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In this study, we present a traceable method for determining the counting efficiency of optical particle size spectrometers (OPSS), also known as aerosol spectrometers. The primary standard consists of an aerosol generation setup, a vertical flow tube for particle homogenization and a reference optical particle counter. The OPSS under testing and the reference optical particle counter sample aerosol simultaneously through specially designed isokinetic sampling probes at number concentrations ranging from 0.5 cm−3 up to several hundred particles per cm3 (depending on the particle size). Calibration in terms of particle size relies by convention on the use of certified PS (polystyrene) spheres in the size range 100 nm - 10 μm. Here, the counting efficiency profiles of two commonly used OPSS, namely the Model 3330 OPS (TSI Inc., USA) and the 11-D monitor (Grimm GmbH, Germany) are presented for the first time and discussed within the context of the ISO 21501–1:2009 and 21501–4:2018 standards on the calibration of OPSS for indoor/outdoor measurements and optical particle counters (OPC) for clean rooms applications, respectively. We believe that this study can help manufacturers improve the design of their instruments, contribute to the further development of relevant national and international standards and pave the way for a standardised and traceable calibration of OPSS units installed at air quality monitoring stations and industrial/workplace environments.

In this study, a water-based compact handheld condensation particle counter (Hy-WCPC) is developed and its performance is evaluated. The Hy-WCPC is a small and light water-based CPC and the operating principle is the same as the conventional continuous flow conductive cooling alcohol-based condensation particle counters (CPC). This study presents the particle material dependent Hy-WCPC cut-off sizes and the particle concentration counting linearity between the Hy-WCPC and electrometer by generating silver, sodium chloride, zinc and paraffin particles. Moreover, the comparison between the Hy-WCPC and commercially available ultrafine CPC (TSI 3776) for ambient airborne particles is presented. The cut-off sizes of the Hy-WCPC for silver and paraffin particles are 3.61 nm and 5.30 nm, respectively. For sodium chloride and zinc particles, the Hy-WCPC lower detection limit is achieved less than 4 nm. Moreover, the particle concentration counting linearity between the Hy-WCPC and electrometer is presented. The excellent particle number concentration counting linearity agreement between the Hy-WCPC and electrometer is shown for the laboratory generated particles. Also, the particle concentration counting linearity between the Hy-WCPC and the TSI 3776 for outdoor ambient airborne particles is shown. The reasonable agreement between the Hy-WCPC and the TSI 3776 was obtained. In the long-term measurement of outdoor ambient airborne particles for 7 days, this agreement had been maintained, however, after 7 days, the TSI 3776 did not operate properly due to the high humidity, while the Hy-WCPC was operating without the problem.

The size-resolved counting efficiency of an in-house ultrafine condensation particle counter (IUCPC) being challenged by sodium chloride (NaCl) particles was experimentally determined with a reference electrometer TSI 3068B. The influence of several operational parameters including the saturator temperature (35 to 45 ℃), the condenser temperature (10 to 25 ℃), the capillary sample flow rate (30 to 60 mL/min) and the total flow rate (300 to 400 mL/min) on the cut-off size D50 (particle diameter with 50% counting efficiency) was investigated using response surface design of experiments (DoE). Thirty one test points with varying operational conditions including 7 replicated test points were performed to evaluate the primary effects of operational parameters and their interactive effects on the cut-off size D50 of the IUCPC. The results indicated that the saturator temperature and the condenser temperature had a greater impact on the cut-off size D50 than the capillary flow rate and the total flow rate. CFD simulation demonstrated that high capillary flow rate in the IUCPC could induce a wider diffusion zone for the core aerosol flow, making more particles enter low supersaturation area near the wall. According to the ANOVA (analysis of variance), the most influential factor for the cut-off size D50 was the condenser temperature, followed by the saturator temperature, the total flow rate and the capillary flow rate. Some interactive effects from combinations of factors on the D50 are also significant. R-squared value of 0.9176 implied that the ultimate model for the IUCPC D50 consistently fits the experimental results.

A High Temperature Condensation Particle Counter (HT-CPC) is described that operates at an elevated temperature of up to ca. 300 °C such that volatile particles from typical combustion sources are not counted. The HT-CPC is functionally identical to a conventional CPC, the main challenge being to find suitable non-hazardous working fluids, with good stability, and an appropriate vapour pressure. Some key design features are described, and results of modelling which predict the HT-CPC counting efficiency. Experimental results are presented for several candidate fluids when the HT-CPC was challenged with ambient, NaCl and diesel soot particles, and the results show good agreement with modelled predictions, and confirm that counting of particles of diameters down to at least 10 nm was achievable. Possible applications are presented, including measurement of particles from a diesel car engine and comparison with a near PMP system.

The counting efficiency of a new condensation particle counter (Palas UF-CPC) was tested and the lower detection limit regarding the diameter of graphite particles was determined. The influence of the supersaturation of the working fluid butanol was investigated which was varied by adjusting the condenser temperature at a fixed saturator temperature. As expected, the lower detection limit decreased strongly with decreasing saturator temperature. However, a limitation was reached at a particle size of 5 nm which can be explained by a limitation in the growth kinetics for droplets growing on small condensation kernels and an insufficient residence time in the condenser for these particles to grow beyond the detection limit of the optical counter.

A calibration setup has been established to calibrate or validate UN-ECE Regulation 83 compliant CPCs. A spark discharge generator (GFG 1000) is used to produce carbon particles. For charge conditioning an indirect photoelectric charger is combined with an electrostatic precipitator instead of the very common radioactive bipolar charger. The particle number concentration is determined with a Faraday cup electrometer. Detailed studies have been conducted to validate the calibration setup. The particle size classification was checked by a screen-type diffusion battery. Moreover the effect of multiple charged particles was investigated. Three independent measurements of the counting efficiency as well as the linearity of a typical regulation compliant counter were performed. The calibration setup was also compared with a similar system using a radioactive bipolar charger. The obtained results demonstrate that the counting efficiency can be measured in a particle size range from 13 nm to 60 nm with a high repeatability. A linearity check at a particle size of 55 nm is possible in a concentration range of 1000–10 000 cm 3 . The effect of multiple charged particles produced by the indirect photoelectric charger was found to be negligible. Additionally, the difference between a CAST aerosol and a GFG aerosol as a calibration material is discussed.

The detection and quantification of biological particles in the atmosphere is becoming an increasingly important field of study. One instrument designed for this purpose, known as WIBS-4, can measure individual particles and their number-size distributions in two pre-defined size ranges: (i) ∼0.3–12 μm and (ii) ∼3–31 μm (optical diameter, polystyrene latex equivalent) while also making measurements of fluorescence across two wavebands. It can also supply simultaneous information on particle asymmetry. Since particle number concentrations are provided by the technique, the counting efficiency of WIBS-4 needs to be defined. Therefore in the current study, a method for calibration suitable and necessary for use with single particle measuring instruments is described. The lower-end counting efficiency curve for the WIBS-4 was thereby defined in specific size regimes for the first time ( D 50 ∼0.489 μm and D 100 ∼0.69 μm). Experiments were conducted at room temperature and atmospheric pressure using a range of different sized PolyStyrene Latex (PSL) microspheres. A TSI 3010 condensation particle counter, using butanol as a working fluid, was used as a reference particle counter. The results also demonstrated a relationship between fluorescence intensity and the calculated volume of the PSL particles, when λ ex =280 nm and λ em ∼310–400 nm. To our knowledge the current study represents the first to provide the fluorescence particle sensor community with both the counting efficiency of the WIBS-4 and a relationship plot giving a fluorescence intensity-particle size correlation over a broad PSL size range.

Four new, four re-calibrated and six used TSI 3790 condensation particle counters (CPC) were checked using soot particles produced by a mini CAST generator. One of the re-calibrated CPC was also checked with Emery oil (PAO 4) particles (evaporation-condensation method) and its counting efficiencies were in agreement with the manufacturer’s calibration data which were determined with Emery oil particles (electrospray method). However, the counting efficiencies with the soot particles were lower indicating the importance of the calibration material (chemical composition, morphology). Since UN-ECE regulation 83 for light duty vehicles does not specify the material to be used, the validation (check) should be conducted with the same material used by the manufacturer or the differences between the materials should be taken into account. Two used CPCs showed a ∼20% decrease in their counting efficiencies after 1.5 years of measuring engine exhaust aerosol. This drift could not be recognized by the status indicators of the instrument and could be attributed to a degradation of the CPC saturator (wick). Two CPCs also showed a non-linear response; a 7% difference was found between low (10 cm−3) and high concentrations (10,000 cm−3). A non-linear response (up to 40%) was also observed when the temperature difference between the saturator and the condenser was increased to decrease the cut-off size of the CPCs.

The effect of particle chemical composition on the counting efficiency of a commercially available n -butanol condensation particle counter (CPC) was theoretically investigated. The activation probability of particles soluble in n -butanol or covered by a soluble coating was determined by Kohler theory, whereas the activation of insoluble particles was determined by heterogeneous nucleation theory. The theoretically predicted counting efficiencies were fit to experimental data to infer the n -butanol microscopic contact angle on insoluble particles or the volume of a soluble layer coating the particle. The calculated microscopic contact angles were found to depend on particle chemical composition, particle diameter, and the CPC saturator-to-condenser temperature difference. The average n -butanol microscopic contact angle on diesel exhaust and CAST soot was determined to be 5–10°, on Emery oil particles close to 0°, on thermally pre-treated tetracontane (C 40 H 82 ) particles 25°, and on dry sodium chloride particles 15–20° for CPCs operated at a temperature difference of approximately 7 °C (low saturation ratios). The counting efficiencies were very sensitive to particle contamination, as determined by the particle generation method and treatment, an effect that could be reproduced by modified Kohler theory. The dependence of the counting efficiency on particle chemical composition was found to be stronger at lower CPC temperature differences.

A limit on particle number emission from the exhaust of Euro 5/6 engines will take effect in 2011 and engine exhaust particle number concentrations are required to be measured by particle number counters that meet requirements set forth by the UN/ECE particulate measurement programme (PMP). The TSI Model 3790 engine exhaust condensation particle counter (EECPC) was developed to meet these PMP requirements. This paper describes an experimental study that evaluated the performance of the EECPC. Experimental setup and procedures for calibrating EECPCs were evaluated. It was found that the EECPC counting efficiency strongly depended on the aerosol material. Among several materials tested, the counting efficiencies were highest for poly-α-olefin and lowest for sodium chloride. Errors in the concentration measurement due to the aerosol material dependence were estimated and found to be significant. Considerations for selecting aerosol materials for EECPC calibration are discussed with regard to best match with engine testing conditions.

The optical particle sensor (OPS), using light scattering from particles, is widely used in clean-rooms and in atmospheric environmental monitoring. However, parameters that affect the particle counting of the OPS have been less explored previously. The present study examines the effect of the nozzle shape on particle counting performance of the OPS. Experiments and simulation studies were carried out for four different nozzle shapes in conjunction with three different particle sizes. The effect of nozzle shape is evaluated not only by experiments analyzing the intensity of scattered light and particle velocity but also by simulation. Fluent was used to simulate the flow field and particle trajectories. We observed that particle velocity and trajectory are strongly dependent on the input nozzle shape, which in turn has an effect on the particle counting performance. Using these results, the design of OPS can be optimized to provide higher counting efficiency.

The sizing accuracies of two widely used yet hitherto unevaluated optical particle counters (OPCs—Grimm Model 1.109 and Palas Model WELAS 2100) as well as one high-resolution, non-commercial OPC were evaluated. The measured data were compared to scattering intensity calculations based on Mie theory. Additionally, the counting efficiency for all three counters was measured, as was the influence of coincidence effects for the OPC with the lowest (manufacturer specified) upper concentration limit. Beside the traditional polystyrene latex calibration, a little-known, very fast and precise “multimodal” calibration method was used, which is based on the simultaneous generation of up to eight sharp multiple-charge modes from polydisperse di-ethyl-hexyl-sebacate (DEHS) particles by electrical mobility classification.

In this study calibration measurements of new TSI condensation particle counter models, using either butanol or water as working fluid, are described. Experiments were carried our at ambient, laboratory conditions for two particle materials, silver and sodium chloride. The obtained counting efficiency curves are presented.

A Fast Integrated Mobility Spectrometer (FIMS) has been developed for sub-second aerosol size distribution measurements based on the description presented in the preceding paper (Paper I). The performance of FIMS was characterized using DMA classified aerosols in the size range 15–170 nm. An excellent agreement was observed between the mean particle diameter measured by FIMS and the DMA centroid diameter. Comparison of particle concentrations measured by FIMS and a Condensation Particle Counter (CPC) shows that counting efficiency of FIMS is 100% for particles larger than 20 nm, and higher than that of the CPC for particles with diameters less than 15 nm. Experimentally determined FIMS mobility resolution ranged from 5 to 14 for particle diameters between 22 to 170 nm, and agreed with theoretical predictions made using FIMS transfer theory, though there was some deviation observed at particle sizes that correspond to high theoretical mobility resolution.

The aerodynamic particle sizer (APS) measures the size distributions of particles with aerodynamic diameter between 0.5 and 20 μ m in real time. To provide accurate size distributions, the APS must measure both particle size and concentration correctly. The objective of this study was to characterize the counting efficiency of the APS as a function of particle size (0.8– 10 μ m ), particle type (liquid or solid), and APS model number (3310 vs. 3321). For solid particles, counting efficiencies ranged between 85% and 99%. For liquid droplets, counting efficiencies progressively declined from 75% at 0.8- μ m drops to 25% for 10- μ m drops. Fluorometric wash tests indicated that transmission losses occur when larger droplets impact on the instrument's inner nozzle. However, transmission losses did not account entirely for the reduced droplet counting efficiencies, indicating that additional losses may have occurred downstream of the inner nozzle. Between instrument comparisons revealed that although multiple APSs report similar number concentrations, small deviations in particle sizing can produce substantial errors when number concentrations are converted to mass concentrations.

The particle size distributions measured by the optical microscope (OPM) were compared with those by the light scattering particle counter (PC) to validate the microscopic method for particle size distribution quantification. While the OPM concentrations increased with the PC concentrations, the OPM concentrations tended to be higher than those by the PC. To explain the difference between the two methods, we estimated their relationship based on the Mie scattering theory. The calculation roughly estimated the particle geometric diameters in theory were 1.7–2.0 times as large as the corresponding PC readouts. Using these theoretical factors, the size ranges of the PC were converted to match with the OPM measurements ( PC ∗ ) . Overall, the OPM concentrations were lower than the PC ∗ concentrations. The advantage in the OPM method particularly for ambient aerosols lied in its accuracy of particle sizing although the counting efficiency might be lowered due to its intrinsic limitations such as inability of counting particles having the similar refractive index of the filter.

A Differential Mobility Particle Sizer (DMPS) system has been adapted and tested for reliable aerosol characterization at stratospheric pressures and temperatures in the AIDA aerosol chamber of Forschungszentrum Karlsruhe. To avoid partial or complete evaporation of volatile aerosol particles (e.g. solution droplets like sulfuric acid droplets), the DMA is operated at almost the same temperature and pressure as the AIDA aerosol vessel. In this study, we describe the experimental setup and technical modifications to the TSI standard DMA 3071 and CPC 3010 used for the DMPS system, discuss the results of low pressure Latex calibration and CPC counting efficiency measurements, and demonstrate the performance of the entire system in a case study with sulfuric acid aerosol.

The aerodynamic particle sizer (APS) model 3321 (TSI, Inc., St. Paul, MN) aims to resolve issues identified with an earlier APS, model 3320. These issues include discrepancies between concentrations measured in summing and in correlated modes, and the creation of “anomalous”, large particles caused by recirculation within the detection region. In the present work, the number concentration of a laboratory aerosol was measured with the APS 3321 to be statistically the same in summing mode and in correlated mode for all particles except those in bin 1, μm . Further, anomalous large particles were not measured with the APS 3321. The counting efficiency of the APS 3321 was lower than that for the APS 3320 and ranged from 40% to 60% for particles from 0.8 to 4 μm , respectively. Thus, concentrations reported by the APS 3321 were lower than those measured by the impactor. However, because counting efficiencies were roughly constant with particle size and anomalous particles were absent, the shape of the size distribution was similar to that obtained using the impactor.

This paper presents the results of the laboratory evaluation of the Ultraviolet Aerodynamic Particle Size Spectrometer, the novel instrument for real-time continues monitoring of bioaerosols. The main focus of this study was on evaluating selectivity, sensitivity, counting efficiency, and the detection limits of the UVAPS. The tests were performed with two types of aerosols, bacterial (e.g., Bacillus subtilis spores or vegetative cells, and Pseudomonas fluorescens) and non-bacterial (e.g., NaCl, latex, peptone water, and nutrient agar/broth). To control viability of airborne bacteria, the bioaerosols were simultaneously sampled with the AGI-30 impingers. The study has demonstrated the UVAPS cross-sensitivity to the non-bacterial organic materials and the need for careful preparation (washing) of test bacteria, in order to avoid the interference with the fluorescence signals of nutrient media used to grow bacteria. The results were indicative of strong sensitivity of the UVAPS to the type of airborne bacteria. The limitations in the capability of the UVAPS to measure bacterial spores were also found. Counting efficiency of the fluorescent particles was shown to depend on particle concentration with the upper limit of detection of the UVAPS approximately 6×107 particles/m3.

This comment adds performance data for a modified version of one of the optical particle counters investigated in Heim et al. (2008) , namely the WELAS 2100. The new version was found to have a counting efficiency much closer to unity for larger particle sizes as well as some improvement in the lower 50% detection limit.

The aerodynamic particle sizer (APS, Model 3320, TSI Inc., St. Paul, MN) is an instrument that counts and sizes particles by time-of-flight, an aerodynamic property, and/or by light-scattering intensity, an optical property. If the counting efficiency of the APS 3320, defined as the number of particles counted divided by the number sampled is not 1.0 for particles of all sizes, then the reported size distributions and particle concentrations will be biased. A laboratory aerosol was sampled with two APS 3320s alternating between collecting only time-of-flight data in summing mode and collecting simultaneous time-of-flight and light-scattering intensity data in correlated mode. Collecting data in correlated mode resulted in errors in the reported aerodynamic size distributions and concentrations. The magnitude of the concentration error was an inverse function of concentration, ranging from approximately 10% at 500 particles / cm 3 to 45% at 50 particles / cm 3 . Experiments were also conducted to determine the counting efficiency of the APS 3320 in summing mode by comparing size distributions obtained with the analyzer to those obtained with a cascade impactor. Counting efficiency increased from 30% for 0.5 μm particles to 100% for 0.9 μm particles, then decreased to 60% for 5 μm particles. For particles larger than about 5 μm , the size distribution reported by the APS 3320 was distorted by artificial particle counts. To determine accurate particle size distributions and concentrations, the values reported by this instrument must be adjusted for counting efficiency.

The low-pressure counting efficiency of three modified condensation particle counters (CPCs, TSI Model 7610) was investigated. In this study, we describe the modifications of the counters, present a “new” low-pressure calibration set-up, and show the resulting CPC counting efficiency curves as function of operating pressure (160– 1000 hPa ) and temperature difference between the saturator and condenser block (10.5–26.0°C). Furthermore, particle coincidence in the CPC optics was studied. The presented CPCs are able to measure particle number concentrations of up to 40,000 particles/cm3 at pressures down to 160 hPa . The lower threshold diameter of the CPCs can be varied between 4 and 23 nm .

A condensation nucleus counter (CNC) capable of detecting sub-20 nm contaminant particles in chemically reactive gases has been developed. The new instrument was constructed from corrosion-resistant materials, and uses a chemically inert working fluid. A test apparatus was also constructed to check the counting efficiency of the CNC. The tests confirmed the sensitivity of the new instrument in 13 different gases. The CNCs lower size sensitivity varied with the physical properties of the gas. The measured lower size sensitivity among the gases ranged from 19 nm to

The Aerosizer (Amherst Process Instruments, Inc. Hadley MA) is a time-of-flight instrument frequently used to measure the size distribution of an aerosol. However, if the Aerosizer’s counting efficiency, defined as the number of particles counted divided by the total number entering the instrument, is not 100% or varies with particle size, the resulting size distribution will be inaccurate. Experiments were conducted to determine the effect of particle diameter, particle concentration, photomultiplier tube (PMT) voltage, and model type on the Aerosizer’s counting efficiency. To calculate counting efficiency, the number of particles between 0.3 and 10 μm recorded by the Aerosizer was divided by the number of particles of the same size collected on each stage of a cascade impactor. Particle diameter, aerosol concentration, Aerosizer model, PMT voltage, and the diameter interaction terms influenced counting efficiency. Counting efficiencies were less than 1% for particles smaller than 0.45 μm, and more than 100% for particles larger than 7 μm. Increasing the PMT voltage increased the counting efficiency for the smaller particles, but also created false, larger particles. Counting efficiency decreased as count rate increased for count rates greater than 20,000 particles per second. The Aerosizer LD counted particles more efficiently than the Aerosizer Mach 2 because of improved laser and optics systems. Four regression models that relate counting efficiency to the salient operating parameters were developed, one for each combination of Aerosizer model and photomultiplier tube voltage studied.

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.

Using a combined DMA-CNC-test-system for high sensitive particle counters the counting efficiency of the PMS-model HS-LAS was measured.

An experimental study has been made of the performance of the continuous flow condensation nuclei counter with air, argon and helium serving as the carrier gas. The finite counting efficiency of the instrument has been found to be due to the non-uniform supersaturation in the condenser tube, rather than particle loss by diffusion. The final droplet size at the condenser outlet has been found to be a function of the initial size of the condensation nuclei. The final droplet size is significantly reduced when the initial nuclei size is smaller than 10 nm. For air as a carrier gas, the final droplet size ranges from approximately 10 to 13 μm. For argon, the final droplet size is about 5% smaller than that in air. In the case of helium, the final droplet size is about 15 μm and this does not depend strongly on the initial nuclei size. The activation efficiency of the condensation nucleus counter for argon is similar to that for air. However, for helium the activation efficiency is higher. The final droplet size and the activation efficiencies of the condensation nucleus counter predicted by theory are in good agreement with the experimental results in all cases.

Five types of commercial optical particle counters have been studied. The response curves of each counter were determined using spherical, non-absorbing particles (DOP, PSL). The response curves of all OPCs were in a reasonable agreement with theoretical curves and those given by the manufacturers. In the case of absorbing particles (methylene blue) there was a significant decrease in the response of all counters. The resolution of the counters was studied by measuring the widths of the pulse height distributions for monodisperse DOP-particles. Noticeable differences between the counters in this respect were observed. The counting efficiencies of the instruments for solid particles in calm air were determined with the aid of filter samples. Most of the counters gave relatively reliable readings up to about 8 μm. One of the counters (Climet 250) gave apparently too low readings obviously because of the particle loss in the sampling system. Another counter (Royco 218) gave too high readings when large particles were measured using a low discriminator setting. The maximum measurable concentrations were estimated by measuring the pre-amplifier pulse length distributions for each counter. The effect of long pulses, probably caused by the recirculation, were found to be significant. The concentrations for counters without a sheath air system were considerably smaller compared to the concentrations calculated from the detection volumes given by the manufacturers.