Visibility is important information not only for meteorological analysis but also for operations of transport and monitoring air pollution. In this study, climatological features of visibility in the Tokyo urban area are investigated. The number of days with low visibility decreases year by year. The factors can be drying in urban areas and the improvement of air quality, and the reduction of suspended particle matters contributes more to improve the visibility than the relative humidity. The visibility shows seasonal changes; during summer, visibility decreases when photochemical smog is likely to occur, whereas the visibility increases in winter. Visibility in Tokyo can be largely affected by anthropogenic hygroscopic aerosols, which decrease visibility when relative humidity is high.
