Tapio Kalliohaka

Performance of ventilation filtration technologies on characteristic traffic related aerosol down to nanocluster size

ABSTRACT Near traffic routes and urban areas, the outdoor air particle number concentration is typically dominated by ultrafine particles. These particles can enter into the nearby buildings affecting the human exposure on ultrafine particles indoors. In this study, we demonstrate an aerosol generation system which mimics the characteristic traffic related aerosol. The aerosol generation system was used to determine the size-resolved particle filtration efficiencies of five typical commercial filters in the particle diameter range of 1.3–240 nm. Two different HEPA filters were observed to be efficient in all particle sizes. A fibrous filter (F7) was efficient at small particle sizes representing the nucleation mode of traffic related aerosol, but its efficiency decreased down to 60% with the increasing particle size. In contrast, the filtration efficiency of an electrostatic precipitator (ESP) increased as a function of the particle size, being more efficient for the soot mode of traffic related aerosol than for the nucleation mode. An electret filter with a charger was relatively efficient (filtration efficiency >85%) at all the observed particle sizes. The HEPA, F7 and electret filters were found to practically remove the particles/nanoclusters smaller than 3 nm. All in all, the filtration efficiencies were observed to be strongly dependent on the particle size and significant differences were found between different filters. Based on these results, we suggest that the particulate filter test standards should be extended to cover the ultrafine particles, which dominate the particle concentrations in outdoor air and are hazardous for public health. Copyright

Experimental comparison of probes for air discharge measurements

Publisher Summary This chapter presents a study on the performance of three different kinds of passive resistor-transmission line discharge probes—an unshielded ball probe developed at Physikalish-Technische Bundesansalt (PTB-probe), a shielded ball probe having an earthed hemispherical shield with the electrostatic discharge (ESD) current collected on a coaxial wire tip and developed at Electrostatics Solutions Ltd. (ESL-probe), and a needle-like shielded probe developed at SP Swedish National Research and Testing Institute (SP-probe). Different kinds of probes have been developed during the past years for the measurement of air discharges—spark and brash discharges—to evaluate the ESD risks without the use of explosive atmospheres or destructive tests of electronics. The chapter evaluates their possible application in assessment of ignition hazards or ESD damage risks to electronic components. The results show that there is no single probe type that is ideal for all kinds of situations. There are significant differences among the probe responses in their ability to initiate ESD, charge transferred, and peak ESD current.