Beschreibung:
<jats:p>Extensive populations of large HNO<jats:sub>3</jats:sub>‐containing particles were observed in situ in the 1999–2000 Arctic winter vortex. Assuming nitric acid trihydrate (NAT) composition, the associated values of instantaneous gravitational flux of HNO<jats:sub>3</jats:sub> are between 1·10<jats:sup>8</jats:sup> and 5·10<jats:sup>10</jats:sup> molec cm<jats:sup>−3</jats:sup> km day<jats:sup>−1</jats:sup> and are the largest ever derived from in situ measurements. The relationship between these observed populations and observed denitrification in the 1999–2000 Arctic vortex is developed using constraints of NAT formation and sedimentation. This analysis of the 1999–2000 winter provides a useful guide to interpreting future observations of polar stratospheric clouds and denitrification in the polar regions.</jats:p>