AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
A Two-Stage Condenser to Improve the Detection of Sub-3 nm Particles Using Diethylene Glycol Condensation Particle Counter
Mo Xue, Michel Attoui, JINGKUN JIANG, Tsinghua University, Beijing, China
Abstract Number: 172 Working Group: Instrumentation and Methods
Abstract To improve the detection of sub-3 nm particles using diethylene glycol condensation particle counter (DEG-CPC), increasing their activation efficiency and counting as many particles as possible are both important. Comparing to the conventional one stage condenser, a two-stage condenser with different temperature helps to enlarge the domain with high supersaturation of diethylene glycol vapor, and subsequently increasing the activation efficiency of sub-3 nm particles. In comparison to the sheath-capillary condenser design of ultrafine CPC (UCPC), CPC with the unsheathed condenser design has higher particle concentration by eliminating the dilution effect of sheath flow. In this study, a diethylene glycol CPC with unsheathed two-stage condenser (TS-CPC) was developed. Temperatures of the saturator and two stages of the condenser are 51°C, 2°C, and 20°C, respectively. A warmer temperature of the second stage helps to prevent homogeneous nucleation of diethylene glycol vapor. Aerosol flowrate in the TS-CPC condenser is 1 lpm, significantly higher than that used in the DEG-UCPC condenser, i.e., increasing the number of particles to be counted. The new TS-CPC was theoretically and experimentally evaluated. Theoretical analysis confirms this design expands the domain with high vapor supersaturation and increases the number of particles to be counted. 50% detection efficiency diameter, Dp50, for negative and positive charged tungsten oxide particles were measured to be ~1.5 nm and ~1.8 nm. In addition, we show that Dp50 increased from ~1.5 nm to ~3 nm when the temperature of the first stage was increased from 2 °C to 20 °C. Scanning the temperature of the first-stage offers additional benefits. Sequentially stepping every 2 °C from 2 °C to 20 °C is given as an example and stabilized detection efficiency was observed within ~36 seconds for each step.