nephelometers

A nephelometer is an instrument designed to measure the scattering of light by particles suspended in a medium, most commonly air or liquids. In aerosol science, it estimates properties of atmospheric aerosols by detecting light scattered by airborne particles at a known angle or over a range of angles. The basic components include a light source, an optical chamber through which the sample flows or passes, and a photodetector that converts scattered light into an electrical signal. The detected signal is related to the concentration and optical properties of the particles, and is typically reported as a scattering coefficient or, with calibration, as a mass concentration.

There are several classifications of nephelometers. A traditional forward- or side-scatter nephelometer measures light scattered at a fixed angle, often around 90 degrees, to determine the amount of scattering per unit volume. Integrating or wide-angle nephelometers collect scattered light over a broad solid angle, providing a signal proportional to total scattering. In liquids, nephelometers (often called turbidity meters) measure the scattering of light caused by suspended particles to assess sample clarity or concentration.

Applications include ambient air quality monitoring, occupational hygiene, and aerosol research, where nephelometers serve as fast, continuous proxies for particle loading. In liquid analytics, they are used to assess turbidity and particle concentration. Calibration against reference methods (such as gravimetric mass or known standards) is common, and measurements can be influenced by particle size distribution, refractive index, humidity, and multiple scattering, requiring careful interpretation.