红色预警期间北京市PM_(2.5)浓度特征及应急措施效果评估

Characteristics and effects of emergency measures on the concentration of PM_(2.5) in Beijing during the red alerts in 2015

综合利用监测数据并结合数值模型,分析了2015年北京市第2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:污染初期北京市南部地区PM_(2.5)浓度明显偏高,且PM_(2.5)极端高值往往出现在北京南部站点.污染输送阶段,北京市PM_(2.5)小时浓度在短时内呈爆发式增长,浓度积累速率可达5~10μg·m^(-3)·h^(-1).污染缓解阶段,偏北风作用,空气质量转好.预警期间北京市空气质量南北差异较大.应急措施实施后,北京市PM_(2.5)环境浓度下降约20%~25%.PM_(2.5)累积速率呈现出交通站>城区站>背景站的特征,与重污染日平均值相比交通站下降幅度最大,表明减排措施在交通站更加显著.气象条件对重污染的形成和结束起着决定性作用,为了更好的做好空气质量预警预报工作,应加强对小尺度天气系统的研究,同时关注不同方位PM_(2.5)浓度峰值及重污染持续时间的变化,形成北京市分区预报预警的经验.

Variations of PM2.5 concentrations and effects of pollution control measures during the second red alert for air pollution in 2015 in Beijing were analyzed based on atmospheric pollutant monitoring data and numerical simulations. Results showed that in the early period of the red alert, PM2.5 concentrations were significantly higher with the highest record in the southern area of Beijing. In the air pollution transport phase, PM2.5 concentrations appeared to be in an explosive growth and the PM2.5 accumulation rate could reach up to 5- 10 μg·m-3·h-1. In the alleviated pollution stage, the PM2.5concentrations significantly decreased due to northerly winds. The PMz5 concentrations decreased by 20% -25% after the implementation of emergency response measures. The accumulation speed of PM2.5 was the highest at traffic sites and lowest at background sites. The accumulation speed of PMz5 decreased significantly at traffic sites compared to their average values from all heavily polluted days due to even and odd-numbered license plate restriction on motor vehicles. Regional weather conditions played a critical role in the formation of air pollution. In order to improve air quality forecasting and early warnings, we should strengthen investigation of small-scale weather systems and pay attention to the changes of PM2.5 peaks and duration of heavy air pollution in different directions, thereby accumulating experiences in air quality forecasting and early warning in different districts of Beijing.