the production of aldehydes during photochemical degradation of precursors. Investigations of NMHC fluxes in strongly polluted forest ecosystems (BIATEX, Frankfurter Stadtwald, Frankfurt, Germany; BEMA, Castelporziano, Rome, Italy) revealed a complex flux pattern for selected biogenic and anthropogenic NMHCs, which is possibly a result of the heterogeneity of vegetation in the main wind direction.
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- Investigations on Emissions of Low Molecular Weight Compounds (C2–C10) from Vegetation
- Springer Berlin Heidelberg