Determination of total particulate sulfur at Whiteface mountain, New York, by pyrolysis microcoulometry

Abstract

Total paniculate sulfur (TPS) in air samples can be determined by a technique based on thermal volatilization at 1000°C, followed by controlled oxidation of sulfur compounds to SO 2 and coulometric titration of SO 2 with iodine. Calibration curves are linear within 5% from 0.1 to 10 μgS, the detection limit is 0.10μg S (equivalent to 20ng Sm −3 when ~ 1800m 3 of air are filtered), and the relative standard deviations ( n = 10) are 48 and 5.1% at the 0.10 and 4.0 μgS levels. Recoveries for 20 organic and inorganic compounds, including refractory sulfates, elemental sulfur, sulfides, sulfites, sulfonates and sulfones, vary from 79 to 88%. No interferences are observed for a number of non-sulfur-containing compounds, including nitrates, benzene, acetone, glucose, cellulose, silicates and carbonates. The technique was also used to determine the presence of non-sulfates and of non-water-soluble sulfates. Both TPS, using this technique, and water-soluble sulfate (WSS), using the methyl thymol blue method, were determined in daily air particulate samples collected at Whiteface Mountain, NY during both winter and summer. Comparision of TPS and WSS values showed that WSS could usually account for all of the sulfur present in the samples. The TPS concentrations ranged from 0.1 to 9.7μg Sm −3 and the contribution from acid-soluble sulfites and sulfides, elemental sulfur and volatile, S-containing organic compounds was negligible ( < 0.05 μgS m −3).