Improving the indoor / outdoor ratio of (ultra)fine particles in a school

Buildings located close to busy roads, industry or stock farms, are of risk of increased indoor particle concentrations, which negatively impacts the health of the building occupants. In order to reduce the exposure of the building occupants, it is important to take measures to reduce the concentration of particulate matter indoors. Solutions for existing buildings include application of improved filters in the air handling units, using local air cleaners and limit the use of operable windows. However, little is known about the overall effectiveness of these measures in existing buildings that are in use. The aim of our study was to quantify the effectiveness of particle reducing measures in buildings at high traffic locations. We performed a field study in a school in a neighbourhood between highways. In this school the effect of improved filters in the air handling unit, a HEPA filter at room level as well as the combination of both interventions on the particle concentrations indoors were studied. We quantified the effect of the interventions by momentary measurements of PM2,5 and ultrafine particles (≥4 nm). Moreover, PM2.5 was continuously measured outdoors and indoors. The ePM1 85% filters in the AHU seemed effective on the reduction of (ultrafine) particles (nearly 75% reduction of PM2,5). The use of a HEPA filter was not effective in our test situation.