Measurement of Ultrafine Particulates Guidance Notes
The process of measuring aerosol particles has been divided into three separate stages: sampling, transport and sizing/counting. This report highlights the problems associated with each of these three stages with repect to ultra-fine particulates. In the first stage the processes which govern unbiased sampling have been discussed for sampling from a moving air stream and from calm air. It has been concluded that there will only be a bias for small particles in extreme conditions and that under normally encountered situations effects are negligible. Transporting the particles from the sampling point to the sizing/counting instrument is considered in terms of the potential for particle losses due to a series of mechanisms. Small particles will only be significantly affected by diffusional forces and both gravitational and inertia effects will be small. In cases were there is a temperature gradient in the gas (eg warm gas in a cold sampling pipe) particles may be deposited through thermophoresis. Equations to estimate these losses have been given and can used to correct measured data. Finally, instruments have been listed that can be used to measure ultra-fine particles. This list highlights the techniques employed by the instruments to size/count ultrafine particles but is not intended to be an exhaustive compalation of what is available commercially.
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