Intensified modulation of aerosol pollution in China by El Niño with short duration

Abstract. El Nino-Southern Oscillation (ENSO), a phenomenon of periodic changes in sea surface temperature in the equatorial central eastern Pacific Ocean, is the strongest signal of interannual variability in the climate system with a quasi-period of 2–7 years. El Nino events have been shown to have important influences on meteorological conditions in China. In this study, the impacts of El Nino with different durations on aerosol concentrations and haze days during December-January-February (DJF) in China are quantitatively examined using the state-of-the-science Energy Exascale Earth System Model version 1 (E3SMv1). We find that PM2.5 concentrations are increased by 1–2 µg m−3 in the northeastern and southern China and decreased by up to 2.4 µg m−3 in central-eastern China during El Nino events relative to the climatological means. Compared to long duration (LD) El Nino events, El Nino with short duration (SD) but strong intensity causes northerly wind anomalies over central-eastern China, which is favorable for aerosol dispersion over this region. Moreover, the anomalous southeasterly winds weaken the wintertime prevailing northwesterly in northeastern China and facilitate aerosol transport from South and Southeast Asia, enhancing aerosol increase in northeastern China during SD El Nino events relative to LD El Nino events. In addition, the modulation on haze days by SD El Nino events is 2–3 times more than that by LD El Nino events in China. The aerosol variations during El Nino events are mainly controlled by anomalous aerosol accumulation/dispersion and transport due to changes in atmospheric circulation, while El Nino-induced precipitation change has little effect. The occurrence frequency of SD El Nino events has been increasing significantly in recent decades, especially after 1940s, suggesting that El Nino with short duration have exerted increasingly intense modulation on aerosol pollution in China over the past few decades.