In-Situ Laser Detection for Aerosols and Toxic Chemicals associated with Aerosols

本研究证明了激光击穿是通过两种主要的电离机制引起的。一个是多光子电离，另一个是级联电离。从氮气气体的击穿中发现，在低激光能量（<20mJ ~ 30mJ/脉冲）下，级联电离效应较小，多光子电离效应较大，而在高激光能量（>20mJ ~ 30mJ/脉冲）下，级联电离是主要的电离机制。将气溶胶引入氮气中，会促进氮气的级联电离，这是由于气溶胶上产生了电子。吸附在TiO_2气溶胶上的Eu击穿等离子体的发射强度大于游离在TiO_2上的Eu。这是因为气溶胶的大小。众所周知，破裂的可能性随着气溶胶的大小而增加。另一方面，随着Eu吸附量的增加，Ti I的强度降低，这意味着TiO_2被吸附Eu的电子引起的级联电离击穿。此外，粒子在水溶液中完全分散，并通过自然环境水体验证了击穿光谱技术的实现。结果表明，该技术可用于现场定量检测大气和环境中的气溶胶/分散颗粒，以及有毒化学品，特别是与气溶胶和颗粒有关的重金属。

In this study, it was proved that laser breakdown causes through two main ionization mechanisms. One is multiphoton ionization, and the other is cascade ionization. From the breakdown of N_2 gas, it was founded that at low laser energy (<20mJ〜30mJ/pulse), cascade ionization effect was small, and multiphoton ionization effect was relatively large, and that at high laser energy(>20mJ〜30mJ/pulse), cascade ionization was main a mechanism. Introducing aerosols into N_2 gas led to promoting of cascade ionization of N_2 That is because of electrons produced on aerosols. Emission intensity from breakdown plasmas of Eu adsorbed on TiO_2 aerosols was founded to be larger than that of Eu existing freely from TiO_2. This is because of the size of aerosols. It is known that breakdown probability increases with the size of aerosols. On the other hand, the intensity of Ti I decreased as the amount of adsorbed Eu increased, meaning that TiO_2 was breakdowned by cascade ionization induced by electrons from adsorbed Eu.Furthermore, the particles were completely dispersed in aqueous solutions and the realization of breakdown spectroscopic technique was validated by using the natural environmental waters. It was confirmed that the technique is useful for In-Situ quantitative detection of aerosols/dispersed particles in atmosphere and in environments and of toxic chemicals especially heavy metals associated with aerosols and particles.