Variations of O3, NO2 and O4 densities in association with NAO indices during winter/spring of 1993/94 and 1994/95 at sub-Arctic station

A study of the atmospheric trace constituents like O3, NO2 and O4 has been made in the visible spectral region 550-595 nm. The data for the above study have been obtained from the daily observations of the light intensity taken at twilight hours in the early morning and evening by using an automatic spectrometer at the sub-Arctic station Reykjavik (64DGN, 22.6DGW) for the months December-April (winter/spring) of 1993/94 and 1994/95. The Differential Optical Absorption Spectroscopy (DOAS) technique has been used to obtain slant column density (SCD) of O3, NO2 and O4 from the above light intensity. Further, vertical column densities (VCDs) of O3 and NO2 have also been calculated at solar zenith angle (SZA) 90DG by dividing above SCD with a proper value of air mass factor. The results of the above analyses have shown that there exists a predominant daily variation in the VCDs of O3 and VCDs of NO2 at both morning and evening twilight hours. There exists one oscillation within the daily variations of O3 and NO2; this oscillation is confined to the same period of 3-10 days (visual appearance). These periodic oscillations are found to have coincided with the oscillation of the stratospheric warm and cold episodes during the above period of observations. It is interesting to note that the evening twilight hour magnitudes of O3 and NO2 are slightly higher than those of the morning twilight hour magnitudes, but they are in phase with each other. The variations of the VCD O3 and VCD NO2 have been correlated with the North Atlantic oscillation (NAO) index. The correlation coefficients are +0.21 and +0.25 between VCD O3 and NAO index in 1993/94 and 1994/95, respectively. But VCDs of NO2 seldom show any relationship with NAO index. Also, the daily variations in SCDs of O4 are studied in connection with the different types of clouds prevailing at the Arctic station during winter/spring of 1993/94 and 1994/95. There exists strong variability of O4 with variations of the type of clouds.