Compensating for sink effects in emissions test chambers by mathematical modeling

Abstract

Evidence is presented that interior surfaces of a state-of-the-art emissions test chamber can act as a transient sink for organic emissions. The major contribution of this paper is to present a class of mechanistic, mathematical models which accounts for this phenomenon as well as the effect of increasing chamber concentration on the emission rate of the source. A key point is that the effect of the chamber sink can be adjusted out simply by first fitting the appropriate model, then setting to zero the rate constant which governs sink adsorption-absorption. As a consequence of this mathematical development, a source emission rate as a function of time and a steady-state emission rate factor are given precise definitions. Applications involve modeling 1,4-dichlorobenzene emission from moth crystal cake, and mixed emissions from latex caulk. In the first case, at a low air exchange rate and low humidity, the repressive effect of increasing vapor pressure tends to overshadow the sink effect. Increased humidity tends to offset the increase in emission rate which otherwise would occur with increased air exchange. Temperature is the principal determinant of the steady-state emission rate. For the latex caulk, the effect of a sink is to retard the apparent emission rate but lengthen the period of emissions.