山地型城市冬季大气重污染过程特征及成因分析

以阳泉市2018年12月26日~2019年1月20日发生的典型大气重污染过程为例，研究了山地型城市冬季大气重污染过程特征及成因.结果表明，重污染发生时段首要污染物为PM_2.5，水溶性离子和碳质组分是PM_2.5主要组分，其中二次离子SO₄^2-、NO₃^-和NH₄⁺是主要水溶性离子成分（共占离子组分的87.7%），二次有机碳（SOC）是碳质组分的主要成分（71.6%）.二次离子在重污染发生时的浓度较发生前增加5.3倍，是导致PM_2.5快速增长的重要组分.气象条件分析显示，PM_2.5及其主要组分皆与相对湿度呈显著正相关关系而与风速呈显著负相关，随相对湿度增加以及平均风速降低，污染程度逐渐加重.山地型城市相对湿度较高、温度变化幅度大等气象特征使二次污染物的生成加快，是导致PM_2.5污染程度快速加重的主要原因.另外，山地型城市相对封闭的地形导致的平均风速降低使得大气污染物扩散条件相对较差是污染物累积的原因之一.PMF模型解析结果为：二次源（46.0%）对PM_2.5贡献显著，其次为燃煤源（32.6%）、机动车源（19.8%）和扬尘源（1.6%）.因此，山地型城市更应该重视对二次组分，特别是二次离子形成的前体物的管控.

Characteristics and Cause Analysis of Heavy Air Pollution in a Mountainous City During Winter

Taking the typical heavy air pollution process in Yangquan from December 26, 2018 to January 20, 2019 as an example, the characteristics and cause analysis of heavy air pollution in a mountainous city in winter were analyzed in this study. The results showed that fine particle mass (PM_2.5) was the primary pollutant during the heavy pollution period. The water-soluble ions and carbonaceous components were the main components of PM_2.5. The secondary ions of SO₄^2-, NO₃^-, and NH₄⁺ had the lager contribution to water-soluble ions (87.7%), and the secondary organic carbon (SOC) was the main component of the carbonaceous components (71.6%). The concentration of the secondary ions during the heavy pollution period increased by 5.3 times compared to levels before the heavy pollution period, and was an important component resulting in the fast increase of PM_2.5. An analysis of meteorological conditions showed that PM_2.5 and its main components had a significantly positive relationship with humidity and a significantly negative relationship with wind speed. And that pollution became stronger with an increase in humidity and a decrease in wind speed. The typical meteorological characteristics of mountainous cities are high relative humidity and large temperature variations, which can accelerate the formation of secondary pollutants and are the main reasons for the rapid aggravation of PM_2.5. In addition, the lower average wind speed caused by the relatively closed terrain in mountainous cities makes the diffusion conditions of air pollutants relatively poor, which is one of the reasons for the accumulation of pollutants. The source apportionment results showed that the secondary sources (46.0%) were the most important source of PM_2.5, followed by coal combustion (32.6%), vehicle exhaust (19.8%), and fugitive dust (1.6%). Therefore, mountainous cities should pay more attention to controlling secondary components, especially secondary ions.