Evaluation of evaporation and concentration distribution models--a test chamber study

Occupational exposure to airborne volatile organic compounds is governed by the source strength and dispersion of the pollutant into workroom air. The purpose of the present test chamber study was to validate suggested models for the prediction of evaporation rates and concentration distributions. The study design was organized into different scenarios to simulate workplace conditions. Evaporation rates of organic compounds of different volatilities were recorded gravimetrically and the corresponding concentrations in air were measured at various locations equally distributed in the test chamber. The evaporation models generally showed a fair agreement with experiments but tended to underestimate the evaporation rate especially at low air velocity. Based on factorial experiments a new simple evaporation model was suggested. The performances of the concentration distribution models were of different quality. The model developed by Roach (Annals of Occupational Hygiene 24, 105-132, 1981) cannot be used in predicting the concentration distribution in case of a convective air flow. If knowledge of the evaporation rate and pollutant concentration at some distances from the source were available, the model suggested by Scheff et al. (Applied Occupational and Environmental Hygiene 7, 127-134, 1992) generated a concentration distribution in reasonable agreement with the observed data. The box-model (Sinden, Building and Environment 13, 21-28, 1978) generally offered a fair performance but tended to underestimate the pollutant concentration in a region close to the source in the direction of the main air flow.