Global uptake of carbonyl sulfide (COS) by terrestrial vegetation: Estimates corrected by deposition velocities normalized to the uptake of carbon dioxide (CO<sub>2</sub>)

Abstract

Abstract. COS uptake by trees, as observed under dark/light changes and under application of the plant hormone abscisic acid, exhibited a strong correlation with the CO 2 assimilation rate and the stomatal conductance. As the uptake of COS occurred exclusively through the stomata we compared experimentally derived and re-evaluated deposition velocities (V d ; related to stomatal conductance) for COS and CO 2 . We show that V d of COS is generally significantly larger than that of CO 2 . We therefore introduced this attribute into a new global estimate of COS fluxes into vegetation. The new global estimate of the COS uptake based on available net primary productivity data (NPP) ranges between 0.69-1.40 Tg a −1 . However, as a COS molecule is irreversibly split in contrast to CO 2 which is released again by respiration processes, we took into account the Gross Primary Productivity (GPP) representing the true CO 2 leaf flux the COS uptake has to be related to. Such a GPP based deposition estimate ranged between 1.4-2.8 Tg a −1 (0.73-1.50 Tg S a −1 ). We believe that in order to obtain accurate global COS sink estimates such a GPP-based estimate corrected by the different deposition velocities of COS and CO 2 must be taken into account.

Soil atmosphere exchange of carbonyl sulfide (COS) regulated by diffusivity depending on water-filled pore space

“…The global annual source and sink strengths are estimated to be 1.31±0.25 Tg a −1 and 1.66±0.79 Tg a −1 , respectively (Watts, 2000). However, recent investigations by Sandoval-Soto et al (2005) reveal that current estimates for the uptake of COS by vegetation seem to be underestimated and indicate that the global atmospheric budget of COS may be considered as unbalanced again.…”

“…Besides photolysis and the reactions with OH and O in the stratosphere, vegetation and soils are regarded as the dominating terrestrial sinks (Brown and Bell, 1986;Goldan et al, 1988;Kettle et al, 2002;Sandoval-Soto et al, 2005;Chin and Davis, 1993;Kesselmeier et al, 1999). On the other hand, COS has also a chemical sink in the troposphere through reaction with OH (Chin and Davis, 1995;Kjellström, 1998).…”

Seasonal fluxes of carbonyl sulfide in a midlatitude forest

“…Ecosystem-scale fluxes of OCS have been proposed as a means to directly determine the photosynthetic uptake of carbon in the biosphere, independently of soil and plant respiration (1,13,14,19). However, for this approach to work as proposed, a number of requirements must be met, many of which are not realized year-round at Harvard Forest.…”

“…Leaf-scale studies have confirmed the OCS link to photosynthesis (14,15). Initial OCS ecosystem flux estimations were made using flask sampling followed by analysis via gas chromatography-mass spectrometry (GC-MS) (13,16), but these studies did not have sufficient resolution to examine daily or hourly controls on the OCS flux.…”

Positive trends in Southern Hemisphere carbonyl sulfide

“…differ [Campbell et al, 2008;Sandoval-Soto et al, 2005;Suntharalingam et al, 2008], and therefore, large uncertainties in the OCS budget remain [Kettle et al, 2002;Montzka et al, 2007] [Griffith et al, 1998;Kohlhepp et al, 2012;Paton-Walsh et al, 2004]. To ensure that differences in OCS behavior across the three sites are unaffected by the configuration of the retrieval, the same retrieval settings were used at all three sites, i.e., fitting four microwindows covering the p19 (2053.98-2054.24 [Rinsland et al, 1998]) is designed to retrieve vertical profiles of one or more gases from solar absorption FTS spectra.…”