Little is known about workplace exposures to airborne nanoparticles, even though such exposures are common and instruments capable of measuring both their concentrations and size distributions have been available for many years. To date, aerosol nanoparticle measurements have required complex and expensive instruments that have been available to few groups. Particle number concentrations have been measured with condensation particle counters (CPCs) that are capable of detecting particles as small as 2.5nm diameter. Particle size has been measured by electrophoretic mobility classification in a differential mobility analyzer (DMA). Rapid size distribution measurements are made by classifying particles in a time-varying electric field in a scanning mobility particle sizer (SMPS) that combines the DMA with CPC detection. Commercially available instruments can measure particle size distributions in as little as 1min extending as low as a few nanometers in diameter. This talk will discuss new developments that enable measurements to 1nm diameter or below with a new radial flow differential mobility analyzer. We will also present a new opposed migration aerosol classifier (OMAC) that reduces the size and complexity of aerosol mobility analyzers to the point that personal nanoparticle exposure monitors become possible.