The Uptake of SO2 on α-Fe2O3 and Mineral Dust Surfaces in the Temperature Range 250 K to 600 K

Abstract

Abstract The uptake of SO2 on α-Fe2O3 and Saharan dust has been studied in the temperature range 250 K to 600 K using a Knudsen cell reactor. SO2 adsorbs readily and irreversibly on both mineral oxides with a mean initial uptake coefficient of γ ini = (5.9±0.3) · 10−2 on dry surfaces, independent of the surface temperature. In the presence of adsorbed water the initial uptake coefficients at T = 300 K are slightly higher with values of γ ini = (8.4±0.2) · 10−2 for Fe2O3 and γ ini = (7.3±0.4) · 10−2 for mineral dust. The uptake of SO2 is time-dependent and influenced by diffusion into the bulk of the sample at longer timescales. The adsorption capacity has been determined to be (3.0±0.4) · 1018 molecules g−1 for Fe2O3 and (2.6±1) · 1019 molecules g−1 for mineral dust. Sulphite has been identified as the primary reaction product on both surfaces which is readily oxidized to sulphate under atmospheric conditions. Oxidation of sulphite to sulphate only takes place at elevated temperature. From these results a mechanism for the uptake of SO2 onto mineral oxides is inferred, which has been used to compare the experimental concentration-time-profiles with simulated ones.