It is proposed a diagnostic method for the on-line, semi- continuous determination of the size and density of individual particles in the 5 nm to 100 nm size range. This is accomplished through a double size spectrometry system. Particles are first sized by their Stokes diameter, and then sized by their aerodynamic diameter. The Stokes diameter sizing gives the geometric diameter of the particle for round particles. The aerodynamic sizing is dependent on particle density as well as Stokes diameter. The result is a distribution of particle densities at each selected Stokes diameter. The Stokes sizing is done by an electrical mobility separation, the aerodynamic sizing is done using a single-stage hypersonic impactor. Since particles are singly charged, the rate of particle capture in can be measured on-line using an electrometer. The system is effective over the 5 to 100 nm diameter range.
