The Relationship Between Early-winter Haze Pollutions In North China And Arctic Sea Ice

In recent years,haze pollution has become the most concerning environmental issue in China due to it dramatically damaging human health and the social economy.In this study,we emphasized the close connection between the number of haze days in early winter in the North China Plain and the September-October sea ice in the west of the Beaufort Sea(R=0.51)via both observational analyses and numerical experiments.Due to efficient radiative cooling,the responses of atmospheric circulations partially manifested as reductions of surface wind speed over the Beaufort Sea and Gulf of Alaska,resulting in a warmer sea surface in the subsequent November.The sea surface temperature anomalies over the Bering Sea and Gulf of Alaska acted as a bridge.The warmer sea surface efficiently heated the above air and led to suitable atmospheric backgrounds to enhance the potential of haze weather(e.g.,a weaker East Asian jet stream and a Rossby wave-like train propagated from North China and the Sea of Japan,through the Bering Sea and Gulf of Alaska,to the Cordillera Mountains).Near the surface,the weakening sea level pressure gradient stimulated anomalous southerlies over the coastal area of China and brought about a calm and moist environment for haze formation.The thermal inversion was also enhanced to restrict the downward transportation of clear and dry upper air.Thus,the horizontal and vertical dispersion were both limited,and the fine particles were apt to accumulate and cause haze pollutionFurthermore,we focused on the enhanced responses of December-January haze days in North China to September-October sea ice in the Beaufort Sea during 1998–2015.Via both observation and numerical approaches,compared with the former period(1980–1997),the sea ice concentration in the Beaufort Sea presented large variability during 1998–2015.During1980–1997,the Beaufort Sea mainly covered by perennial ice,and the ablation and freezing of sea ice mainly occurred at the south edge of the Beaufort Sea.Thus,heavy sea ice in autumn induced negative sea surface temperature anomalies across the Gulf of Alaska in November.However,the colder sea surface in the Gulf of Alaska only induced a weak influence on the haze-associated atmospheric circulations.In contrast,during 1998–2015,the drastic change in sea ice existed near the center of the Arctic Ocean,due to the massive melting of multiyear sea ice in the western Beaufort Sea.The perennial ice cover in the western Beaufort Sea has been replaced by seasonal ice.The broader sea ice cover resulted in positive sea surface temperature anomalies in following November.Then,suitable atmospheric backgrounds were induced for haze pollution in December and January.Simultaneously,the response of the number of haze days over North China to sea ice cover increased.These findings were verified by the CESMLE simulations and aided in deepening the understanding of the cause of haze pollution.