Proton-transfer chemical-ionization mass spectrometry allows real-time analysis of volatile organic compounds released from cutting and drying of crops

The wounding and drying of plant material during crop harvest could be a si gnificant source of volatile organic compounds (VOCs) that enter the atmosp here. Here, we show that these primarily oxygenated VOCs can be measured us ing proton-transfer chemical-ionization mass spectrometry (PT-CIMS), a meth od that allows online and simultaneous monitoring of oxygenated VOC levels. For clover, alfalfa, and corn, leaf wounding and in particular drying were shown to lead to strongly enhanced emissions of a series of Cs aldehydes, alcohols, and esters derived from (Z)-3-hexenal. Additionally, for the fora ge crops clover and alfalfa, enhanced emissions of methanol, acetaldehyde, acetone, and butanone were observed. The identities of the measured carbony l compounds were confirmed using high-pressure liquid chromatography. For c lover, initial cutting led to a VOC release of about 175 mu g of C (g dry w t)(-1), while during drying the cut clover released >1000 mu g of C (g dry wt)(-1); qualitatively, similar amounts of VOCs were released from alfalfa, the major hay crop in the United States. The atmospheric implications of t hese findings may include effects on the local air quality in agricultural areas, contributions to long-range transport of pollutants, and effects on the formation of HOx (=OH + HO2) radicals in the upper troposphere.