title: Turbulent eddy diffusion models in exposure assessment - Determination of the eddy diffusion coefficient.
abstract: The use of the turbulent eddy diffusion model and its variants in exposure assessment is limited due to the lack of knowledge regarding the isotropic eddy diffusion coefficient, DT. But some studies have suggested a possible relationship between DTand the air changes per hour (ACH) through a room. The main goal of this study was to accurately estimate DTfor a range of ACH values by minimizing the difference between the concentrations measured and predicted by eddy diffusion model. We constructed an experimental chamber with a spatial concentration gradient away from the contaminant source, and conducted 27 3-hr long experiments using toluene and acetone under different air flow conditions (0.43-2.89 ACHs). An eddy diffusion model accounting for chamber boundary, general ventilation, and advection was developed. A mathematical expression for the slope based on the geometrical parameters of the ventilation system was also derived. There is a strong linear relationship between DTand ACH, providing a surrogate parameter for estimating DTin real-life settings. For the first time, a mathematical expression for the relationship between DTand ACH has been derived that also corrects for non-ideal conditions, and the calculated value of the slope between these two parameters is very close to the experimentally determined value. The values of DTobtained from the experiments are generally consistent with values reported in the literature. They are also independent of averaging time of measurements, allowing for comparison of values obtained from different measurement settings. These findings make the use of turbulent eddy diffusion models for exposure assessment in workplace/indoor environments more practical.
authors.affiliation: a Division of Environmental Health Sciences , School of Public Health, University of Minnesota , Minneapolis , Minnesota.
authors.forename: Yuan
authors.initials: Y
authors.lastname: Shao
authors.affiliation: b Department of Biomedical Engineering , Johns Hopkins University , Baltimore , Maryland.
authors.forename: Sandhya
authors.initials: S
authors.lastname: Ramachandran
authors.affiliation: a Division of Environmental Health Sciences , School of Public Health, University of Minnesota , Minneapolis , Minnesota.
authors.forename: Susan
authors.initials: S
authors.lastname: Arnold
authors.affiliation: c Department of Environmental Health Sciences , Bloomberg School of Public Health, Johns Hopkins University , Baltimore , Maryland.
authors.forename: Gurumurthy
authors.initials: G
authors.lastname: Ramachandran
mesh_terms: D000096:Acetone / Q000032:analysis; D000392:Air Movements; D000395:Air Pollutants, Occupational / Q000032:analysis; D016902:Air Pollution, Indoor / Q000032:analysis*; D004058:Diffusion; D008962:Models, Theoretical; D014050:Toluene / Q000032:analysis; D014691:Ventilation
chemical_list: D000395:Air Pollutants, Occupational; D000096:Acetone; D014050:Toluene
keywords: Diffusion model; eddy diffusivity; exposure assessment; indoor air pollution; turbulent eddy diffusion coefficient (DT)