Analysis of volatile nanoparticles emitted from diesel engine using TOF-SIMS and metal-assisted SIMS (MetA-SIMS)

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and metal-assisted SIMS (MetA-SIMS), which is TOF-SIMS analysis of metaldeposited sample surfaces, were applied to analyze small quantities of volatile nanoparticles emitted from a light-duty diesel engine under idling and deceleration conditions. We investigated nucleation materials, i.e., >C35 hydrocarbons, oxidation products, etc., which have lower volatility than the main components of volatile nanoparticles and control the formation of volatile nanoparticles. Oxygenated hydrocarbons were detected by TOF-SIMS in volatile nanoparticles under idling condition. Their relative intensities increased as particle diameter decreased. This resulted in the oxygenated hydrocarbons acting as nucleation materials for volatile nanoparticles under idling condition. High-molecular-weight hydrocarbons of greater than C35 were detected in volatile nanoparticles under deceleration condition by MetA-SIMS. It was concluded that the detected hydrocarbons originated in lubricants and acted as nucleation materials for volatile nanoparticles under deceleration condition. TOF-SIMS makes it possible to detect traces of low-volatility molecules due to its high-vacuum environment. MetA-SIMS is the only method of directly detecting high-molecular-weight hydrocarbons in small quantities of nanoparticles. TOF-SIMS and MetA-SIMS were proved to be useful tools for analyzing of the properties of volatile nanoparticles.