By Jim Shorey
PM2.5 is Particulate Matter smaller than 2.5 microns in size.
Particulate Matter such as wood smoke is often measured using the principle of Beta Radiation Attenuation and Nephelometer Light Scattering Detection.
Looking at the flow diagram below, particulate is drawn into the Inlet via a vacuum pump. The Inlet has a PM10 Impactor combined with a PM2.5 Cyclone, to reduce the particulate size down to PM2.5. The Nephelometer assembly senses the light scattered by the particulate passing through an 880 nanometer illumination light beam. The nephelometry response is linear with particulate concentration in micrograms per cubic meter. Afterwards, the particulate matter is deposited onto a glass fiber filter tape. The filter tape will accumulate a particulate sample towards a threshold value, where the filter tape will automatically advance prior to reaching saturation. During the collection of particulate onto the detector filter tape, the Monitor uses the radiometric principle of beta radiation attenuation through a known sample area to continuously collect and detect the deposited particulate.
Particulate Analyzer Component Layout