ATMOSPHERIC NO3 OBSERVATIONS OVER LOW-LATITUDE NORTHERN-HEMISPHERE DURING NIGHT

Nighttime column abundance of NO3 has been measured in the low latitud e region by visible absorption spectroscopy technique. For that, direc t moonlight irradiance on the surface of the Earth has been measured n ear full Moon in the 655.0- to 667.0-nm region. Errors due to solar Fr aunhofer effect, atmospheric aerosol and Rayleigh scattering, atmosphe ric water vapor and ozone contents have been removed. High zenith angl e direct solar spectrum and low zenith angle lunar spectrum have been used as background spectra. The vertical column abundance of NO3 was f ound to be about 10 times higher than that reported earlier by others for a low latitude region.