Formation of carbonyl sulfide (OCS) from carbon monoxide and sulfur vapor and applications to Venus

We use gas chromatography to identify and measure the amounts of carbonyl sulfide (OCS) formed in a gas-flow system via the net thermochemical reactions 1 SO2 + 3 CO = OCS + 2 CO2 2 3 FeS2 (pyrite) + 4 CO2 + 2 CO = Fe3O4 (magnetite) + 6 OCS 3 2 CO + S-2, = 2 OCS at temperatures of 470-612 degrees C and ambient atmospheric pressure. The goal of our work is to evaluate the importance of reactions (1) to (3), which have been proposed as potential sources of OCS in Venus' lower atmosphere. Our results show OCS formation by reaction (3), but not by reactions (1) or (2) under our experimental conditions. Based on our results, experimental data from the literature, and theoretical models in the literature, we conclude that (1) the reaction of S-2 and CO is an important source of OCS in Venus' lower atmosphere, and (2) probably neither reaction (1) nor reaction (2) is an important source of OCS on Venus. Finally, we use thermodynamic data for reaction (3) and Venera spacecraft observations of CO and sulfur vapor at 0-12-km altitude to calculate an OCS equilibrium abundance of 1-14 ppmv, with a nominal value of 5 ppmv, for reaction (3) near Venus' surface. (C) 1997 Academic Press.