Effect of Aerosols on the Estimation of Total Ozone in an Atmospheric Column from the Measurements of Its Ultraviolet Radiance

Abstract

Values of the total ozone content of an atmospheric column are estimated from the simulated five-wave-length measurements of the intensity of radiation backscattered by a horizontally homogeneous earth-atmosphere system along the nadir direction, and after making use of an estimation procedure similar to the one developed by Mateer et al. (1971) for obtaining total ozone values from the backscatter ultraviolet (BUV) spectrometer data aboard the Nimbus 4 satellite. Model atmospheres with different ozone contents and with different kinds of aerosols but with a fixed surface pressure (1000 mb) are assumed to rest on a Lambert surface of 0.2 reflectivity. In general, estimated ozone amounts are found to differ significantly from the corresponding input to the models with the difference between these two values depending on several factors such as solar zenith angle, aerosol parameters and the wavelength pair used in the estimation. For an aerosol attenuation optical thickness of about 0.2 at 0.3800 μm (average haziness under clear sky conditions), this difference is about 0.006 atm-cm provided the analysis is restricted to cases with solar zenith angles <85°. For strong hazy conditions represented by the aerosol attenuation optical thickness of about 1.0 at 0.3800 μm, this difference is found to be as large as 0.025 atm-cm. It is also shown that the effect of tropospheric particulate pollutants on total O3 estimation can be reduced by a very significant factor in many cases if an additional spectral measurement is made available in the region of very weak O3 absorption. Such an additional measurement assists in estimating the spectral dependence of the effective albedo of the earth-lower troposphere system.