Volatile organic compound emissions from Miscanthus and short rotation coppice willow bioenergy crops

Miscanthus × giganteus and short rotation coppice (SRC) willow (Salix spp.) are increasingly important bioenergy crops. Above-canopy fluxes and mixing ratios of volatile organic compounds (VOCs) were measured in summer for the two crops at a site near Lincoln, UK, by proton transfer reaction mass spectrometry (PTR-MS) and virtual disjunct eddy covariance. The isoprene emission rate above willow peaked around midday at ∼1 mg m−2 h−1, equivalent to 20 μg gdw−1 h−1 normalised to 30 °C and 1000 μmol m−2 s−1 PAR, much greater than for conventional arable crops. Average midday peak isoprene mixing ratio was ∼1.4 ppbv. Acetone and acetic acid also showed small positive daytime fluxes. No measurable fluxes of VOCs were detected above the Miscanthus canopy. Differing isoprene emission rates between different bioenergy crops, and the crops or vegetation cover they may replace, means the impact on regional air quality should be taken into consideration in bioenergy crop selection.