Eddy covariance measurements of oxygenated volatile organic compound fluxes from crop harvesting using a redesigned proton-transfer-reaction mass spectrometer

A redesigned proton-transfer-reaction mass spectrometer was deployed in the field to measure atmospheric fluxes of volatile organic compounds (VOCs) r eleased following the cutting and drying of hay. The instrument has a fast response, around 0.1 s, allowing use of the eddy covariance technique. Meas urements were done over a 3-day period in a hay field in the eastern part o f Tirol, Austria, in the early growing season and are compared to earlier r esults obtained using a slower-response instrument in the late growing seas on [Karl et al., 2000]. Peak upward fluxes of the order of 9.9 x 10(-6) g m (-2) s(-1) for methanol, 1.5 x 10(-6) g m(-2) S-1 for acetaldehyde, and 1.5 x 10(-6) g m(-2) s(-1) for the sum of hexenals, hexenols, hexanal, penteno ls, 3-methylbutanal, and butanone were observed during and after harvesting . Time-integrated values for the first day were of the order of 65 +/- 20 m g m(-2) (130 +/- 40 mug per gram dry weight(gdw)(-1)) for methanol and 13 /- 4 mg m(-2) (26 +/- 8 mug gdw(-1)) for acetaldehyde. VOC fluxes measured in this study were generally higher than in August 1999, which can be expla ined by higher temperatures and higher photosynthetic productivity. Good ag reement with another means for estimating VOC fluxes, the surface gradient method, was achieved. This paper presents measurements of eddy covariance f or a wide variety of oxygenated VOCS and shows that hay harvesting can infl uence the local air quality in many regions in the Alps on a short-term bas is.