Trichlorofluoromethane (CCl₃F; CFC-11) and dichlorodifluoromethane (CCl₂F₂; CFC-12) have been widely used as tracers of oceanic circulation and mixing on decadal timescales. In order to estimate their transfer rate across the air-sea interface, liquid-phase diffusion coefficients are needed In this study the diffusivities of CFC-11 and CFC-12 in pure water were measured over the temperature range 0.6–30°C. Diffusivities of CFC-11 in pure water ranged from (5.24±0.25)×10⁻⁶ cm²S⁻¹ at 0.6°C to (1.13±0.05)×10⁻⁵ cm²S⁻¹ at 30.3°C and a fit to the data yielded the equation D _CFC-11 = 0.015 exp (−18.1/RT), where R is the universal gas constant in kJ mol⁻¹ K⁻¹ and T is the temperature in Kelvin. Diffusivities of CFC-12 in pure water ranged from (5.38±0.22)×10⁻⁶ cm² s⁻¹ at 0.6°C to (1.26±0.05)×10⁻⁵ cm² s⁻¹at 30.3°C and the temperature dependence can be expressed as D_CFC-12= 0.036 exp (−20.1/RT). The estimated uncertainty in both equations is <3%. Experiments were also carried out in seawater for each compound. For CFC-11 the diffusivity in seawater was not significantly different from that in pure water. However, the diffusivity of CFC-12 in seawater was found to be 7.2±3.0% lower than that in pure water. Schmidt numbers for both CFC-11 and CFC-12 in pure water and seawater were estimated from the data.

Measurements of seawater dimethylsulfide (DMS), atmospheric dimethylsulfide, and sulfur dioxide (SO₂) were made on board the R/VDiscoverer in the Southern Ocean, southeast of Australia, as part of the First Aerosol Characterization Experiment (ACE 1). The measurements covered a latitude range of 40°S–55°S during November-December 1995. Seawater DMS concentrations ranged from 0.4 to 6.8 nM, with a mean of 1.7±1.1 nM (1σ). The highest DMS concentrations were found in subtropical convergence zone waters north of 44°S, and the lowest were found in polar waters south of 49°S. In general, seawater DMS concentrations increased during the course of the study, presumably due to the onset of austral spring warming. Atmospheric DMS concentrations ranged from 24 to 350 parts per trillion by volume (pptv), with a mean of 112±61 pptv (1σ). Atmospheric SO₂ was predominantly of marine origin with occasional anthropogenic input, as evidenced by correlation with elevated ²²²Rn and air mass trajectories. Concentrations ranged from 3 to 1000 pptv with a mean of 48.8± 49 pptv (1σ) and a median 15.8 pptv. The mean SO₂ concentration observed in undisturbed marine air was 11.9±7.6 pptv (1σ), and the mean DMS to SO₂ ratio in these conditions was 13±9 (1σ). Diurnal variations in SO₂ were observed, with a daytime maximum and early morning minimum in agreement with model simulations of DMS oxidation in the marine boundary layer. Steady state calculations and photochemical box model simulations suggest that the DMS to SO₂ conversion efficiency in this region is 30–50%. Comparison of these results with results from warmer regions suggests that the DMS to SO₂ conversion efficiency has a positive temperature dependence.

We present a detailed evaluation of the atmospheric sulfur cycle simulated in the Georgia Tech/Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model. The model simulations of SO₂, sulfate, dimethylsulfide (DMS), and methanesulfonic acid (MSA) are compared with observations from different regions on various timescales. The model agrees within 30% with the regionally averaged sulfate concentrations measured over North America and Europe but overestimates the SO₂ concentrations by more than a factor of 2 there. This suggests that either the emission rates are too high, or an additional loss of SO₂ which does not lead to a significant sulfate production is needed. The average wintertime sulfate concentrations over Europe in the model are nearly a factor of 2 lower than measured values, a discrepancy which may be attributed largely to the sea-salt sulfate collected in the data. The model reproduces the sulfur distributions observed over the oceans in both long-term surface measurements and short-term aircraft campaigns. Regional budget analyses show that sulfate production from SO₂ oxidation is 2 to 3 times more efficient and the lifetimes of SO₂ and sulfate are nearly a factor of 2 longer over the ocean than over the land. This is due to a larger free tropospheric fraction of SO₂ column over the ocean than over the land, hence less loss to the surface. The North Atlantic and northwestern Pacific regions are heavily influenced by anthropogenic activities, with more than 60% of the total SO₂ originating from anthropogenic sources. The average production efficiency of SO₂ from DMS oxidation is estimated at 0.87 to 0.91 in most oceanic regions.

The goals of the International Global Atmospheric Chemistry (IGAC) Program's First Aerosol Characterization Experiment (ACE 1) are to determine and understand the properties and controlling factors of the aerosol in the remote marine atmosphere that are relevant to radiative forcing and climate. A key question in terms of this goal and the overall biogeochemical sulfur cycle is what factors control the formation, growth, and evolution of particles in the marine boundary layer (MBL). To address this question, simultaneous measurements of dimethylsulfide (DMS), sulfur dioxide (SO₂), the aerosol chemical mass size distribution, and the aerosol number size distribution from 5 to 10,000 nm diameter were made on the National Oceanic and Atmospheric Administration (NOAA) ship Discoverer. From these data we conclude that the background MBL aerosol during ACE 1 often was composed of four distinct modes: an ultrafine (UF) mode (D_p  = 5–20 nm), an Aitken mode (D_p  = 20–80 nm), an accumulation mode (D_p  = 80–300 nm), and a coarse mode (D_p  > 300 nm). The presence of UF mode particles in the MBL could be explained by convective mixing between the free troposphere (FT) and the MBL associated with cloud pumping and subsidence following cold frontal passages. There was no evidence of major new particle production in the MBL. Oceanic emissions of DMS appeared to contribute to the growth of Aitken and accumulation mode particles. Coarse mode particles were comprised primarily of sea salt. Although these particles result from turbulence at the air-sea interface, the instantaneous wind speed accounted for only one third of the variance in the coarse mode number concentration in this region.