Emissions of volatile organic compounds (primarily oxygenated species) from pasture

The volatile organic compound (VOC) emissions from pasture at a site in southeastern Victoria, Australia, were monitored over a 2 year period using a static chamber technique. Fluxes up to 23,000 mu g(C) m(-2) h(-1) were detected, with the higher fluxes originating from clover rather than from grass species. Gas chromatographic analyses indicated that emissions from both grass and clover were high in oxygenated hydrocarbons including methanol, ethanol, propanone, butanone, and ethanal, and extremely low in isoprene and monoterpenes. In the case of clover, butanone made up 45-50% of the total emissions. When grass and clover were freshly mown, there were significantly enhanced emissions of VOCs. These enhanced emissions included both those oxygenates emitted from uncut pasture and also C-6-oxygenates, including (Z)-3-hexenal, (E)-2-hexenal, (2)-2-hexen-1-ol, (Z)-3-hexen-1-ol, and (Z)-3-hexenyl acetate. Emissions from the undisturbed pasture increased markedly with temperature and the intensity of solar radiation, peaking at midday and ceasing at night. The fluxes, when normalized to a temperature of 30 degrees C and a light intensity of 1000 mu E m(-2) s(-1) were, for grass and clover respectively, about one eighth and two fifths of the equivalent fluxes reported to occur from U.S. woodlands. The annual integrated emission from the pasture was approximately 1.9 g(C) m(-2) or 1.3 mg(C) g(-1) (dry matter). The large transient fluxes that occurred following physical damaging of the pasture, when integrated over time, could be of the same order as those emissions that were observed from undisturbed pasture. In the case of methanol, and perhaps ethanol, the emissions from grasslands may be significant global sources of these gases.