You are here:
TOXIC MODELING SYSTEM SHORT-TERM (TOXST)
Description:
The Toxic Modeling System Short-Term (TOXST) addresses the problem of estimating expected exceedances of specified short-term health effects thresholds in the vicinity of continuous and intermittent toxic releases. Certain industrial facilities emit airborne toxic chemicals known to be harmful when their concentrations exceed a specified health effect threshold value for a specified length of time. However, releases of such chemicals often occur intermittently. This random emission pattern makes it difficult to predict the frequency with which ambient concentrations will exceed the health effect threshold (exceedance rate) in the vicinity of a source, since the particular atmospheric dispersion conditions coinciding with each release period cannot be known in advance. An analysis in which worst-case dispersion conditions are assumed to coincide with each release would tend overestimate the exceedance frequency, since a certain proportion of releases is likely to occur under more favorable dispersion conditions. On the other hand, assuming that each release occurs in conjunction with some more favorable dispersion condition, or that the source operates continuously at some long-term average emission rate, would likely underestimate the exceedance rate.