Cosmogenic 7Be: Particle size distribution and chemical composition of 7Be-carrying aerosols in the atmosphere in Japan

Abstract

The particle size distributions of airborne aerosols with 7Be were measured using cascade impactors at Dazaifu, a city in western Japan, in 2018 to observe their seasonal variation. Beryllium-7 was found to be adsorbed to aerosols with a particle size of less than 2.1 μm; in general, particles sized 0.43–0.65 μm had the highest 7Be activity concentrations. The activity median aerodynamic diameter (AMAD) of 7Be fluctuated less over the year within the range of 0.40–0.52 μm, which is the size range of particles that can reach human alveoli, and had an annual mean of 0.43 ± 0.034 μm. The activity concentrations of 7Be were significantly lower in summer, which affected 7Be activity concentration for each particle size fraction. The particle size distribution of 7Be-carrying aerosols was also affected by that of the aerosol particles in the atmosphere. Finally, findings suggest that 7Be was mainly adsorbed to sulfate aerosols (particularly ammonium sulfate aerosols).