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

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 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 V_d 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 Tga^-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 Tga^-1 (0.73-1.50 TgSa^-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.