||We have refined our model for the prediction ofthe brightness ofthe night sky due to man-made light pollution by the addition of an ozone layer, by the use ofa more accurate representation ofthe atmospheric molecular density variation as a function ofheight, and by using a better mathematical representation ofthe scattering angular function of aerosols. Each ofthese modifications leads to a small reduction in the predicted brightness ofthe night sky. We have also added to our model a thin layer ofdust ofarbitrary optical thickness and height above sea level. We have studied dust clouds at various heights and ofvarious optical thicknesses. Most ofour calculations have been performed for Kitt Peak National Observatory. Most calculations have used scattering and absorption coefficients appropriate for volcanic clouds; a few calculations refer to desert dust. Light pollution is reduced by a dust cloud ofmoderate density whose altitude is below about 10 km (for the V band) and increased for dust clouds at greater altitudes. Observations from good sites are not likely to be greatly affected by the increases in light pollution caused by volcanic clouds at altitudes oforder 20 km.