The heterogeneous reactivity of gaseous nitric acid on authentic mineral dust samples, and on individual mineral and clay mineral components

Abstract

The heterogeneous reaction between HNO₃ and various authentic dust, mineral and clay mineral surfaces has been investigated by means of the Knudsen reactor technique at ≈296 K. Authentic dust surfaces from both the Saharan and Chinese dust regions were investigated, as were the minerals and clay minerals: kaolinite, ripidolite, illite, illite/smectite, Ca-montmorillonite, Na-montmorillonite, palygorskite, dolomite and orthoclase. A modified Knudsen reactor design and HNO₃ concentrations as low as 10⁹ cm⁻³ helped eliminate experimental artefacts. In all cases a large and irreversible uptake was observed, with uptake coefficients ranging from 8.1 × 10⁻² (orthoclase) to 19.6 × 10⁻² (palygorskite). These results strongly suggest that mineral dust can modify tropospheric photochemical cycles involving NO_x and NO_y.