The amplification effect of El Niño on winter heavy pollution frequency in Beijing

Abstract China has implemented stringent emission controls to reduce PM 2.5 pollution, but the impact of the El Niño-Southern Oscillation (ENSO) on regional heavy pollution events in this process remains understudied. We use the WRF-SMOKE-CMAQ modeling system to innovatively reconstruct the meteorologically-driven trends of PM 2.5 pollution in Beijing from 2013 to 2023 by setting up fixed emission scenarios and minimize the interference of anthropogenic emissions. The results show that the heavy pollution frequency (HPF) in Beijing in winter is significantly correlated with the intensity of ENSO ( r = 0.72, p < 0.05): the intensity of El Niño events is positively correlated with the HPF, and the intensity of La Niña events is negatively correlated with the HPF. Further analysis reveals that ENSO triggers anomalous 850 hPa southerly winds and 500 hPa northwesterly winds mainly through coupling with the East Asian Winter Monsoon, thus altering the low-level warm and humid transport and mid-level diffusion conditions. In addition, the ENSO-driven trans-regional transport also led to the formation of distinct spatial distribution patterns of pollution between Beijing and Tianjin–Tangshan areas.