AMAD activity median aerodynamic

AMAD = activity median aerodynamic GSD = geometric standard deviation... 

AMAD (activity median aerodynamic diameter). The value of aerodynantic diameter such that 50% of the airborne activity in a specified aerosol is associated with particles smaller than the AMAD and 50% of the activity is... 

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. 

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 ... 

The half-life of nickel in the lungs of rats exposed by inhalation has been reported to be 32 hours for nickel sulfate (mass median aerodynamic diameter [MMAD] 0.6 pm) (Hirano et al. 1994b), 4.6 days for nickel subsulfide ( Ni3S2 activity, median aerodynamic diameter [AMAD] 1.3 pm), and 120 days for green nickel oxide ( NiO, AMAD 1.3 pm) (Benson et al. 1994). Elimination half-times from the lung of rats of 7.7, 11.5, and 21 months were calculated for green nickel oxide with MMADs of 0.6, 1.2, and 4.0 pm, respectively (Tanaka et al. 1985, 1988). 

The activity median aerodynamic diameter (AMAD) for the particles is assumed to be 1.5-2.1 pm average 1.8 pm (see Pozzani 1949). Mortality, body weight changes, standard hematology (except in the... 

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. 

Depending on the plutonium compound, it may be either soluble or insoluble. Plutonium as the citrate or nitrate was more soluble than the dioxide compound. Plutonium dioxides prepared at temperatures of 700°C or higher had a slower absorption rate compared to air-oxidized forms (Sanders and Mahaffey 1979). The absorption of plutonium was also dependent upon its respirable fraction, or that fraction of the total concentration of plutonium which may deposit in the nonciliated part of the lung. The respirable fraction of plutonium is composed of particles less than 10 om Activity Median Aerodynamic- Diameter (AMAD), which indicates that only particles less than 10 om AMAD would be retained in the nonciliated part of the lung and would be available for absorption (NEA/OECD 1981 Volchoketal. 1974). 

From the 11 measurements carried out over a 2-year period including all seasons, Papastefanou and loannidou (1995) reported that the activity median aerodynamic diameter (AMAD) varied from 0.76 to 1.18 pm (average 0.90 pm) and the geometric standard deviation (a ) varied from 1.86 to 2.77 (average 2.24). The AMAD and (ag) calculations were made by plotting the cumulative distributions on log-normal probability paper. They also showed that 60% of the Be activity was associated with particles with diameter smaller than 1.1 pm. 

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. 

The " Pb activity median aerodynamic diameters, AMADs, determined with the low pressure impactors (LPI) varied from 0.10 to 0.37 pm (mean value 0.16 pm). For Pb, the AMADs varied from 0.07 to 0.245 pm (mean value, 0.13 pm). These AMAD calculations were made assuming log-normal distributions. An abbreviated version of these results is presented in Table 2.3 (Papastefanou and Bondietti, 1987). 

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. 

Activity median aerodynamic diameters (AMADs, in jim) of Chernobyl fission products and cosmogenic Be measured at Oak Ridge, Tennessee... 

In contrast to the findings of Bondietti and Brantley (1986), lost et al. (1986) found no increase of the activity median aerodynamic diameter, AMAD, during the measurement period. They believed that this increase might not reflect the original release at Chernobyl, but was due to transport effects. Apart from this, the activity size distribution of Cs from the Chernobyl fallout was very similar to the activity size distribution in the fallout from nuclear weapons tests (Lockhart et al., 1965b), in contrast to the activity size distribution found in the stratosphere, which is shifted towards smaller particles (Persson and Sisefsky, 1971). 

Lujaniene et al. (1997) reported that the activity median aerodynamic diameter, AMAD, of the soluble aerosols of Cs of Chernobyl origin varied in the range 0.10 to 0.86 pm at Vilnius, Lithuania (54°41 N, 25°19 E), and the size of caesium radioisotopes stuck to insoluble aerosol particles in all the samples was similar (about 1 pm). 

Activity median aerodynamic diameter (AMAD) of atmospheric aerosol particles (pm)... 

A method for estimating the residence time of tropospheric aerosol particles associated with the cosmic-ray produced radionuclides, such as Be, is based on the aerosol particle growth rate, which is the change of particle diameter with time, which was estimated to be 0.004 to 0.005 pmh (McMurry and Wilson, 1982) and the difference between the activity median aerodynamic diameter, AMAD, of a radionuclide, e.g. Be, and the size of the Aitken nuclei in the size distribution of the aerosol particles, which is 0.015 pm (NRC, 1979). The AMAD of all radionuclides is in the accumulation mode of the size distribution of atmospheric aerosol particles which ranges between 0.1 and 2.0 pm (NRC, 1979 Papastefanou and Bondietti, 1987). 

Table 4.1 shows data for the activity median aerodynamic diameter, AMAD, of atmospheric aerosol particles associated with Be and Pb atoms. Regarding the Be aerosols, the AMAD values varied from 0.33 to 1.18 pm (Bondietti and Brantley, 1986 Papastefanou and loannidou, 1995 Reineking and Porstendbrfer, 1995 Winkler et al., 1998 Yu and Lee, 2002 Porstendbrfer and Griindel, 2003), while for the Pb-aerosols, the AMAD values varied from 0.28 to 0.77 pm (Sanak et al., 1981 Reineking and Porstendorfer, 1995 WinMer et al., 1998 Porstendorfer and Griindel, 2003). The residence time, tr, is described by the formula... 

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