Emissions of volatile organic compounds (VOC) from mountain grassland ecosystems

 

VOC, the majority of which are emitted by plants, play an important role in atmospheric chemistry and thus air quality and climate change. For example, in the presence of NO_x (NO, NO₂) and sunlight, VOC react to form tropospheric ozone, a risk to human health and plant growth. Ozone itself is a greenhouse gas and furthermore photo-chemical reactions may indirectly reinforce global warming by decreasing the concentration of the hydroxyl radical (OH), which in turn affects the lifetime and concentration of radiatively active trace gases such as methane in the atmosphere. A further consequence of the photo‑oxidation of VOC is the formation of condensable matter and eventually secondary organic aerosols (SOA), which have adverse effects on human health and interact with the precipitation process and thus in turn with climate change.

The objective of this study is to quantify which VOC are emitted by mountain grasslands, to quantify their emission strength and how it varies with changes in environmental conditions and ecosystem status, and to use a process‑based model to simulate these VOC emissions.

To this end, measurements of VOC fluxes haven been made over a mountain grassland managed as a hay meadow (Neustift) during the vegetation periods 2008 and 2009 by our group in collaboration with Ion-Molecule-Reactions& Environmental Physics group from the Department of Ion Physics and Applied Physics of the University of Innsbruck.

Our major findings are that the major species emitted from this grassland is methanol (Bamberger et al., 2010), its emission being controlled largely by temperature and stomatal conductance (Hörtnagl et al., in preparation). We also observed acetaldehyde and acetone fluxes, but in contrast to methanol their fluxes were at least one order of magnitude lower and did not exhibit consistent diurnal cycles - during some times fluxes were directed downwards, during others upwards (Wohlfahrt et al., in preparation). During and after the cutting events the VOC species flux composition changed dramatically due to the wounding and drying of the cut plant material (Bamberger et al., 2010; Ruuskanen et al., in preparation). We also successfully tested the new TOF-PTR-MS for making eddy covariance VOC flux measurements (Müller et al., 2010).

 

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Funding for this project was/is provided by:

FWF P198490