Coupled aerodynamic and optical sizing of airborne particles

A method for aerodynamic sizing of particles, comprising:

• introducing an airflow containing particles into an inlet;
• passing the airflow through a focusing acceleration nozzle, the nozzle having an axial length, the nozzle having a output orifice sized to rapidly accelerate the flow at an exit of the acceleration nozzle;
• directing a single light beam focused near the exit of the focusing acceleration nozzle within a measurement chamber surrounding the exit of the focusing acceleration nozzle having;
• detecting light scattered from individual particles passing through the collimated light beam to provide a pulse signal;
• measuring the elapsed time between two points in the pulse signal to provide a transit time for each detected particle;
• recording the transit time of individual particles crossing the light beam to provide a count of particles at each transit time over a measurement interval;
• determining an effective air sample volume during the measurement interval from the flow rate of the airflow and the duration of the measurement interval;
• and
• outputting a particle aerodynamic size distribution from the count of particles at each transit time divided by the effective air sampling volume, wherein the aerodynamic diameter is determined from the transit time through calibration.