基于PMF模型的北京市PM_(2.5)来源的时空分布特征

Spatial and temporal variations of ambient PM_(2.5) source contributions using positive matrix factorization

2012年8月至2013年7月,对北京市定陵、车公庄、东四、石景山、通州、房山、亦庄和榆垡等8个站点的大气细颗粒物PM2.5进行了12个月次的同步采样观测,并测定了其中元素碳、有机碳、水溶性离子和无机元素的浓度水平.利用PMF模型对PM2.5的来源进行解析.结果表明,北京市PM2.5的主要来源为二次源、燃煤、地面扬尘、机动车排放、工业源和建筑尘等,年均贡献率分别为42%、19%、19%、10%、6%和4%.PM2.5的来源具有显著的季节变化,春季大风天气频繁、地面扬尘源为主要来源,而夏、秋、冬季均以二次源为主,尤其是夏季二次源贡献达56%,冬季燃煤源对PM2.5的贡献显著提升为25%.污染源贡献也存在一定空间差异,冬春季燃煤源对郊区点的贡献显著高于城区点,而二次污染源具有区域性污染特征.在区域性积累型重污染日,二次源对PM2.5的贡献均占主要地位,对气态前体物NOx、SO2和VOCs等的控制对PM2.5的减少至关重要.

Ambient PM2.5 samples were collected simultaneously at 8monitoring sites（Dingling, Chegongzhuang, Shijingshan, Dongsi, Tongzhou, Liangxiang, Yizhuang and Yufa） in Beijing, from August 2012 to July 2013. And positive matrix factorization（PMF） was used to identify the sources of PM2.5 based on ambient PM2.5 compositional data including concentrations of organic carbon（OC）, elemental carbon（EC）, ions and metal elements. Results from PMF indicated that the six major sources of ambient PM2.5 were secondary sources, coal combustion, soil dust, vehicle emission, industrial sources and construction dust, with an annual average contribution of 42%, 19%, 19%, 10%, 6% and 4%, respectively. The contributions of the sources to PM2.5 in Beijing showed significant seasonal variations. Soil dust was the primary source in spring because of the highest frequency of windy weather. Secondary sources became the major contributor in summer, autumn and winter, and even covered 56% in summer. Coal combustion exhibited increased contributions in winter with values of 25%. The contributions of the PM2.5 sources also showed some spatial differences. Coal combustion showed significantly higher contributions in suburban areas than in urban areas,whereas the secondary sources were regional. And the secondary sources were dominated during the cumulative pollution events, accounting for more than 50% of the PM2.5 mass. Strengthening the controls of gaseous precursors（NOx, SO2 and VOCs） was of great significance for the reduction of PM2.5 in Beijing.