How does El Niño-Southern Oscillation modulate the interannual variability of winter haze days over eastern China?

The haze pollution over eastern China has evident interannual variability. Based on the observed daily visibility at the meteorological stations from 1980 to 2018, the interannual variability of winter haze days (WHD) and its relation to El Niño-Southern Oscillation (ENSO) are investigated. ENSO has a significant negative modulation on the WHD over southern China (south of 30°N) and an insignificant positive modulation on the WHD over North China (north of 35°N). Based on the analyses on the haze-prone weather condition and climate variability conducive to excessive WHD anomaly at interannual time scale, anomalous subsidence with suppressed precipitation plays a dominant role for haze over southern China where wet deposition is the most important, while southerly wind anomaly plays a dominant role for haze over North China. An anomalous anticyclone (cyclone) over western North Pacific is stimulated by El Niño (La Niña) during its peak phase in winter, and the anomalous ascending (descending) motion on the northwestern flank of this anomalous anticyclone (cyclone) induces a significant excessive (deficient) precipitation over southern China, conducive to less (more) WHD over southern China during El Niño (La Niña) winters via wet deposition. The insignificant southerly (northerly) wind anomaly associated with weakened (enhanced) winter monsoon during El Niño (La Niña) is responsible for the slightly more (less) haze days over North China during El Niño (La Niña) winters.