Henry's Law constants and the air-sea exchange of various low molecular weight halocarbon gases



The McAuliffe (1971) multiple equilibration technique has been used to measure the Henry's Law constants (H) for a variety of low molecular weight halocarbon gases in distilled and sea waters at a number of temperatures. The following equations are best-fit lines from van't Hoff plots of the results: Freon-11, In H = −2652/T + 10.50 (seawater) and In H = −2312/T + 9.25 (distilled water); Methyl Iodide, In H = −3541/T + 10.34 (distilled water); Chloroform, In H = −3649/T + 10.63 (seawater); Methyl Chloroform, In H = −3905/T + 13.04 (seawater) and In H = −2915/T + 9.15 (distilled water); Carbon Tetrachloride, In H = −3230/T + 11.27 (seawater) and In H = −2918/T + 9.77 (distilled water); where T is the temperature in degrees absolute.

Halocarbon measurements made on an oceanographic cruise from 48° N to 65° S in the Atlantic in late 1981 indicate a small but statistically significant difference in atmospheric concentrations of Freon-11 between N and S hemispheres (198.8 and 184.7 pptv, respectively). In contrast, similar measurements for carbon tetrachloride show no significant inter-hemispheric gradient. Surface water concentrations of carbon tetrachloride are much higher at low southern latitudes compared to further north, concomitant with the lower water temperatures, and hence higher solubilities, between 30 and 60° S. However, using the Henry's Law constants reported in this paper, the surface water over the whole section appears to be close to equilibrium with respect to the concentration of carbon tetrachloride in the overlying air, a situation identical to that currently found for Freon-11 in the N. Pacific (Gammon et al., 1982).