Total column density variations of NO2 and O3 by automatic visible spectrometry over Pune, India

A single scattering radiative transfer model has been developed to calculate the air mass factors (AMFs) of NO2 and O3 for scattered light observations. The direct and scattered intensities reaching the ground have been calculated using this model, which are utilized for computation of AMFs of these species. AMFs have been used to derive the total column densities (TCDs) from slant column densities (SCDs). Daily intensity data obtained by spectroscopic observations made at Pune (18°32'N, 73°51'E) during May 2000-May 2001 are used for the computation of SCDs of NO2 and O3 by differential optical absorption spectroscopy (DOAS) technique. NO2, O3, H2O and O4 have characteristic absorption features in the visible range 462-498 nm. These features have been used in the DOAS technique. The percentage differential optical depths (DODs) of NO2, O3, H2O and O4 have been computed. The TCD of O3 has also been derived by other methods. They are in good agreement with Dobson spectrophotometer observations. Here, the daily and seasonal variations in TCDs of NO2 and O3 at Pune for the above period are discussed