The most abundant sulfur gas in the lowest layer of the Earth's atmosphere is carbonyl sulfide. While carbonyl sulfide is formed naturally, it is also produced through a chemical reaction in the atmosphere involving carbon disulfide, a chemical produced by a variety of industrial processes. Human-produced carbonyl sulfide has attracted attention as a possible source of increased levels of sulfate particles, or aerosols, in the atmosphere, which have been linked to depletion of the ozone layer. Sulfate aerosols also influence global climate, causing cooling effects by scattering incoming solar rays and reducing the amount of radiation that reaches the Earth.
New estimates obtained from ice core samples collected from the Siple Dome, West Antarctica, suggest that human activities have contributed approximately 25 percent of the modern carbonyl sulfide in the atmosphere. The results of the study, based on the first such measurements taken from ice, by Murat Aydin and colleagues at the University of California at Irvine, are published this month in the journal, Geophysical Research Letters, published by the American Geophysical Union.
The collected ice core samples provide researchers with an archive of air from 1616 to 1694, allowing them to determine the concentration of carbonyl sulfide prior to industrial inputs. To collect air trapped within the ice, the researchers crushed the eleven core samples within a vacuum. The samples were then analyzed to obtain a mean carbonyl sulfide mixing ratio, or concentration of carbonyl sulfide in the sample, expressed in parts per trillion by volume (pptv), over the 78-year period.
This pre-industrial mixing ratio is approximately three-quarters that of the modern carbonyl sulfide mixing ratio, suggesting that approximately 25 percent of the modern atmospheric carbonyl sulfide is generated through human activity.
The researchers also found no loss of carbonyl sulfide from the ice cores over time. This means that with further measurements, it should be possible to generate a record of atmospheric carbonyl sulfide concentrations further back through time, and allow researchers to develop a baseline against which to measure current carbonyl sulfide levels. Because the gas is generated both naturally and through human activities, a baseline would help scientists assess the effect of human activity on carbonyl sulfide, and ultimately sulfate aerosols, in the upper atmosphere.
The researchers also note that developing a paleoatmospheric record of carbonyl sulfide will allow them to better understand the natural variability associated with the complicated sources and sinks of carbonyl sulfide, and to study how climate influences biogeochemical cycles over time.