DMS Emissions Research Articles

Production and release of dimethyl sulfide from the Great Lakes

Dimethyl sulfide has been detected in all the water samples from Lakes Superior, Erie and Ontario. The average concentrations in the surface waters were 5.2 ng l-1 for Lake Superior, 16 ng l-1 (June) and 7.3 ng l-1 (August) for Lake Erie and 27 ng l-1 (June) and 13 ng l-1 (August) for Lake Ontario. The profiles in the water column and the seasonal variations (with highest concentrations following after the crash of spring diatom bloom) suggest that DMS production in these lakes stems primarily from the microbial decomposition of dead algal cells. Only a small fraction (>5%) of the sulfur used in planktonic protein synthesis is converted to DMS, however. The emissions of DMS to the atmosphere were calculated to 49-107-be and 69 tonnes year-1 respectively in Lakes Superior, Erie and Ontario. The biogenic sulfur emissions from the lakes are thus insignificant compared to the contributions from anthropogenic sources in the Great Lakes basin.

Wet deposition of excess sulfate at Macquarie Island, 54� S

Annual wet deposition of excess sulfate at Macquarie Island has been estimated from 5 months of rainwater composition data covering the Austral summer of 1985/86. The resulting figure of 2.1±0.6 mmol/m2/yr is at the low end of previous estimates of maritime excess sulfate deposition by precipitation. Within estimated uncertainty limits this figure is consistent with the DMS emission flux which would be predicted for latitude 50°–60° S, based solely on available Northern Hemispheric DMS measurements.

Emissions of biogenic sulfur gases from a danish estuary

The diurnal variations in sulfur emission were studied at seven sites in a Danish estuary, Norsminde Fjord. The sites comprised grass vegetation, intertidal mud flats, accretions of green algae, an exposed shore and a river outlet. Direct measurements of emission rates from soil and water were done by a dynamic flux chamber technique in connection with gas Chromatographie detection and separation of the cryogenically trapped sulfur gases. Sulfur gas concentrations in air and sea water were measured together with emission rates at 0.5–1 h intervals over 25–40 h periods. DMS was the most important sulfur gas released from grass and algae, while mostly H 2S was released from intertidal mud flats. OCS, CH 3SH and CS 2 were released from most sites at lower rates. Emission of DMS followed the daylight variations, often with a delay towards maximum emission rates in the evening. H 2S was mostly emitted at night or in short outbursts during low tides. Total sulfur emission rates were 1–10μmol Sm −2 d −1. Extreme rates of 335μmol DMSm −2 d −1 were measured over decomposing green algae ( Ulva lactuca). H 2S emission fractions were < 10 −6 to 2.10 −4. H 2S was detected, along with DMS, CH 3SH, OCS and CS 2, in the oxic seawater of the estuary at diurnal mean concentrations of 0.1–6.5nmol S/ol −1 . This may indicate a more widespread occurrence of H 2S in shallow, near-shore waters at nanomolar levels.

On the global natural sulphur emission

A critical review is presented as well as a new attempt to estimate global natural sulphur emission. In view of the considerable uncertainties involved the global biogenic sulphur emission can only be estimated in the range from 50 to 100 Tg S y −1. The open ocean is excluded as a significant source of H 2S; it emits mostly DMS, probably in the order of 30 Tg S y −1. Global emission of OCS and H 2S taken together amounts to about 10% of the total emission of DMS and H 2S. Both the ocean and the continents have a share of about 50% in global biogenic sulphur emission. Inland soils account for about 1 4 of global biogenic sulphur emission. For volcanic sulphur a small value of about 2 Tg S y −1 is considered as being likely. OCS represents about 80% of the total S content of the atmosphere.

Global distribution of sulfur compounds in the troposphere estimated in a height/latitude transport model

A global two‐dimensional time‐dependent model has been used to estimate the tropospheric distributions of sulfur compounds resulting from natural emissions of H2S or DMS and from man‐made emissions of SO2. Comparisons of observations of H2S, DMS, SO2, and SO4− in remote areas with the model estimates indicate that the global flux of H2S and DMS, taken together, amounts to at most a few tens of Tg S yr−1. The present man‐made emissions Of SO2 (about 80 Tg S yr−1) can account for a dominant part of the SO2 and SO4− observed in the lower troposphere of the northern hemisphere. On the other hand, neither natural emissions of H2S and DMS at the surface nor man‐made emissions of SO2 seem to be able to explain the relatively high values of SO2 observed in the middle and upper troposphere in both hemispheres. Our calculations indicate that a relatively long‐lived precursor must be involved as a source for this SO2. The amount of SO2 produced by the oxidation of CS2 and OCS does not seem sufficiently high. Average residence times in the atmosphere for H2S, SO2, and SO4− have been estimated to about 1, 1.5, and 5 days, respectively. If only higher portions of the troposphere are considered, the residence times increase considerably.