Temporal disparity of the atmospheric systems contributing to interannual variation of wintertime haze pollution in the North China Plain

Previous studies indicated that the meridional (northerly or southerly) wind anomalies over East China play an important role in modulating interannual variation of the winter haze pollution in the North China Plain (NCP) mainly via changing surface wind speed and humidity. Here, we report that the factors for the formation of the meridional wind anomalies over East China related to interannual variation of winter haze pollution experienced a significant interdecadal change around the mid-1990s. Before the mid-1990s, two upstream atmospheric wave trains contribute to generation of the meridional wind anomalies over East China via inducing significant geopotential height anomalies over northeast Asia. The first occurred over mid-latitude Eurasia and propagated eastward into East Asia, resembling the East Atlantic-west Russia (EAWR) pattern. The second propagated eastward along the subtropical Asian jet. Furthermore, during this period, the change in the intensity of East Asian trough (EAT) was closely linked with interannual variation of the winter haze variation in the NCP. By contrast, after the mid-1990s, the atmospheric wave train along the Asian subtropical jet was not observed. Furthermore, the connection between the EAT intensity and the winter time NCP haze variation was weak. The mid-latitude EAWR-like pattern and the El Nino-Southern Oscillation-related sea surface temperature anomalies in the tropical Pacific were possible factors that explain the meridional wind anomalies over East China. Understanding the change in the atmospheric anomalies contributing to interannual variation of the haze is essential for the prediction of haze in the NCP.