HR: 0800h
AN: A21C-0759    [Abstracts]
TI: Nitric Acid in Cirrus and Polar Stratospheric Clouds
AU: * Voigt, C
EM: Christiane.Voigt@dlr.de
AF: DLR-Institute for Physics of the Atmosphere, Oberpfaffenhofen , Wessling, D-82234 Germany
AU: Schlager, H
EM: Hans.Schlager@dlr.de
AF: DLR-Institute for Physics of the Atmosphere, Oberpfaffenhofen , Wessling, D-82234 Germany
AU: Luo, B P
EM: beiping.luo@env.ethz.ch
AF: ETH-Institute for Atmosphere and Climate, ETH-Zurich, H”nggerberg HPP, Zurich, CH-8093 Switzerland
AB: Cirrus clouds and PSCs were observed by in-situ instruments on the high altitude research aircraft Geophysica in the Arctic winter 2002/3. Cirrus clouds were detected during several flights at temperatures between 200 and 215K. Besides optical particle parameters, the water and nitric acid content in the gas and the condensed phase were measured. First results of the uptake of nitric acid in or on Arctic cirrus clouds will be presented and compared to other measurements and models. Also, at altitudes above 18 kilometers small nitric acid containing particles - probably nitric acid trihydrate (NAT) - with diameters up to 6 micrometers and low number densities ($<2*$10-4 cm-3) were measured in a PSC on 6 February 2003. Interestingly, the NAT particles formed in less than a day at temperatures more than 3.5 K above the ice frost point. The detection of particles in this unique experimental situation at threshold PSC formation conditions allows to constrain current hypothesis of NAT formation. We derive a nucleation rate of NAT nucleation on meteoritic smoke, which might explain the present observations. After growth, those NAT particles have potential to remove HNO3 from the stratosphere (denitrification), which enhances polar ozone loss. We compare the measured denitrification with results from global model simulations.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0305 Aerosols and particles (0345, 4801)
DE: 0320 Cloud physics and chemistry
DE: 0340 Middle atmosphere--composition and chemistry
DE: 0365 Troposphere--composition and chemistry
SC: Atmospheric Sciences [A]
MN: 2004 AGU Fall Meeting