a micro - fabricated double condenser method and apparatus for the measurement of number - size distribution of airborne nanoparticles is provided . the invention is an instrument which can measure particle size under 100 nanometers in - situ . the present invention includes features such as a small nanoparticle airborne particulate analyzer , with a voltage - stable and feedback - controlled instrument package . the invention features also include a micro - fabricated nanoparticle charging and sorting device . the present invention provides a portable , lightweight , and efficacious particle - sizing instrument that is able to effectively count and size nanoparticles over a wide range of operating conditions .