Redistribution of total reactive nitrogen in the lowermost Arctic stratosphere during the cold winter 2015/2016

• Published in: Atmospheric Chemistry and Physics
• Main Authors: H. Ziereis, P. Hoor, J.-U. Grooß, A. Zahn, G. Stratmann, P. Stock, M. Lichtenstern, J. Krause, V. Bense, A. Afchine, C. Rolf, W. Woiwode, M. Braun, J. Ungermann, A. Marsing, C. Voigt, A. Engel, B.-M. Sinnhuber, H. Oelhaf
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2022
• Subjects: Physics; QC1-999; Chemistry; QD1-999; Arctic; Kiruna
• Online Access: https://doi.org/10.5194/acp-22-3631-2022; https://doaj.org/article/114e769e1f8d40a28f31efa7ed994950

During winter 2015/2016, the Arctic stratosphere was characterized by extraordinarily low temperatures in connection with a very strong polar vortex and with the occurrence of extensive polar stratospheric clouds. From mid-December 2015 until mid-March 2016, the German research aircraft HALO (High Altitude and Long-Range Research Aircraft) was deployed to probe the lowermost stratosphere in the Arctic region within the POLSTRACC (Polar Stratosphere in a Changing Climate) mission. More than 20 flights have been conducted out of Kiruna, Sweden, and Oberpfaffenhofen, Germany, covering the whole winter period. Besides total reactive nitrogen (NO y ), observations of nitrous oxide, nitric acid, ozone, and water were used for this study. Total reactive nitrogen and its partitioning between the gas and particle phases are key parameters for understanding processes controlling the ozone budget in the polar winter stratosphere. The vertical redistribution of total reactive nitrogen was evaluated by using tracer–tracer correlations (NO y –N 2 O and NO y –O 3 ). The trace gases are well correlated as long as the NO y distribution is controlled by its gas-phase production from N 2 O. Deviations of the observed NO y from this correlation indicate the influence of heterogeneous processes. In early winter no such deviations have been observed. In January, however, air masses with extensive nitrification were encountered at altitudes between 12 and 15 km. The excess NO y amounted to about 6 ppb. During several flights, along with gas-phase nitrification, indications for extensive occurrence of nitric acid containing particles at flight altitude were found. These observations support the assumption of sedimentation and subsequent evaporation of nitric acid-containing particles, leading to redistribution of total reactive nitrogen at lower altitudes. Remnants of nitrified air masses have been observed until mid-March. Between the end of February and mid-March, denitrified air masses have also been observed in connection with high ...