Variability of stratospheric and tropospheric nitrogen dioxide observed by the visible spectrophotometer at Zvenigorod, Russia

We present an analysis of the results of measurements of nitrogen dioxide (NO2) content at the Zvenigorod Research Station of the A. M. Obukhov Institute of Atmospheric Physics, which is located 50 km west of Moscow. Systematic NO2 observations at Zvenigorod started in 1990 and are carried out with a zenith viewing grating spectrophotometer in the 435-450 nm wavelength range during morning and evening twilight. Measurements within a wide range of air-mass factors allow the retrieval of vertical profiles of NO2 and the determination of stratospheric and tropospheric NO2 content. Analysis shows that stratospheric and boundary-layer NO2 exhibit very different temporal behaviours. Stratospheric NO2 undergoes very prominent and regular diurnal and annual cycles associated with photochemical processes, as well as less regular intra-annual and inter-annual variations. Boundary-layer NO2 is very changeable and is significantly affected by pollution episodes. Boundary-layer NO2 exhibits irregular diurnal, weekly, intra-annual (within 15-100 day periods) and annual variations. Intra-annual variations of stratospheric and boundary-layer NO2 content with similar time scales can be coherent, but the time lag between these variations varies with time.