Leading experts contend that surface area, rather than mass, should be measured for nanoparticles, because nanoparticles have far more surface area for the same amount of mass. This increases the chance of reaction with the body.
and another slightly smaller und less costly product is on the market, the DISCmini, developed by Matter Aerosol, now a Testo Company:
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.
This gap is now closed with Matter Aerosol’s handheld version of the “Diffusion Size Classifier”, DiSCmini. The DiSCmini is a portable sensor for the measurement of particle number and average diameter with a time resolution of up to 1 second (1 Hz). The simultaneous capture of number concentration and particle size allows the specification of other characteristic parameters, such as the particles surface (Lung Deposited Surface Area, LDSA). The instrument is battery powered with a lifetime of up to 8 hours; data can be recorded on a memory card, and transferred to a external computer via USB cable.
PS. updated and corrected march 2014.