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

The heterogeneous reaction between HNO3 and various authentic dust, mineral and day mineral surfaces has been investigated by means of the Knudsen rea ctor technique at approximate to 296 K. Authentic dust surfaces from both t he Saharan and Chinese dust regions were investigated, as were the minerals and clay minerals: kaolinite, ripidolite, illite, illite/smectite, Ca-mont morillonite, Na-montmorillonite. palygorskite, dolomite and orthoclase. A m odified Knudsen reactor design and HNO3 concentrations as low as 10(9) cm(- 3) helped eliminate experimental artefacts. In all cases a large and irreve rsible uptake was observed. with uptake coefficients ranging from 8.1 x 10( -2)(orthoclase) to 19.6 x 10(-2) (palygorskite). These results strongly sug gest that mineral dust can modify tropospheric photochemical cycles involvi ng NOx and NOy.