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

Abstract

Abstract. El Niño–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 Niño events have been shown to have important influences on meteorological conditions in China. In this study, the impacts of El Niño with different durations on aerosol concentrations and haze days during December–January–February (DJF) in China are quantitatively examined using the state-of-the-art Energy Exascale Earth System Model version 1 (E3SMv1). We find that PM2.5 concentrations are increased by 1–2 µg m−3 in northeastern and southern China and decreased by up to 2.4 µg m−3 in central-eastern China during El Niño events relative to the climatological means. Compared to long-duration (LD) El Niño events, El Niño 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 southern and southeast Asia, enhancing aerosol increase in northeastern China during SD El Niño events relative to LD El Niño events. In addition, the modulation effect on haze days by SD El Niño events is 2–3 times more than that by LD El Niño events in China. The aerosol variations during El Niño events are mainly controlled by anomalous aerosol accumulation/dispersion and transport due to changes in atmospheric circulation, while El Niño-induced precipitation change has little effect. The occurrence frequency of SD El Niño events has been increasing significantly in recent decades, especially after the 1940s, suggesting that El Niño with short duration has exerted an increasingly intense modulation on aerosol pollution in China over the past few decades.

Abrupt emissions reductions during COVID-19 contributed to record summer rainfall in China

“…Some uncertainties in this study should be noted. Because the simulated aerosol concentrations in China are underestimated in the model in part due to the lack of treatment of nitrate and ammonium aerosols, strong wet scavenging, and less transformation from gas to particles 39 , the impact of aerosol emissions reductions on extreme precipitation could have been underestimated. In addition to the aerosol impacts on meteorological fields, studies also found that unfavorable atmospheric conditions could intensify aerosol pollution during the COVID-19 pandemic over the North China Plain 40,41 , which possibly explains the observed PM 2.5 increases in northern China (Supplementary Fig.…”

ENSO modulation of summertime tropospheric ozone over China

“…The pure ENSO influences can be more cleanly isolated using general circulation models driven by prescribed SSTs with and without ENSO signal (Zeng et al 2021). The composite differences in meteorological parameters between El Niño and La Niña years from MERRA-2 reanalysis are validated here by comparing with ERA5 reanalysis (figure S7).…”

Climate impacts of emission reductions in China during 2013–2017

“…AClean: same as Base, but anthropogenic emissions of aerosols and precursors over China are fixed at year 2017. concentration decreases with maximum decreases in the range of 12-18 μg m -3 . The low biases in CAM6 are caused by many factors including the lack of nitrate and ammonium representation, the absence of natural aerosols in the calculation of modeled PM2.5 concentrations, strong aerosol wet removal, and uncertainties in new particle formation, which have been reported in many previous studies (Yang et al, 2017a, b;Zeng et al, 2021;Ren et al, 2021). The model generally captures the percentage decreases in PM2.5 concentrations by about 20-40% in seven sub-regions over central-eastern China (Fig.…”

“…To mitigate the serious air pollution, China issued the Air Pollution Prevention and Control Action Plan in 2013 (Clean Air Alliance of China , 2013), in which a decrease in PM2.5 (PM with diameter less than 2.5 μm) by 15%-25% by year 2017, compared to 2013, was proposed for various regions of China. The emissions of major air pollutants have been reduced since then and aerosol concentrations have substantially decreased across China (Li et al, 2021). In 74 key cities in China, the annual average of observed PM2.5 concentrations decreased by 33.3% from 2013 to 2017 (Huang et al, 2018).…”