北京市铺装道路降尘污染特征及来源

为研究北京市道路降尘在不同季节的污染特征及来源，选取北京市4条典型道路得到64个采样点的道路尘样品，采集的道路尘样品经过预处理得到75 μm以下的颗粒物，经过再悬浮及实验室分析得到PM_2.5的粒径分布和化学成分谱.结果表明:不同采样高度及不同道路类型的颗粒物粒径大体分布规律一致，颗粒物质量频率存在三个峰值，分别为0.75 μm（微粒径）、2.50 μm（小粒径）、4.50 μm（大粒径）；各季节的降尘颗粒物的化学组分中质量分数最大的是元素，主要元素（含量>1%）季节变化为冬季>春季>秋季>夏季，元素富集因子法得到污染元素为Cr、Cd、Sn、Cu、Zn、Pb、As，双重元素为Bi、Ti、Ni、W、Mg、Ca、TI、Mo、V、Fe、Zr、Ba，其余16种为非富集元素；颗粒物中离子质量分数在夏季最大为9.31%，春季、秋季、冬季的离子质量分数相差不大，其中Ca2+、NO₃-、Cl-、SO₄2-占总离子质量的80%左右；碳素中w（OC）和w（EC）的季节变化均为夏季>秋季>春季>冬季，OC/ECw（OC）/w（EC）]的季节变化规律为冬季>春季>秋季>夏季.不同季节w（OC）和w（EC）的相关性大小为夏季>秋季>春季>冬季.对PM_2.5中化学组分来源分析表明，污染元素受机动车和建筑尘影响较大，与机动车尾气相比，机动车磨损造成的污染也不容小视；燃煤影响一直存在，但供暖期污染有所改善.机动车尾气、建筑尘及土壤尘对离子均有贡献，在夏季土壤尘、建筑尘、二次反应的综合影响较大，春季土壤尘影响更为突出.碳在夏秋季节受汽车尾气和建筑尘的影响较大，夏季二次反应影响不大；冬季除气象因素外，燃煤和生物质燃烧也不可忽视；春季土壤尘影响较为突出. 

Pollution Characteristics and Source Analysis of Road Dust Deposition in Beijing

A total of 64 road dust samples were collected from four typical roads in Beijing to study the pollution characteristics and sources of dust deposition in different seasons. The collected dust samples were pretreated to obtain particles below 75 μm, then particle size distribution and chemical composition spectrum of PM_2.5 were obtained through the resuscitation experiment and laboratory analysis. The distributions of particle size were consistent with different sampling height and different road types, with three larger existence probability peaks of 0.75, 2.50 and 4.50 μm. Elements were the largest proportion of chemical composition in each season. The seasonal variation of main elements (content >1%) was winter > spring > autumn > summer. The polluted elements Cr, Cd, Sn, Cu, Zn, Pb and As and double elements Bi, Ti, Ni, W, Mg, Ca, TI, Mo, V, Fe, Zr and Ba were obtained through enrichment factors. The remaining 16 species were non-enriched elements. The highest content of ions in summer was 9.31%, nearly identical to those of spring, autumn and winter. Ca2+, NO₃-, Cl- and SO₄2- accounted for about 80% of the total ion mass. The seasonal variation of w(OC) and w(EC) in carbon was the same (summer > autumn > spring > winter) while the OC/ECw(OC)/w(EC)] was winter > spring > autumn > summer. The correlation of w(OC) and w(EC) in different seasons was summer > autumn > spring > winter. Source analysis of chemical compositions in PM_2.5 indicated that vehicles and building dust had the greatest impacts on elements. The pollution of motor vehicle wear couldn't be overlook compared to exhaust emissions. The effects of coal combustion existed, but the heating period had improved. The ions were contributed by motor vehicle exhaust, building dust and soil dust. The influence of soil dust, building dust and secondary reaction was greater in summer, and the soil dust was prominent in spring. The influence of automobile exhaust and building dust was larger in summer and autumn, and the secondary reaction was not significant in summer. In addition to weather factors in winter, the influence of coal and biomass combustion couldn't be ignored, and soil dust was prominent in spring.