| Abstract
| - The heterogeneous reaction between HNO3 and various authentic and synthetic mineral dust/mineral oxidesurfaces has been investigated using a low-pressure Knudsen reactor operating at 298 K. The surfaces usedwere Saharan dust from Cape Verde, Arizona dust, CaCO3, and Al2O3. In all cases, a large irreversible uptakewas observed. An uptake coefficient of γ = (11 ± 3) × 10-2 was determined for Saharan dust, and γ = (6± 1.5) × 10-2 was obtained for Arizona dust. The uptake coefficients for HNO3 on heated CaCO3 and onunheated CaCO3 are given by γ = (10 ± 2.5) × 10-2 and (18 ± 4.5) × 10-2, respectively, and are in goodagreement with previous results. CO2 and H2O were formed as gas-phase products. Measurements of theuptake coefficient of HNO3 on grain-size selected samples of Al2O3, γ = (13 ± 3.3) × 10-2, and systematicvariation of sample mass enabled us to show that the geometrical surface area of the dust sample is appropriatefor calculation of uptake coefficients in these experiments. The high reactivity of HNO3 toward dust sampleshighlights the potentially important role of mineral dust in redistributing nitrate from the gaseous to theparticulate phase and modifying tropospheric photochemical oxidation cycles.
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