William R. Wiley Environmental Molecular Sciences Laboratory , Pacific Northwest National Laboratory , Richland , Washington 99354 , United States.
Department of Chemistry , University of California , Berkeley , California 94720 , United States.
Anal Chem. 2018 Aug 21;90(16):9761-9768. doi: 10.1021/acs.analchem.8b01410. Epub 2018 Jul 31.
Environmental transmission electron microscopy was employed to probe transformations in the size, morphology, and composition of individual atmospheric particles as a function of temperature. Two different heating devices were used and calibrated in this work: a furnace heater and a Micro Electro Mechanical System heater. The temperature calibration used sublimation temperatures of NaCl, glucose, and ammonium sulfate particles, and the melting temperature of tin. Volatilization of Suwanee River Fulvic Acid was further used to validate the calibration up to 800 °C. The calibrated furnace holder was used to examine both laboratory-generated secondary organic aerosol particles and field-collected atmospheric particles. Chemical analysis by scanning transmission X-ray microscopy and near-edge fine-structure spectroscopy of the organic particles at different heating steps showed that above 300 °C particle volatilization was accompanied by charring. These methods were then applied to ambient particles collected in the central Amazon region. Distinct categories of particles differed in their volatilization response to heating. Spherical, more-viscous particles lost less volume during heating than particles that spread on the imaging substrate during impaction, due to either being liquid upon impaction or lower viscosity. This methodology illustrates a new analytical approach to accurately measure the volume fraction remaining for individually tracked atmospheric particles at elevated temperatures.
环境透射电子显微镜被用于探测大气颗粒的尺寸、形态和组成在温度作用下的变化。本工作使用了两种不同的加热装置，并对其进行了校准：炉式加热器和微机电系统（MEMS）加热器。温度校准使用了 NaCl、葡萄糖和硫酸铵颗粒的升华温度以及锡的熔点。苏旺尼河富里酸的挥发进一步验证了校准至 800°C 的结果。经校准的炉式加热器用于检查实验室生成的二次有机气溶胶颗粒和野外采集的大气颗粒。在不同加热阶段对有机颗粒进行扫描透射 X 射线显微镜和近边缘精细结构光谱的化学分析表明，高于 300°C 时，颗粒的挥发伴随着碳化。然后将这些方法应用于在亚马逊中心区域采集的环境颗粒。不同类型的颗粒在加热时的挥发响应有所不同。在撞击时呈球形、更粘稠的颗粒比在撞击时在成像衬底上扩散的颗粒在加热过程中损失的体积更小，这是由于撞击时呈液态或粘度较低。这种方法为在高温下准确测量单独追踪的大气颗粒的剩余体积分数提供了一种新的分析方法。
