Nucleus Counter Research Articles

Calibration of a photoelectric cloud condensation nucleus counter

Calibrations were performed for the photodetector output of a static thermal-gradient diffusion chamber by comparing the detector signals with visual counts of the number of droplets developing in the chamber. The calibrations cover the supersaturation range 0.3% to 1 %. For each supersaturation, the CCN concentration was found to be proportional to the detector output. During the activation and growth of droplets, the time of peak signal corresponds well to the time at which droplet count is a maximum within the sample volume. The use of an average output signal over a period bracketing the mean position of the peak is a slightly better measure of droplet concentrations than the peak value. The calibration equations here derived are specific to the CCN counter used to obtain the data. Also, the calibration constants can be expected to be dependent on the type of aerosol which serve as CCN; the limited data so for available show only weak variations in the constants.

Lower Detection Limit of Aerosol Particle Counters

Aerosol particle counters based on light-scattering have a broad range of applications including cleanroom monitoring, air pollution research, and pharmaceutical studies. Each application may deal with particle materials having various refractive indices. The effect of the particle refractive index on the lower detection limit of aerosol particle counters was investigated using the Mie theory. Counting efficiency measurements were made to verify the theoretical results. Measurements were performed with PSL (polystyrene latex), silicon, silicon nitride, and silicon dioxide particles. Two commercial aerosol counters and a condensation nucleus counter were used in the study. The theoretical study showed that both the real and the imaginary parts of the particle refractive index play an important role in the lower detection limit of an aerosol counter. For transparent particles, as the absolute difference between the particle and medium refractive index increases, the lower detection limit of a counter is decreased. Light-absorbing particles generally showed a smaller lower detection limit than transparent particles. Experimental measurements agree well with the theoretical results. Among the test particles used, silicon had the largest refractive index, followed by silicon nitride, PSL, and silicon dioxide. The lower detection limit of the counters studied showed a decreasing trend with an increasing real part of the refractive index as the particle material is changed from silicon dioxide to PSL, silicon nitride, and silicon. The difference between the theoretically calculated and experimentally determined lower detection limits were found to be less than 10 percent.

Experimental comparison of an alternating temperature gradient cloud chamber and four commercial condensation nucleus counters

Experimental comparison of an alternating temperature gradient cloud chamber and four commercial condensation nucleus counters

Variation in Quantitative Respirator Fit Factors Due to Fluctuations in Leak Size During Fit Testing

Variation in fit factors during quantitative respirator fit testing was studied for a high degree of fit (aerosol fit factors > 1000) and a low degree of fit (aerosol fit factors < 1000). In a controlled human study, fit factors were determined sequentially for three different exercises by (1) an aerosol fit test (using a portable condensation nuclei counter and room aerosol as the test agent) and (2) the newly developed dichotomous-flow fit test (Dichot). For the higher level of respirator fit, the aerosol fit factors were 30 to 60 times the corresponding flow fit factors, and for the lower level of respirator fit they were 2 to 4 times the flow fit factors. A coefficient of variation (CV) of 84% (GSD 1.6) for the higher respirator fit and 178% (GSD 2.2) for the lower respirator fit data was observed in the human study when aerosol fit factors for the three exercises were pooled. In a similar mannequin study, the center sampling probe gave aerosol fit factors with a CV of 5.4% (GSD 1.05). The flow fit factors for all three exercises pooled had a CV of 36% (GSD 1.3) for the higher respirator fit and 40% (GSD 1.5) for the lower respirator fit data, while the mannequin study gave flow fit factors with a CV of 2.2% (GSD 1.02). Thus, the variation in fit factors obtained in the human study was much higher than that obtained in a mannequin study. However, the variation in the aerosol method relative to the flow method, in the human study, os of the same order of magnitude as in the mannequin study.(ABSTRACT TRUNCATED AT 250 WORDS)

Direct-reading instruments for aerosols. A review.

Direct-reading instruments for aerosols have not had the popularity within the industrial hygiene community that similar instruments for gases and vapours have enjoyed. There are several reasons for this: aerosols have complex properties that are difficult to characterize with a single measurement, commercial instruments often do not provide an accurate measure of a useful aerosol property and aerosol instruments are relatively expensive for industrial hygiene use. A variety of instruments are commercially available and are briefly reviewed. Two general classes of instruments used for industrial hygiene measurements are covered: field instruments and research instruments. The International Symposium on Air Sampling Instrument Performance held in Research Triangle Park, NC, USA, in October, 1991 included a workshop on direct-reading aerosol instruments that produced several recommendations to advance the state of the art. The two primary recommendations approved by the symposium attendees were to develop voluntary consensus standards for aerosol mass measuring instruments and optical particle counters and to develop an accurate, portable, direct-reading aerosol mass monitor. Some progress is being made on the latter recommendation through a project supported by the US Bureau of Mines. Other instruments have found specific application in industrial hygiene measurements. A miniaturized condensation nucleus counter is being used to estimate fit factors for respirators. A fibre monitor is used for monitoring asbestos, especially in asbestos abatement operations. Optical particle counters are used for low-concentration aerosols, especially in clean rooms. Aerosol research instruments are being used to evaluate and improve field instrumentation, such as respirable, thoracic and inhalable samplers and cascade impactors.(ABSTRACT TRUNCATED AT 250 WORDS)

Nanometer and ultrafine aerosols from radon radiolysis

The ability of ionizing radiation to produce condensation nuclei aerosols in filtered air is well known. Recent studies have indicated that radiolysis results initially in the production of highly diffusive, nanometer-sized (<2 nm) clusters. Aerosols in the 1–10 nm range are also produced by other processes mostly involving nucleation, e.g. for purposes of materials synthesis. Radiolytic nuclei can be formed by the binary ion-induced nucleation of the precursor vapors, such as sulfuric acid and water; ultrafine particles (>5 nm) can then evolve by coagulation and growth processes. The nanometer nuclei are, however, poorly detected by condensation nuclei counters (CNCs) since CNC efficiencies drop sharply for particle sizes <5 nm. In this work, the formation of: (1) PoO x molecular cluster aerosols from the decay of radon, and (2) sulfuric acid nanometer nuclei and ultrafine aerosols from the radiolytic oxidation of SO 2 in radon-air mixtures, were studied through wire screen-based size distribution measurements of the 218Po radioactivity associated with the aerosols. Comparisons with conventional diffusion battery-CNC derived number size distributions are also presented.

Thermal plasma synthesis of ultrafine iron particles

Ultrafine iron powder was synthesized in an atmospheric-pressure radio-frequency plasma reactor by injecting relatively course iron powder into the plasma, where it evaporated. The renucleated iron particles were characterized by means of a sampling capillary and dilution system interfaced to an electrical aerosol analyzer, a condensation nucleus counter and an electrostatic aerosol sampler. Volume-mean particle diameters for samples obtained near the downstream end of the reactor ranged from about 20 to 70 nm, with particle size increasing as the feed rate of injected iron powder was increased. A two-dimensional numerical model was developed, which solved the plasma conservation equations to predict temperature and velocity distributions, heating and evaporation of the injected iron powder, nucleation and growth of iron particles, and particle transport by convection, diffusion and thermophoresis. Mean particle diameters predicted by the model were in good agreement with the experimental data, although the data indicated broader size distributions and flatter radial profiles of particle concentration than predicted by the model.

Respirator Leak Detection by Ultrafine Aerosols: A Predictive Model and Experimental Study

The leak performance of half-mask, maintenance-free respirators was studied theoretically and experimentally. A predictive model for the theoretical protection factor and leakage flow has been developed that uses the equation of particle conservation inside and outside the respirator. An experimental study was conducted using NaCl particles of 10 nm in diameter and a condensation nucleus counter as the particle detector. A respirator fitted with controlled leak holes of 20–3000 μm in diameter was tested at steady flow rates of 10, 32, and 100 L/min. Results showed that the aerosol penetration into a respirator was strongly influenced by the filter efficiency, leak hole size, and flow rate through the respirator. The results are in good agreement with theory, but some discrepancy has been noted at lower flow rates and smaller leak hole sizes. For the dust/mist respirators, the experimental protection factor for ultrafine 0.01-μm NaCl particles ranged from 3145 to as low as 3. For the high efficiency dust/m...

Stratospheric sulfate aerosol in and near the northern hemisphere polar vortex: The morphology of the sulfate layer, multimodal size distributions, and the effect of denitrification

Measurements were made of stratospheric sulfate aerosols using a passive cavity aerosol spectrometer and a condensation nucleus counter on a NASA ER–2 aircraft in the Airborne Arctic Stratospheric Experiment of 1989. The problems of representative and accurate sampling and particle evaporation were explicitly addressed in the design of the inlets and reduction of the data. The measurements suggest that the sulfate aerosol is bimodal in the polar vortex above the mass mixing ratio maximum in the sulfate layer. It appears that a nuclei mode of small, newly formed particles exists in this region. A stronger case is made for a nuclei mode in the upper few kilometers of the troposphere and in the lower few kilometers of the stratosphere. This mode is probably a global phenomenon occurring in all seasons. Comparison of denitrified and nondenitrified air suggests that denitrification removes some of the larger sulfate particles.

Measurements of atmospheric condensation nuclei size distributions in Siberia

The least investigated atmospheric aerosol is the one in remote continental areas. In this study, measurements of condensation nuclei size distributions near Lake Baikal, Siberia, were performed. Data for total aerosol number concentration and aerosol size distribution were obtained. The measurement equipment consisted of a TSI screen diffusion battery (SDB) Model 3040 and a TSI condensational nuclei counter (CNC) Model 3020. The average aerosol number concentration was about 10 4 cm −3. The evolution of aerosol number concentration during the day is correlated with the solar radiation. The inversion problem was solved using Tihonov's regularisation procedure. The possibility of applying this algorithm was tested in computer simulations. Different forms of aerosol size distributions were observed. The maximum radius of the distributions changes from 10 nm to about 100 nm. The data obtained are in agreement with existing theories. It is planned to continue the measurements in the next years to obtain further results.

Comparison of Performances among Continuous Flow Condensation Nucleus Counters

Comparison of Performances among Continuous Flow Condensation Nucleus Counters

Characterization of Radon Decay Products in a Domestic Environment

Field measurements of the concentration and activity size distribution of radon decay products were conducted in a one-story house located in the Princeton, NJ area. Radon concentration and particle number concentration were also measured. The concentration and activity-weighted size distribution of radon decay products were determined using a microcomputer-controlled, semi-continuous screen diffusion battery system with 6 parallel sampler/detector units. A condensation nuclei counter was used for the measurements of indoor panicle number concentration. Several measurements were made in the living room as well as more than one hundred measurements in the master bedroom of the Princeton house. Aerosols were generated from taking a shower, burning a candle, smoldering a cigarette, vacuuming, and cooking. Therefore, the influence of various indoor panicle sources on the behavior of radon decay products was investigated. With panicles generated from typical household activities, Potential Alpha Energy Concentration (PAEC) increases and the unattached fraction decreases. Larger panicles generated from cigarette smoke and cooking dramatically shifted most of the radon decay products into the attached mode (15-500 nm). With regard to the higher attachment rate, the size distributions of radon decay products remained stable for long periods of time after particle generation. On the other hand, aerosols produced from candle burning and vacuuming were much smaller, with an average attachment diameter of 15 nm. These panicles did decrease the unattached fraction, especially during the aerosol generation period. However, the size distributions of radon decay products returned to the background condition within ISO minutes after the end of particle generation. In these cases, the panicles had a higher deposition rate and a lower attachment rate. The dose of alpha radiation per unit radon concentration resulting from each of these aerosol conditions was calculated using the measured activity size distributions and the most recent James dosimetric model. These doses to basal cells at a breathing rate of 0.45 m3 hr1 ranged from 3 to 14 μGy Bq−1 hr while the dose to secretory cells at a breathing rate of 1.5 m3 hr1 ranged from 13 to 77 μGy Bq−1 hr for the various aerosol conditions.

Size and critical supersaturation for condensation of jet engine exhaust particles

In situ measurements of jet engine exhaust from a Sabreliner were made by instruments on board the NCAR Electra during a brief period of coordinated flying. Particle size distribution and critical supersaturation spectra were monitored before, during, and after the encounter with the jet exhaust plume by a condensation nucleus counter, an active scattering aerosol spectrometer probe (ASASP), and a cloud condensation nuclei (CCN) spectrometer. The relationships between particle size and corresponding critical supersaturation in the background air and within the jet exhaust plume are developed. Results indicate that background particles are much more active as CCN than exhaust particles of the same size, of which less than 1:100 are active at 0.8% supersaturation. An estimate of the engine sooting efficiency lies between 3×10−5 and 10−6.

Counting Efficiency of an Improved 30-Å Condensation Nucleus Counter

The ultrafine aerosol condensation nucleus counter (UFACNC) developed by Stolzenburg and McMurry (1990) has been improved. This new instrument can detect particles as small as 30 Å in nitrogen at a sample flow rate of 2.5 cm3·s−1. This flow rate is five times that of the earlier design with the same particle counting efficiency. An increased sample flow rate causes an increase in the arrival rate of detected particles. This improves accuracy in estimating the true particle concentration in ultraclean gas systems. In order to demonstrate its high accuracy the new UFACNC was used to measure the concentration of contaminant particles in ultrafiltered nitrogen. This represents the first accurate determination of ultrafine contamination levels in large ultraclean gas systems. The nitrogen was found to contain as few as 1.28 × 10−4 particles/cm3 (3.62/ft3). The higher volumetric flow rate of the new counter reduced the sample standard deviation of the measured count rate. Therefore, in the case of a low particulate count rate, the difference between the measured and instrument noise background count rates could be more accurately resolved. In addition, the new UFACNC was used to demonstrate a new technique for size classifying ultrafine contaminant particles using only a UFACNC, i.e., without a separate size classifier. The results demonstrate that ultrafine particle size distributions can be obtained directly from a stand-alone UFACNC

An Ultrafine Aerosol Condensation Nucleus Counter

The development of a condensation nucleus counter (CNC) for detecting ultrafine aerosol (UFA) particles (particle diameter ≤20 nm) is described here. This instrument is designed specifically for high-efficiency detection and counting of ultrafine particles. It is a modified version of the TSI model 3020 continuous flow, single-particle-counting condensation nucleus counter with sequential saturator and condenser. Design modifications incorporating aerosol sheathing techniques have minimized inlet sampling losses and optimized nucleus detection efficiency. Overall counting efficiency for the UFACNC is theoretically predicted including inlet sampling, nucleus activation, and droplet detection efficiencies. The theory was experimentally verified for low concentration, mono-disperse NaCl aerosols in the 2 to 15 nm particle diameter range. The UFACNC has a counting efficiency of > 70% for particles down to 3.5 nm in diameter. Below this size counting efficiency drops sharply to zero at about 2.6 nm with 50% ef...

Calibration of a TSI Model 3025 Ultrafine Condensation Particle Counter

The registration efficiency of the TSI model 3025 ultra-fine condensation particle counter for Ag and NaCl particles of between 2 and 20 nm in diameter was determined. Taking into account the different shapes of the input aerosol size distributions entering the differential mobility analyzer (DMA) and the transfer function of the DMA, the counting efficiencies of condensation nucleus counters (CNC) for monodisperse Ag and NaCl particles were estimated. In addition, the dependence of the CNC registration efficiency on the particle concentration was investigated.

Performance of TSI 3760 Condensation Nuclei Counter at Reduced Pressures and Flow Rates

This article describes an experimental study of the performance of the TSI model 3760 clean room condensation nuclei counter (CNC) at various pressures and flow rates. Studies were made to determine the counting efficiency of the instrument in the pressure range of 0.1–1 atm and flow rate range of 0.15–1.4 L/min. The counting efficiency curves were found to be shifted to larger particle sizes as the pressure or flow rate was reduced. The low pressure and low flow rate limits of the instrument were also determined. The numerical model developed in our previous study (Zhang and Liu, 1990) was used to predict the performance of the CNC. The numerical results were compared with the experimental data and found to agree well in the pressure range of 0.2–1.0 atm and flow rate range of 0.3–1.4 L/min. Discrepancies were found to be more significant at the lower pressures and flow rates.

Performance of Disposable Respirators

AbstractAn experimental study of the filtration performance of several commercially available, NIOSH‐approved, disposable respirators was conducted using monodisperse DOP and NaCl particles with diameters in the 0.035 to 4 μm range.The aerosol penetration through the respirators were measured at flow rates of 16, 28 and 48 L/m using a condensation nucleus counter, an aerodynamic particle sizer, and a laser optical particle counter for purposes of comparison. The results obtained by these instruments were found to be in good agreement with each other in the overlapping region of particle size of the instruments.The peak penetration through the respirator filters was found to range from approximately 1.2% to 30% at 16 L/m, 3.5% to 37% at 28 L/m, and 6% to 45% at 48 L/m. The most penetrating particle size was found to lie in the 0.1 to 0.4 μm diameter range. Further, no significant difference in penetration for NaCl and DOP particles was found, suggesting that the particlebounce effect was not important in the present study.

Aerosol climatology measurements with a Nolan-Pollak counter

Abstract The Nolan-Pollak photoelectric nucleus counter was originally developed in the 1940s for aerosol climatology measurements although its versatility led subsequently to many other applications in aerosol science. It has been widely used in manual, automatic and modified forms in many parts of the world to record ambient concentraions of Aitken nuclei. The design, calibration and performance of an automatic counter is described. Measurements of Aitken nuclei at Mace Head, Ireland, are used to discuss its suitability for the purpose of aerosol climatology.

The Persistence of Seeding Effects in a Winter Orographic Cloud Seeded with Silver Iodide Burned in Acetone

Abstract A single case-study of a winter orographic cloud over the central Sierra Nevada is presented in which the effects of aerial seeding with silver iodide, an AgI NH4C1O4 mixture burned in acetone, were observed to persist for over 90 min after seeding and 100 km downwind of the seedline. A research aircraft was able to locate and track the line source of AgI using an ice nucleus counter. High ice crystal concentrations due to seeding were not apparent until more than one hour after seeding. This may have been partially due to the high natural concentrations of ice, but post-mission analysis revealed that most sampling passes during the first hour following seeding were made below the AgI seeded volume. Ice nucleus measurements confirmed sampling of the seedline from 1–1.5 h after seeding, with associated increases in ice crystal concentrations. The effectiveness of the seeding material in the field was higher than laboratory measurements would suggest.