Fog occurs more frequently over urban areas than rural areas. It may occur due to increased air pollution emanating from variety of sources in the urban areas. The increased pollution levels may lead to the atmospheric reactions resulting into the formation of secondary pollutants that may also lead to the needed cloud condensation nuclei. Northern regions of India experience severe foggy conditions during the winter period (November–January) each year. In this study, we have simultaneously measured the particulate mass concentration (0.23 µm to 20 µm), meteorological parameters and atmospheric visibility in Mega city Delhi during a winter month of the years 2007– 2008 in order to have an improved understanding of their role in fog formation. The effects of aerosols on fog formation are discussed through an analysis of trends in fog frequency and comparison with meteorological parameters, and visibility as an indicator of aerosol load. This satisfies the precondition for using these relations. The association between the meteorological parameters (visibility, depression temperature) and air pollutants are examined. The Windows software SPSS (version 17.0) is used to fit a linear regression model. The model explained the variation in visibility due to depression temperature and aerosols load.