Volcanic Impact of Nishinoshima Eruptions in Summer 2020 on the Atmosphere over Central Japan: Results from Airborne Measurements of Aerosol and Trace Gases

Abstract

Aerosol number concentrations and trace gases (SO₂, O₃, HCHO, and H₂O₂) were measured over Imizu City, Toyama Prefecture, Japan on 5 August 2020, from a helicopter. The concentrations of fine particles (0.3-0.5 μm) were high at ground level and at an altitude of approximately 1200 m due to the volcanic plume from Nishinoshima. However, concentrations of aerosol particles were low at an altitude of approximately 2400 m. The volcanic plume did not significantly affect the lower free troposphere. High concentrations of SO₂ were also observed. The H₂O₂ concentrations (0.27-0.56 ppb) were much lower than those during previous observations in the summer (2.0-6.7 ppb) and significantly lower than the SO₂ concentrations (1.8-3.3 ppb). The concentrations of HCHO (2.1-2.5 ppb) were higher than those of H₂O₂. The oxidation of S(IV) to H₂SO₄ in cloud water might have been suppressed over the studied area.