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Evaluating HEPA filters for Indoor Air Quality

Poor air quality is responsible for an eighth of the planet’s premature deaths annually. That’s about eight million people, or “thirteen Bostons” as Olin College student Jennifer Vaccaro put it. Vaccaro, together with her faculty mentor, Dr. Scott Hersey, presented research on the effectiveness and affordability of different high efficiency particulate air filters to combat this problem at a recent lunchtime research talk at Olin.


High efficiency particulate arrestance (HEPA) filters have a fan that pulls dirty air through a densely fibered filter and removes particles ranging in source from animal dander and dust to vehicle exhaust and smoke.  Emerging evidence suggests that ultrafine particles (UFP), or particles smaller than 100 nm in diameter, are the most dangerous to human health.


Hersey’s team is focusing its research on the UFP levels in older residences in Boston, such as the triple decker houses common in Roxbury and South Boston, which are close to the highways and may not be as sealed against the elements as newer homes. The team recommends putting a HEPA filter on the floor of the room people spend the most time in. Part of the research also involved testing different HEPA filters to figure out which was most effective.


This past semester, the team focused on how well different HEPA filters can remove particles 7-150 nanometers in diameter, and this summer they are measuring particles over the range 6-1000 nanometers. According to Vaccaro the filter industry needs new standards of filter classification, because current measurements of how efficient particles are at being moved through the system is leaving out a critical part of the equation.


“Knowing how many particles are being taken out is not super useful if there are still particles coming into the room,” Vaccaro said. “What we need is ‘how long does it take [a HEPA filter] to remove particles in comparison to how fast dirty air is coming back in.”


Comparing competing filters by their rate of particle removal, the Oliners were able to model the impact of these filters on indoor particle concentrations in real-world settings.  This model will allow researchers to record both the long-term benefit of HEPA filters at and the effectiveness they have in completely cleaning the area for the first time.


HEPA filters can run from $200 to over $3,000, but the research results also showed that the difference in particle removal rate can be negligible between filters at extremes of the price range. . That’s good news for those in lower-income, inner-city areas where air pollution may be high.