Characterization of visibility and its affecting factors over Nanjing,China

【摘要】：正Visibility,Air Pollution Index(API) and meteorological parameters over Nanjing during 2004 are analyzed using multiple statistic tools to study the characterization of visibility and the relevant affecting factors.The mean visibility during this year is 8.82km,with 57.9%less than 10km and only 0.5%more than 20km.Visibility exhibits a significant diurnal variations over Nanjing with its maximum(10.7km) at 07:00 LT and minimum(6.6km) at 16:00 LT.Significant seasonal variation of visibility is observed,with a summer maximum(9.82km) and winter minimum(8.12km).No significant weekend effect of visibility over Nanjing is found.Wavelet analysis reveals the existence of significant periodic variations in visibility,with a major period of synoptic scale(2～8days) and a quasi-two-week scale(8～17days).By using a high pass filtering technique to eliminate the seasonal trend,correlation analysis and principle component analysis (PCA) were carried out to investigate the relations between visibility and relevant factors and to understand the dominated processes/causes to the synoptic changes in visibility.Our results highlight the significant impact of synoptic weather on visibility and air pollution in Nanjing.