The heterogeneous chemical kinetics of N2O5 on CaCO3 and other atmospheric mineral dust surrogates

Uptake experiments of N2O5 on several mineral dust powder samples were carried out under continuous molecular flow conditions at 298 +/- 2 K. At [N2O5] 0=(4.0 +/- 1.0) x 10(11) cm(-3) we have found gamma(ss) values ranging from (3.5 +/- 1.1) x 10(-2) for CaCO3 to (0.20 +/- 0.05) for Saharan Dust with gamma(ss) decreasing as [N2O5](0) increased. The uptake coefficients reported in this work are to be regarded as upper limiting values owing to the fact that they are based on the geometric ( projected) surface area of the mineral dust sample. We have observed delayed production of HNO3 upon uptake of N2O5 for every investigated sample owing to hydrolysis of N2O5 with surface-adsorbed H2O. Arizona Test Dust and Kaolinite turned out to be the samples that generated the largest amount of gas phase HNO3 with respect to N2O5 taken up. In contrast, the yield of HNO3 for Saharan Dust and CaCO3 is lower. On CaCO3 the disappearance of N2O5 was also accompanied by the formation of CO2. For CaCO3 sample masses ranging from 0.33 to 2.0 g, the yield of CO2 was approximately 42 - 50% with respect to the total number of N2O5 molecules taken up. The reaction of N2O5 with mineral dust and the subsequent production of gas phase HNO3 lead to a decrease in [NOx] which may have a significant effect on global ozone.