Abstract: A total of 61 meteorological stations were selected according to their positions,distances among the urban and suburban stations,data record duration and continuity.These stations were then grouped into four types,i.e.,the urban stations,the suburban stations,the outer suburban stations,and the rural stations.Based on meteorological data such as visibility,relative humidity measured at 02:00,08:00,14:00 and 20:00 as well as daily weather phenomena in Liaoning province from 1960 to 2013, the characteristics of haze day in urban and suburban regions were statistically analyzed.The results indicate that monthly variations in haze days in urban,suburban and outer suburban,and all over regions in Liaoning province all exhibit a "W"-shape pattern.The largest monthly mean number (7.6 d) of haze days occurs in the suburban area,and those in the urban and suburban (6.8 d) regions are obviously larger than those in the outer suburban area (4.9 d) and rural areas (2.3 d).Among the four areas,the haze day numbers in suburban regions are the largest,followed by the urban,outer suburban,and rural areas.In the suburban regions,the number of haze day is 31.7 d in winter,14.6 d in spring,22.1 d in summer,22.9 d in autumn.The annual mean haze day numbers in four type regions and in the whole Liaoning province all decrease during 1980 to 2013,especially in the urban region with a decreasing trend of -9.9 d/10 a but only -0.1 d/10 a in the suburban regions.The inter-decadal mean haze day number in Liaoning province slightly decreases and that in the urban area decreases significantly; it fluctuates and decreases in suburb area and outer suburb area.The monthly,seasonal,annual,and inter-decadal haze day numbers have various spatial distributions,with a multi-center distribution,which means the maximum and minimum center of haze days depend on different time scales.The largest haze day number center and the second one both occur at the urban and suburban stations such as the Shenyang,Sujiatun and Liaoyang County stations,while the lowest haze day number centers mostly occur at the outer suburban stations.The analysis results suggest that haze pollution is heavier in suburban areas.The annual haze day numbers observed at typical stations in urban,suburban,and outer suburban regions vary significantly,which is closely related to the local economic development and environmental conditions.

Key words: Haze day, Urban area, Suburban area, Outer suburban area