The atmospheric chemistry of sulfur dioxide over the tropical South Pacific Ocean is investigated by using results from field measurements and numerical models. Simultaneous real time measurements of sulfur dioxide and its biogenic precursor dimethylsulfide were made at 12°S, 135°W for a 6-day period from March 3 through March 9, 1992. The mean SO₂ and DMS mole fractions were 71 ± 56 pmol mol⁻¹ (1σ) and 453 ± 93 pmol mol⁻¹ (1σ) respectively. These concentrations are compared to those predicted by a time-dependent photochemical box model of the marine boundary layer. Model estimates of the yield of SO₂ from DMS oxidation range from 27% to 54%. Even with low yields, DMS is the dominant source of SO₂ in this region. Estimates of vertical entrainment velocities based on the tropospheric ozone budget suggest that vertical entrainment is a minor source of SO₂. The relative rates of various loss mechanisms for SO₂ are dry deposition to the sea surface (58%), in-cloud oxidation (9%), OH oxidation (5%), and uptake by sea-salt aerosols (28%).

Sulfur hexafluoride has been widely used in field studies and laboratory experiments to develop a relationship between gas transfer and wind speed. The interpretation of the data from such studies requires the diffusion coefficient of SF₆ (D _SF6), which has not previously been measured. In this study, D _SF6 has been determined in pure water and in 35‰ NaCl over a temperature range of 5–25°C. The measurements were made using a continuous-flow diffusion cell where SF₆ flows beneath an agar gel membrane while helium flows above the gel. The experimental data for pure water yielded the following equation: D _SF6=0.029 exp (−19.3/RT, where R is the gas constant and T is temperature in kelvins). Measurements of D _SF6 in 35‰ NaCl were not significantly different from the pure water values. On the basis of our data, we estimate the Schmidt numbers for seawater over the temperature range 5–25° C to be Sc=3016.1–172.00t+4.4996t ²−0.047965t ³, where t is temperature in degrees Celsius.

We have attempted to measure gaseous H₂O₂ in air using an aqueous trapping method. With continuous bubbling, H₂O₂ levels in the traps reached a plateau, indicating that a state of dynamic equilibrium involving H₂O₂ destruction was established. We attribute this behavior to the interaction of ozone and its decomposition products (OH, O₃ ⁻) with H₂O₂ in aqueous solution. This hypothesis was investigated by replacing the air stream with a mixture of N₂, O₂ and O₃. The results of this experiment show that H O was both produced and destroyed in the traps. These results have led us to question the validity of techniques which employ aqueous traps to measure H₂O₂in air.

In this paper we present measurements of methanesulfonate in the Greenland Ice Sheet Project 2 (GISP2) ice core. Methanesulfonate is an atmospheric oxidation product of dimethylsulfide. The GISP2 methanesulfonate record contains information about the atmospheric loading of biogenic sulfur over the past 110 kyr and its relationship to climate change. The GISP2 data set supports the inferences made from the Renland ice core from Greenland that the glacial atmosphere over Greenland had reduced concentrations of biogenic sulfur compared with the present day [Hansson and Saltzman, 1993]. We conclude that the flux of biogenic sulfur from the North Atlantic Ocean must have been lower during glacial times and speculate that this decrease may have been related to differences in phytoplankton speciation. The data suggest that changes in direct radiative forcing from biogenic sulfur aerosols would act as negative feedback to the glacial/interglacial climate cycles in this region.