The effects of El Niño–Southern Oscillation on the winter haze pollution of China

Abstract

Abstract. It has been reported in previous studies that El Niño-Southern Oscillation (ENSO) influenced not only the summer monsoon, but also the winter monsoon over East Asia. This contains some clues that ENSO may affect the winter haze pollution of China, which has become a serious problem in recent decades, through influencing the winter climate of East Asia. In this work, we explored the effects of ENSO on the winter (from December to February) haze pollution of China statistically and numerically. Statistical results revealed that the haze days of southern China tended to be fewer (more) than normal in El Niño (La Niña) winter, whereas the relationships between the winter haze days of northern and eastern China and ENSO were not significant. Results from numerical simulations also showed that ENSO influenced the winter atmospheric anthropogenic aerosol content over southern China more obviously than it did over northern and eastern China. Under the emission level of aerosols for the year 2010, winter atmospheric anthropogenic aerosol content over southern China was generally greater (less) than normal in El Niño (La Niña) winter. This was because the transport of aerosols from South and Southeast Asia to southern China was enhanced (weakened), which masked the better (worse) scavenging conditions for aerosols in El Niño (La Niña) winter. The frequency distribution of the simulated daily surface concentrations of aerosols over southern China indicated that the region tended to have fewer clean and moderate (heavy) haze days, but more heavy (moderate) haze days in El Niño (La Niña) winter.

Modulation of the ENSO on Winter Aerosol Pollution in the Eastern Region of China

“…The El Niño impacts on WAP in ERC in this study is largely consistent with that in a case study (Chang et al, ). And the aerosol responses to La Niña events are similar in AOD (Figure b) and aerosol loading (Figure 9e of Zhao et al, ) over northeastern and southern China. However, our simulated and observational results related to El Niño are quite different from those of Zhao et al () over northern China, who argued that southern China is the most significant region affected by ENSO rather than northern China.…”

“…And the aerosol responses to La Niña events are similar in AOD (Figure b) and aerosol loading (Figure 9e of Zhao et al, ) over northeastern and southern China. However, our simulated and observational results related to El Niño are quite different from those of Zhao et al () over northern China, who argued that southern China is the most significant region affected by ENSO rather than northern China. This implies that there are higher uncertainties in the regional impact of El Niño events than that of La Niña events.…”

“…In ERC, the PM2.5 concentration in the North China Plain is usually intensified during the strong El Niño event due to the anomalously southeasterly winds across the North China Plain (Chang et al, ). Different from that of Chang et al (), a recent study revealed that winter haze days in northern and eastern China are not significantly related to ENSO (Zhao et al, ), while those in southern China tended to be fewer (more) than normal in El Niño (La Niña) winter.…”

“…For example, Chang et al () attempted to explain the effect of an El Niño event on PM2.5 pollution only by comparing its concentration differences between the El Niño year (2015) and the previous year (2014), which could arouse uncertainty due to lack of climatologically statistical significance using long data. In addition, the results of Chang et al () are very different from those of Zhao et al () for the North China and Northeast China region, implying that the disagreement which needs further clarification. It is of great significance to further explore the effects of ENSO on winter aerosol pollution (WAP) over ERC from the climatological perspective.…”

“…South Asian absorbing aerosol emissions composed of dust and black carbon aerosols may amplify the response of the Indian summer monsoon to ENSO forcing through radiative processes (Kim et al, ). In comparison, in the study about the effects of ENSO on aerosol contamination, it is found that ENSO has a significant effect on aerosol distribution in the atmosphere (Chang et al, ; DeFlorio et al, ; Kim et al, ; Zhao et al, ; Zhou et al, ). For example, The aerosol column concentration in the lower (middle) tropical stratosphere is usually higher (lower) than normal 6 months after El Niño, while conditions during La Niña are roughly the opposite (Zhou et al, ).…”