Nitric Acid Trihydrate (NAT) formation at low NAT supersaturation in Polar Stratospheric Clouds (PSCs)

• Main Authors: Voigt, C., Schlager, H., Luo, B. P., Dörnbrack, A., Roiger, Anke, Stock, P., Curtius, J., Vössing, H., Borrmann, S., Davies, S., Konopka, P., Schiller, C., Shur, G., Peter, T.
• Other Authors: DLR Institut für Physik der Atmosphäre (IPA), Deutsches Zentrum für Luft- und Raumfahrt Oberpfaffenhofen-Wessling (DLR), Institute for Atmospheric and Climate Science Zürich (IAC), Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology Zürich (ETH Zürich), Max-Planck-Institut für Chemie (MPIC), Max-Planck-Gesellschaft, School of Environment, Forschungszentrum Jülich GmbH, Helmholtz-Gemeinschaft = Helmholtz Association, Central Aerological Observatory (CAO), Russian Federal Service for Hydrometeorology and Environmental Monitoring (Roshydromet)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2005
• Subjects: [SDU.OCEAN]Sciences of the Universe [physics]/Ocean; Atmosphere; Arctic
• Online Access: https://hal.science/hal-00295666; https://hal.science/hal-00295666/document; https://hal.science/hal-00295666/file/acp-5-1371-2005.pdf

International audience A PSC was detected on 6 February 2003 in the Arctic stratosphere by in-situ measurements onboard the high-altitude research aircraft Geophysica. Low number densities (~10 -4 cm -3 ) of small nitric acid (HNO 3 ) containing particles ( d <6µm) were observed at altitudes between 18 and 20km. Provided the temperatures remain below the NAT equilibrium temperature T NAT , these NAT particles have the potential to grow further and to remove HNO 3 from the stratosphere, thereby enhancing polar ozone loss. Interestingly, the NAT particles formed in less than a day at temperatures just slightly below T NAT ( T > T NAT -3.1K). This unique measurement of PSC formation at extremely low NAT saturation ratios ( S NAT ?10) constrains current NAT nucleation theories. We suggest, that the NAT particles have formed heterogeneously, but for certain not on ice. Conversely, meteoritic particles may be favorable candidates for triggering NAT nucleation at the observed low number densities.