Atmospheric Sulfur Species Research Articles

Coherence between seasonal cycles of dimethyl sulphide, methanesulphonate and sulphate in marine air

THEeffect of cloud condensation nuclei (CCN) in controlling cloud albedo and hence global climate has prompted questions about the factors that control CCN populations. Charlson et al.1 suggested that marine phytoplankton might control CCN populations. The effect would be strongest over the oceans, where low stratiform clouds are common, and CCN are composed mostly of ammonium sulphate believed to be produced by atmospheric oxidation of gaseous dimethyl sulphide (DMS) emitted by phytoplankton. Here we present twenty months of data from a clean marine site at 40° S, which confirm the connection between atmospheric DMS and aerosol sulphur species that is central to the hypothesis of Charlson et al.1. The relationships between DMS, aerosol sulphate and CCN are nonlinear, implying that at this site there would be significant nonlinearities in the climate feedback mechanism. In addition, our data on atmospheric sulphur species show a strong seasonal cycle, indicating that it should be possible to look for large, natural, seasonal variations in cloud albedo as a rigorous test of the Charlsonet al. hypothesis.

The atmospheric sulfur cycle over the Amazon Basin: 2. Wet season

We determined the fluxes and concentrations of atmospheric sulfur species at ground level and from aircraft over the Amazon Basin during the 1987 wet season, providing a comprehensive description of the sulfur cycle over a remote tropical region. The vertical profile of dimethylsulfide (DMS) during the wet season was found to be very similar to that measured during the dry season, suggesting little seasonal variation in DMS fluxes. The concentrations of hydrogen sulfide (H2S) were almost an order of magnitude higher than those of DMS, which makes H2S the most important biogenic source species in the atmospheric sulfur cycle over the Amazon Basin. Using the gradient‐flux approach, we estimated the flux of DMS at the top of the tree canopy. The canopy was a source of DMS during the day, and a weak sink during the night. Measurements of sulfur gas emissions from soils, using the chamber method, showed very small fluxes, consistent with the hypothesis that the forest canopy is the major source of sulfur gases. The observed soil and canopy emission fluxes are similar to those measured in temperate regions. The concentrations of SO2 and sulfate aerosol in the wet season atmosphere were similar to dry season values. The sulfate concentration in rainwater, on the other hand, was lower by about a factor of 5 during the wet season. Due to the higher precipitation rate, however, the wet deposition flux of sulfate was not significantly different between the seasons. The measured fluxes and concentrations of DMS, H2S, and SO2 were consistent with a model describing transport and chemistry of these sulfur species in the boundary layer. The concentrations of aerosol and the sulfate deposition rate, on the other hand, could only be explained by import of significant amounts of marine and anthropogenic sulfate aerosol into the Amazon Basin.

Study Traces Most SO Emissions To Burning of Moderate-Sulfur Coal

Electric utilities burning moderatesulfur coal—not those that use highsulfur coal—are the major source of sulfur dioxide emissions implicated in acid rain, a study by the Department of Energy's Pittsburgh Energy Technology Center (PETC) concludes. These emissions could be cut in half without having to change coal sources or boilers if promising coal-cleaning technologies are successfully developed, the study finds. The results of the acid rain control initiative study were presented by PETC chemist Dennis H. Finseth at a symposium on controlling emissions from coal combustion. The session was part of a three-day symposium on acid rain that included presentations on atmospheric sulfur species and the effects of acid deposition on soil, water, and materials, as well as strategies for controlling emissions of acid precursors. We need to know where sulfur dioxide is coming from—both the geographical origin and what combustion technology produces it, Finseth says. Without that information it is hard to cons...

An analysis of the first year of MAP3S rain chemistry measurements

We have analysed rain chemistry measurements from the MAP3S program to derive numerical values of parameters for theoretical models of wet deposition of sulfur. These agree generally with values estimated earlier for Western Europe; the probability of rain is approximately equal to 0.12, the characteristic rainout rate about 0.3 h −1, and the residence time for atmospheric sulfur species about 100 h. Both SO 4 2− and NO 3 − affect the pH at all stations. Factor analyses and meteorological analysis of selected high deposition events reveal inadequacies in present reporting and collecting procedures. From these we derive recommendations for future rain chemistry measurement programs.

Saharan aerosols over the tropical North Atlantic — Mineralogy

Quantitative aerosol samples were collected on filters during three major Saharan dust outbreaks as they passed across the tropical North Atlantic Ocean during the summer of 1974. The sampling sites were: Sal Island, Cape Verde Islands; Barbados, West Indies; Miami, Florida. The dominant mineral group was mica—illite; the mean concentration at each station ranged from 54% at Sal Island to 64% at Barbados. Quartz was the second most abundant mineral with concentrations ranging from 20% at Sal Island to 14% at Barbados and Miami. Also present were kaolinite, chlorite, microcline, plagioclase and calcite — all at concentrations less than 10%. At each sampling site, the composition of the dust was relatively constant during all three dust episodes. However, there were significant differences between the mean composition at Sal Island and those at Barbados and Miami; the most notable difference was that the concentration of quartz decreased and that of the clays increased during the transit of the Atlantic. These changes are ascribed to the more rapid removal of quartz (relative to the clays) because of its relatively larger mass median diameter and, consequently, its greater settling velocity in the atmosphere. The dusts did not contain any primary halite or gypsum; abundant amounts of gypsum were measured in the samples but this gypsum was found to be a conversion product of calcite reacting with atmospheric sulfur species. The mineralogy of the Saharan dusts is similar to that of the clay fraction of sediments in the tropical North Atlantic with the exception of montmorillonite which was barely detectable in the dusts; this discrepancy may be ascribed, at least in part, to differences in analytical techniques. The mineralogy of Saharan dust is similar to that of an average shale. This similarity can be attributed to genetic factors and to the effect of winnowing.