Negative health effects due to nanoparticles appear to correlate particularly well with number concentration or surface. Epidemiological and toxicological studies are still mainly based on total mass, or they use fuzzy proxies like "distance from a busy road" to describe personal exposure, although the health-related effects of particle number concentration are well known. We believe that this contradictory situation is due to the lack of adequate sensors on the market.

DiSCmini is based on the electrical charging of the aerosols. Positive air ions generated in a corona discharge are mixed with the aerosol. The charged particles are then detected in two stages by electrometers. The first detector stage is a pile of steel grids; small particles will preferably deposit on it by diffusion. The second stage is a high-efficiency particle filter which captures all the other particles. The mean particle size can be obtained by analysis of the two currents measured on the stages. The particle count is determined with the total current. DiSCmini detects particles ranging in size from 10 to about 500 nm, while the modal value should lie below 200 nm. The concentration range is from about 1'000 to over 1'000'000 particles per cubic centimeter. The accuracy of the measurement depends on the shape of the particle size distribution and number concentration, and is usually around 10-15% compared to a reference CPC. The unit should be serviced and calibrated once a year.