Sulfuryl fluoride in the global atmosphere

Abstract

The first calibrated high-frequency, high-precision, in situ atmospheric and archived air measurements of the fumigant sulfuryl fluoride (SO[subscript 2]F[subscript 2]) have been made as part of the Advanced Global Atmospheric Gas Experiment (AGAGE) program. The global tropospheric background concentration of SO[subscript 2]F[subscript 2] has increased by 5 ± 1% per year from ∼0.3 ppt (parts per trillion, dry air mol fraction) in 1978 to ∼1.35 ppt in May 2007 in the Southern Hemisphere, and from ∼1.08 ppt in 1999 to ∼1.53 ppt in May 2007 in the Northern Hemisphere. The SO[subscript 2]F[subscript 2] interhemispheric concentration ratio was 1.13 ± 0.02 from 1999 to 2007. Two-dimensional 12-box model inversions yield global total and global oceanic uptake atmospheric lifetimes of 36 ± 11 and 40 ± 13 years, respectively, with hydrolysis in the ocean being the dominant sink, in good agreement with 35 ± 14 years from a simple oceanic uptake calculation using transfer velocity and solubility. Modeled SO[subscript 2]F[subscript 2] emissions rose from ∼0.6 Gg/a in 1978 to ∼1.9 Gg/a in 2007, but estimated industrial production exceeds these modeled emissions by an average of ∼50%. This discrepancy cannot be explained with a hypothetical land sink in the model, suggesting that only ∼2/3 of the manufactured SO[subscript 2]F[subscript 2] is actually emitted into the atmosphere and that ∼1/3 may be destroyed during fumigation. With mean SO[subscript 2]F[subscript 2] tropospheric mixing ratios of ∼1.4 ppt, its radiative forcing is small and it is probably an insignificant sulfur source to the stratosphere. However, with a high global warming potential similar to CFC-11, and likely increases in its future use, continued atmospheric monitoring of SO[subscript 2]F[subscript 2] is warranted.