Sub-3nm Particle Detection with Commercial TSI 3772 and Airmodus A20 Fine Condensation Particle Counters

摘要

In this work, we explored the possibility to detect sub-3nm particles with commercially available TSI 3772 and Airmodus A20 Condensation Particle Counters (CPCs), when operated under modified temperature and inlet flow settings. We generated highly monodisperse sub-3nm nanoparticles and characterized the CPCs with temperature differences between the saturator and the condenser varying from 36oC (the 36/37 settings) to 40oC (the 40/40 settings), while the factory settings were 17 and 24oC. The 36/37 settings yielded no homogeneously nucleated background in dry conditions. With these settings, the detection efficiency was significantly improved from the factory settings, resulting in the detection of the smallest charged particles down to below 1.5nm compared with the nominal cut-sizes of 10 and 7nm. With the 40/40 settings and consequently higher supersaturation, homogeneous nucleation produced a background of around 0.5-2cm(-3), while the CPCs were sensitive to charged particles down to 1nm in mobility diameter. The supersaturation field corresponding to the new operation conditions with the 36/37 settings was modeled by using COMSOL and OpenFOAM. The observations were reproduced very well by applying the heterogeneous nucleation theory to the obtained supersaturation field. Our work shows that the TSI 3772 and Airmodus A20 fine CPCs can have a comparable performance with a more expensive ultrafine CPC, such as TSI 3776, thus offering a widely available tool for the detection of sub-3nm particles.