NO. 3 MEASUREMENT OF OZONE — WULF AND ZIMMERMAN 3 



It is the purpose of the present work to provide an adequate method 

 using the visible absorption in order that this may be employed gener- 

 ally wherever the transmission of the atmosphere for radiation in this 

 spectral region can be measured. At the same time the method yields 

 information concerning the character of the atmospheric scattering 

 at the time of the observations. Also it is beHeved that the results of 

 the application of this method will serve as a calibration for a relative 

 mxCthod of ozone determination from a single measurement of the 

 relative intensities of the radiation across the visible region. A pre- 

 liminary description of this has been given elsewhere.^ 



3. METHOD 



The optical density of the atmosphere at any particular wavelength, 

 that is, the negative logarithm of the transmission coefficient at this 

 wavelength, may be expressed very roughly as the sum of two terms, 

 one in the — 4th power of the wavelength representing pure molecular 

 scattering, and the other a term independent of wavelength but differ- 

 ing from day to day, representing a "white" scattering or ground-glass 

 effect arising from relatively large particles of dust and haze. Where 

 selective absorption by an individual atmospheric constituent is also 

 present, an additional term describing this must be included. An 

 example of this last is the absorption of ozone in which we are 

 interested. 



In general, however, owing to the presence of haze of small and 

 intermediate particle size, some additional scattering will be present, 

 requiring, as a closer approximation to the actual scattering, an addi- 

 tional term in the wavelength. Depending upon the size of the haze 

 particles, this term might contain the wavelength to the —4th or to 

 some lower power.^ For most of the observational data used in the 

 present work the wavelength-dependent scattering in excess of the 

 pure Rayleigh scattering is not large. However, if relatively heavy 

 haze were present it might become large, and an additional term or 

 termis might be required to adequately describe the scattering. 



From a study of the data used in the present work we believe that a 

 term in the wavelength to the power —2 describes the additional 

 scattering in this observational data sufficiently closely for the purpose 

 of the ozone determination. On relatively hazy days the scattering 



''' Wulf, O. R., Ann. Astrophys. Obs., Smithsonian Inst., vol. 7, p. 177, 1954. 



s It should be noted that Tien Kiu (see footnote 6) studied the behavior of 

 data from the Montezuma station using an expression containing a constant term 

 and a term in the — 4 power of the wavelength with a variable coefficient. See 

 also Dermendjian and Sekera, Journ. Opt. Soc. Amer., vol. 43, p. 1158, 1953. 



