NO_<i>y</i> partitioning and aerosol influences in the stratosphere

Abstract

The Cryogenic Infrared Spectrometers and Telescopes for the Atmosphere (CRISTA) instrument measured a variety of trace gases globally with high spatial resolution during two Space Shuttle missions. This paper concentrates on members of the NO y family and highlights differences between CRISTA 1 (November 1994) and CRISTA 2 (August 1997). A sequential assimilation technique is used to combine the CRISTA measurements of total NO y fields with corresponding model forecasts based on the National Center for Atmospheric Research Research for Ozone in the Stratosphere and its Evolution (ROSE) model. For this study we use a model version driven by wind and temperature data provided by the UK Met Office. NO 2 and N 2 O show large‐ and medium‐scale structures caused by dynamical processes. N 2 O 5 shows a strong dependence on the aerosol load and solar zenith angles. N 2 O 5 and NO 2 changes from CRISTA 1 to CRISTA 2 are consistent with a reduction of aerosol concentrations in the Southern Hemisphere and minor aerosol changes in the Northern Hemisphere. For both missions the model reproduces well the measured diurnal cycles of the NO y family members. Measured diurnal variations of N 2 O 5 and NO 2 are consistent with the nighttime production of N 2 O 5 from NO 2 . Compared to the effect of heterogeneous chemistry, the influence of ozone and temperature changes on the NO y partitioning is rather small. A model run based on a three‐dimensional aerosol field derived from CRISTA observations indicates that zonal asymmetries in the background aerosol have strong local effects on the N 2 O 5 and NO 2 distribution.