Nanoparticle emissions from traffic have a major effect on human health. A good air filter can prevent such nanoparticle emissions from entering the indoor air of buildings. However, there are no particulate filter test standards for ultrafine particles, which dominate the particle concentrations in outdoor air and are hazardous.

Panu Karjalainen, Tampere University of Technology (TUT), Finland, and colleagues have developed a technique to compare and evaluate the performance of air filters and the mechanisms for filtering nanoparticles out of indoor air. The team used an aerosol generation system which mimics the characteristic traffic related aerosol and compared five typical commercial filters: an F7 class glass-fiber filter, two different HEPA-class filters, an electret filter, and an electrostatic precipitator (ESP).

All of the filters removed nanocluster particles smaller than 3 nm. Differences were observed in the filtration performance and energy efficiency. The filtration efficiencies were found to strongly depend on the particle size. The type of filter also affects the load endurance and service intervals.

The researchers suggest that the particulate filter test standards should be extended to cover ultrafine particles.

• Performance of ventilation filtration technologies on characteristic traffic related aerosol down to nanocluster size,
  Panu Karjalainen, Sampo Saari, Heino Kuuluvainen, Tapio Kalliohaka, Aimo Taipale, Topi Rönkkö,
  Aerosol Sci. Technol. 2017.
  http://dx.doi.org/10.1080/02786826.2017.1356904