Liu, W; Kaufman, SL; Osmondson, BL; Sem, GJ; Quant, FR; Oberreit, DR
TSI Inc. (Shoreview, MN) has introduced three new waterbased
condensation particle counters (WCPCS) that were designed, to detect airborne particles larger
than 2.5 nm (model 3786), 5 nm (model 3785), and either 10 or 20 nm (model 3782). These WCPCs are
well suited for real-time, environmental monitoring of number concentration of airborne ultrafine
particles. Their unique design incorporates the use of water as the working fluid instead of
alcohol. Water is odor free, readily available, and eliminates the problem of water condensation
and absorption into alcohol working fluids during operation in humid environments. In this study,
the performance of three TSI WCPCs was characterized for several aerosol compositions, including
sucrose, salt (NaCl), dioctyl sebacate (DOS), dioctyl phthalate (DOP), emery oil (poly-alpha-
olefin), silver, impurity residue particles, and ambient aerosol particles. All particles were
size selected using a nano differential mobility analyzer (nano-DMA; model 3085, TSI Inc.) to
create monodisperse challenge aerosols. The challenge aerosol was mixed uniformly With clean
makeup flow and split into a WCPC and a reference instrument to determine the counting efficiency
of the WCPC. For the model 3785 WCPC, the D-50 (i.e., the particle diameter with 50% counting
efficiency) was de-, termined to be 3.1 nm for salt particles, 4.7 nm for sucrose and ambient
particles, 5.6 nm for silver particles, and > 50 nm for ultrapure oil particles. The sensitivity
to oil droplets increased dramatically (D-50 < 10 nm) when the oil was slightly contaminated. The
D-50 of model 3786 ultrafine water-based CPC (UWCPC) was 2.4 nm for impurity residue particles.
The D50 of the model 3782 WCPC was 10.8 (with a nominal setting of 10 nm) or 19.8 nm (with a
nominal setting of 20 nm) for sucrose particles. All three WCPCs have response times of less than
2 or 3 sec and are therefore able to detect fast-changing events.