Removal of airborne sub-3 nm particles using fibrous filters and granular activated carbons

The filtration efficiencies of fibrous filters and a granular activated carbon (GAC) for sub-3 nm particles were investigated, which were not previously well-studied. The sub-3 nm particles were classified by a high resolution differential mobility analyzer and measured by an aerosol electrometer. The penetration of sub-3 nm particles through the GAC was well-matched with the previous results using 3-30 nm particles. All tested fibrous filters showed 100% filtration efficiency for the sub-3 nm particles and were still sufficiently powerful to eliminate nanoparticles in the air down to 1.5 nm. Although the GAC showed lower filtration efficiency than the fibrous filters, GACs can be used to reduce the concentration of both gas molecules and nanoparticles simultaneously with a low pressure drop. The single sphere efficiency of the GAC for the sub-3 nm particles was a power-law of the Peclet number, and the exponent was -0.35. The exponent was higher than that for 3-30 nm particles, -0.5. Moreover, the exponent for 1.5-30 nm particles was -0.43, which was the same as that of the single fiber efficiency observed by others. This requires a new particle filtration model of porous filter media such as GACs.