Effect of temperature on stability of sulfur dioxide samples collected by the federal reference method. Final report

This report describes an evaluation of the effect of temperature on the stability of samples collected according to the Environmental Protection Agency procedure for measurement of ambient sulfur dioxide. This evaluation was carried out over the range 35 to 278 micrograms per cubic meter of air sampled. Collected samples were found to decay at a critical temperature-dependent rate. The rate of decay increases five-fold for every 10 degree centigrade increase in temperature over the range 20 to 40 degrees. The rate of decay is independent of concentration over the range studied, and the decay reaction follows first-order kinetics. A mathematical model was developed that allows sample decay to be calculated if the temperature history of the sample is known. Temperature specifications and changes in the procedures necessary to eliminate the decay problem are proposed. (GRA)