Analysis of Sulfur in Deposited Aerosols by Thermal Decomposition and Sulfur Dioxide Analyzer

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A thermal decomposition method that measures aerosol sulfur at the nanogram level directly from the collection substrate is described. A thermal decomposition apparatus was designed. A stainless steel strip was used as the aerosol collection substrate. A 0.1 mol/L MnCl2 solution was added as the thermal decomposition catalyst. Currents were passed through the strip where aerosol particles had been deposited. In this way, the strip was heated at 780 +/- 10 degrees C, and particulate sulfur was evaporated. A sulfur dioxide analyzer (SDA) with flame photometric detector (FPD) was used to detect gaseous sulfur. High sulfur recoveries from (NH4)2SO4 and other inorganic sulfates, such as NH4HSO4, K2SO4, MgSO4, and CaSO4, were obtained. From the sulfur blank and the calibration, a lower limited detection of 0.2 ng of sulfur and the determination range of 3.3-167 ng of sulfur were estimated. The method is effective for measuring the sulfate size distributions of urban aerosols in a small sample air volume of 50-60 L. The method is applicable to measuring the sulfur in aqueous extracts of size-segregated urban aerosols collected by impactor and comparing the results with the sulfate data measured by ion chromatography.