雾和霾对北京地区大气能见度影响对比分析

Comparison of Influence of Fog and Haze on Visibility in Beijing

2011年10月8日—12月7日,在北京城区对ρ(BC)(BC为黑碳)、ρ(PM2.5)、大气能见度和气象要素进行连续观测,利用该资料分析雾和霾对大气能见度下降的影响.结果表明:观测期间大气能见度为0.6～26.7 km,其中40%以上的时间大气能见度不足5 km,ρ(PM2.5)和ρ(BC)小时平均值最高分别达416.0和17.87μg/m3.大气能见度小于5 km且持续时间超过24 h的过程出现5次,过程1～5持续的时间分别为84、79、70、35和66 h.过程1和2主要由霾导致,大气RH(相对湿度)小,持续时间长;过程3和5则均由雾引起,大气能见度平均值分别仅为1.70和1.99 km.尽管过程4持续时间最短,但是由于存在低层逆温的大气层结,并且地面风速<1 m/s,导致颗粒物在水平和垂直方向的扩散均受到抑制,加之大气平均RH达到90.8%,形成雾霾复合影响,造成颗粒物污染程度超过其余4个过程,ρ(PM2.5)和ρ(BC)平均值分别达到192.1和10.15μg/m3.

Black carbon, PM2.5 , visibility and meteorological factors were measured in Beijing from 8 October to 7 December 2011, and the differences between the effects of fog and haze on visibility were explored. The visibility ranged from 0. 6 to 26. 7 km during the observation period, and was lower than 5 km for over 40% of the period. The hourly maximum concentrations of PM2.5 and BC were 416. 0 and 17.87 μg/m3 , respectively. During the observation period, there were five episodes in which the visibility was continuously less than 5 km; these five episodes were sustained for 84, 79, 70, 35 and 66 h, respectively. Episodes 1 and 2 were induced by haze, while episodes 3 and 5 were due to fog. Episodes 1 and 2 were maintained longer than the other episodes. Episodes 3 and 5 displayed low visibility of 1.70 and 1.99 km during the observation period. Episode 4 lasted for only a relatively short period, but because of the temperature inversion and the high relative humidity （90. 8% ） , the combination of both haze and fog formed and the particulate pollution exceeded those in the other episodes. This resulted in the accumulation of PM2.5 and BC with mean values of 192. 1 and 10. 15μg/m3.