Activity median diameter aerosols

The fraction of unattached daughters (fp), the equilibrium factor (F) and the activity median diameter (AMD) are plotted in Figure 6 for all the measurements. The AMD is derived from the aerosol measurements. These three parameters are important in the dosimetric models. At the top of Figure 6 the effective dose equivalent is plotted, computed with two models called the J-E (Jacobi-Eisfeld) and J-B (James-Birchall) models in the NEA-report (1983, table 2.9, linear interpolation between AMD=0.1 and 0.2 ym). The figure also shows the effective dose equivalent calculated from the equilibrium equivalent radon concentrations with the NEA dose conversion factor (NEA,1983, table 2.11). 

Table I. Calculated activity median diameter for attached radon daughters from measured aerosol characteristics (Tu, 1986).

Plutonium is so toxic that processing and fabrication are always done in sealed cells or glove boxes, but accidental dispersions of aerosol occur from time to time. Following combustion of Pu metal chips in a production area at Rocky Flats, Colorado, in 1964, airborne contamination was widespread. Alpha tracks from individual particles caught on membrane filters were detected on nuclear film, and the Pu content, and hence the particle size, was deduced (Fig. 5.2, curve E). The activity median diameter was 0.3 /urn (Mann Kirchner, 1967). The same method, used during normal operations in a production area at Los Alamos, gave activity median diameters in the range 0.15 to 0.65 /urn (Moss et al., 1961). However, when a spill occurred, followed by clean-up operations, the Pu particles were found to be associated with inert dust particles of mass median diameter 7 /urn. 

Activity Median Aerodynamic Diameter (AMAD)—The diameter of a unit-density sphere with the same terminal settling velocity in air as that of the aerosol particle whose activity is the median for the entire size distribution of the aerosol. 

The mean values of the activity and aerosol median diameters together with the best estimate of the standard deviation, an, based on the total number of measurements made for each parameter, are listed in Table V. Figures 5-8 show representative size distributions ... 

Table IV. Activity and Aerosol Size Distributions, Count Median Diameter (CMD) and the Geometric Standard Deviation (indicated in brackets)...

Based on 46 measurements, the activity median aerodynamic diameter of Pb-212 averaged 0.13 pm (0g = 2.97), while Pb-214 averaged 0.16 pm (Og = 2.86). The larger median size of Pb-214 was attributed to a-recoil depletion of smaller aerosols following decay of aerosol-associated Po-218. 

Aerodynamic Size Distributions of Naturally-Radioactive Aerosols. Measurements of radionuclide distributions using cascade impactors indicate that Be-7 and Pb-210 are associated with larger aerosols than Pb-212 and Pb-214 (Robig et al., 1980 Papastefanou and Bondietti, 1986). Measurements of Pb-210 associations over oceans indicated activity median aerodynamic diameters (AMAD) near 0.6 pm (Sanak et al., 1981). The impactor measurements of Moore et al. (1980) on Pb-210, Bi-210, and Sr-90 sizes in continental air indicated that about 80% of the activity from all three nuclides was associated with aerosols below 0.3 pm. That work also determined that the mean age of aerosol Pb-210 was about a week. Knuth et al. (1983) compared Pb-210 and stable Pb sizes at a continental location and found that 78% of the Pb-210 found below 1.73 pm was smaller than 0.58 pm. Young (1974) reported that the most of the Be-7 in the atmosphere was associated with submicron aerosols. 

Table II. Summary of Mean Monthly Activity Median Aerodynamic Diameters (AMAD) and Geometric Standard Deviations (tfg) of Radon and Thoron Daughter Size Distributions in Ambient Aerosols...

The aerodynamic size distributions of Pb-214, Pb-212, Pb-210, Be-7, P-32, S-35-SoJ , and stable SO4 were measured using cascade impactors. Pb-212 and Pb-214, measured by alpha spectroscopy, were largely associated with aerosols small than 0.52 11m. Based on over 46 low-pressure impactor measurements, the mean activity median aerodynamic diameter (AMAD) of Pb-212 was found to be 0.13 11m, while for Pb-214 the AMAD was larger—0.16 lim. The slightly larger size of Pb-214, confirmed with operationally different impactors, was attributed to a-recoil-driven redistribution of Pb-214 following decay of aerosol-associated Po-218. A recoil model was presented that explained this redistribution. Low-pressure impactor measurements indicated that the mass median aerodynamic diameter of SoJ ... 

Improved control devices now frequently installed on conventional coal-utility boilers drastically affect the quantity, chemical composition, and physical characteristics of fine-particles emitted to the atmosphere from these sources. We recently sampled fly-ash aerosols upstream and downstream from a modern lime-slurry, spray-tower system installed on a 430-Mw(e) coal utility boiler. Particulate samples were collected in situ on membrane filters and in University of Washington MKIII and MKV cascade impactors. The MKV impactor, operated at reduced pressure and with a cyclone preseparator, provided 13 discrete particle-size fractions with median diameters ranging from 0,07 to 20 pm with up to 6 of the fractions in the highly respirable submicron particle range. The concentrations of up to 35 elements and estimates of the size distributions of particles in each of the fly-ash fractions were determined by instrumental neutron activation analysis and by electron microscopy, respectively. Mechanisms of fine-particle formation and chemical enrichment in the flue-gas desulfurization system are discussed. 

Dogs of both sexes (11-12 M, 9-10 E) were exposed to uranium tetrachloride in inhalation chambers for 6 hours a day, M-E and 3 hours on Saturday (5.5 days a week) for 1 year at concentrations of 0, 0.05, and 0.20 mg U/ml (Doses were analytically determined, not estimated.) The activity median aerodynamic diameter (AMAD) of the aerosols was 1-2 pm. The animals were monitored for body weight alterations, clinical signs of toxicity, and biochemical alterations in the blood and urine. At the termination of the study, the animals were sacrificed and selected organs were histopathologically examined. 

Winkler et al. (1998) in 46 measurements in a period of 1 1/3 years (December 1994-March 1996) at Munich-Neuherberg, Germany (48 13 N, 11°36 E) showed that the activity median aerodynamic diameter, AMAD, of Be-aerosols ranged from 0.44 to 0.74 pm (average... 

Yu and Lee (2002) in 14 measurements in Hong Kong (22°18 N, 114 10 E) for a 3 1/2 month period (26 November 2001-8 March 2002) demonstrated that the activity median aerodynamic diameter, AMAD, of Be-aerosols varied from 0.33 to 1.15 pm (average 0.67 pm). They concluded that the AMADs of Be-aerosols are anticorrelated with Be concentrations in air, are correlated with relative humidity, RH and mean cloud cover, while temperature does not affect the AMADs of the Be-aerosols. 

E). The data rather indicate that the activity median aerodynamic diameter, AMAD, of Be-aerosols increases with increasing latitude (latitudinal effect). As cosmic radiation increases with latitude, the numbers of Be atoms and ions formed also increase with latitude and so there are more Be atoms and ions available either to form small aerosol particles in the nucleation (Aitken nuclei) mode and then growing or to be attached directly to the existing large particles in the accumulation and in the coarse particle modes thereby increasing the AMAD of the Be-aerosols. 

Summary of mean monthly activity median aerodynamic diameters (AMADs) and geometric standard deviations (ffg) of radon ( Rn) and thoron ( °Rn) decay products size distributions in ambient aerosols... 

Winkler et al. (1998) reported that the activity size distribution of Pb in ambient aerosols was unimodal (log-normal) and associated with submicron aerosols of about 0.5 to 0.6 pm. On average, the activity median aerodynamic diameter, AMAD, of Pb-aerosols (0.53 pm) has been found to be significantly lower than the average mass median aerodynamic diameter, MMAD (0.675 pm), and higher than or at most equal to the respective surface median aerodynamic diameter, SMAD, (0.465 pm) of the aerosols SMAD < AMAD < MMAD. Variation of the atmospheric processes resulted in a variability of the activity median aerodynamic diameter, AMAD, between 0.28 and 0.74 pm for Pb. While in the winter period (October to April) the AMAD of Pb averaged 0.595 pm, in the summer period Pb was associated with significantly smaller aerosols (AMAD 0.43 pm). 

The activity median aerodynamic diameters (AMADs) of Pb (Table 2.3) and mass median aerodynamic diameters (MMADs) of SO (Table 2.4) determined from a series of low- pressure (LPI) cascade impactor measurements made during the period January to October (1985) by Papastefanou and Bondietti (1987) are illustrated in Figure 2.7. The Pb data were derived from measurements made at the same time as and from measurements made to compare Pb versus Pb. The mean aerodynamic diameter of Pb was about three times smaller than that of SO ". Much less sulfate was found in the aerosol fraction below 0.08 pm... 

Table 2.4 summarises the activity median aerodynamic diameter (AMAD) of Pb and Be and the mass median aerodynamic diameter (MMAD) of SO found in measurements made in the spring period. Beryllium-7 activity size distributions are substantially smaller than 804 , regardless of the time of year. The Pb data included in Table 2.4, while limited, suggest that summer aerosol particle sizes are larger than winter aerosol particle sizes. 

---