Kinetics and mechanism of the uptake of N2O5 on mineral dust at 298 K

The heterogeneous reaction of N2O5 with mineral ( Saharan) dust has been studied at T=298K using a combination of Knudsen and DRIFTS cells for kinetic and product investigations, respectively. The initial uptake coefficient has been determined to be gamma =( 8.0 +/- 0.3) center dot 10(-2). This uptake slowly saturates into a steady state uptake of gamma =(1.3 +/- 0.3) center dot 10(-2) suggesting that reaction of N2O5 with the mineral dust surface and hydrolysis of N2O5 on the surface take place simultaneously. Both uptake coefficients have been calculated on the basis of the geometric ( projected) surface area of the sample and must therefore be regarded as upper limits. In addition, the product investigations show that N2O5 is irreversibly taken up to form nitrate on the surface. Recent model calculations suggest that the uptake rates of N2O5 on Saharan dust which we measured may be large enough to influence the photo-oxidant budget of the atmosphere.