Retrieval of stratospheric O_3 and NO_2 vertical profiles using zenith scattered light observations

摘要

Daily zenith scattered light intensity observations were carried out in the morning twilight hours using home-made UV-visible spectrometer over the tropical station Pune (18°31′, 73°51′) for the years 2000-2003. These observations are obtained in the spectral range 462-498 nm for the solar zenith angles (SZAs) varying from 87° to 91.5°. An algorithm has been developed to retrieve vertical profiles of ozone (O_3) and nitrogen dioxide (NO_2) from ground-based measurements using the Chahine iteration method. This retrieval method has been checked using measured and recalculated slant column densities (SCDs) and they are found to be well matching. O_3 and NO_2 vertical profiles have been retrieved using a set of their air mass factors (AMFs) and SCDs measured over a range of 87-91.5° SZA during the morning. The vertical profiles obtained by this method are compared with Umkehr profiles and ozonesondes and they are found to be in good agreement. The bulk of the column density is found near layer 20-25 km. Daily total column densities (TCDs) of O_3 and NO_2 along with their stratospheric and tropospheric counterparts are derived using their vertical profiles for the period 2000-2003. The total column, stratospheric column and tropospheric column amounts of both trace gases are found to be maximum in summer and minimum in the winter season. Increasing trend is found in column density of NO_2 in stratospheric, tropospheric and surface layers, but no trend is observed in O_3 columns for above layers during the period 2000-2003.