It was not until the advent of controlled electrical energy that ozone was discovered. Van Marum, observed a peculiar odor after passing an electrical discharge through oxygen and the Swiss Chemist Schonbein noted that the same odor occurred in oxygen and called it ozone.
Early scientists measured atmospheric ozone by exposing paper that had been impregnated with potassium iodide in a solution containing starch. Schonbein’s qualitative scale was used. This particular scale represented by the blueness of the exposed paper indicated the relative quantity of ozone on a scale of 1 to 10.
Today basically the methods used for measuring ozone involve optical or chemical techniques. In the global network, the Dobson spectrophotometer is the designated standard instrument for total ozone measurements. It is also used as a calibration base for other total ozone observing systems. Dobson’s determination of total ozone is based on assumptions, ie., the middle or lower layer of the stratosphere is the major part of the ozone layer. There are still many uncertainties associated with the calibrations as was pointed out by Dobson in a series of published papers in 1975. Some uncertainties involve:
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1. the possible inaccuracy of the effective ozone absorption coefficient used with the Dobson spectrophotometer and the temperature dependence of these coefficients.
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2. possible nonlinear variation of aerosol scattering coefficients in the Huggins band.
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3. the need for correction for polarized light associated with zenith or cloudy sky observations.