Construction and Performance Verification of a Multi-Stage Standardization System for Sulfur Gases

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The primary goal of this project is to design, construct, and validate a reliable calibration system for preparing ultra- trace gas standards for five sulfur-containing compounds; hydrogen sulfide, sulfur dioxide, carbonyl sulfide, carbon disulfide, and dimethylsulfide. Although these sulfur species are of major atmospheric importance, the measurement equivalency of the different analytical methods used for their analysis is often unknown. Consequently, an intercomparison project is being developed by the scientific community to address this issue. The central calibration system built during this initial phase of the overall intercomparison project will provide the reference gas standards required to access the performance characteristics of the various analytical techniques. This calibration system will consist of a three-stage dynamic dilution apparatus that contains a source of sulfur-free zero dilution air, an all-Teflon flow network, compressed gas cylinders as the source of each sulfur gas, electronic mass- flow controllers for the precise regulation of all gas flows, and separate inlet systems for the introduction of potential matrix interferences. Concentrations of the sulfur gas standards prepared by the calibration system will cover a range from 950 pptv to 12pptv and have a maximum uncertainty of less than 7%.//