The Measurement of Activity-Weighted Size Distributions of Radon Progeny

Abstract

Over the past 5 y, there have been significant improvements in measurement of activity-weighted size distributions of airborne radon decay products. The modification of screen diffusion batteries to incorporate multiple screens of differing mesh number, called graded screen arrays, have permitted improved size resolution below 10 nm such that the size distributions can now be determined down to molecular sized activities (0.5 nm). In order to ascertain the utility and reliability of such systems, several intercomparison tests have been performed in a 2.4 m3 radon chamber in which particles of varying size have been produced by introducing SO2 and H2O along with the radon to the chamber. In April 1988, intercomparison studies were performed between direct measurements of the activity-weighted size distributions as measured by graded screen arrays and an indirect measurement of the distribution obtained by measuring the number size distribution with a differential mobility analyzer and multiplying by the theoretical attachment rate. Good agreement was obtained in these measurements. A second set of intercomparison studies among a number of groups with graded screen array systems was made in April 1989 with the objective of resolving spectral structure below 10 nm. Again, generally good agreement among the various groups was obtained although some differences were noted. It is thus concluded that such systems can be constructed and can be useful in making routine measurements of activity-weighted size distributions with reasonable confidence in the results obtained.

A Chamber Study of Secondary Organic Aerosol (SOA) Formed by Ozonolysis of d-Limonene in the Presence of NO

“…The chamber was described by Ramamurthi et al (1990) and Hopke et al (1992) and has been used in a number of prior studies of ozone-terpene reaction studies (Chen and Hopke, 2009a, b;2010;Liu and Hopke, 2014). The environment in the chamber was dark.…”

Lung Depth Dose from Inhalation of 222Rn Progeny

“…Po alpha particles emitted either from the top of 11 m thick gel and sol layer, or from the top of the 6 m thick sol layer or from the interface between the sol layer and the underlying epithelium (curves 1-3). Corresponding calculations for 214 Po alpha particles nuclides within epithelial tissue refer either to a uniform distribution of nuclides across the epithelium or to a nuclide distribution decreasing in a linear fashion with increasing depth in tissue (curves [4][5]. Curves 1-3 show that the dose decreases rapidly with increasing depth.…”

“…This distribution has been determined by tagging natural aerosol particles with radon progeny. However, some measurements for attached and unattached activity size distributions of 222 Rn progeny have been performed in the indoor air under realistic natural conditions (4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17) . Most of the observed data have shown that the size distribution of radon progeny consists of ultrafine clusters with median diameters below 4 nm (unattached activity) and progenies associated with ambient aerosol particles in sizes ranging between 100 and 1000 nm (attached activity).…”

Deposition of Aerosol Particles below 10 nm on a Mixed Screen-Type Diffusion Battery

“…A special type of diffusion battery for measuring the particle size of aerosols is the so called graded screen array (GSA) and was first developed by Holub and Knutson (1987) in the 1980s, in which several screens differing in their geometric characteristics (wire diameter, screen thickness, opening and solid volume fraction) are arranged in series within a filter holder (e.g., Solomon and Ren, 1992). GSAs were used in several studies of radon decay product behavior (e.g., Strong, 1988;Ramamurthi and Hopke, 1989;Ramamurthi et al, 1990;Winklmayr et al, 1990;Li and Hopke, 1991;Hopke et al, 1992;Solomon and Ren, 1992;Cheng et al, 2000). The Cheng-Yeh wire screen penetration theory in the molecular cluster size range was confirmed the validity by Ramamurthi et al (1990) using a well-defined and radioactive 218PoO x cluster aerosol, highly disffusive D avg = 0.078 ± 0.003 cm 2 /s (dp ≈ 0.6 nm).…”