Particle-free (filtered) air enters the Sheath Flow inlet of the DMA and passes to an annular chamber at the top of the DMA. The flow then goes through a double screen of fine nylon (Dacron®) mesh to straighten the flow. The air flows downward axially through the classifier region. The Polydisperse Flow enters the DMA though an inlet pipe from the top and flows in an axial direction between two narrow concentric cylinders to evenly distribute the concentric flow and concentration distribution. This thin annular flow is introduced into the classifier region and smoothly merged with the laminar sheath-air flow.Particles with negative charge stick to the outer electrode, whereas,.moncharged (neutral) particles are removed unaffected with the Excess Flow. Positively charged particles are carried axially downward with the sheath airflow while also being attracted radially toward the center electrode due to the electric field. Particles with a narrow range of electrical mobility reach a circumferential slit with twelve holes in the center electrode and exit the DMA through the lower insulator as the Monodisperse Flow. If the optional positive polarity High Voltage controller is used, negatively charged particles with the narrow range of electrical mobility exit the DMA through the circumferential slit.