2000-2019年兰州地区秋冬季大气环流下的污染特征分析

Pollution Characteristics Under Atmospheric Circulations in Autumn and Winter in Lanzhou from 2000 to 2019

利用Lamb-Jenkinson大气环流分型法,对2000-2019年兰州地区秋冬季(当年11、12月及次年1、2月)850 hPa、700 hPa、500 hPa环流场进行环流指数分型,并分析该地区主要环流型与空气污染之间的关系。结果表明:850 hPa高度层以平直环流型为主,NE型(东北型)是主要环流型,700 hPa及500 hPa高度层均以混合型环流为主,主要环流型均为CE型(气旋东风型)。通过分析环流型与空气污染之间的关系发现,850 hPa、700 hPa和500 hPa高度层配合形成的组合环流型中,NE-CNE-CE、CNE-CE-CE、NE-CE-CE型是兰州秋冬季较易造成污染的环流型。在这3类环流型下,气团主要经由兰州市东北部进入市区,途经污染排放源地区,是造成兰州地区秋冬季污染的主要原因。NE-C-CE和E-C-CE环流型属于有利于传输扩散的环流型。在这2类环流型控制下兰州市位于低压区,气压梯度小,全天以弱上升气流为主,上升气流有利于污染物浓度降低。空气污染指数与环流型存在较好的对应,但并不能一直保持一致变化,这是因为污染变化相对于环流型变化具有一定的滞后性。

Based on daily 850 hPa,700 hPa and 500 hPa geopotential height data in Lanzhou during autumns and winters(November and December to next January and February),2000-2019,the Lamb-Jenkinson circulation classification scheme was applied to obtain circulation index types in Lanzhou.The relationship between circulation types and air pollution in Lanzhou was analyzed preliminary.The results showed that the 850 hPa level is dominated by the flat circulation type and the NE type(Northeast type)is the main circulation type.Mixed circulation occurs frequently at both 700 hPa and 500 hPa levels with CE(cyclonic easterly wind type)as a major one.By analyzing the relationship between circulation patterns and air pollution,we have found that in the combined circulation patterns at 850 hPa,700 hPa and 500 hPa,the circulation patterns of NE-CNE-CE,CNE-CE-CE,NE-CE-CE are three circulation patterns which are prone to cause pollution weather in Lanzhou.Under the control of these circulation patterns,air masses flow into the urban area mainly from the northeast of Lanzhou,passing through the area with serious pollution emission source areas,which is the main cause for the autumn and winter heavy pollution in Lanzhou.The circulations of NE-C-CE and E-C-CE are favorable for atmospheric diffusion.Dominated by the two circulation patterns,Lanzhou lies in the low pressure zone with small pressure gradient.The weak updraft is throughout the day,which is conducive to the removal of pollutants.The air pollution index and circulation patterns share a good correspondence,but cannot keep a consistent variation trend all the time,because the change of pollution has a certain delay compared with that of circulation pattern.