Sulfur containing particles and gases are found in ambient air everywhere over land and sea. Due to the reactivity and aerosol-forming properties of sulfur compounds, they play major roles in acid rain, Arctic haze, air pollution, and cloud formation. In recent years, there has been growing interest in the magnitude and composition of natural sulfur emissions, mainly because these compounds make a significant contribution to the atmospheric loading of sulfate aerosols. Evidence suggest that sulfate aerosols have a significant influence on the climate, comparable to that produced by greenhouse gases. The uncertainty of this influence is not know to a factor of 2 or 3 however.
The largest natural source of sulfur to the atmosphere is dimethyl sulfide (DMS) which results from the metabolism of phytoplankton, ubiquitous in the surface waters of the world's oceans. Indirect evidence strongly suggests that Arctic ocean regions may contribute significantly to the atmospheric sulfur budget through DMS production. The evidence includes: (1) satellite measurements of ocean color (as an indicator of phytoplankton biomass) show high biological productivity in polar ocean regions, (2) Chukchi Sea seawater DMS measurements are relatively high compared to the rest of the Pacific Ocean, and (3) several DMS airborne measurements in the marine boundary layer near Barrow are among some of the highest concentrations ever measured, although atmospheric measurements of DMS in Arctic regions have been few.
In an effort to assess the spatial and temporal variability of Arctic ocean region DMS emissions, we first constructed a sulfur chemiluminescence detector (SCD). We then interfaced the SCD to a gas chromatograph (GC) specifically equipped to separate the sulfur species of interest. The GC-SCD is selective and sensitive enough to quantify many sulfur gases in the atmosphere at the parts -per-trillion level, but because it requires a computer, gas cylinders and accessories it is not very transportable or rugged enough yet to withstand strong seas. A sampling method using molecular sieve as adsorbent enables collecting DMS samples for later laboratory analysis. During September of 1995, 76 sulfur gas samples were collected from the R/V Alpha Helix while on a research cruise in the Bering and Chukchi Seas. Sampling locations and some preliminary results are indicated on the map. Once all the samples are analyzed and validated, correlations between DMS emissions and parameters such as, chlorophyll content, cloud cover, sea and air temperatures, salinity, and presence of ice will be investigated. These correlations may become part of a global climate model or be used in an algorithm for estimating global DMS flux using remotely sensed data of the important parameters.
This research is currently on-going, and will become part of a larger field campaign scheduled for the spring of 1996 at Katchemak Bay, Alaska. Our research group will be studying the transformation of the sulfur gases through oxidized sulfur species to sulfate aerosols. This will help answer some of the current questions being asked about how sulfate aerosols are influencing climate both locally and globally.
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