Carbonyl sulfide exchange on an ecosystem scale: soil represents a dominant sink for atmospheric COS

The soil/plant/atmosphere exchange of carbonyl sulfide (COS) was investigat ed in an open oak woodland ecosystem at a rural site in northern California . Measurements of atmospheric concentrations of COS were made in June and i n December 1994. We found a significant diel cycle with a drop of COS level s by approximately 150 ppt during the night in both seasons. The mean COS d aytime background mixing ratios showed a distinct seasonal difference with 465 +/- 77 ppt in summer and 375 +/- 56 ppt in winter. The nighttime bulk C OS flux into the ecosystem was estimated using a micrometeorological model. To address the observed depletion of COS during stable nocturnal boundary layer conditions, the potential of various ecosystem compartments to act as a sink for COS was investigated. Studies using dynamic enclosures flushed with ambient air excluded vegetation as an important sink during nighttime due to high stomatal resistance. Results from soil chamber measurements ind icate that the soil can act as a dominant sink for atmospheric COS. (C) 199 9 Elsevier Science Ltd. All rights reserved.