The release of volatile organic compounds (VOCs) by drying grass and clover leaves and stems was studied in the laboratory using proton-transfer chemical-ionization mass spectrometry, which enables the simultaneous, on-line monitoring of VOC concentrations. A burst of VOC emissions due to cutting the leaves and stems was followed by a second, more intense emission lasting for several hours when the vegetation was starting to dry out. In addition to (Z)-3-hexenal, (Z)-3-hexenol, and hexenyl acetate, that were emitted by the plant tissue in response to the wounding, enhanced emissions of methanol, acetaldehyde, acetone, butanone, and possibly formaldehyde were observed. These findings may have important implications for regional air quality in agricultural and urban areas. ¿ 1999 American Geophysical Union