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.

Abstract. 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-sak 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 o:•idation 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 f•orn anthropogenic sources. The average production efficiency of' SO2 from DMS oxidation is estimated at 0.87 to 0.91 in most oceanic regions.

[1] In this study, direct measurements of the air/sea flux of acetone were made over the North Pacific Ocean. The results demonstrate that the net flux of acetone is into, rather than out of the oceans. The extrapolated global ocean uptake of 48 Tg yr À1 requires a major revision of the atmospheric acetone budget. This result is consistent with a recent reevaluation of acetone photodissociation quantum yields. Citation: Marandino, C. A., W. J. De Bruyn, S. D.Miller, M. J. Prather, and E. S. Saltzman (2005), Oceanic uptake and the global atmospheric acetone budget, Geophys. Res. Lett., 32, L15806,

[1] Shipboard measurements of air/sea fluxes and sea surface concentrations of dimethylsulfide (DMS) were made over the tropical and midlatitude North Pacific Ocean. Atmospheric pressure chemical ionization mass spectrometry was used to measure DMS levels in ambient air and in air equilibrated with surface seawater drawn from a depth of 5 m. Air/sea fluxes were obtained using eddy covariance. Corrections and uncertainties involved in the calculation of fluxes from shipboard data are discussed. The surface ocean DMS concentrations measured during this study ranged from 1 to 10 nM, and atmospheric mixing ratios ranged from 20 to 1000 ppt. Air/sea fluxes ranged from 0.47 to 39 mmol m À2 d À1 . Most of the variance in the fluxes can be accounted for by variations in sea surface concentration (37%) and wind speed (19%). Gas transfer coefficients derived from the measurements are generally consistent with those derived from deliberate inert gas tracer experiments and eddy covariance measurements of CO 2 . The gas transfer coefficients exhibit wind speed dependence, but the variance in the data is sufficiently large that they do not constrain the functionality of the wind speed dependence of gas exchange.

Biogenic reduced sulfur species are emitted from the oceans and then oxidized in the marine boundary layer. The gas‐liquid interactions of these oxidized species must be understood in order to evaluate the relative contributions to marine boundary layer aerosol levels from anthropogenic and biogenic sources and to assess the overall impact of these aerosols on global climate. A key parameter in understanding these interactions is the mass accommodation coefficient, which is simply the probability that a gas phase molecule enters into a liquid on striking the liquid surface. The mass accommodation coefficients for dimethylsulfoxide, dimethyl sulfone, and methanesulfonic acid into water have been measured as a function of temperature (260–280 K), pH (1–14), and NaCl concentration (0–3.5 M). The experimental method employs a monodispersed train of fast droplets in a low‐pressure flow reactor. The mass accommodation coefficients show a negative temperature dependence varying from ∼0.1 to ∼0.2 over the range of temperatures studied. The measured uptake is independent of pH and NaCl concentration in the ranges studied. The mass accommodation coefficients are well expressed in terms of an observed Gibbs free energy ΔGobs# = ΔHobs# ‐ TΔSobs# as α/(1 ‐ α) = exp (−ΔGobs#/RT). The results are discussed in terms of a previously described uptake model. In the marine boundary layer, mass transfer of these species into aerosols will be limited by mass accommodation for aerosols with diameters of less than 2 μm.

Abstract. Simultaneous air-sea fluxes and concentration differences of dimethylsulfide (DMS) and carbon dioxide (CO 2 ) were measured during a summertime North Atlantic cruise in 2011. This data set reveals significant differences between the gas transfer velocities of these two gases ( k w ) over a range of wind speeds up to 21 m s −1 . These differences occur at and above the approximate wind speed threshold when waves begin breaking. Whitecap fraction (a proxy for bubbles) was also measured and has a positive relationship with k w , consistent with enhanced bubble-mediated transfer of the less soluble CO 2 relative to that of the more soluble DMS. However, the correlation of k w with whitecap fraction is no stronger than with wind speed. Models used to estimate bubble-mediated transfer from in situ whitecap fraction underpredict the observations, particularly at intermediate wind speeds. Examining the differences between gas transfer velocities of gases with different solubilities is a useful way to detect the impact of bubble-mediated exchange. More simultaneous gas transfer measurements of different solubility gases across a wide range of oceanic conditions are needed to understand the factors controlling the magnitude and scaling of bubble-mediated gas exchange.

No abstract

Biogenically produced reduced sulfur compounds, including dimethylsulfide (DMS, CH3SCH3), hydrogen sulfide (H2S), carbon disulfide (CS2), methyl mercaptan (CH3SH), and carbonyl sulfide (OCS), are a major source of sulfur in the marine atmosphere. This source is estimated to contribute 25-40% of global sulfur emissions. These species and their oxidation products, dimethyl sulfoxide (DMSO), dimethyl sulfone (DMSO2), and methane sulfonic acid (MSA), dominate the production of aerosol and cloud condensation nuclei (CCN) in the clean marine atmosphere. The multiphase chemical processes for these species must be understood in order to study the evolving role of combustion-produced sulfur oxides over the oceans. Using a newly developed bubble column apparatus, a series of aqueous phase uptake studies have been completed for the reduced sulfur species DMS, H2S, CS2, CH3SH, and OCS. Aqueous phase uptake has been studied as a function of temperature (278-298 K), p H (1-14), H20 2 concentration (0-1 M), NaC1 concentration (0-5 M), and (NH4)2SO 4 concentration (0-4 M). The Henry's law coefficients for CH3SH and CS2 were determined for the first time, as were the Setchenow coefficients for all the species studied. BRUYN ET AL.' REDUCED SULFUR SPECIES 7247 98, 199-209, 1990. Barret, T. J., G. M. Anderson, and J. Lugowski, The solubility of hydrogen sulfide in 0-5 m NaCI solution at 25øC-95øC and one atmosphere, Geochim. Cosmochim. Acta, 52,807-811, 1988. Barta, L., and D. J. Bradley, Extension of the specific interaction model to include gas-solubilities in high temperature brines, Geochim. Cosmochim. Acta., 49, 195-203, 1985. Chameides, W. L., and A. W. Stelson, Aqueous phase chemical processes in deliquescent sea-salt aerosols: A mechanism that couples the atmospheric cycles of S and sea salt, J. Geophys. Res., 97, 20,565-20,580, 1992. BRUYN ET AL.: REDUCED SULFUR SPECIES 7251