Accurate measurement of nanoparticle charge, number and size with the ELPI+™ instrument

Abstract

Nanoparticle characterization is mainly carried out by microscopy techniques and measurements of size and concentration. However to be able to comprehensively understand the behavior of the aerosol, information on particle charge level is critical. Particle charge has a major effect on the coagulation, deposition and transport as well as on the health effects of the particles. While aged aerosols generally are mainly neutral in terms of charge, freshly generated or resuspended particles can have high charge levels that vary depending on the size, material and generation method of the particles. Charging processes for particles are problematic as they are usually both time dependent and material dependent with sudden changes in magnitude. This makes the charge of a particle nearly impossible to predict without detailed studies and direct measurements. ELPI+™ instrument is a completely new aerosol measurement instrument based on the widely used Electrical Low Pressure Impactor (ELPI) technique. ELPI+™ measures particle concentration and size in a wide size range from 6nm to 10μm in real-time. The operation is based on first charging the particles in a corona charger and then size segregating them in a cascade impactor where all impactor stages are electrically insulated. With the ELPI+™ instrument it is possible to measure not only the particle size and concentration in real-time, but also the charge distribution of the particles. As the particle size classification is made with an impactor, the measured particles can be subsequently analyzed if needed with a suitable technique.