Abstract
The aerodynamic size distribution of 7Be aerosol particles in ambient air was determined by using 1-ACFM and high-volume (HVI) cascade impactors, 20 m above the ground on the roof of the Faculty of Science building, Aristotle University of Thessaloniki at Thessaloniki Greece (40o38’N, 22o58’E) from November 2006 to June 2008. The activity concentration of 7Be aerosols was determined by gamma spectrometry (Eγ = 0.477 MeV). The activity size distribution of 7Be-aerosols was largely associated with submicron aerosol particles in the accumulation mode (0.4-2.0 μm). The activity median aerodynamic diameter, AMAD varied from 0.76-1.18 μm (average 0.90 μm), indicating post-condensation growth either in the upper atmosphere or after mixing into the boundary layer. The geometric standard deviation, σg varied from 1.86-2.77 (average 2.24). The activity size distribution of 7Be-aerosols peaked in the 0.7-1.1 μm size range in the 65% of the measurements carried out by the 1-ACFM cascade impactor. In estimating lifetimes of 7Be-aerosols in ambient air, a mean residence time of about 8 days averaged for atmospheric aerosols of 0.90 μm AMAD size.
Highlights
IntroductionBeryllium-7 is a relatively short-lived (T1/2 = 53.3 days, τ = 1/λ = 77 days) naturally occurring radionuclide of cosmogenic origin which is formed by spallation processes of light atmospheric nuclei, such as carbon (Z = 6), nitrogen (Z = 7) and oxygen (Z = 8), when
Beryllium-7 is a relatively short-lived (T1/2 = 53.3 days, τ = 1/λ = 77 days) naturally occurring radionuclide of cosmogenic origin which is formed by spallation processes of light atmospheric nuclei, such as carbon (Z = 6), nitrogen (Z = 7) and oxygen (Z = 8), whenEssentially, the 7Be atoms are produced by high-energy spallation interactions
Beryllium-7 Aerosol Size Distribution A typical plot of the activity size distribution of 7Be versus aerodynamic diameter (Dp) is represented in Fig. 3 This distribution was selected from 11 measurements made over an almost 2-y period
Summary
Beryllium-7 is a relatively short-lived (T1/2 = 53.3 days, τ = 1/λ = 77 days) naturally occurring radionuclide of cosmogenic origin which is formed by spallation processes of light atmospheric nuclei, such as carbon (Z = 6), nitrogen (Z = 7) and oxygen (Z = 8), when. The 7Be atoms are produced by high-energy spallation interactions. The calculated global average production rate of cosmogenic 7Be per unit surface area of the earth is 810 atoms/m2/s and the average concentration of 7Be in the troposphere is 12.5 mBq/m3 (UNSCEAR 2000). Once 7Be is formed in the troposphere, it rapidly associates primarily with submicronsized aerosol particles (Bondietti et al, 1984; 1987).
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