Kauko Janka

Improved laser-induced fluorescence method for bio-attack early warning detection system

Laser Induced Fluorescence (LIF) could permit fast early warning systems either for point or stand-off detection if a reliable classification of warfare biological agents versus biological or non-biological fluorescing background can be achieved. In order to improve LIF discrimination capability, a new system is described in which the fluorescence pattern is enriched by the use of multiple wavelength delayed excitation while usual spectral fluorescence analysis is extended to time domain to use both aspects as criteria for classification. General considerations and guidelines for the system design are given as well as results showing good discrimination between background and simulants.

Optimization of filtration efficiency and ozone production of the electrostatic precipitator

An electrostatic precipitator is an air cleaner in which particles are first charged by an electric current coming from corona wires in high voltage. Then the particles are collected by the electric field between collecting plates. The principle of the operation of an electrostatic precipitator is shown in Fig. 1. An important property of the electrostatic precipitator is the filtration efficiency. For high efficiency the charging current and collecting voltage must be sufficiently high. The higher the current the more ozone is produced. The high collection voltage may also cause ozoneproducing discharges between collection plates. The aim of this study was to investigate the filtration efficiency and ozone-production dependence on charging current and collecting voltage. This knowledge can be used when electrostatic precipitators for dwellings and public rooms are designed.

Virtual Impactor as an Accessory to Optical Particle Counters

A method to improve the sensitivity of optical particle counters for large particles is presented. The basic idea is to increase the concentration in the sample air by connecting a virtual impactor to the sample inlet of an optical particle counter. For particles with D p > 3 μm, the number concentration is increased by a factor of 20. The improvement in statistical accuracy is particularly useful in Alter testing and clean room measurements. The differences in the size distributions measured with and without the virtual impactor are used in estimating the relationship between the aerodynamic and optical sizes of different aerosols. *This paper is based on a presentation given at the First International Aerosol Conference held September 17–21, 1984, Minneapolis, Minnesota.

An electrical sensor for long-term monitoring of ultrafine particles in workplaces

Pegasor Oy Ltd. (Finland) has developed a diffusion charging measurement device that enables continuous monitoring of fine particle concentration at a low initial and lifecycle cost. The innovation, for which an international process and apparatus patent has been applied for, opens doors for monitoring nanoparticle concentrations in workplaces. The Pegasor Particle Sensor (PPS) operates by electrostatically charging particles passing through the sensor and then measuring the current caused by the charged particles as they leave the sensor. The particles never touch the sensor and so never accumulate on its surfaces or need to be cleaned off. The sensor uses an ejector pump to draw a constant sample flow into the sensing area where it is mixed with the clean, charged pump flow air (provided by an external source). The sample flow containing charged particles passes through the sensor. The current generated by the charge leaving the detection volume is measured and related to the particle surface area. This system is extremely simple and reliable – no contact, no moving parts, and all critical parts of the sensor are constantly cleaned by a stream of fresh, filtered air. Due to the ejector pump, the sample flow, and respectively the sensor response is independent of the flow and pressure conditions around the sampling inlet. Tests with the Pegasor Particle Sensor have been conducted in a laboratory, and at a workplace producing nanoparticles for glass coatings. A new measurement protocol has been designed to ensure that process workers are not exposed to unusually high nanoparticle concentrations at any time during their working day. One sensor is placed inside the process line, and a light alarm system indicates the worker not to open any protective shielding or ventilation systems before concentration inside has reached background levels. The benefits of PPS in industrial hygiene are that the same monitoring technology can be used at the source as well as at the worker breathing zone. Up to eight sensors can be installed in series for centralized monitoring of the whole process in real time.

Characterization and Response Model of the PPS-M Aerosol Sensor

The Pegasor PPS-M sensor is an electrical aerosol sensor based on diffusion charging and current measurement without particle collection. In this study, the role and effect of each component in the instrument is discussed shortly and the results from a thorough calibration measurements are presented. A comprehensive response model for the operation of the PPS-M sensor was developed based on the calibration results and computational fluid dynamics (CFD) modeling results. The obtained response model, covering the effects of the particle charger, the mobility analyzer, and both diffusion and inertial losses, was tested in the laboratory measurements with polydisperse test aerosols, where a good correlation between the model and the measured results was found. Copyright 2014 American Association for Aerosol Research

The control of radon progeny by air treatment devices

The effect of air treatment devices on the behaviour of radon decay products has been studied in laboratory conditions. An HEPA filter and an electrostatic precipitator were used. Both of the filters were found to decrease the equilibrium factor of daughters and increase the unattached fraction of decay products. In a clean air they also decreased the activity of unattached daughters. The effect of the devices on the health risk caused by radon progeny was estimated by dosimetric calculations. The results corresponding to different models show considerable discrepancy, mainly due to different assumptions about the influence of unattached decay products on the dose.

Optical chamber design for aerosol particle fluorescent measurement

Optical chamber for aerosol particle fluorescence measurements is designed. With the designed chamber, UV-induced fluorescent spectrum of single particles can be measured. The design includes two-nozzle flow system, with sheath air flow and virtual impactor concentrator integrated into the chamber. The operation of the flow system was verified with computational fluid dynamics (CFD). The chamber is intended to be used with pulsed UV-laser source, and it includes triggering of the laser pulse to hit individual particles.

Pulse interval and pulse width measurements in determining the flow characteristics in the viewing volume of single particle optical counters

Abstract The characteristics of the sample air flow influence some properties of single particle optical counters. The direct measurements of these effects are difficult. In this paper two indirect methods to study these characteristics have been considered. In one method the pulse interval distribution is measured and this is compared with the theoretical distribution. As a result, one can recognize the possible recirculation and the oscillating sample air flow. The other method uses the pulse width distribution to indicate the homogeneity of air flow. The pulse width distribution can also be used to determine the volume of the viewing region. The experimental measurements show that these methods give information about properties and faults of the air flow systems.

Sedimentation Method in Calibrating Optical Particle Counters

The use of a horizontal elutriator in calibrating optical particle counters according to aerodynamic particle size has been studied. As elutriator a ceramic component with 4800 parallel square channels with dimensions of 0.1 × 0.1 × 15.2 cm has been used. The advantage of the present method is that the particle penetration characteristic of the elutriator can be easily changed simply by varying the flow rate. The elutriator has been used in studying the properties of an optical particle size analyzer (PMS Las-X). The relationship between the equivalent aerodynamic particle size and the corresponding particle size indicated by the analyzer has been determined by using Arizona road dust particles and dioctylphthalate particles. The practical size range of the method is Dp ≥ 0.3 μm.