Using Boundary Layer Theory to Improve the Accuracy of Air Release Factors Used in Environmental Exposure Estimations

A realistic release estimation is key when assessing whether the use of a chemical can be considered as environmentally safe. For practically all industrial, professional and consumer use patterns, air emission measurements are absent or available for only 1 or, at best, a handful of volatile chemicals. When using such empirical data in the release estimation of other chemicals, environmental risks will be underpredicted for more volatile chemicals or unnecessarily overpredicted for less volatile chemicals. This short communication describes a pragmatic method to extrapolate release rates between chemicals with different physico-chemical properties used in similar conditions. The method is based on boundary layer theory and confirmed with empirical data. It is applicable to evaporative release from liquids and (semi-)solids. To demonstrate its value and ease-of-use in improving environmental risk assessments, the method was used to generate vapor pressure specific air release factors for hydrocarbons used as industrial laboratory reagents.