Canopy and leaf level 2-methyl-3-buten-2-ol fluxes from a ponderosa pine plantation

Canopy and leaf level 2-methyl-3-butene-2-ol (methylbutenol, MBO) emissions were measured from a ponderosa pine plantation in the Sierra Nevada mountains from July to October 1998. Canopy scale fluxes were measured using a gradient approach, leaf level fluxes used a flow-through chamber. Emissions were dependent on ambient light and temperature levels and showed a diurnal cycle very similar to isoprene in deciduous forests. Maximum fluxes occurred between 1000 and 1700 h with an average of 2 mg C m(-2) h(-1) in July and August, which equaled approximately 0.3-0.5% of the simultaneously measured gross carbon uptake. MBO mixing ratios and fluxes over the pine plantation were also measured with a relaxed eddy accumulation (REA) system operated during part of our measurement campaign (Baker et al., 1999 Journal of Geophysical Research, in press). Mixing ratios measured by both systems were in good agreement but the gradient approach estimated MBO fluxes twice as high than the REA approach. Leaf level investigations revealed a seasonal cycle in basal emission rate (emissions at 1000 mu mol m(-2) s(-1) PAR and 30 degrees C) with a maximum in August, decreasing towards the end of the season. We developed an emission model to scale MBO fluxes from the leaf level to the ecosystem level based on the well-known isoprene algorithm. The model estimates are substantially lower than our gradient flux measurements, and match better with the REA flux measurements, and we conclude that the gradient approach overestimated MBO fluxes at this site. Comparing seasonal changes of measured with modeled fluxes showed a pattern of basal emission rates similar to those observed at the leaf level, and the basal emission rate was related to daytime air temperatures. While MBO contributes substantially to local photochemistry and its oxidation contributes significantly to the regional acetone budget, the latter probably does not represent a significant global source of atmospheric acetone. (C) 2000 Elsevier Science Ltd. All rights reserved.