京津冀地区冬半年空气污染天气分型研究

Circulation weather type classification for air pollution over the Beijing-Tianjin-Hebei region during winter

利用ERA-Interim再分析资料,采用PCT方法,对2013~2015年冬半年京津冀地区海平面气压场进行了客观分型;利用同期空气污染资料和常规气象观测资料,分析了不同天气类型下京津冀地区空气污染和气象要素特征,并选取典型重污染月份,分析了京津冀地区重污染天气过程特征及形成原因.结果表明,京津冀地区天气形势可分为9种类型,包括高压前部和高压南部等不易污染天气类型,以及高压场、高压后部、鞍型场和冷锋前部等污染天气类型;污染天气类型多表现为高湿小风,稳定能量大,最大混合层厚度低,不利于污染物扩散,各城市AQI均值多在150以上;2014年2月两次重污染过程均发生在连续多日维持高压场等污染天气型的情况下;污染过程期间高压系统演变引起北部偏北风增大,抑制了北部城市空气污染持续加重的趋势,而偏南风输送使得北部城市污染物浓度迅速升高.

Circulation weather types were identified over the Beijing-Tianjin-Hebei(BTH)region during winter based onsea surface pressure fields from ERA-Interim reanalysis dataset from2013to2015using the PCT(principal componentanalysis in T-mode)method.The characteristics of air pollution associated with key meteorological parameters underdifferent atmospheric conditions was analyzed using the corresponding time period of air pollution data and conventionalmeteorological observations.Also the causes of the occurrence of high pollution episodes and the characteristic weatherfeatures over the BTH region were investigated by analyzing typical data collected in the most polluted month.The resultsshowed that there were nine main circulation types over the BTH region,i.e.,non-polluted circulation types with highpressure to the front of the BTH region or to south of this region,and polluted circulation types with high pressure fields,the rear of high pressure,col pressure field or ahead of the cold front.Overall,the polluted circulation types werecharacterized by high relative humidity with weak winds,high stable energy and low maximum mixing depth,whichreduced the possibility of dilution of pollutants from the local area,therefore,the observed averaged air quality index(AQI)values in most cities were above150.Two heavy air pollution episodes occurred in February2014caused by thepersistent high pressure fields which lasted for a few days.The evolution of the high pressure system led to strengtheningof the northerly wind,which reduced the concentrations of pollution over north cities of the BTH,however,southerlywinds carried air pollutants to make the concentration increase rapidly in the north cities of the BTH.