Global uptake of carbonyl sulfide (COS) by terrestrial vegetation: Estimates corrected by deposition velocities normalized to the uptake of carbon dioxide (CO2)

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 CO2 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 CO2. We show that Vd of COS is generally significantly larger than that of CO2. 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 CO2 which is released again by respiration processes, we took into account the Gross Primary Productivity (GPP) representing the true CO2 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 CO2 must be taken into account