[Comparative analysis methods of haze distinction over Yangtze River Delta Region ]

It is crucial to compare the difference and applicability of different haze discrimination methods and its criteria in haze study. Due to the requirement of methods and limitation of data, 4 common methods in two views of regional and temporal in one site are analyzed and studied. Based on the meteorological data from 38 observatories from 1980-2009, haze-day and haze-hour number are both counted for each station, employing Method 1 and 2 (with daily mean observation) and Method 3 (with 14:00 observation). The characteristics and applicability of these three methods are also compared and summarized. Statistical results via these methods are all capable to represent the long-term trend of haze, but haze-day numbers counted via these methods show differences, which become less remarkable with decadal changes. Haze days are the most by using Method 1. Method 3 considering the weather phenomenon is more reasonable than Method 1 and 2. According to the data of visibility, relative humidity and PM2.5 concentration in northern Nanjing from May, 2012 to April, 2013, employing 4 haze discrimination methods including the additional one (QX/T 113-2010, i. e. Method 4) , haze-day and haze-hour numbers are counted and compared. The result shows that: the haze-day number obtained employing Method 3 is less than others, while the haze-day number obtained employing Method 4 is between those with Method 1 and 3; using all Methods but Method 3 can distinguish the severity of haze significantly.