Aerosol mobility imaging

Abstract

A system and method to measure a size distribution of particles based on their electrical mobility. The method includes: introducing, via a sheath flow inlet, a particle free sheath flow into a chamber formed by two parallel walls which are separated by a gap, the chamber having a width and a length, the sheath flow having a direction along the length of the chamber and flowing a laminar manner; introducing an aerosol sample flow into the chamber downstream of the sheath inlet such that the aerosol sample flow joins the particle free sheath flow in a laminar manner; applying an electric field between the two parallel walls of the chamber, the field having a strength which varies across the width of the chamber; extracting an output aerosol flow through a first outlet downstream of the sample inlet; and outputting an excess flow equal to a sum of the sheath flow and aerosol sample flow minus the output aerosol flow. The method may also include: passing the output aerosol flow through a growth cell in a laminar manner, the growth cell having a region of wetted walls with two or more temperature regions such that the particles within the output aerosol flow grow by condensation to form droplets, and such that relative positions of droplets are indicative of particle electrical mobility; and counting and capturing a spatial position of individual droplets exiting the growth cell.