2015年北京市两次红色预警期间PM_(2.5)浓度特征

Concentration Characteristics of PM_(2.5) in Beijing During Two Red Alert Periods

利用北京市及周边地区大气污染物监测数据,综合分析了2015年北京市两次空气重污染红色预警期间PM_(2.5)浓度变化特征并初步评估了减排措施对PM_(2.5)浓度的影响.结果表明:第1次红色预警期间,北京市PM_(2.5)平均最高小时浓度出现在12月9日19:00,为282μg·m^(-3),单站最高小时值出现在京东南市界永乐店站,浓度达496μg·m^(-3).第2次红色预警期间,PM_(2.5)全市平均最高小时浓度出现在12月22日20:00,为421μg·m^(-3);单站最高小时值出现在京西南市界琉璃河站,浓度达831μg·m^(-3).两次红色预警累积持续时间均呈现出南部站>城区站>北部站的特征,且第2次红色预警期间PM_(2.5)浓度南北差异明显大于第1次,PM_(2.5)平均浓度在150μg·m^(-3)以上的面积明显大于第1次,第2次红色预警期间重污染面积可达总面积的93%.两次预警期间气象条件均不利于污染物的扩散,均存在不同程度的二次转化和区域输送现象,极端气象条件是重污染形成的外因,区域污染物排放量大才是导致重污染形成的内因.初步评估结果显示红色预警应急措施实施后,北京市PM_(2.5)环境浓度下降约20%~25%,减排效果显著.

Variations of PM_（2.5）concentrations and effects of pollution control measures during two red alert periods in 2015 in Beijing were analyzed based on atmospheric pollutant monitoring data. The results showed that during the first red alert,the highest hourlyaveraged PM_（2.5）concentration occurred at 19： 00 on 9th December with a value of 282 μg·m^（-3）and the highest hourly PM_（2.5）concentration appeared at Yongledian station which is near the southeast border of Beijing,with the peak concentration of 496 μg·m^（-3）.During the second red alert,the highest hourly-averaged concentration of PM_（2.5） occurred at 20： 00 on 22 th with a value of 421 μg·m^（-3）.The highest hourly PM_（2.5）concentration was monitored at Liulihe station which is near the southwest border of Beijing,with the peak concentration of 831 μg·m^（-3）. During the duration period of both red alerts,the concentrations at the southern stations were higher than those at downtown stations and the PM_（2.5）concentrations at northern stations were found to be the smallest. The difference between these two red alerts was that during the second red alert,the PM_（2.5）concentrations in southern Beijing were significantly higher than those in the northern area,while the magnitude of this south-to-north gradient was much smaller during the first one. During the second red alert,up to 93% of Beijing area showed an average PM_（2.5）concentration of above 150 μg·m^（-3）,which was much larger than that in the first one. The meteorological conditions during the two red alerts were both not conducive to the spread of pollutants. Formation of secondary pollutants and regional pollutant transport existed as well. Though the stagnant weather conditions were in favor of the development of severe pollution,large regional-wide pollutant emission was the main reason for these two heavy air pollutions in Beijing. PM_（2.5）concentrations were decreased by 20%-25% after the implementation of emergency response measures,which showed the significance of emission reduction in air pollution control.