Beta attenuation monitoring

The technique allows for the detection of PM10 and PM2.5, which are monitored by most air pollution regulatory agencies.

The main principle is based on a kind of Bouguer (Lambert–Beer) law: the amount by which the flow of beta radiation (electrons) is attenuated by a solid matter is exponentially dependent on its mass and not on any other feature (such as density, chemical composition or some optical or electrical properties) of this matter.

[1] So, the air is drawn from outside of the detector through an "infinite" (cycling) ribbon made from some filtering material so that the particles are collected on it.

[4] To discriminate between particle of different sizes (e. g., between PM10 and PM2.5), some preliminary separation could be accomplished, for example, by cyclone battery.

This allows to obtain not only cumulative measurement of particle mass, but also to detect their average chemical composition (technique works for potassium and elements heavier than it).

The schematic of a beta attenuation monitor (BAM). The detector allows to assess cumulative mass concentration of suspended particulate matter (PM) in the ambient air. Notation: 1 – air inlet; 2 – cycling ribbon; 3 and 4 – beta radiation sources; D1 and D2 – beta radiation detectors; 5 – air pump; 6 – air exhaust.