Evaluation of the DMS flux and its conversion to SO2 over the southern ocean

Shon, Zang–Ho; Davis, Douglas D.; Chen, G.; Grodzinsky, G.; Bandy, A. R.; Thornton, D. C.; Sandholm, S. T.; Bradshaw, J. D.; Stickel, R. E.; Chameides, W. L.; Kok, Gregory L.; Russell, Lynn M.; Mauldin, L.; Tanner, David J.; Eisele, F. L.

doi:10.1016/s1352-2310(00)00166-7

Cited by 41 publications

(26 citation statements)

References 42 publications

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“…The oxidation of DMS in the atmosphere has been modeled previously given an estimate of OH (Shon et al, 2001;Nowak et al, 2001). Using a similar approach and building upon Eq.…”

Section: Reproducing the Diurnal Cycle Of Dmsmentioning

confidence: 99%

Constraining the concentration of the hydroxyl radical in a stratocumulus-topped marine boundary layer from sea-to-air eddy covariance flux measurements of dimethylsulfide

2009

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Abstract. The hydroxyl radical (OH) is an important oxidant in the troposphere due to its high reactivity and relative abundance. Measuring the concentration of OH in situ, however, is technically challenging. Here we present a simple method of estimating an OH-equivalent oxidant concentration ("effective OH") in the marine boundary layer (MBL) from the mass balance of dimethylsulfide (DMS). We use shipboard eddy covariance measurements of the sea-to-air DMS flux from the Vamos Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REx) in October and November of 2008. The persistent stratocumulus cloudcover off the west coast of South America and the associated strong inversion between MBL and the free troposphere (FT) greatly simplify the dynamics in this region and make our budget estimate possible. From the observed diurnal cycle in DMS concentration, the nighttime entrainment velocity at the inversion is estimated to be 4 mm s −1 . We calculate 1.4(±0.2)×10 6 OH molecules cm −3 from the DMS budget, which represents a monthly effective concentration and is well within the range of previous estimates. Furthermore, when linearly proportioned according to the intensity of solar flux, the resultant diel OH profile, together with DMS surface and entrainment fluxes, enables us to accurately replicate the observed diurnal cycle in DMS (correlation coefficient over 0.9). The nitrate radical (NO 3 ) is found to have little contribution to DMS oxidation during VOCALS-REx. An upper limit estimate of 1 pptv of bromine oxide radical (BrO) would account for 30% of DMS oxidation and lower the OH concentration to 1.0×10 6 OH molecules cm −3 . Our effective OH estimate includes the oxidation of DMS by such radicals.

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“…The oxidation of DMS in the atmosphere has been modeled previously given an estimate of OH (Shon et al, 2001;Nowak et al, 2001). Using a similar approach and building upon Eq.…”

Section: Reproducing the Diurnal Cycle Of Dmsmentioning

confidence: 99%

Constraining the concentration of the hydroxyl radical in a stratocumulus-topped marine boundary layer from sea-to-air eddy covariance flux measurements of dimethylsulfide

2009

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“…We adopt a time constant for this process that results in 95% equilibration over ∼1 h, in keeping with the observations and models of Harrison and Kitto [50] and Quinn et al [22] Initial conditions and default parameter values are selected to represent typical 'average' conditions in the global remote ocean and MBL, particularly the Southern Ocean. The seawater ammonium concentration is taken as a high-latitude average concentration of 150 nM after Johnson [21] ; the sulfate input is considered as a per-unit area flux and is taken as the mean value of the Southern Ocean DMS flux observed by Shon et al [51] (1.3 µmol m −2 day −1 ), multiplied by their mean observed SO 2 conversion factor of 0.6, giving a sulfate input of 0.5 nmol m −2 min −1 . The aerosol loss term is selected to maintain a constant sulfate loading, although the NH + 4 : nss-SO 2− 4 ratio is entirely insensitive to this term as ammonium and sulfate are removed from the model atmosphere in the same ratio as they exist in the aerosol.…”

Section: Model Descriptionmentioning

confidence: 99%

Coupling between dimethylsulfide emissions and the ocean - atmosphere exchange of ammonia

Johnson

Bell

2008

Environ. Chem.

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Environmental context. Dimethylsulfide (DMS) is recognised as a potentially significant climate-forcing gas, owing to its role in particle and cloud formation in the marine atmosphere, where it is the dominant source of acidity. Ammonia, the dominant naturally occurring base in the atmosphere, plays an important role in neutralising particles formed from DMS oxidation products and may even enhance the formation rate of new particles. A biogeochemical coupling has previously been proposed between DMS and ammonia fluxes from the ocean to the atmosphere, in the form of coproduction of the two gases in seawater. We revise this suggestion by introducing the concept of 'co-emission' of the gases, where DMS emission controls the rate of emission of ammonia from the ocean by acidifying the atmosphere. Abstract.A strong correlation between aerosol ammonium and non-sea salt sulfate is commonly observed in the remote marine boundary layer. It has been suggested that this relationship implies a biogeochemical linkage between the nitrogen (N) and sulfur (S) cycles at the cellular biochemical level in phytoplankton in the ocean, or a linkage in the atmosphere (see P. S. Liss and J. N. Galloway, Interactions of C, N, P and S biogeochemical cycles and global change (Springer, 1993), and P. K. Quinn et al. in J. Geophys. Res. -Atmos. 1990, 95). We argue that an oceanic linkage is unlikely and draw on mechanistic and observational evidence to make the argument that the atmospheric connection is based on simple physical chemistry. Drawing on an established analogous concept in terrestrial trace gas biogeochemistry, we propose that any emission of dimethylsulfide (DMS) from the ocean will indirectly influence the flux of NH 3 from the ocean, through the neutralisation of acidic DMS oxidation products and consequent lowering of the partial pressure of NH 3 in the atmosphere. We present a simple numerical model to investigate this hypothesised phenomenon, using a parameterisation of the rate and thermodynamics of gas-to-particle conversion of NH x and explicitly modelled oceanatmosphere NH 3 exchange. The model indicates that emission of acidic sulfur to the atmosphere (e.g. as a product of DMS oxidation) may enhance the marine emission of NH 3 . It also suggests that the ratio of ammonium to non-sea salt sulfate in the aerosol phase is strongly dependent on seawater pH, temperature and wind speed -factors that control the ocean-atmosphere ammonia flux. Therefore, it is not necessary to invoke a stoichiometric link between production rates of DMS and ammonia in the ocean to explain a given ammonium to non-sea salt sulfate ratio in the aerosol. We speculate that this mechanism, which can provide a continuous resupply of ammonia to the atmosphere, may be involved in a series of biogeochemical-climate feedbacks. His research interests are biogeochemical cycles taking place both within and between the ocean and its overlying atmosphere, with a focus on biogenic trace gases. He is currently working with Peter Liss as part of the Surfac...

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“…But it was not until a field campaign deployed on Christmas Island in the Equatorial Pacific that a clear diurnal pattern was observed in both species, 180°out of phase (Bandy et al 1996). Since then others have confirmed similar relationships (De Bruyn et al 1998Shon et al 2001) but the SO 2 yield remains uncertain. A recent survey of 20 modeling and experimental studies by Faloona (2009) illustrates the scientific ambiguity of this single product yield, which ranges from 0.3 to 0.98.…”

Section: Introductionmentioning

confidence: 99%

Sulfur dioxide in the tropical marine boundary layer: dry deposition and heterogeneous oxidation observed during the Pacific Atmospheric Sulfur Experiment

et al. 2009

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Research flights with the National Center for Atmospheric Research (NCAR) C-130 airborne laboratory were conducted over the equatorial ocean during the Pacific Atmospheric Sulfur Experiment (PASE). The focused, repetitive flight plans provided a unique opportunity to explore the principal pathways of sulfur processing in remote marine environments in close detail. Fast airborne measurements of SO 2 using the Drexel University APIMS (Atmospheric Pressure Ionization Mass Spectrometer) instrument further provided unprecedented insight into the complete budget of this important sulfur gas. In general, turbulent mixing in the marine boundary layer (MBL) continuously depletes SO 2 due to the shallow convection of the tropical trade wind regime by venting the gas into the buffer layer (BuL) above. However, on nearly one-third of the flights a net import of SO 2 into the MBL from the BuL was observed. Concurrent measurements of the DMS budget allowed for a heterogeneous S(IV) oxidation rate to be inferred from the SO 2 budget residual. The average heterogeneous loss rate was found to be 0.05 h −1 , which taken in conjunction with the observed aerosol surface area distributions and O 3 levels indicates that the supermicron aerosols maintain a near neutral pH. The average dry deposition velocity of SO 2 was found to be 0.4 cm s −1 , about 30% lower than predicted by standard parameterizations. The yield of SO 2 from DMS oxidation was found to be near unity. The mission averages indicate that approximately 57% of the SO 2 in the MBL is lost to aerosols, 27% is subject to dry deposition, 7% is mixed into the BuL, and 10% is oxidized by OH.

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Evaluation of the DMS flux and its conversion to SO2 over the southern ocean

Cited by 41 publications

References 42 publications

Constraining the concentration of the hydroxyl radical in a stratocumulus-topped marine boundary layer from sea-to-air eddy covariance flux measurements of dimethylsulfide

Constraining the concentration of the hydroxyl radical in a stratocumulus-topped marine boundary layer from sea-to-air eddy covariance flux measurements of dimethylsulfide

Coupling between dimethylsulfide emissions and the ocean - atmosphere exchange of ammonia

Sulfur dioxide in the tropical marine boundary layer: dry deposition and heterogeneous oxidation observed during the Pacific Atmospheric Sulfur Experiment

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