中国东部秋季大气黑碳分布和来源的数值模拟

Numerical simulation of black carbon distribution and sources in autumn over eastern China

应用耦合黑碳源示踪方法的区域大气化学WRF-Chem模式,对中国东部秋季黑碳气溶胶(BC)分布特征进行研究.研究发现中国中东部BC浓度较高(>2μg/m^(3)),BC高值区(>4μg/m^(3))分布在华北平原、长江三角洲、两湖及四川东部等地区.工业源、居民生活源、交通源是BC的主要排放源,其中工业源会造成近地层BC分布呈点状高值,地形及气象条件也是影响BC累积和传输的重要因素.BC浓度较高的京津冀BC以本地源贡献为主,在不同的风场及大气扩散条件下,外来源对京津冀BC贡献占比的变化较大.BC来源可分为两种情形:一是传输型:地面风速较大,外来源贡献占比达35.1%;二是静稳型:地面风速小,大气条件静稳,以本地贡献(80.1%)为主,来自京津冀周边省份(山东、河南、山西和陕西)的贡献较少(6.9%).本地源与外来源对京津冀BC贡献比呈相反的日变化特征,其中傍晚~早上,本地贡献占比维持在较高水平;午后本地贡献占比减小,外来输送明显增强.当京津冀地区受外来输送影响更大时,日变化特征更明显,外来贡献在午后占比可超过40%.

In this paper,the regional atmospheric chemistry WRF-Chem model coupled with black carbon source tracing method was used to study the distribution characteristics of black carbon(BC)in autumn in eastern China.It was found that the BC concentration in central and eastern China was higher(>2%)μg/m^(3)),and BC high value area(>4μg/m^(3))was distributed in North China Plain,Yangtze River Delta,two lakes,Eastern Sichuan and other regions.Industrial sources,residential sources and traffic sources were the main sources of black carbon emission.Among them,industrial sources can cause the distribution of near stratum BC to be in point shape and high value.Terrain and meteorological conditions were also important factors affecting the accumulation and transmission of BC.For the North China Plain with high BC concentration,the source and daily variation characteristics of Beijing-Tianjin-Hebei BC in the heavily polluted area were analyzed.It was found that Beijing-Tianjin-Hebei BC was mainly contributed by local sources,and the contribution proportion of outside sources to Beijing-Tianjin-Hebei BC varied greatly under different wind fields and atmospheric diffusion conditions.The BC sources feature can be divided into two types:1)transport type:the surface wind speed was large,and the contribution of external sources accounted for 35.1%.2)Stable type:the surface wind speed was small,the atmospheric conditions were static and stable,mainly local contribution(80.1%),and less contribution(6.9%)from provinces around Beijing-Tianjin-Hebei(Shandong,Henan,Shanxi and Shaanxi).The diurnal variation characteristics of the contribution ratio of local and outside sources to BC in Beijing,Tianjin and Hebei were opposite.From evening to the next morning,the proportion of local BC contribution remained at a high level;In the afternoon,the proportion of local contribution decreased and the external transportation increased significantly.When Beijing-Tianjin-Hebei region was more affected by external transportation,the daily variation characteristics were more obvious,and the external contribution can account for more than 40%in the afternoon.The results of this study can provide a scientific basis for ambient air quality assessment and pollution control in Beijing-Tianjin-Hebei region.