On the cryogenic removal of NOy from the Antarctic polar stratosphere

R. L. de Zafra, G. Muscari, S. Smyshlyaev


We review current knowledge about the annual cycle of transport of nitrogen oxides to, and removal from, the
polar stratosphere, with particular attention to Antarctica where the annual winter denitrifi cation process is both
regular in occurrence and severe in effect. Evidence for a large downward fl ux of NOy from the mesosphere to
the stratosphere, fi rst seen briefl y in the Limb Infrared Monitor of the Stratosphere (LIMS) data from the Arctic
winter of 1978-1979, has been found during the 1990s in both satellite and ground-based observations, though this
still seems to be omitted from many atmospheric models. When incorporated in the Stony Brook- St. Petersburg
two dimensional (2D) transport and chemistry model, more realistic treatment of the NOy fl ux, along with sulfate
transport from the mesosphere, sulfate aerosol formation where temperature is favorable, and the inclusion of a
simple ion-cluster reaction, leads to good agreement with observed HNO3 formation in the mid-winter middle to
upper stratosphere. To further emphasize the importance of large fl uxes of thermospheric and mesospheric NOy
into the polar stratosphere, we have used observations, supplemented with model calculations, to defi ne new
altitude dependent correlation curves between N2O and NOy. These are more suitable than those previously used
in the literature to represent conditions within the Antarctic vortex region prior to and during denitrifi cation by
Polar Stratospheric Cloud (PSC) particles. Our NOy -N2O curves lead to a 40% increase in the average amount
of NOy removed during the Antarctic winter with respect to estimates calculated using NOy-N2O curves from the
Atmospheric Trace Molecule Spectroscopy (ATMOS)/ATLAS-3 data set.


polar stratosphere;reactive nitrogen;heterogeneous chemistry;tracer-tracer correlations

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DOI: https://doi.org/10.4401/ag-3402
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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X