In situ isoprene measurements from foliage using a fast-response hydrocarbon instrument

This manuscript reports on the findings of two research activities. First, a fast-response flame ionization hydrocarbon sensor is described and employed to investigate the environmental responses of isoprene emissions from intact leaves. The principal features of the instrument include high portability, linear response to changes in hydrocarbon concentrations, no baseline drift with time, fast-response (∼1 s) to changes in airstream hydrocarbon concentrations, and a low carbon detection limit of 100 parts per trillion (pptC). The instrument was field tested and employed to investigate hydrocarbon emissions from boreal and mixed temperate forests in Canada. Foliage gas exchange systems were readily interfaced with the hydrocarbon detector to study the environmental controls on hydrocarbon emissions from foliage still attached to plants. On average, the sensor outputs agree within 4% of the results obtained with traditional hydrocarbon measurement methodologies such as gas chromatography. Second, evidence is provided to demonstrate that the foliage isoprene emission capacity is highly sensitive to the recent exposure of low (<10 °C) ambient temperature.