AbstractThe atmospheric impacts of volcanic ash from explosive eruptions are rarely considered alongside those of volcanogenic gases/aerosols. While airborne particles provide solid surfaces for chemical reactions with trace gases in the atmosphere, the reactivity of airborne ash has seldom been investigated. Here we determine the total uptake capacity (N_i^M) and initial uptake coefficient (γ_M) for sulfur dioxide (SO₂) and ozone (O₃) on a compositional array of volcanic ash and glass powders at ~25°C in a Knudsen flow reactor. The measured ranges of N_i^SO2 and γ_SO2 (10¹¹–10¹³ molecules cm⁻² and 10⁻³–10⁻²) and N_i^O3 and γ_O3 (10¹²–10¹³ molecules cm⁻² and 10⁻³–10⁻²) are comparable to values reported for mineral dust. Differences in ash and glass reactivity toward SO₂ and O₃ may relate to varying abundances of, respectively, basic and reducing sites on these materials. The typically lower SO₂ and O₃ uptake on ash compared to glass likely results from prior exposure of ash surfaces to acidic and oxidizing conditions within the volcanic eruption plume/cloud. While sequential uptake experiments overall suggest that these gases do not compete for reactive surface sites, SO₂ uptake forming adsorbed S(IV) species may enhance the capacity for subsequent O₃ uptake via redox reaction forming adsorbed S(VI) species. Our findings imply that ash emissions may represent a hitherto neglected sink for atmospheric SO₂ and O₃.