AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Modeling Exposure Close to Air Pollution Sources in Mechanically Ventilated Rooms: Association of Turbulent Diffusion Coefficient with Ventilation Power Input
KAI-CHUNG CHENG, Yan Zheng, Lynn M. Hildemann, Stanford University
Abstract Number: 12 Working Group: Indoor Aerosols
Abstract The turbulent diffusion coefficient has been used to model elevated exposures close to an indoor air pollution source. However, its highly variable magnitudes have been difficult to predict in the field, especially for indoor spaces with mechanical ventilation (i.e., HVAC systems or in-house fans). We conducted 11 experiments in 2 different-sized indoor spaces (a residential garage and an office), varying the operating speeds of two household fans to create a range of mechanical ventilation conditions. In each, we used SidePak monitors to sample PM2.5 every 10 s at 15-16 points at different horizontal distances and angles from a controlled continuous particle emission source. An eddy diffusion model was used to deduce the turbulent diffusion coefficient from the measured spatial spreads of PM2.5. Values ranged from 0.0008-0.0117 m2/s for ventilation power inputs of 0-10.62 W, estimated by measuring air velocities at the fan registers. The model reasonably describes the observed PM2.5 concentrations at different radial distances (0.25-4 m). By factoring in the room dimensions, we found a significant relationship between the turbulent diffusion coefficient and the ventilation power input, consistent with a derived theoretical expectation and generalizable across two different sized rooms. The ability to predict the turbulent diffusion coefficient using routinely measured indoor air quality (IAQ) parameters (i.e., ventilation power input and room dimensions) is useful for accurately modeling elevated exposures in close proximity to an indoor air pollution source.