The detection of large HNO3-containing particles in the winter arctic stratosphere

Large particles containing nitric acid (HNO3) were observed in the 1999/200 0 Arctic winter stratosphere. These in situ observations were made over a L arge altitude range (16 to 21 kilometers) and horizontal extent (1800 kilom eters) on several airborne sampling flights during a period of several week s. With diameters of 10 to 20 micrometers, these sedimenting particles have significant potential to denitrify the Lower stratosphere. A microphysical model of nitric acid trihydrate particles is able to simulate the growth a nd sedimentation of these Large sites in the Lower stratosphere, but the nu cleation process is not yet known. Accurate modeling of the formation of th ese Large particles is essential for understanding Arctic denitrification a nd predicting future Arctic ozone abundances.