Flugzeuggetragene Messungen von Stickoxidverbindungen und Eiswolken in der tropischen Tropopausenregion

Kurzfassung

Uptake of nitric acid in cirrus clouds has extensively been studied during field missions in the last decade with the aim to understand the interactions of trace gases with ice crystals and cirrus cloud formation. Further, the uptake of nitric acid in aerosol and ice particles can change the partitioning of the reactive NOy species and influence the ozone budget of the tropical tropopause region. Nitric acid has been detected in tropical cirrus clouds above Darwin during the SCOUT campaign 2005. The HNO3 content of the ice crystals is evaluated in terms of HNO3/H2O molar ratios in ice and the fraction of total HNO3 bound in ice crystals is determined. Both values increase with decreasing temperature. We compare our data to results from previous field campaigns in subtropical, midlatitude and polar regions. The observations at temperatures above 200 K can be explained by uptake of HNO3 in ternary aerosol serving as freezing nuclei and subsequent trapping of HNO3 during ice crystal growth.