Frederick R. Quant

A Laminar-Flow, Water-Based Condensation Particle Counter (WCPC)

A new water-based condensation particle counter (WCPC) is presented. The WCPC is a thermally diffusive, laminar flow instrument. Condensational enlargement is achieved through the introduction of a saturated airflow into a “growth tube” with wetted walls held at a temperature higher than that of the entering flow. An unsheathed, 1 L/min instrument utilizing this principle has been evaluated with various aerosols. The particle size detected with an efficiency of 50% is at or below 4.8 nm for particles sampled from vehicular emissions or ambient air, and for various laboratory-generated inorganic salts. The cut point is higher for the organic materials tested, ranging from 8 nm to 30 nm depending on the compound and purity level. An empirically determined dead-time correction factor is applied to the coincidence correction, which allows extension of the single-count mode to higher concentrations. The counting efficiencies for 80 nm oil and salt aerosols are equal, and above 97% for concentrations approaching 10 5 cm −3 . When subject to a step-fucntion change in input concentration the time required to attain 90% of the final value, including a 0.5 s lag, is 1.3 s. The corresponding exponential time constant is 0.35 s. The WCPC evaluated here is marketed as the TSI Model 3785.

Performance of condensation particle counters with three continuous-flow designs

Abstract Performance characteristics of condensation particle counters (CPCs) that use three different continuous-flow designs have been experimentally measured. Tested parameters include particle counting efficiency as a function of particle diameter and ambient temperature, particle concentration range, and response time.

Water-based condensation particle counters for environmental monitoring of ultrafine particles.

Abstract TSI Inc. (Shoreview, MN) has introduced three new water-based 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 D50 (i.e., the particle diameter with 50% counting efficiency) was determined 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 (D50 < 10 nm) when the oil was slightly contaminated. The D50 of model 3786 ultra-fine 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.

An Ultrafine, Water-Based Condensation Particle Counter and its Evaluation under Field Conditions

An ultrafine, water-based condensation particle counter (U-WCPC, TSI Model 3786) has been compared to a butanol-based ultrafine counter (U-BCPC, TSI Model 3025) for measurement of atmospheric and freeway-tunnel aerosols. The U-WCPC utilizes a warm, wet-walled growth tube to activate and grow particles through water condensation in a laminar-flow. It has an aerosol sampling rate of 0.3 L/min, and a nominal detection limit near 3 nm. Several field comparisons were made to the butanol-based instrument with the same nominal detection limit. For measurements of size-selected aerosols with diameters of 5 nm and larger the two instruments generally agreed, with a mean response within 5%. At 3 nm particle size differences were observed, and these differences varied with the data set. Measurements of ambient aerosol in Boulder, Colorado showed higher counting efficiency at 3 nm with the U-BCPC, while in a California freeway tunnel the opposite trend was observed, with higher counting efficiencies at 3 nm observed by the U-WCPC. For direct measurement of atmospheric aerosols, the two types of instruments yielded equivalent concentrations, independent of particle number concentration.

White-light Detection for Nanoparticle Sizing with the TSI Ultrafine Condensation Particle Counter

Several of the most common methods for measuring nanoparticle size distributions employ the ultrafine condensation particle counter (UCPC) for detection purposes. Among these methods, the pulse height analysis (PHA) technique, in which the optical response of the UCPC detector is related to initial particle diameter in the 3–10 nm range, prevails in applications where fast sampling is required or for which concentrations of nanoparticles are frequently very low. With the PHA technique, white light is required for particle illumination in order to obtain a monotonic relationship between initial particle diameter and optical response (pulse height). However, the popular, commercially available TSI Model 3025A UCPC employs a laser for particle detection. Here, we report on a novel white-light detection system developed for the 3025A UCPC that involves minimal alteration to the instrument and preserves normal counting operation. Performance is illustrated with pulse height spectra produced by differential mobility analyzer (DMA) – generated calibration aerosols in the 3–50 nm range.