Beryllium-7 aerosols in ambient air

Abstract

The aerodynamic size distribution of 7Be in ambient aerosol particles was determined using l-ACFM cascade impactors. The activity distribution of 7Be measured by gamma spectrometry (Eγ = 477 keV) was largely associated with submicrometer aerosols in the accumulation mode (0.4 to 2.0 μm). The activity median aerodynamic diameter (AMAD) ranged from 0.76 to 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, σ g, ranged from 1.86 to 2.77 (average 2.24). In 65% of the cascade impactor measurements, the activity distributions of 7Be showed maxima in the 0.7 to 1.1 μm size range. Low AMADs as low as 0.62 to 0.74 μm of 7Be aerosols have been observed at locations characterized with relatively low pollution. Some dependency of AMADs on height has been also observed. In marine environments, the 7Be activity size distribution was dominant in the upper size range of aerosol particles.