Characteristics of atmospheric visibility and its controlling factors in Chongqing

Based on statistical analysis of atmospheric visibility observation data from 2000 to 2005 in Chongqing,the characteristics of atmospheric visibility were analyzed.The results showed that the visibility was mainly in poor condition and its seasonal and daily variations were obvious.Furthermore,the mean daily visibility declined with a little extent during recent years.Correlation analysis indicated that relative humidity and surface wind velocity were the main controlling factors to atmospheric visibility among meteorological factors.The visibility had significantly negative correlation with relative humidity in each season,while it had positive correlation with surface wind velocity.On the other hand,PM_(10) was the main cause of visibility degradation among pollution factors.Its influence on visibility degradation varied with the season and was relatively strong in winter and summer.