The heterogeneous chemical kinetics of N 2O 5 on CaCO 3 and other atmospheric mineral dust surrogates
Uptake experiments of N 2O 5 on several mineral dust powder samples were carried out under continuous molecular flow conditions at 298±2 K. At [N 2O 5] 0=(4.0±1.0)×10 11 cm −3 we have found γ ss values ranging from (3.5±1.1)×10 −2 for CaCO 3 to (0.20±0.05) for Saharan Dust with γ ss decreasing as [N 2O 5] 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 HNO 3 upon uptake of N 2O 5 for every investigated sample owing to hydrolysis of N 2O 5 with surface-adsorbed H 2O. Arizona Test Dust and Kaolinite turned out to be the samples that generated the largest amount of gas phase HNO 3 with respect to N 2O 5 taken up. In contrast, the yield of HNO 3 for Saharan Dust and CaCO 3 is lower. On CaCO 3 the disappearance of N 2O 5 was also accompanied by the formation of CO 2. For CaCO 3 sample masses ranging from 0.33 to 2.0 g, the yield of CO 2 was approximately 42–50% with respect to the total number of N 2O 5 molecules taken up. The reaction of N 2O 5 with mineral dust and the subsequent production of gas phase HNO 3 lead to a decrease in [NO x] which may have a significant effect on global ozone.