Measurement of sulfur isotope ratios in micrometer-sized samples by NanoSIMS B. Winterholler a, * , P. Hoppe b , M.O. Andreae a , S. Foley c a Max Planck Institute for Chemistry, Department of Biogeochemistry, P.O. Box 3060, D-55020 Mainz, Germany b Max Planck Institute for Chemistry, Particle Chemistry Department, P.O. Box 3060, D-55020 Mainz, Germany c Johannes Gutenberg University, Department of Mineralogy, Joh.-J.-Becher-Weg 21, D-55099 Mainz, Germany Received 12 September 2005; accepted 15 February 2006 Available online 12 May 2006 Abstract Sulfur isotope ratios of atmospheric aerosol particles can provide detailed information with regard to the origin and the transport of sulfur in the environment. The new Cameca NanoSIMS 50 ion microprobe technique permits analysis of individual aerosol particles with volumes down to 0.5 mm 3 and a precision for d 34 S of 3–10% (2s). This technique will set new standards in the analysis of isotope ratios in atmospheric aerosol. For the first time it is possible to directly compare chemical and isotopic composition of individual aerosol particles, identify internal and external mixtures and investigate reactions of anthropogenic gases with natural aerosol such as sea salt and mineral dust. # 2006 Elsevier B.V. All rights reserved. Keywords: Sulfur isotopic composition; Aerosol particles; NanoSIMS 1. Introduction Sulfate particles formed by the condensation of gaseous precursors contribute significantly to the sub-micron aerosol. As these particles are extremely efficient light scatterers and cloud condensation nuclei, their direct and indirect radiative effects influence the Earth’s climate [1]. Gaseous precursors are released as a result of anthropogenic activity (fossil fuel and biomass burning, 60–100 Teragram sulfur per year (TgS/year) as well as from natural sources (volcanic gases and dimethyl sulfide (DMS), 30–100 TgS/year) [2,3].A major contribution to the coarse mode sulfate comes from mineral dust as well as sea salt. However, in competition to direct nucleation, gaseous species also condense on existing surfaces and undergo reactions. The new NanoSIMS technique [4] will for the first time enable direct investigation of the importance of reactions of anthropogenic and biogenic sulfur on natural surfaces such as sea salt aerosol and mineral dust. Sulfur isotope analysis of aerosol provides information about the sources of atmospheric sulfate. Bulk analyses of aerosol samples show values of d 34 S, [5] d 34 S ¼  ð 34 S= 32 SÞ sample ð 34 S= 32 SÞ VCDT   1   1000; ð 34 S= 32 SÞ ViennaCannonDiaboloTroilite ¼ 0:044163 between 40 and +40% (Fig. 1) [5]. Extreme ratios in bulk samples are closely related to point sources with a distinct isotopic composition. Typical values for sulfate bulk analysis fall between +5 and +20% [6]. The new single particle tech- nique permits to quantify the contribution of distinct sources more precisely and even identify sources that do not contribute substantially to the average isotopic composition of the sample. 2. Experimental Two samples were chosen to assess the potential of the new technique. Aerosol sample #1 was taken during a cruise in the tropical South Atlantic (18–20 March 1991 [7]). Sample #2 was taken on a cruise in North Atlantic (478N, 198W) on a day the ship encountered a dust storm (29/30 April 1992 [8]). For the SIMS and SEM analyses a piece of both Nuclepore filters was www.elsevier.com/locate/apsusc Applied Surface Science 252 (2006) 7128–7131 * Corresponding author. Fax: +49 6131 305 579. E-mail address: winterho@mpch-mainz.mpg.de (B. Winterholler). 0169-4332/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.apsusc.2006.02.150