Air showers in the Earth's atmosphere emit UV light detectable from space. The impact of atmospheric conditions on light emission/transmission has been studied for a space-based CR observatory. The importance of scattering/ground reflection on the fraction of Cherenkov and fluorescence light received is pointed out. Measuring UV light from above, the attenuation by the ozone layer cannot be disregarded. Based upon air shower simulation, quantitative numbers of ozone attenuation are presented.