Visibility variation trends from 1980 to 2005 have been constructed using four different statistical methods:Ridit analysis,cumulative percentiles,frequency of "very good" visibility,and annual and seasonal means.Improvements in visibility were experienced from 1980 to 1984.A decline trend can be observed after 1985 with some fluctuations in the process.In these 26 years,the mean daily visibility was 8.59 km with the maximum at 29.25 km and the minimum at 0.55 km,respectively.There were obvious seasonal and daily variation features in visibility.It was worst in winter and best in summer in one year while it was worst at 08:00 BST and best at 14:00 BST in one day.Visibility showed a positive correlation with wind speed and a negative correlation with relative humidity.However,temperature and atmospheric pressure showed comparatively little correlation with it.PM₁₀ was the major pollutant in Nanjing.Curve estimation of daily mean PM₁₀ mass concentration and the visibility presented a negative correlation and the coefficient was the largest in autumn and the smallest in summer.A regression model based on relative humidity,PM₁₀,wind speed and temperature has been developed.There were seasonal differences in the coactions of air pollution and meteorological condition on visibility,which was worse in summer than that in the other three seasons.