Intra-seasonal differences in the atmospheric systems contributing to interannual variations of autumn haze pollution in the North China Plain

Our understanding of the factors influencing the interannual variation of autumn haze pollution in the North China Plain (NCP) remains quite limited. Here, we investigate interannual variations of atmospheric haze pollution and associated atmospheric anomalies in the NCP during autumn (September, October, and November). Pronounced anticyclonic anomalies tend to be observed around northeastern Asia when more severe haze pollution occurs over the NCP during this season. However, the processes underlying the impact of the atmospheric anomalies on the NCP haze show considerable intra-seasonal differences. In September, anticyclonic anomalies impact the NCP haze via modulating the surface relative humidity (SRH) and boundary layer height (BLH), while changes in surface wind speed (SWS) are not found to be related to the NCP haze. In contrast, the interannual variation of the NCP haze has a close relationship with the changes of SWS, SRH, and BLH in both October and November. The factors responsible for formation of the anticyclonic anomalies around northeastern Asia are found to differ greatly over the 3 months. In September, the formation of anticyclonic anomalies is related to the East Atlantic (EA) pattern, which triggers an eastward propagating atmospheric wave train extending from Europe to northeastern Asia. In October, the Scandinavia teleconnection is crucial for generating anticyclonic anomalies. While in November, the formation of the anticyclonic anomalies is largely due to the joint effect of the Scandinavia and East Atlantic/Western Russian teleconnections, as well as the non-negligible influence caused by sea surface temperature anomalies in the tropical central-eastern Pacific.