Dust and Particulate Measurement by Optical Scattering

How does optical scattering work?

Airborne particles scatter incident light in various directions. In the optical scattering method, sample air passes through a light beam, and the scattered light is measured by a detector. The scattered light intensity is proportional to particle concentration; after calibration, this signal is converted to mass concentration (mg/m³).

Portable and area monitors use a near-infrared light source such as 880 nm, and cyclone heads separate fractions such as PM10-PM4 or PM2.5-PM1. For stack and duct measurement, a laser transmitter and receiver are positioned on either side of the duct; scattering mode is used at low dust loads and transmission (light attenuation) mode at high dust loads.

What optical scattering measures and where it is used

The method gives real-time dust concentration. Areas of use:

• Workplace hygiene and personal breathing zone exposure
• Dust monitoring at construction, mining and industrial sites
• Dust and filter failure monitoring in stacks and process ducts
• Ambient air PM monitoring (in systems combined with beta measurement)

Where optical scattering works well and where it struggles

Optical scattering measures instantly and continuously, with a measurement range extending to high concentrations. Portable instruments are practical for short campaigns. Stack-type laser instruments require no sampling and can also be used in high-temperature processes.

Limitations: because scattered light intensity depends on particle size, shape and refractive index, results should be calibrated by comparison with a gravimetric reference measurement specific to the dust type. Moisture and fog can cause falsely high readings in ambient measurements. When optical windows become contaminated, the signal falls; periodic cleaning is required.

Choosing an instrument for optical scattering

When selecting, the purpose of use (personal exposure, area monitoring or stack), measurement range, cut size and optical path length are determined. A site-specific calibration factor should be determined by gravimetric comparison appropriate to the type of dust measured. Tetra carries out periodic zero and flow checks and optical cleaning of instruments as part of service.

Tetra and dust monitors

Tetra supplies, installs, commissions, calibrates and services optical scattering dust monitors in Türkiye. The product range includes the Thermo Scientific ADR-1500 ambient dust monitor, the pDR-1500 personal dust monitor, the NEO Monitors LaserDust LP/MP/XLP stack dust monitor and the 5030i SHARP, which combines light scattering with beta measurement.