Carbonyl Sulfide OCS

Carbonyl sulfide is the most abundant sulfur gas in the global background atmosphere because of its low reactivity in the troposphere and its correspondingly long residence time. It is the only sulfur compound that survives to enter the stratosphere. (An exception is the direct injection of S02 into the stratosphere in volcanic eruptions.) In fact, the input of OCS into the stratosphere is considered to be responsible for the maintenance of the normal stratospheric sulfate aerosol layer. 

On the basis of atmospheric measurements, Chin and Davis (1995) estimated the total quantity of OCS in the atmosphere to be 5.2 Tg, of which 4.63 Tg is in the troposphere and 0.57 Tg in the stratosphere. Based on the estimated global OCS source strength of 0.86 Tg yr 1, the global atmospheric lifetime of OCS is estimated to be about 6 years. We will return to the global cycle and chemistry of OCS in Chapter 5 in connection with the stratospheric aerosol layer. 

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El0.7 Carbonyl sulfide (OCS) is a linear molecule with a moment of inertia of 137 x 10-40 g em2. The three fundamental vibrational frequencies are 521.50, 859.2, and 2050.5 cm-1, but one is degenerate and needs to be counted twice in calculating the entropy. A Third Law measurement of the entropy of OCS (ideal gas) at the normal boiling point of T = 222.87 K andp = 0.101325 MPa gives a value of 219.9 J-K- -mol"1. Use this result to decide which vibrational frequency should be given double weight. 

Khalil, M.A.K. and Rasmussen, R.A. Global sources, lifetimes and mass balances of carbonyl sulfide (OCS) and carbon disulfide (CS2) in the earth s atmosphere, Atmos. Environ., 18(9) 1805-1813, 1984. 

The hydrogen sulfides (H2S, SH-, S2 and their metal complexes) are well known in restricted reducing regions of the world ocean such as anoxic basins (1), but they have traditionally been dismissed as unimportant for, or even nonexistent in, most oxic seawaters 12-41. Several lines of reasoning are now beginning to suggest that sulfides actually do exist in the surface ocean, and enter into a rich metal chemistiy there. Extensive measurements of carbonyl sulfide (OCS) in seawater (5.61 permit the quantification of a mixed layer source, the hydrolysis reactions f7-111... 

Biogenic Sulfur Emissions from the Ocean. The ocean is a source of many reduced sulfur compounds to the atmosphere. These include dimethylsulfide (DMS) (2.4.51. carbon disulfide (CS2) (28). hydrogen sulfide (H2S) (291. carbonyl sulfide (OCS) (30.311. and methyl mercaptan (CH3SH) ( ). The oxidation of DMS leads to sulfate formation. CS2 and OCS are relatively unreactive in the troposphere and are transported to the stratosphere where they undergo photochemical oxidation (22). Marine H2S and CH3SH probably contribute to sulfate formation over the remote oceans, yet the sea-air transfer of these compounds is only a few percent that of DMS (2). 

Although there have been only a few studies to date, it has been suggested that coastal plumes and estuaries may be important atmospheric sources of DMS. Other sulfur compounds such as carbonyl sulfide (OCS) and carbon disulfide (CS2) have also been shown to possible sources of S in estuaries. 

In the last 150 years the anthropogenic emission of sulfur has increased dramatically, primarily due to combustion processes [1]. In the 1950s anthropogenic emission surpassed natural emission and the atmospheric sulfur cycle is one of the most perturbed biogeochemical cycles [1,2]. The oceans are the largest natural source of atmospheric sulfur emissions, where sulfur is emitted in a reduced form, predominantly as dimethyl sulfide (DMS) and to a much lesser extent carbonyl sulfide (OCS) and carbon disulfide (CS2) [3]. Ocean emitted DMS and CS2 are initially oxidised to OCS, which diffuses through the troposphere into the stratosphere where further oxidation to sulfur dioxide (SO2), sulfur trioxide (SO3) and finally sulfuric acid (H2SO4) occurs [1-4]. 

In the 1980s, the discovery of spectral windows allowed Earth-based IR observations of the subcloud atmosphere on Venus nightside (Allen and Crawford, 1984). High-resolution IR spectroscopy in these windows led to the discovery of carbonyl sulfide (OCS) and the first measurements of HCl and HF below the clouds (Bezard et al., 1990). The Galileo and CASSINI flybys of Venus (see Table 1) utilized these spectral windows to image the surface at near IR wavelengths. 

Compounds of sulfur with carbon having the general formula are characterized through a series of linear poly carbon sulfides C S (n = 2-9), some of which can be detected in interstellar clouds. Carbon disulfide (CS2) occurs in the atmosphere and oceans of the Earth. Carbonyl sulfide (OCS) is also well known in nature and is one of many polycarbon oxide sulfides represented by the formula OC S where n < 6. 

Hong Y. and Fegley B. (1997) Formation of carbonyl sulfide (OCS) from carbon monoxide and sulfur vapor and applications to Venus. Icarus 130(2), 495-504. 

The Intramolecular Dynamics of Highly Excited Carbonyl Sulfide (OCS)... 

An interesting exception to the patchiness of atmospheric sulfur compounds is carbonyl sulfide (OCS). This compound, which may be emitted directly or produced by the oxidation of CS2, is highly stable against further oxidation (until it reaches the stratosphere) and so is unavailable for... 

Carbonyl sulfide OCS 500 pptv Biogenic, volcanic, anthropogenic... 

The stratospheric aerosol is composed of an aqueous sulfuric acid solution of 60-80% sulfuric acid for temperatures from — 80 to — 45°C, respectively (Shen et al. 1995). The source of the globally distributed, unperturbed background stratospheric aerosol is oxidation of carbonyl sulfide (OCS), which has its sources at the Earth s surface. OCS is chemically inert and water insoluble and has a long tropospheric lifetime. It diffuses into the stratosphere where it dissociates by solar ultraviolet radiation to eventually form sulfuric acid, the primary component of the natural stratospheric aerosol. Other surface-emitted sulfur-containing species, for example, S02, DMS, and CS2, do not persist long enough in the troposphere to be transported to the stratosphere. 

Precise measurements of the effect of isotopic substitution on hyperfine Zeeman splitting effects [64] have provided the correct direction of the dipole moment for carbon monoxide, CO [65], deuterium iodide, DI [66], and carbonyl sulfide, OCS [67],... 

Ozone-Depleting Potential of Halocarbons 212 Effect of Aircraft Emissions on Stratospheric Ozone 215 Carbonyl Sulfide (OCS) and the Stratospheric Aerosol Layer 216... 

Aydin, M., W. J. De Bruyn and E. S. Saltzman (2002) Pre-industrial atmospheric carbonyl sulfide (OCS) from an Antarctic ice core. Geophysical Research Letters 29, doi 10.1029/ 2002GL014796... 

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