Airflow in the exhaust piece of a fluid delivery device is forced through a series of gaps to achieve a split airflow. One component has a velocity and direction to impact on the source of the aerosol thus sweeping and entraining the aerosol off the aerosol generator into the directional air. The other airflow is used to protect the internal surfaces from aerosol deposition. The two air flows then recombine and are swept over a three dimensional surface or porous medium, used as an impaction or filtration site for determining the amount and particle size of the entrained aerosol at the exhaust exit.
