Combined scanning electron microscopy and image analysis to investigate airborne submicron particles: A comparison between personal samplers

The main objectives of this study were: (i) to compare commonly used personal samplers and verify their collection efficiency with regards to submicron particles; (ii) to investigate how the submicron particles deposit onto the filter surface in order to assess the homogeneity of the deposition; (iii) to estimate the biases which could affect results when number concentration values have to be determined by particle counting.A method based on image analysis (IA) and scanning electron microscopy (SEM) is developed and adopted to investigate a large numbers of particles. Four different personal samplers were tested: the IOM sampler, the Button sampler and the German GSP for the inhalable aerosol fraction; the PEM sampler for the thoracic aerosol fraction.In order to investigate how particles distribute on the filters surface, the area of each filter was virtually divided into circular concentric areas or deposition zones (DZ). Results from different DZ of the same filter were compared.Uniformity of deposition was mostly observed for three of the four tested samplers. A significant radial distribution was observed only for the GSP sampler. The major homogeneity was found for the Button sampler.In order to estimate the relative collection efficiency between samplers, particles number concentrations determined by particle counting were compared. The GSP sampler provided the greatest concentrations but also the greatest variability. The PEM sampler provided the lowest concentrations. The homogeneity of particle deposition on the filter surface mostly affected results when counting is performed on localized areas of the filter.