Eddy covariance measurement of biogenic oxygenated VOC emissions from hay harvesting

Biogenic oxygenated volatile organic compound (VOC) fluxes have been direct ly measured by eddy covariance using the combination of a fast response, re al-time VOC sensor and an acoustic anemometer. VOC detection is based on pr oton-transfer reaction mass spectrometry which has currently a response tim e of ca. 0.8 s and the system is suitable for making nearly unattended, lon g-term and continuous measurements of VOC fluxes. The eddy covariance syste m has a detection limit, for most VOCs. of less than 0.1 mg m(-2) h(-1). Th e system was field tested above a hayfield near St. Johann, Austria where c ut and drying grasses released a variety of VOCs. High fluxes were observed for about 2 days after cutting and were dominated by methanol (1-8.4 mg m( -2) h(-1)), acetaldehyde (0.5-3 mg m(-2) h(-1)), hexenals (0.1-1.5 mg m(-2) h(-1)) and acetone (0.1-1.5 mg m(-2) h(-1)). The eddy covariance measureme nts generally agreed with flux estimates based on enclosure measurements an d surface layer gradients. The sensitivity and selectivity of the system ma ke it suitable for quantifying the fluxes of the dominant biogenic VOCs fro m a variety of landscapes and sources. (C) 2000 Published by Elsevier Scien ce Ltd.