Abstract
Vertical structure of the size distribution and number concentration of particulates in atmospheric fog and haze near Grafenwöhr, West Germany, were measured with a balloonborne light-scattering aerosol counter for periods spanning parts of eight days in February 1976. For haze (∼5 km visibility) conditions, little vertical variation is seen; but for low visibility (<1 km) fog conditions, significant vertical increases in concentration of droplets with radii larger than 4 μm are seen over the first 150 m altitude. For haze, the particle size distribution is approximated by a log-normal with geometric mean radius rg≈0.2 μm and geometric standard deviation σg≈1.9. For fog, a bimodal distribution is found with a relative maximum for the larger particle mode at radii of 4 to 6 μm and corresponding values rg≈5 μm and σg≈1.6; the smaller particle mode has values of rg≈0.3 μm to rg≈0.6 μm and σg≈1.8 to σg≈2.5. Liquid water content values for haze and fog range from 10−4 to 0.45 g m−3. Extinction calculated from the particle size distributions shows an approximate 1/λ wavelength dependence for haze conditions, but nearly neutral (wavelength independent) extinction for heavy fog. A correlation exists between calculated particulate extinction and calculated liquid water content, independent of particle size distribution, for the fogs and hues studied.
