The automated sulfur gas dilution system (ASGDS) was used during the Gas-Phase Sulfur Intercomparison Experiment (GASIE) to generate and analyze test gas mixtures containing pptv levels of SO2 in the presence of various suites of potential measurement interferent gases. These test gas mixtures were provided in a 100 standard liters per minute air matrix manifold, allowing simultaneous sampling by all seven intercomparison participants. The test gas mixtures were homogeneous within the 90-min test periods of the synthetic air phases of GASIE, allowing rigorous intercomparison of any two or more data points obtained during a given test period. A number of delivered SO2 concentrations were successfully replicated throughout the experiment, permitting the collection of a sufficient amount of data for statistical evaluation. The SO2 concentrations measured by the ASGDS quality control instrumentation agreed with values obtained by the intercomparison participants but were different from the set point values.¿ 1997 American Geophysical Union