Abstract
Abstract. This paper presents the spatio-temporal distribution of NOy species at altitudes between 14 and 31 km as measured with the MIPAS-B instrument on the morning of 21 March 2003 in northern Scandinavia. At lower altitudes (below about 22 km), temperature variations, the distribution of ClONO2, and the tracer N2O reveal the dynamics through the edge of the late arctic polar vortex. At higher altitudes, continuous measurement before, during, and after sunrise provides information about photochemistry illustrating the evolution of the photochemically active gases NO2 and N2O5 around sunrise. The measured temporal evolution of NO2 and N2O5 is compared to box modelling that is run along backward calculated trajectories. While the comparison of measured and modelled N2O5 reveals significant differences, there is a good agreement between the model and observations for NO2 in terms of volume mixing ratios but the simulated decrease shortly after sunrise is underestimated compared to the measurements. The differences are attributed to the photolysis rates used in the box model calculations.
Highlights
Odd reactive nitrogen (NOy) can be divided into reactive radicals NOx and the less reactive reservoir species (Brasseur et al, 1999)
While the photolysis rate in the model increases rather linearly with decreasing solar zenith angle (SZA), the photolysis rate deduced from the measurement is close to zero for SZAs above 93.5 degrees and increases linearly below
The results presented here show the ability of MIPAS-B to measure the diurnal variations of photochemically active NOy species with high temporal resolution
Summary
Odd reactive nitrogen (NOy) can be divided into reactive radicals NOx and the less reactive reservoir species (Brasseur et al, 1999). The time constants for the photolytic reactions are quite different for the various species. Photolytic reactions of NO2 and NO3 are very fast (in the order of minutes), while photolysis of N2O5 is slower (in the order of several hours), and photolysis of HNO3 and ClONO2 is almost negligible in the lower stratosphere (Wayne, 2000) at high altitudes in winter. In the middle and lower stratosphere, the reformation of NO2 after sunset is about as fast as its photolytic dissociation after sunrise. While the overall reactive nitrogen content NOy is invariant at short timescales, the partitioning changes rapidly around sunset. Wiegele et al.: Spatio-temporal variations of NOy species measured with MIPAS-B
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