城市化对北京霾日数影响统计分析

近年来,随着超大城市/城市群大气灰霾等复合污染加剧,引起人们对区域生态环境与及公共健康问题越来越多的关注。应用北京地区1980—2012年气候资料及同期城市发展统计指标,统计分析了城、郊区间霾日数的变化特征,并在此基础上探讨了北京城市化及局地气候差异对霾日数的影响。分析表明：北京城区霾日数要明显多于郊区,在2007年以前城、郊区站点均有相似的波动增长趋势,但城区站霾日数增加速率（约21 d/10 a）要远大于郊区站（约7.2 d/10 a）;北京各地霾日数与主要城市发展指数之间的相关系数均超过0.001显著性水平,随着城市化而迅速增加的能源消耗和机动车尾气排放是导致北京地区灰霾天气逐渐增多的主要污染源,污染源的不均匀分布是导致城、郊霾日数差异的主要因素。分析还发现,城市化导致的区域气候差异对局地灰霾亦有较明显的影响。伴随着城市化的快速发展,城、郊区气候差异逐渐变大,城市下垫面粗糙度增加导致近地面层风速减小。大城市热岛效应背景下,更容易出现较厚的逆温层,这将阻碍空气垂直方向的对流输送。此外,城区气温持续上升,相对湿度下降,平均风速减小,小风频率增加,也会阻碍空气的水平流通,使得城市排放颗粒污染物的扩散难以扩散,有利于霾日增加。这表明北京地区城市气候效应对区域生态环境具有不可忽视的影响。

Statistical analysis of the effects of urbanization on haze days in Beijing area

Regional ecological environment and public health problems are given more and more focus in recent years as the atmospheric pollution in metropolis or city cycle becoming more serious. In this study, based on the annual meteorological data, hazy days and major urban development indicators during 1980--2012 in Beijing area, the trends of hazy days, major urban development indicators and climate factors trends in Beijing are analyzed, and the effect of local climate change and urbanization process on hazy days is also explored. The results show that a similar increasing trend of hazy days is found in urban and rural area before 2007, but the increasing rate of urban hazy days is larger than that of the rural, with values of 21 d/10 a and 7.2 d/10 a, respectively. The correlation coefficients between haze days and some major urban development indicators in Beijing area have a statistical significance level of 0.001, and this implies that the ever-increasing energy consumption and vehicle emissions are one of the major sources resulting in an increase in haze days in Beijing area. Furthermore, the distinct of hazy days between the urban and rural areas is mainly due to the asymmetric distribution of pollution sources. In addition, we found that the climate difference between the urban and rural caused by urbanization also has an effect on local haze days. The rapid urbanization in Beijing area intensifies the climate difference between the urban and rural. The urban surface wind speed is decreasing due to the increasing roughness of underlying surface, and under the metropolis heat island effect the deep temperature inverse occurs easily and baffles the air vertical convection; moreover, the air horizontal advection is also baffled due to the urban increasing temperature and decreasing humidity and average wind speed. These cause difficulties in the urban contamination diffusion and benefit the increasing of hazy days. Our results imply that the effect of urbanization and urban climate on regional ecological environment cannot be ignored in Beijing.