Since 2013, China has implemented a series of emission reduction policies, such as the "Clean Air Action" and the "Blue Sky Protection Campaign." Accordingly, the concentrations of air pollutants have generally decreased significantly. However, PM_2.5 pollution still occurs in China under unfavorable weather conditions. El Niño–Southern Oscillation (ENSO) is the strongest signal that modulates the interannual variations in the ocean–atmosphere system near the equator. It oscillates between its warm period (El Niño) and cold period (La Niña) and can significantly influence aerosol concentrations.

Recently, a team lead by Prof. Yang Yang from Nanjing University of Information Science and Technology studied the variability of wintertime PM_2.5 concentrations in four megacity clusters in China during ENSO events from 2014 to 2021.

Their paper reveals that the wintertime PM_2.5 concentrations in the Beijing–Tianjin–Hebei and Fenwei Plain regions during El Niño years are higher than those during La Niña years, which can be explained by the anomalous winds during ENSO events. In the Pearl River Delta region, PM_2.5 concentrations decrease in El Niño relative to La Niña years owing to the enhanced precipitation in El Niño events. In the Yangtze River Delta region, the comprehensive effects of wind and precipitation anomalies lead to the unpredictability of the impacts of ENSO on PM_2.5.

"ENSO's modulation of PM_2.5 can be stronger than the year-by-year emission changes," says Prof. Yang. The results have been published in Atmospheric and Oceanic Science Letters.

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