Emissions of ethene, propene, and 1-butene by a midlatitude forest

Measurements of nonmethane hydrocarbon concentrations and gradients above Harvard Forest (42 degrees 32' N, 72 degrees 11' W) are reported for January through December 1993, along with inferred whole-ecosystem emission rates for ethene, propene, and I-butene. Emissions were calculated using a micrometeorological technique where the ratio of observed CO2 fluxes and gradients were multiplied by the observed hydrocarbon gradients. Average emissions of ethene propene, and I-butene during summer were 2.63. 1.13. and 0.41 x 10(10) molecules cm(-2) s(-1), respectively. Emission of these olefins was correlated with incident solar radiation, implying a source associated with photosynthesis. In the northeastern United States, summertime biogenic emissions of propene and 1-butene exceed anthropogenic emissions, and biogenic emissions of ethene contribute approximately 50% of anthropogenic sources. Our measurements suggest that terrestrial biogenic emissions of C-2-C-4 olefins may be significant for atmospheric photochemistry.