In cleanroom and high concentration particle measurement tasks, it is often necessary to accurately dilute aerosol particles while maintaining the particle size distribution unchanged before and after dilution. Sometimes, by using aerosol dilution, the same measurement device can be used to measure aerosols with both high and low particle concentrations. The instrument collects a portion of the aerosol particles through a fine capillary tube, with the capillary flow ratio remaining constant. The rest of the aerosol is bypassed and filtered out by a HEPA filter. The two streams of air from the capillary and bypass are then uniformly mixed, diluting the particle concentration within the capillary. Maintaining a consistent ratio of capillary to bypass allows for a fixed particle dilution ratio.