Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 5 2005 10.5194/acpd-5-10369-2005 http://www.atmos-chem-phys-discuss.net/5/10369/2005/ http://www.atmos-chem-phys-discuss.net/5/10369/2005/acpd-5-10369-2005.html http://www.atmos-chem-phys-discuss.net/5/10369/2005/acpd-5-10369-2005.pdf 10369 10408 2005-10-24 The heterogeneous chemical kinetics of N<sub>2</sub>O<sub>5</sub> on CaCO<sub>3</sub> and other atmospheric mineral dust surrogates F. Karagulian C. Santschi M. J. Rossi Ecole Polytechnique Fédérale de Lausanne, Laboratoire de Pollution Atmosphérique et Sol (EPFL, LPAS), Bâtiment CH H5, Station 6, CH-1015 Lausanne, Switzerland Uptake experiments of N<sub>2</sub>O<sub>5</sub> on several mineral dust powder samples were carried out under continuous molecular flow conditions at 298&plusmn;2 K. At [N<sub>2</sub>O<sub>5</sub>]<sub>0</sub>=(4.0&plusmn;1.0)&times;10<sup>11</sup> cm<sup>&minus;3</sup> we have found &gamma;<sub><i>ss</i></sub> values ranging from (3.5&plusmn;1.1)&times;10<sup>&minus;2</sup> for CaCO<sub>3</sub> to (0.20&plusmn;0.05) for Saharan Dust with &gamma;<sub><i>ss</i></sub> decreasing as [N<sub>2</sub>O<sub>5</sub>]<sub>0</sub> increased. We have observed delayed production of HNO<sub>3</sub> upon uptake of N<sub>2</sub>O<sub>5</sub> for every investigated sample owing to hydrolysis of N<sub>2</sub>O<sub>5</sub> with surface-adsorbed H<sub>2</sub>O. At high and low [N<sub>2</sub>O<sub>5</sub>] Arizona Test Dust and Kaolinite turned out to be the samples to produce the largest amount of gas phase HNO<sub>3</sub> with respect to N<sub>2</sub>O<sub>5</sub> taken up. In contrast, the yield of HNO<sub>3</sub> for Saharan Dust and CaCO<sub>3</sub> are lower. On CaCO<sub>3</sub> the disappearance of N<sub>2</sub>O<sub>5</sub> was also accompanied by the formation of CO<sub>2</sub>. For CaCO<sub>3</sub> sample masses ranging from 0.33 to 2.0 g, the yield of CO<sub>2</sub> was approximately 42&ndash;50% with respect to the total number of N<sub>2</sub>O<sub>5</sub> molecules taken up. The reaction of N<sub>2</sub>O<sub>5</sub> with mineral dust and the subsequent production of gas phase HNO<sub>3</sub> leads to a decrease in [NO<sub>x</sub>] which may have a significant effect on global ozone.