Visibility forecast in the phase of pre-condensation

Abstract

The effect on visibility of the swelling of aerosol particles due to increasing humidity is studied. The swelling can be described by <em>r(f)/r</em>(0) = (1 - <em>f</em>)^{–1/<em>μ</em>} where <em>r</em>(<em>f</em>) = particle radius at relative humidity <em>f</em> and <em>μ</em> = const μ ≈ 4 on the average. The visibility variation is expressed as <em>V</em>(<em>f</em>)/<em>V</em>(<em>f</em>₀) = [(1 - <em>f</em>)/(1 - <em>f</em>₀)]^{(<em>v</em>*–1)/<em>μ</em>} where <em>v</em>* = exponent of the aerosol size distribution ≈ 3 on the average. The last formula allows to compute the standard visual range <em>V</em>(<em>f</em>) at relative humidity <em>f</em> from the present standard visual range <em>V</em>(<em>f</em>₀) at present relative humidity <em>f</em>₀.