Intercomparison of mobility particle sizers (MPS)

Particles smaller than 100 nm in diameter are generally called ultrafine particles. Ultrafine aerosol particles are ubiquitous: They are found outdoors and indoors, in the environment as well as at workplaces. Most of them are derived from combustion and industrial processes, heating systems, and motor vehicles. The diesel engine is probably the dominant source of ultrafines in urban environment today. Adverse health aspects caused by the inhalation of ultrafine particles have been investigated intensively by e. g. Oberdorster [1]. However, neither standards nor commonly accepted guidelines exist defining requirements for suitable measuring devices and for a procedure and methodology to measure ultrafine aerosols. To provide support for ultrafine aerosol measurements at least for the workplace, ten European in stitutions active in the field of occupational safety and health published a preliminary convention on the principles which should be taken into account [2]. Several methods for measuring number concentrations and size distributions of ultrafine aerosols are known (see for example the electrical low-pressure impactor, ELPI). The measuring principle of combining a differential mobility analyzer (DMA) with a condensation particle counter (CPC) has turned out to be the preferable and most widely used method for environmental and workplace measurements. The physical principle is that the aerosol particles are first brought into charge equilibrium and then classified in a DMA according to their electrical mobility. Electrical mobility is a measure of the particle’s ability to move in an electrical field and is inversely proportional to the particle diameter. The electrical mobility diameter is particularly relevant for ultrafine particles as it is related to their diffusion and deposition (e. g. in the human lung). Once the particles are classified, their number concentration is measured by a CPC. A more