PM10 / PM2.5 Measurement by Beta Attenuation

How does beta attenuation work?

In the beta attenuation method, ambient air is drawn at a set flow and particles are collected on a filter tape. Beta rays from a low-energy radioactive source pass through the filter and are absorbed more as the mass of collected particles increases. The reduction in ray intensity reaching the detector is a measure of the dust mass on the filter. The increase in mass and the volume of air sampled are assessed together to calculate concentration in µg/m³.

The tape advances to present a clean area for each measurement, so measurement can continue uninterrupted for long periods. In dual beta arrangements, PM10 and PM2.5 values are obtained simultaneously using two separate lines.

What beta attenuation measures and where it is used

The method measures the mass concentration of particulate matter in air and gives PM10, PM2.5 or PM1 fractions depending on the inlet selected. Main areas of use:

• Urban and industrial air quality monitoring stations
• National and local measurement networks
• Environmental impact assessment and field campaigns
• Mobile measurement cabinets

Where beta attenuation works well and where it struggles

Because beta attenuation measures mass largely independently of particle color and chemical composition, it is widely used in ambient air monitoring. It produces data automatically at hourly or shorter intervals and can run unattended.

Limitations: moisture and volatile components can affect the measurement, so moisture control (heating or drying) is needed in the sample line. The filter tape is a consumable and must be replaced periodically. The method is verified by comparison with the gravimetric reference method; this comparison is part of field calibration. Because it contains a radioactive source, the instrument must be transported and stored in accordance with the relevant legislation.

Related standards

The reference gravimetric method is described in EN 12341, and the conformity assessment of automated measuring systems in EN 16450. Instrument type approvals are addressed under the EN 15267 certification system.

Choosing an instrument for beta attenuation

When selecting, the target fraction (PM10, PM2.5, PM1), sample moisture control and station infrastructure are assessed. In monitoring networks, periodically comparing the instrument with gravimetric reference samplers is common practice for maintaining data quality.

Tetra and beta particulate monitors

Tetra supplies, installs, commissions and calibrates beta attenuation particulate monitors in Türkiye and provides spare parts and service support. The Thermo Scientific 5014i beta particulate monitor, the 5028i dual beta particulate monitor and the 5030i SHARP, which combines light scattering with beta measurement, are products using this method. Tetra also integrates these monitors into air quality monitoring station cabinets.