Missing ozone at high altitude: Comparison of in situ and satellite data

Abstract

An experiment was designed to measure ozone at a site on the Andes Mountains, near La Paz, Bolivia, at a height of 3420 m, with the objective of investigating the ozone reduction seen over the mountains and the increased UV-B radiation. A Brewer spectrophotometer was used for surface measurements of the vertical ozone column and UV-B radiation; the spatial ozone variation around the mountain site was obtained using Total Ozone Mapping Spectrometer (TOMS) data. The ozone column values show a decrease over the mountain region, which maximizes at about 20 Dobson units, in comparison to the values in the Pacific regions, to the west, and the continental values to the east, at about the same latitude. To investigate the reason for this missing ozone, the vertical ozone distribution was measured using electrochemical concentration cell ozonesondes. The ozone profiles were integrated downward to sea level. It is shown that this integral corresponds to the missing ozone over the mountain area. The strongest consequence of the reduced atmosphere at high altitude on the UV-B intensities is not the reduction of the ozone column but that of the Rayleigh-scattering effect. The absence of scattering considerably increases the UV-B radiation at high altitudes. For example, the ozone effect on the ratios of UV-B intensities between La Paz and Natal, a sea level station, is only 1.15, while for the Rayleigh-scattering reduction, the ratio between stations is 1.75, at 306.3 nm. Measured UV-B intensities at both sites show La Paz/Natal ratios of this order of magnitude. Copyright 2002 by the American Geophysical Union.