Researchers from the University of Maryland(UMD) and the National Institute of Standards and Technology (NIST)have developed a new and improved technique for the simultaneousmeasurement of sulfur isotopic ratios and concentrations of atmosphericsulfate using snow samples from Greenland and Kyrgyzstan.
Sulfur plays an important role in the Earth's climate. Sulfateparticles in the atmosphere scatter and absorb sunlight, provide"seeds" for cloud formation, and affect the reflectivity and radianceof clouds, and thus the temperatures at the Earth's surface.Atmospheric sulfate comes from natural sources, including oceans andvolcanoes, but a large fraction comes from the burning of fossil fuels.Researchers can distinguish between various natural and anthropogenicsources in snow by measuring sulfur isotopes--forms of the element withdifferent numbers of neutrons.
To study how these particulates have changed over time,scientists dig holes in snow that provide an archive of atmosphericparticles deposited on the Earth's surface. The standard analysistechnique, gas-source isotope ratio mass spectroscopy (GIRMS), requiresrelatively large samples--up to four kilograms (about 9 pounds) of snowand ice, but the cycling of sulfur in the atmosphere is dynamic andvariable, so samples this large blur seasonal changes.
To solve this problem, the UMD/NIST team developed a newanalytical tool based on thermal ionization mass spectrometry (TIMS),which requires much smaller samples. The researchers used an advancedcalibration technique known as double isotopic spiking to correctmeasurement drift and obtain isotope ratio measurements comparable toor better than GIRMS. The smaller snow samples required for TIMS makeit possible to distinguish seasonal changes in sulfur particulatecomposition. The technique also can be used for making highly preciseand accurate measurements of sulfur in low-sulfur fossil fuels, andsimilar applications.
The new technique was presented in a poster* at the 230th NationalMeeting of the American Chemical Society (2005). A description of thetechnique has been accepted for publication in Rapid Communications inMass Spectrometry.
* J. Mann and W.R. Kelly. Measurement of sulfur isotopicsignatures in two high elevation snow pits. American Chemical SocietyAnnual Meeting (2005).
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