Ionization efficiency of evolved gas molecules from aerosol particles in a thermal desorption aerosol mass spectrometer: Numerical simulations
Ionization efficiency of evolved gas molecules from aerosol particles in a thermal desorption aerosol mass spectrometer: Numerical simulations
复制标题
热解吸气溶胶质谱仪中气溶胶颗粒逸出气体分子的电离效率：数值模拟
DOI：
10.1080/02786826.2019.1612512
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发表时间：
2019
影响因子：
5.2
通讯作者：
and Nobuyuki Takegawa
中科院分区：
文献类型：
--
作者：
Yu Ide;Kento Uchida;and Nobuyuki Takegawa
电子电离热解吸气溶胶质谱仪被广泛用于气溶胶化学成分的定量测量。影响演化出的气体分子电离效率的物理和化学机制尚不完全清楚。我们开发了一个数值模型来模拟由气溶胶粒子演化而来的气体分子的动力学。仿真模型主要由两个部分组成。第一部分模拟了演化气体分子在汽化源附近的小区域（碰撞域）的弹性碰撞，其中分子的平均自由程比周围高真空环境中的分子短得多。第二部分模拟了从第一部分的边界到电离器的自由分子动力学。评价了从碘化铵颗粒中析出的氨和氢化氢分子的电离效率。我们的研究结果表明，在羽流膨胀的早期，分子碰撞和这些碰撞引起的分子速度的变化可能是影响观测到的电离效率变化的重要机制。然而，tdams中气溶胶粒子汽化和电离的物理和化学过程可能过于复杂，无法使用简化的数值模型定量再现。版权所有©2019美国气溶胶研究协会
Thermal desorption aerosol mass spectrometers (TDAMSs) with electron ionization are widely used to quantitatively measure aerosol chemical compositions. The physical and chemical mechanisms affecting the ionization efficiency of evolved gas molecules are not fully understood. We have developed a numerical model for simulating the dynamics of gas molecules evolved from aerosol particles. The simulation model is composed of two main sections. The first section simulates the elastic collisions of the evolved gas molecules in a small region near the vaporization source (collision domain), where the mean free paths of the molecules are much shorter than those in the surrounding high vacuum environment. The second section simulates the free-molecular dynamics from the boundary of the first section to the ionizer. The ionization efficiencies of ammonia and hydrogen iodide molecules that evolved from ammonium iodide particles were evaluated. Our results suggest that the molecular collisions during the early stage of plume expansion and possible changes in the molecular velocities induced by these collisions could be an important mechanism affecting the observed variability in the ionization efficiency. However, the physical and chemical processes of the vaporization and ionization of aerosol particles in TDAMSs may be too complex to be quantitatively reproduced using simplified numerical models.Copyright © 2019 American Association for Aerosol Research