资源环境科技发展态势分析平台

In recent years, persistent heavy PM_2.5 pollution (PHP) events occurred frequently over the Beijing-Tianjin-Hebei (BTH) region in China, which posed a great threat to human life. This study investigates the evolution of PHP over the BTH region in China and its relation with atmospheric quasi-biweekly oscillation. A significant periodicity of 10–16 days of the PM_2.5 concentration over the BTH region is observed in winters of 2013–2017, which notably contributes to the occurrence of PHP. A total of 12 PHP events are identified in the five winters. The life cycle of PM_2.5 pollution containing those PHP events is divided into eight phases according to the quasi-biweekly variation of PM_2.5 pollution over the BTH region. The phase composites of circulation fields show that the atmospheric quasi-biweekly oscillation provides favorable conditions for the persistence of air pollution over the BTH region in winter. During the PHP events, the quasi-biweekly southerly anomalies prevail persistently over eastern China. The East Asian winter monsoon is weakened and more moisture is transported to the BTH region continuously. The anomalous warming in the lower troposphere indicates a stable stratification on a quasi-biweekly time scale. Moreover, in the mid-troposphere, the variation of East Asian trough's intensity is significantly correlated with PHP over the BTH region. It is suggested that the quasi-biweekly oscillation of East Asian trough can be traced back to a precursor signal over northwestern Eurasia about 11 days earlier, through a southeastward wave train propagation. Thus, the meteorological conditions conducive to PHP over the BTH region can be predicted on the quasi-biweekly time scale.