Experimental Measurements of Near-Source Exposure Modeling Parameters

Air concentrations near pollutant sources can be modeled using two-zone and turbulent diffusion models. Each type of model requires a specific pollutant transport parameter: the interzonal air flow (β) is used in the two-zone model and the turbulent diffusion coefficient (DT) in the diffusion model. In this study β and DT were determined experimentally by using concentrations measured around the release of a tracer vapor. A robot arm provided motion in the space near the source to simulate worker actions. Eighty-two experiments were conducted at two room locations and with different robot arm motion programs. β and DT for were calculated using room geometry, ventilation parameters and the measured concentrations during the experiments. The near zone geometry was a 0.4 m hemisphere. The presence of motion in the vicinity of the source was important for the appropriate application of both models. The values of β were log-normally distributed with a mean of 2.03 m3/min, a geometric mean (GM) of 1.65 m3/min (1.42-1.93 95% C.I.) and a geometric standard deviation of 1.82. DT was also log-normally distributed with a mean of 0.586 m2/min, a GM of 0.545 m2/min (0.493-0.600 95% C.I.) and GSD of 1.45. The location within the room had an influence on the value of both β and DT. The use of random airspeed and the free surface area around the source was confirmed as an appropriate method for determining β. A recently developed algorithm was supported as useful for determination of DT. The results strengthen the application of both the two-zone and turbulent diffusion models for worker exposure modeling.