Surface and Microanalysis Science Division, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, United States.
Environ Sci Technol. 2011 Sep 1;45(17):7380-6. doi: 10.1021/es2009049. Epub 2011 Aug 10.
Elemental mapping with energy-dispersive X-ray spectroscopy (EDX) associated with scanning electron microscopy is highly useful for studying internally mixed atmospheric particles. Presented is a study of individual particles from urban airsheds and the analytical challenges in qualitatively determining the composition and origin of heterogeneous urban-air particles from high-resolution elemental maps. Coarse-mode particles were taken from samples collected in three U.S. cities: Atlanta, Los Angeles, and Seattle. Elemental maps distinguished particles with heterogeneously mixed phases from those with homogeneously mixed phases that also contained inclusions or surface adducts. Elemental mapping at low and high beam energies, along with imaging at an oblique angle helped to classify particles by origin. The impact of particle shape on X-ray microanalysis was demonstrated by having the beam enter the particle at ≥ 52° from normal. Potential misinterpretations of particle composition due to artifacts in the elemental maps were minimized by tilt imaging to reveal particle surface roughness and depth, mapping at low beam energies, noting the position of the EDX detector in the map field, and assessing differences in the mass absorption coefficients of the particle's major elements to anticipate X-ray self-absorption.
元素mapping 与能量色散 X 射线光谱学（EDX）相结合，对研究内部混合的大气粒子非常有用。本文介绍了对城市大气粒子中单个粒子的研究，以及从高分辨率元素图谱中定性确定异质城市空气粒子的组成和来源的分析挑战。采用来自美国三个城市（亚特兰大、洛杉矶和西雅图）采集的样品获取粗模态粒子。元素图谱将异质混合相的粒子与同质混合相的粒子区分开来，同质混合相的粒子还包含包裹体或表面加合物。在低能和高能束条件下进行元素映射，并以倾斜角度成像，有助于按来源对粒子进行分类。通过使光束以≥52°的角度从法线进入粒子，证明了粒子形状对 X 射线微分析的影响。通过倾斜成像揭示粒子表面粗糙度和深度、在低能束条件下进行映射、注意 EDX 探测器在图谱场中的位置以及评估粒子主要元素的质量吸收系数的差异，最小化了由于元素图谱中的伪影而对粒子成分产生的误解，以预测 X 射线自吸收。
