During the NASA Chemical Instrumentation Test and Evaluation 3 sulfur intercomparison over the western Atlantic Ocean, five techniques for the determination of sulfur dioxide were evaluated. The response times of the techniques varied from 3 to 30 min. Based on the ensemble of measurements reported, it was clear that advection of SO2 from the North American continent occurred in the boundary layer (altitude <1 km) with only one exception. The vertical distribution of SO2 above the boundary layer for the northern and southern Atlantic Ocean was remarkably similar during this experiment. ¿ American Geophysical Union 1993