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

Highlights: • Particle size distributions of airborne aerosols with ⁷Be were measured. • Activity median aerodynamic diameter of ⁷Be was in an annual mean of 0.43 ± 0.034 μm. • ⁷Be was mainly adsorbed to sulfate aerosols (particularly ammonium sulfate aerosols). 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).