Filtration Efficiency of Aerosol Particles Below 20 Nanometers

The current work examines the filtration of both charged and uncharged NaCl nanoparticles in the size range of 2.5–20 nm on grounded metal filters and meshes, and on plastic mesh. The methodology thus allows electrostatic and other effects to be differentiated from true thermal rebound effects (Wang and Kasper 1991). The work also compares measurements under identical conditions made with a number of different condensation particle counters, and a number of different experimental methodologies, in order to allow exclusion of certain measurement errors from the results. It was found that even for particle sizes as small as 2.5 nm there was no measurable deviation from the classical single-fiber-efficiency theory. This conflicts with recently published work (Balazy et al. 2004) which claimed that the thermal bounce of nanometer sized aerosol particles begins to occur at a much larger particle size than previously thought. However, peculiarities or artifacts in CPC counting efficiency at small particle sizes were found during experiments which could account for such observations reported in previous work.

Acknowledgments

The authors would like to thank Dr. Einar Kruis from the Universität Duisburg-Essen for the loan of the TSI 3025 CPC. And SEFAR, Switzerland for supplying the PETEX mesh used in the experiments.

Notes

^a Manufacturer specifications.