Assessment of wire and tube penetration theories using a 218PoOx cluster aerosol

Diffusion samplers are commonly used for the measurement of aerosol size distributions (dp<500 nm). In particular, wire screen methods are the only practical means currently available for the detection and measurement of ultrafine molecular cluster aerosols, dp: 0.5-3 nm, such as those associated with radon decay products. The methods have relied upon the Cheng-Yeh wire screen penetration theory [Cheng, Y.S. and Yeh, H.C. (1980) J. Aerosol Sci. ll, 313.] that has been verified for particle sizes dp>3.5-4 nm. The validity of the theory in the ultrafine cluster size range has been assumed. In this study, a well-defined 218PoOx cluster aerosol Davg=0.078±0.0003 cm2s-1 (dp ≅ 0.6 nm) was generated for an assessment of the wire screen penetration theory for two low mesh number wire screens. The results indicated good agreement with the theory, within the domain of its underlying assumptions. In addition, a theoretical expression developed by Ingham [Ingham, D.B. (1975) J. Aerosol Sci. 6, 125.] for uniform flow tube penetration was investigated using the cluster aerosol for its applicability in the estimation of diffusional losses in the entrance of a tube. (author)