The Thermo Scientific Model ADR1500 Dust Monitor utilizes the highly sensitive light-scattering photometer (nephelometer) technology as used in the Thermo Scientific™ pDR series. The intensity of the light scattered by airborne particles passing through the sensing chamber is linearly proportional to their concentration. This optical configuration produces optimal response to particles, providing continuous measurements of the concentrations of airborne particles for total particulate and cut-points ranging from PM10 down to PM1. The ADR1500 incorporates a temperature and relative humidity (RH) sensor coupled with an internal heater to mitigate the positive bias with elevated ambient RH. Additionally, the flow control is truly volumetric and is maintained through digital feedback of the onboard barometric pressure sensor, temperature sensor and calibrated differential pressure across a precision orifice. The principles of true volumetric flow, as incorporated by the ADR1500, result in an accurate sample volume and precise particle cut-point.