On-Line Single Particle Mass Spectrometry of Urban Atmospheric Aerosols

一种新的在线化学分析方法正在开发中。粒子进入质谱仪的源区散射光形成氦氖激光束。散射光触发准分子激光，导致粒子的一步解吸和电离。低激光辐照度优先汽化颗粒表面；较高的辐照度使较大比例的粒子蒸发。随后用飞行时间质量分析仪记录电离物质的完整质谱。该方法将用于研究与大气气溶胶有关的微米级颗粒的表面活性有机和无机涂层。激光解吸区分n气溶胶颗粒表面分子种类与总体积分子种类的能力将作为区分层状颗粒中铵盐表面和总浓度的一种手段进行测试。激光解吸将用于检测干燥过程中颗粒表面的分式结晶。本研究的最终目标是开发一种快速在线大气气溶胶粒子化学分析方法。

A new method for on-line chemical analysis is under development. Particles entering the source region of a mass spectromter scatter light form a helium-neon laser beam. The scattered light triggers an excimer laser cousing one-step desorption and ionization of the particle. Low laser irradiances preferentially vaporize the particle surface; higher irradiances vaporize a larger fraction of the particle. A complete mass spectrum of the ionized material is subsequently recoreded with a time-of-flight mass analyzer. The method will be used to stduy surface-active organic and inorganic coatings on micron-size particles that are relevant to atmospheric aerosols. The ability of laser desorption to distinguish molecular species on the surface of n airosol particle from those in the total volume will be tested as a means of distringuishing surface and total concentrations of ammonium salt in layered particles. Laser desorption will be used to detect fractional crystallization on the surface of a particle during drying. The ultimate goal of this research is the development of a method for rapid on-line chemical analysis of atmospheric aerosol particles.