Automated Scanning Electron Microscopy Analysis of Sampled Aerosol

Airborne fine and ultrafine particles (aerodynamic diameters less than 2.5 and 0.1 μm respectively) have in recent years been recognized as major concerns for public health, due to their ability to penetrate deep into the lungs or even into the blood stream. Recent studies have furthermore found that parameters such as morphology, size, number concentration, surface area, as well as the chemical composition of particles have a high influence on the observed toxicological effects. However current aerosol legislations focus only on aerosol mass, meaning that small particles are poorly regulated due to their small contribution to the total aerosol mass concentration. New or additional legislations and measurement techniques are therefore needed to deal with the complexity of aerosols in order to establish standard procedures for measuring and regulating aerosol exposure.

Here we present the current development of an automated software-based analysis of aerosols using Scanning Electron Microscopy (SEM) and Scanning Transmission Electron Microscopy (STEM) coupled with Energy-Dispersive X-ray Spectroscopy (EDS). The automated analysis will be capable of providing both detailed physical and chemical single particle information not provided by the current standard methods. Physical parameters such as area, diameter, aspect ratio, aggregation state, and estimates of surface area will be obtained for each individual particle based on the acquired images, while automated EDS analysis will yield single particle elemental composition data, allowing size resolved chemical classification of each individual particle. The automated analysis will furthermore be able to systematically map large areas of a sample without user intervention, enabling a fast and repeatable measurement, while obtaining sufficient data for statistical analysis.