The role of biogenic dimethylsulfide from the ocean surface as a source of atmospheric sulfur has so far been largely based on the results of mass balance calculations and on a small number of determinations of DMS in seawater. On a cruise of the R/V Meteor across the Atlantic from Hamburg, F.R.G., to Montevideo, Uruguay, we have sampled the surface ocean at short intervals and analyzed over 300 seawater samples aboard ship immediately after collection. Simultaneously, the atmospheric concentration of DMS has been measured at 13 m above the ocean surface. Biological and chemical oceanographic data have been collected during the cruise to aid in the interpretation of the findings on DMS. A number of vertical profiles to the bottom of the ocean were analyzed for DMS and other parameters. The concentrations of DMS in the surface ocean ranged from 17.7 to 743 ng S(DMS)/1, with a mean of 91 ng S(DMS)/1 (n = 231) for the area traversed. This mean is significantly higher than previous work had suggested. The highest concentrations of DMS were found in productive regions on the continental shelves, in marginal seas and in some estuaries. The vertical distribution of DMS is closely related to the distribution of primary productivity, as measured by chlorophyll and nutrient concentrations. Low concentrations (≤10 ng S(DMS)/1) were found in the deep ocean. From these distributions and from our work on pure cultures of marine algae we conclude that marine primary producers are the dominant source of DMS to seawater and consequently to the atmosphere. The concentrations of DMS in the atmosphere ranged from 2 to 44 ng S(DMS)/m3. The mean concentration of 6.1 ng S(DMS)/m3 is significantly lower than postulated concentrations of 40–200 ng S(DMS)/m3 for marine background atmosphere, thus questioning the rates and mechanisms given for reactions of DMS in this environment. Model calculations for the transfer of DMS across the air‐sea interface, using the data on DMS in seawater and the concentration of DMS in the atmosphere, suggest a global flux of 34–56×1012 g of sulfur in the form of DMS per year from the oceans to the atmosphere.

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A method Is described for the determination of dimethyl sulfide (DMS) at the nanogram level In aqueous solutions. DMS Is removed from aqueous samples by sparging with a He carrier gas stream. The volatile DMS Is trapped cryogenically with liquid nitrogen on a chromatography column that serves as both the trapping and the separation mechanism. After controlled heating to separate DMS from interfering compounds, DMS Is detected by a flame photometric detector. The detection limit Is 0.03 ng of S (DMS), corresponding to a concentration of 0.3 ng L~1 for a 100-mL sample. Precision Is 6.2%. Accuracy, sample storage, and stripping efficiency are also discussed. This procedure has been used to measure DMS In a variety of natural waters.

Prescribed burning is a large aerosol source in the southeastern United States. Its air quality impact is investigated using 3-D model simulations and analysis of ground and satellite observations. Fire emissions for 2002 are calculated based on a recently developed VISTAS emission inventory. March was selected for the investigation because it is the most active prescribed fire month. Inclusion of fire emissions significantly improved model performance. Model results show that prescribed fire emissions lead to approximately 50% enhancements of mean OC and EC concentrations in the Southeast and a daily increase of PM2.5 up to 25 microg m(-3), indicating that fire emissions can lead to PM2.5 nonattainment in affected regions. Surface enhancements of CO up to 200 ppbv are found. Fire count measurements from the moderate resolution imaging spectroradiometer (MODIS) onboard the NASA Terra satellite show large springtime burning in most states, which is consistent with the emission inventory. These measurements also indicate that the inventory may underestimate fire emissions in the summer.