Radon daughter disequilibria in the lower marine boundary layer

Abstract

Radon daughters are produced as free ions, but they become attached to aerosol particles at a rate depending on the particle concentration. In the lower marine boundary layer, most of those which do not become attached plate out on the ocean surface. In this paper a simple model is used to examine the influence of several parameters on radon/radon daughter disequilibria in maritime air. The model is compared with experimental data from Cape Grim.The radon daughter to radon ratio, 'f', decreases from 0.86 to 0.1 as the particle concentration falls from 1000 to 10 cm -3. Estimates of radon concentration at sea level, based on daughter measurements may therefore be in error by as much as a factor of 10 unless allowance is made for particle concentration. At 100 cm -3, the standard deviation of the distribution of measured 'f' values is about 30%, indicating that the particle concentration is not the only factor influencing the loss of radon daughters. The implication is that radon daughters can be used to measure radon concentrations at sea level with an accuracy of about 30%, provided the particle concentration is known.The measurements show that there is a very low proportion of unattached daughers in the air between about 30 and 165 m above sea level. According to the model, this implies that mixing of air up to about 200 m is usually rapid enough to result in plate-out of radon daughters on the ocean on a time scale of less than 100 s.

Lead‐210 observations within CARBOSOL: A diagnostic tool for assessing the spatiotemporal variability of related chemical aerosol species?

“…It is emanating from the soils at a relatively uniform and constant rate into the atmospheric boundary layer [ Dörr and Münnich , 1990; Turekian et al , 1977]. The controlling atmospheric sink of the noble gas 222 Rn is fixed by its radioactive decay with a mean life time of 5.5 d. This life time corresponds to a transfer rate of 18% per day producing 210 Pb atoms which become immediately attached to submicron aerosol particles [ Whittlestone , 1990; Sanak et al , 1981].…”

Radioactivity in the Atmosphere

“…Typical attachment rates for outdoor conditions (aerosol particle concentration (2-7) · 10 4 cm 3 ) were found to be 20-100 h"' [26], corresponding to average attachment times of 40 s to 3 min. For an aerosol particle concentration of only 100 cm" 3 , an attachment time of about 1 hour was observed [27], Of special relevance is the fact, that due to a 112 keV nuclear recoil, the first progeny of the α-emitting nuclide 218 Po, the daughter nuclide 214 Pb, escapes with about 80% probability [28,29] from the particles which have typical median aerodynamic diameters of 50 to 200 nm [28]. In addition, for indoor condition or outdoor situations close to ground, prior to an attachment of the short-lived 222 Rn progenies to aerosol particles, these nuclides may plate-out to nearby-surfaces.…”

Influences of vertical transport and scavenging on aerosol particle surface area and radon decay product concentrations at the Jungfraujoch (3454 m above sea level)

“…1984 , 1993]. Disequilibrium between 222Rn and its decay products has been attributed to precipitation scavenging of aerosol-attached decay products [Malakhov et al, 1966], or to plate-out [Whittlestone, 1990]. However, radioactive equilibrium between 222Rn and 2•4pb is reestablished in less than 3 hours (-•5 x 214pb half-life; Table 1).…”