Figure 2. Characteristics of the aerosol exposure system.

a. Photograph of exposure apparatus during nebulization with Collison generator inside the origin chamber shows the visible cloud of airborne particles in both the left (origin) and right (recipient) chambers. Placement of the Collison generator outside of the origin chamber, connected with 20 cm tubing, resulted in no visible suspended airborne particles in the chambers, and all subsequent experiments reported here had this configuration. The Grimm particle spectrometer is placed on top of the left chamber and the sampling port is located on top of the tunnel. b. The number particle size distribution with GRIMM optical counter. The fitted bimodal distribution has the median diameters of 0.44 and 1.70 µm, and geometric standard deviation of 1.25 and 1.46, for the two size modes, respectively. c. Particle number concentrations detected by Grimm laser-based particle counter sampled during four 30–60 sec intervals of the continuous one-hour nebulization.