Studies on the visibility index-classified system in Shanghai

Based on the analysis of history data of hourly visibility from 1999 to 2002,the visibility class for Shanghai City was established. Through the analysis of meteorological and contaminative factors affecting the change of visibility. The main factors affecting the visibility were contamination, cloudage, relative humidity and weather condition. Based on these, the visibility index-classified system of Shanghai City atmosphere was established; and the main factors affecting each visibility class were discussed. While the visibility is bad, elements arranged according to their importance impacting the visibility are as follows, pollutants, cloudage and relative humidity and weather condition; while the visibility is baddish, the three ones do the same; while the visibility is medium, weather condition plays the most important role, and the visibility is good, there is no necessity to give out the impacting elements.