| This paper illustrates an instrumental methodology developed for sourcing aerosol sulfate collected on 2.5 micron particulate (PM2.5) air filters by the use of sulfur isotope ratios signatures. The technique, utilizing a VG Axiom high resolution inductively coupled plasma mass spectrophotometer (HR-ICP-MS) equipped with a single collector, is capable of distinguishing delta 34S values in 24 hour collection-cycle Federal Reference Material (FRM) PM2.5 and in various coal and petroleum sources (+32 to -30 ppt), generating a precision of 0.055 (0.25% RSD) for 32S/ 34S ratio measurements. The technique precludes usage of specialized introduction equipment or sample preconcentration steps while incorporating magnetic rather than acceleration voltage scanning for mass selection as typical of isotope abundance measurements. An additional benefit is that multielemental analyses can be performed utilizing the same sample preparation and equipment setup. The technique was validated using sulfur isotope standard NIST SRM 8556. Results are presented for sulfur isotope ratio measurements on PM 2.5 derived from large-scale combustion experiments of various fuel oils and coals, from EPA air particulate samples gathered in the Saint Louis area and from locally collected air samples. |
