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) released following the cutting and drying of hay. The instrument has a fast response, around 0.1 s, allowing use of the eddy covariance technique. Measurements were done over a 3‐day period in a hay field in the eastern part of Tirol, Austria, in the early growing season and are compared to earlier results obtained using a slower‐response instrument in the late growing season [ Karl et al ., 2000]. Peak upward fluxes of the order of 9.9 × 10 −6 g m −2 s −1 for methanol, 1.5 × 10 −6 g m −2 s −1 for acetaldehyde, and 1.5 × 10 −6 g m −2 s −1 for the sum of hexenals, hexenols, hexanal, pentenols, 3‐methylbutanal, and butanone were observed during and after harvesting. Time‐integrated values for the first day were of the order of 65±20 mg m −2 (130±40 μg per gram dry weight(gdw) −1 ) for methanol and 13±4 mg m −2 (26±8 μg gdw −1 ) for acetaldehyde. VOC fluxes measured in this study were generally higher than in August 1999, which can be explained by higher temperatures and higher photosynthetic productivity. Good agreement with another means for estimating VOC fluxes, the surface gradient method, was achieved. This paper presents measurements of eddy covariance for a wide variety of oxygenated VOCs and shows that hay harvesting can influence the local air quality in many regions in the Alps on a short‐term basis.