El Niño meets elevated Tibetan Plateau snow cover: Independent and synergistic effects on the winter PM_2.5 dipole pattern in China

Abstract. Snow cover over the Tibetan Plateau (TP) plays a vital role in shaping regional and large-scale atmospheric circulation through snow-albedo feedbacks. However, its influence on fine particulate matter (PM_2.5) pollution in China remains unclear. This study reveals that winter PM_2.5 variability in China is controlled by both anthropogenic emissions and large-scale atmospheric circulation. Large-scale circulation creates a north-south dipole pattern over eastern China, which is mainly contributed by El Niño and snow cover over the northern TP. Observational data and model simulations confirm that El Niño mainly impacts PM_2.5 in southern China by enhancing moisture transport and wet scavenging, while increased snow cover over the northern TP independently promotes accumulation and hygroscopic growth of aerosols in northern China. Moreover, El Niño and TP snow cover interact synergistically, particularly during their positive phases, intensifying circulation anomalies linked to the PM_2.5 dipole. These findings emphasize the importance of cryospheric and oceanic variability in influencing winter air quality and offer valuable insights for improving seasonal prediction of air pollution in China.