Analysis of PM_(2.5) Variations and Affecting Factors in Experimental Cities
Based on analysis of PM 2.5 variations in experimental cities in 2011,it showed that the ratio of nonattainment days ranged from 3.3% to 42.9% and annual PM2.5 concentrations were all seriously over the PM2.5 yearly criterion.PM2.5 concentration and the ratio of PM2.5 /PM10 in hazy days were respectively 80.0% and 4.1% higher than that in non-haze days.In addition,characters during seriously air polluted days in Beijing from Dec.3 to Dec.13 were analyzed,and results showed that higher particle concentration and worse weather condition were two reasons that caused lower visibility.The ratio of OC/EC ranged from 3.6 to 11.4 indicated secondary pollution existed.Particle count concentration showed a negative correlation with visibility,and particle counts in hazy days were obviously higher than that in non-haze days,with diameter of 9l.8% particles less than l μm.The weather conditions over the ground and at 850 hPa had significant influences on PM2.5 concentration.