2013年1月华北平原重霾成因模拟分析

Model Analysis of Haze Formation over the North China Plain in January 2013

2013年1月华北平原出现了罕见的重污染天气过程，并引发连续多天大范围重霾现象。利用中华人民共和国环境保护部公布的空气污染指数日值数据和气象常规观测数据，结合区域空气质量模式系统RAMS-CMAQ的模拟结果，对1月10～15日污染过程的气象要素和关键气溶胶物种时空分布特征进行了详细分析，并对灰霾成因进行了探讨。结果表明，受本次污染过程影响的区域主要分布在北京－天津－唐山、河北省中南部和山东省大部。这些地区细颗粒物（即PM2.5）日均质量浓度超过120 μg m-3，且基本被灰霾覆盖，日均能见度在5～8 km之间。其中在北京、天津、石家庄和济南市及周边地区细颗粒物日均质量浓度可达250～300 μg m-3，部分市区可超过300 μg m-3，而日均能见度则可下降至3 km以下，形成重度灰霾。此外，对气象场的分析显示，本次污染过程期间华北平原大部分地区水平风速较多年平均值偏小约20%，且有明显逆温层覆盖，北京－天津－唐山、河北省南部和山东省北部的相对湿度则较多年平均值偏高达10%～40%。这样的气象条件不仅造成污染物易于堆积，而且有利于吸湿性粒子消光效应的快速增长，使能见度明显下降，是引发灰霾的重要因素之一。在北京地区引发灰霾的主要气溶胶物种为硫酸盐、硝酸盐和铵盐，这3种无机盐对近地面的消光贡献比率达到50%以上。其中硝酸盐的消光贡献比率最高，可达总体效应的1/4，表明在这次污染过程中除相关工业源排放外，交通源排放也是北京地区主要的污染源之一。

Heavy air pollution accompanied by widespread haze clouds occurred in January 2013 over the North China Plain （NCP）. To investigate the controlling factors of the haze formation during the study period of 10-15 January 2013, the air quality modeling system RAMS-CMAQ and multiple observation data including routine weather measurements and the air pollution index （API） released by the Ministry of Environment Protection of China were applied to analyze the temporal and spatial variation features of the meteorological factors and key aerosol components. The simulation results show that a high mass burden of PM2.5, which was higher than the 120 μg m-3 generally distributed in the Beijing-Tianjin-Tangshan region, central and south Hebei Province, and most parts of the Shandong Province. The visibility over these regions broadly ranged from 5 to 8 km. Furthermore, the mass burden of PM2.5 reached 250-300 μg m-3 over Beijing, Tianjin, Shijiazhuang, Jinan, and their surrounding regions and exceeded 300 μg m-3 over their urban areas. Thus, the visibility dropped to 3 km and formed severe haze clouds over these cities. Analysis of the meteorological field shows that compared with the multi-year average, the horizontal wind speed and relative humidity at the surface decreased approximately 20% and increased 10%-40%, respectively, over the Beijing-Tianjin-Tangshan region, central and south Hebei Province, and northern Shandong Province during this pollution episode. Coupled with temperature inversion, these stable atmospheric conditions were favorable for pollutant accumulation, and the extinction ability of soluble particles was significantly enhanced due to the high relative humidity. Thus, the abnormal meteorological field was a primary reason for the haze formation in January 2013 over the NCP. Sulfate, nitrate, and ammonium were the main aerosol components responsible for the haze formation in Beijing. The contribution of these three types of inorganic salts to the total extinction exceeded 50%. Additionally, the nitrate provided the first contribution to the surface extinction at more than 25%, which implies that emissions from the transportation sector, in addition related industry sectors, were major anthropogenic sources of this pollution episode in Beijing.