A novel technique of using the sample tube penetration profile of trace reactive gases has been applied to the sampling and indirect identification of candidate species through their diffusion coefficients. Laboratory studies of trace dimethyl and methyl hydrogen sulfate flow and their deposition as sulfate to a nylon wall demonstrated that this system can be described theoretically by the modified Gormley-Kennedy equation. Atmospheric samples taken with the penetration sampler in Elkmont, Tennessee, Riverside, California, and Detroit, Michigan exhibited mass deposition spectra that correspond to those of dimethyl and methyl hydrogen sulfate. The profiles were used to estimate the apparent gaseous diffusion coefficient and ambient mass concentration. The estimated diffusion coefficients agree well with semi-empirical theoretical estimates from gas kinetic theory. The estimates of ambient mass of the trace sulfate gas equal or exceed the measurements of fine particulate sulfate; these two variables are not correlated.