ON THE ACCURACY OF THE SIZE DISTRIBUTION INFORMATION OBTAINED FROM LIGHT EXTINCTION AND SCATTERING MEASUREMENTS .2. CASE-STUDIES

The spectral extinction coefficient and the volume scattering function both of a laboratory generated aerosol and atmospheric aerosol have been measured for a wavelength range between 400 and 700 nm. The mass size distribution (for aerodynamic diameter) of the aerosols was determined simultaneously using a low pressure impactor. It was converted to a volume size distribution (for geometric diameter). The size distribution of the aerosol and its optical properties are related by an integral equation which is ill-posed; thus the inversion of the optical data to size distribution is difficult. Using a set of several million functions which are the sum of two lognormal size distributions, solutions of the integral equation may be found by selecting those functions giving an extinction coefficient which agreed within the experimental error margin with the measurements. By this it was also possible to estimate the error margin of the inverted size distributions. It is concluded that the approximate size and volume of the accumulation mode can be determined. It appears impossible to make more than a guess about the size and volume of particles larger than 1 mum.