A two-stage condenser to enhance the detection of sub-3 nm particles in a laminar flow condensation particle counter

Maximizing the number of particles counted is critical to improve the detection of sub-3 nm particles using a condensation particle counter (CPC). First, we theoretically compared two commonly used laminar-flow configurations with the sheath-capillary (often referred to as ultrafine CPC or UCPC) and the unsheathed one. Diethylene glycol (DEG) is used as the working fluid. Although the sheathed UCPC has been widely used for counting sub-3 nm particles, the unsheathed configuration offers a higher particle concentration in the condenser by eliminating the dilution effect of sheath flow. To leverage the advantages of high particle concentration in the unsheathed design and more particles going through the high supersaturation region in UCPC, we then designed a two-stage unsheathed condenser. The two-stage condenser allows for different temperatures applied to different stages, enlarging the high-supersaturation zone. The two-stage condenser was then applied to a DEG CPC. Its saturator and two stages of the condenser were set at 51 °C, 2 °C, and 20 °C, respectively. Aerosol flow rate through the condenser is 1.0 LPM, higher than that of UCPC, significantly increasing the total number of detected particles. When measuring negatively charged tungsten oxide nanoparticles, the mobility diameter of 50% detection efficiency (dp,50) is ∼1.5 nm. Additionally, dp,50 increases from ∼1.5 nm to ∼3 nm as the temperature of the first-stage condenser increases from 2 °C to 20 °C. This temperature programming feature also allows a single CPC to do size scanning. Copyright © 2026 American Association for Aerosol Research