Relations between the prevailing visibility, nephelometer scattering coefficient and sunphotometer turbidity coefficient

Abstract

Empirical relations between the visibility, nephelometer scattering coefficient and turbidity coefficients were obtained from nephelometer and sunphotometer measurements taken at the Research Triangle Park, North Carolina and the Raleigh-Durham Airport hourly prevailing visibility observations. The data spanned the period between 1972 and 1976. Using graphical techniques, the relation between the visibility V and the nephelometer scattering coefficient b was determined to be V = Ab −1 with acceptable values of A ranging between 1.5 and 2.3. Various formulae relating the visibility V and the decadic turbidity coefficient B( λ) for wavelengths λ of 380 and 500 nm to the nephelometer scattering coefficient b were obtained by the use of linear regression techniques. Averaging the set of b −1 observed for each V, a correlation coefficient of essentially unity was obtained for each year. A relation between V and b −1, for the same period as the above graphical relation, was determined to be V = 1.7 b −1. A correlation coefficient of approximately 0.8 was obtained for B( λ) and the nephelometer aerosol scattering coefficient b' (nephelometer scattering coefficient minus Rayleigh scattering coefficient). For the total time period, the relations B( λ) = gs( λ) + β( λ) b' where σ(500) = 0.054; β(500) = 1.1 km and σ(380) = 0.064; β(380) = 1.6 km were obtained.