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New method for measuring of aerosol optical thickness

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					 ON POSSIBILITY OF MEASUREMENTS OF RELATIVE WAVELENGTH
  DEPENDANCE OF OPTICAL DENSITY OF ATMOSPHERIC AEROSOL
                         USING THREE WAVES METHOD


                         H.H. ASADOV, E.S. ABBASZADEH
                        Azerbaijan National Aerospace Agency,
                        Azadlig ave., AZ1033, Baku, Azerbaijan
                              hasadzade2001@yahoo.com
         Keywords: optical density, atmospheric aerosol, measurements,
                                 compensation of errors


     According to the Beer’s Law aerosol is one of major components of atmosphere
leading to absorbtion of UV irradiation. Existing methods for measurement of optical
density of aerosol (Langley method and others) do not guarantee the necessary
accuracy, because they do not envisage compensation or full mutual compensation of
such factors as ozone ansorbtion and Reyleigh scattering. The Three Waves method
[1, 2] designated for high accuracy ozone measurement also can be used for
measurements of optical density of aerosol. According to the proposed method,
measurements are to be carried out in three points: 1 , 2 and 3 . Where 1  2  3 .
As a result we shall obtain appropriate itensivities of solar radiation I 1 , I 2 and I 3 .

Then we should carry out calculation using following formula:
                                                 I 1  I 3
                                         I k                  ,                  (1)
                                                    I 2

where k  2   ;  - varying index.
     For simplicity we assume that optical masses of aerosol, ozone and Reyleigh
scattering are equal.
     In this case the Beer formula may be written as
                                         I  I 0  A m  X     ,           (2)
                                                                                                                                          2

where I 0 - initial intensity; m -optical mass, conditionally same for all components;
X -total amount of ozone;  ,  ,  - optical densities of ozone, Reyleigh scattering
and aerosol. Taking into consideration formulaes (1) and (2) we conclude, that
                                                        3                  3                  3        
                   k   I 0 1  I 03         m X  1
                                               
                                                                  2   m  1
                                                                                           2   m  1
                                                                                                                     2  
                                                                                                                            
                                                                                                                            
             I                         A                                                          
                                                         2                         2                         2               
                                                                                                                                  . (3)
                         I 0
                              2


     Using formula (3) we should carry out following steps for measuring of aerosol
optical density:
     1. Measurements by compensation of influence of ozone. The condition for said
compensation is following
                                                               1     3 
                                                                                   21 .                                          (4)
                                                                      2
     Condition (4) can be reached by appropriate selection of wavelength 21 .
     Taking into consideration formulaes (3) and (4) we have
                                                   3                   3         
                                   l n I1  m  1               21   m  1           21  . (5)
                                                    2                      2                 
     2. Measurements by compensation of influence of Reyleing scattering. The
condition for said compensation is following:
                                                             1   3
                                                                                22 .                                             (6)
                                                                      2
     Taking into consideration formulaes (3) and (6) we have
                                         3                                     3         
                        l n I2  m X  1           22                       m 1           22  .                           (7)
                                         2                                       2                 
     Now, by substraction of formula (7) from formula (5) we can obtain following
formula expressing interrelation of increments
                                                     I1
                                               ln        m    X     m   ,                                                (8)
                                                     I2
where
                                                            1   3
                                                                            21
                                                                  2
                                                                                       3

                                            1   3
                                                        22
                                               2                   .
                                        2   1
     It is obvious, that for concrete time and point of measurements
m    X    c o n s t . In this case we can measure relative increments of optical
density of atmospheric aerosol within wavelength interval    21  22  .
     Carrying out n series of experiments ensuring partial overlap of adjacent
interval  i we can construct the resulting relative functional dependence   f   ,
which is illustrated in figure 1.
     It should be noted also, that obtained formula of increments (8) also makes it
possible to carry out fast evaluation of disperse content of aerosol, i.e. shares of fine
and coarse particles within aerosol content.
     In conclusion we would stress out that proposed three waves method as real
alternative for Dobson’s method makes it possible to carry out also other interesting
measurements which proves its universal feature.


1. Patent of Azerbaijan Republic. No. a20030134 dated 23.06.03. Three waves
ozonometer. Authors: Asadov H.H. and Isayev A.A.
2. Asadov H.H., Isayev A.A. Three waves method for measurement of total content
of ozone. Full compensation of measurements error. Proceedings Quadrennial Ozone
Symposium, 1-8 June 2004, Kos, Greece, v.1, p. 477.
                                                                         4

              

            1

      2
     3
    4



                         212                 222 214             2


                  211          221   213           223   224

Figure 1.

				
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Description: The new method for measuring of aerosol optical thickness is suggested