AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
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Size-dependent Particle Filtration Efficiency of Stand-Alone HEPA Filters: Results From In-Home Experiments and Modeling
CAZ NICHOLS, Aidan McLaughlin, Jennifer Vaccaro, Scott Hersey, Franklin W. Olin College of Engineering
Abstract Number: 215 Working Group: Passive Mitigation Strategies to Reduce Exposure to Near-Road Air Pollution
Abstract HEPA filtration is a nearly $3 billion per year industry, with rapid growth in areas impacted by high concentrations of ambient pollutants. Emerging research from environmental epidemiology suggests that the particles most detrimental to human health are the smallest in diameter, with increasing evidence that ultrafine particles (UFP; diameter < 100 nm), are most strongly associated with systemic inflammation, asthma and cardiovascular disease. Regulations dictate that HEPA filters remove 99.97% of particles larger than 300 nm in diameter, meaning that the smallest particles – those most damaging to human health – are not captured in this standard. Further, the rate at which a HEPA filter removes particles is not characterized in standard testing and validation, but is a crucial factor in determining the steady-state indoor concentration of UFPs and total particles. This represents an important gap in knowledge for researchers in the field of environmental health, who regularly employ the devices in studies and interventions on the physiological response to reductions in exposure to ultrafine particles.
This work presents results from a battery of tests performed by undergraduate students from the Affordable Design and Entrepreneurship capstone program at Olin College of Engineering, with commercially available and do-it-yourself HEPA filters. Initial particle concentrations on the order of 200-300,000 cm-3 were generated before turning on HEPA filters and continuously measuring aerosol size distributions and total particle number concentrations (PNC) with a nano-SMPS and water-based CPC, respectively. Results suggest that all HEPA filters are capable of reducing PNC and UFP concentrations to well below 1000 cm-3 in a sealed room with no source, but that the exponential decay constants associated with different filters vary widely. Further, all filters performed well at removing UFP, though removal rates were slower than observed for larger particles.