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 m are seen over the first 150 m altitude. For haze, the particle size distribution is approximated by a log-normal with geometric mean radius rg0.2 m and geometric standard deviation g1.9. For fog, a bimodal distribution is found with a relative maximum for the larger particle mode at radii of 4 to 6 m and corresponding values rg5 m and g1.6; the smaller particle mode has values of rg0.3 m to rg0.6 m and g1.8 to <IMG border="0" src="/charent/GREEK/UNACCENTED/LOWERCASE/sigma.gif">g<IMG border="0" src="/charent/ISO_CHARACTERS_MIXED/LOWERCASE/ap.gif">2.5. Liquid water content values for haze and fog range from 10<IMG border="0" src="/charent/ISO_CHARACTERS_MIXED/LOWERCASE/minus.gif">4 to 0.45 g m<IMG border="0" src="/charent/ISO_CHARACTERS_MIXED/LOWERCASE/minus.gif">3. Extinction calculated from the particle size distributions shows an approximate 1/<IMG border="0" src="/charent/GREEK/UNACCENTED/LOWERCASE/lambda.gif"> 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.