SUMMARY
Study of diurnal and seasonal variation of atmospheric trace gases is essential to understand our atmosphere. For this, daily zenith-sky scattered light observations have been made by UV-visible spectrometer during the period 2000-2003. Slant column densities (SCD) from morning (solar zenith angle SZA = 90º) to evening (SZA = 90º) were retrieved to see the diurnal variation of NO2, O3, H2O and O4. For the study of seasonal behavior of NO2 and O3, vertical column densities (VCD) were retrieved during the above period. For the whole period, NO2 and O3 VCD are found in a positive correlation of r = 0.72 for the morning data and r = 0.79 for the evening data. Satellites borne observations are compared with the spectroscopic observations, which are found in good correlation. It is seen that highest NO2 and O3 VCD are found in summer months (May and June) and lowest in winter months (December and January). Evening NO2 VCD are found higher compared to morning. There is found an interesting seasonal change that at Pune (18º32´ N, 73º51´ E), the evening-to-morning (PM/AM) ratios of NO2 as well as temperature maximum/minimum ratios are higher in winter months and lower in summer months during the above period. In winter months NO2 PM/AM ratio goes up to 3.8 and in summer months lowest ratio is 1.25. During the day, N2O5 can be photolyzed to regenerate NO2, which reflects in the evening hours. In the winter, nights are longest; therefore, during night NO2 to N2O5 conversion is more, hence in the morning NO2 value will be less that leads to high PM/AM ratio. O3 PM/AM ratio is slightly higher in winter months compared to summer months.