Continuous Flow Condensation Nucleus Counter Research Articles

Quantitative Fit Test of a 3D Printed Frame Fitted Over a Surgical Mask: An Alternative Option to N95 Respirator.

Background COVID-19 has spread worldwide and caused severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) led to numerous dead cases. However, with the new COVID-19 outbreaks, there is a shortage of personal protective equipment (PPE) especially N95 masks worldwide including Thailand. This issue had placed the health professional in great need of an alternative mask. Aim This study aimed to measure the fit factor of 3D printed frames by quantitative fit testing (QNFT) to find an alternative facemask by using a mask fitter together with 2 different kinds of the American Society for Testing and Materials (ASTM) level 1 surgical mask. Materials and Methods Two commonly used surgical masks (Sultan Com-Fit Super Sensitive Ear Loop Mask or “White Mask Group,” not water-resistant, and Sultan Blue Com-Fit Super High Filtration Ear Loop Mask or “Blue Mask Group,” water-resistant) with and without 3D printed frame covering. The fit performance was measured by a quantitative fit test (QNFT) device (PortaCount, model 8048, TSI Incorporated, Minnesota, USA) accepted by the Occupational Safety and Health Administration (OSHA). The PortaCount device, which is based on a miniature continuous flow condensation nucleus counter (CNC), assesses the respiratory fit by comparing the concentration of ambient dust particles outside the surgical mask to the concentration that has leaked into the surgical mask. The ratio of these two concentrations (Cout/Cin) is called the fit factor. A fit factor of a 3D printed frame of at least 100 is required and considered as a pass level. Results We found that the mask fitter improves the overall performance of surgical masks significantly. The improved performance is comparable to that of N95. Conclusion The mask fitter improves the performance of surgical masks. The authors suggested that further study on frame material, shape, and expanded sample size would be beneficial to society.

Particle activation and droplet growth processes in condensation nucleus counter—I. Theoretical background

The heat and mass transfer, and droplet growth processes in a continuous flow condensation nucleus counter (CNC) have been studied numerically by solving the equations of convective heat and mass transfer, and the equation of vapor transfer to the growing droplets. The influence of sampling flow rate and the saturator and condenser wall temperatures have been studied. The thermophysical properties of the carrier gas have also been systematically varied to determine their influences on the performance of the CNC. Carrier gasses studied include air, argon and helium. Calculations have been made for conditions similar to those used in the commercially available CNC manufactured by TSI Inc. (model 3020). The results show that the constant supersaturation ratio isopleth in the condenser tube of the instrument has an elongated shape and the elongation is increased in the flow direction as the sampling flow rate is increased. This implies that the activation efficiency does not depend on the sampling flow rate, as long as the highest supersaturation region is within the condenser tube. A few per cent change in the condenser wall temperature or the saturator temperature does not have a great deal of effect on the performances of the counter. The droplet growth processes and its temperature variation have been predicted numerically for air, argon and helium as the carrier gas. The final droplet sizes in air and argon show a strong dependence on the initial nuclei sizes for ultra-fine aerosols, while a relatively small dependence is shown in the case of helium.

Measurement of Nanometer Aerosols

This paper is a review of my work during the past 18 years on nanometer, i.e., submicrometer, aerosols. These aerosols scatter negligible light so they are difficult to study and must be observed by indirect methods such as diffusion batteries and condensation nucleus counters. Several diffusion batteries are described: “cluster tube” batteries, 5.5 km of 1-mm-diam. straight tubing mounted in clusters; collimated holes structures containing 5.1 km of holes, 1/4 mm in diameter; honeycomb structures containing 3.5 km of holes 1/3 mm in diameter; screen batteries containing 55 stainless steel screens in 10 sections; reticulated vitreous carbon batteries containing 60 k interconnected pores per cm5. From theory, the diffusion battery is shown to be only slowly discriminating, so a series of batteries and measurements is required for particle size analysis. Measurements were made with a continuous flow condensation nucleus counter developed to provide the steady flow required by diffusion battery theory. The m...

The Continuous Flow Condensation Nucleus Counter. II

The original version of the continuous flow counter has been improved and redesigned to run automatically with a rotary sequencing valve and data processing system. As previously described, the counter was developed at the Environmental Measurements Laboratory for use with diffusion batteries because they require a constant flow of aerosol for particle size measurement. The automated system is used extensively for measurement of the concentration and particle size distribution of indoor and outdoor aerosols. The operating conditions are evaluated to determine the effect of temperature deviation and alcohol dilution. Laboratory measurements of both the dew point and the light transmission show the diameter of the alcohol drops to vary from 13 μm at nucleus concentration of 1000/cm3 to 5.5 μm at 300,000/cm3. A recent calibration shows the new counter to be nearly 100% efficient for condensation nuclei ranging from 90 to 5 nm in diameter.

New methods for quantitative respirator fit testing with aerosols

Quantitative respirator fit testing is generally performed by measuring the concentration of DOP aerosol leaking into the breathing space between the respirator and the wearer's face. In the conventional technique, the concentrations inside and outside the mask are determined photometrically through measurements of the scattered light intensities from the DOP clouds. DOP, however, has recently been implicated as a potential human carcinogen. We have adapted a continuous-flow condensation nuclei counter (CNC) for fit testing and have been able to use a variety of non-hazardous test aerosols which are not measurable by the conventional technique. The CNC enlarges submicrometer-sized particles into the light scattering range, so virtually any fine particle cloud can be used for fit testing. Comparison tests between photometer and CNC measurements show the utility of the new technique. The potential use of an aerosol electrometer is also discussed.

A continuous flow condensation nucleus counter

A continuous flow condensation nucleus counter has been developed which avoids the intermittent sampling and adiabatic expansion employed in conventional condensation nucleus counters. The number concentration of submicron aerosols can be measured with any type of condensation nucleus counter. However, the measurement of particle size requires, in addition, the use of diffusion batteries for which continuous flow is essential. Two continuous flow nucleus counters have been calibrated by comparison with conventional nucleus counters and an electron microscope, utilizing test aerosols of ultra-fine particles of metallic silver, ambient room aerosol and colloidal silica. A calibration curve is given covering the concentration range from 500 to 10 6 per cm 3. The calibrated counters are being used to measure the concentration of aerosols in the size range 0β002–0β1 μm dia. They are also being used, in conjunction with diffusion batteries, to measure the size and size distribution of particles in this range. Two cumulative particle size distribution curves are given, one calculated by a graphical method and the other by computer, showing the results of measurements on ambient aerosol of 38 nm n.m.d. and 60,000 particles per cm 3.

Effect of relative humidity on the size of atmospheric aerosol particles

In situ measurements of the growth of atmospheric aerosol particles with increasing humidity, from 0 to 98 per cent r.h., were made with the use of miniature diffusion batteries and a continuous flow condensation nuclei counter. Particle size distributions computed from the battery measurements were log normal. The number median diameter (NMD) increased two-fold from 0.018 to 0.036 μm over the range of humidity. The range of geometric S.D. ( σ g ) for the particle size distributions was 1.53–2.06 with the larger NMD having the smaller σ g . This indicates that the smaller particles grew proportionately more than the larger.