Vaporization and ionization processes of aerosol particles in a thermal desorption aerosol mass spectrometer

2019 Fiscal Year Final Research Report

• Project/Area Number: 17H01862
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Environmental dynamic analysis
• Research Institution: Tokyo Metropolitan University
• Principal Investigator: Takegawa Nobuyuki 首都大学東京, 理学研究科, 教授 (00324369)
• Co-Investigator(Kenkyū-buntansha): 三澤 健太郎 首都大学東京, 理学研究科, 助教 (10431991)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 環境分析 / エアロゾル / 質量分析計 / 熱脱離 / イオン化過程

Outline of Final Research Achievements

Thermal desorption aerosol mass spectrometers (TDAMSs) with electron ionization are widely used for quantitative analysis of aerosol chemical composition, and the ionization efficiency of evolved gas molecules from aerosol particles is an important parameter for such analysis. We performed laboratory experiments by using a custom-made TDAMS to investigate the key factors affecting ionization efficiency. Ammonium chloride and ammonium iodide were used as test compounds. The experimental results suggest that the angular distribution of gas molecules could be an important factor affecting the ionization efficiency. To interpret the experimental results, we have developed a numerical model for simulating the dynamics of gas molecules evolved from aerosol particles. The simulation results suggest that the molecular collisions during the early stage of plume expansion could be an important mechanism affecting the observed variability in the ionization efficiency.

Free Research Field

大気化学

Academic Significance and Societal Importance of the Research Achievements

熱脱離型エアロゾル質量分析計は、世界のエアロゾル研究に幅広く活用されており、信頼性の高いデータ構築はこれらの研究の基盤となるものである。一方で、定量の根幹に関わる熱脱離過程やイオン化過程については理論的には十分に理解されておらず、経験式に依存している。本研究では、これまで考慮されてこなかった脱離点近傍での分子衝突の重要性を、実験および理論の両面から初めて示した点に学術的意義がある。