The optical particle counter measures the in-situ concentration of aerosol particles in 31 size bins over the range 0.265 - 34 µm. It can alternatively measure mass concentrations as PM1, PM2.5 and PM10. Atmospheric aerosols which may be present include mineral dust, soot particles, water droplets (although these can evaporate before they can be measured) and (occasionally) volcanic ash. Ambient air is drawn into the instrument through a 50 cm inlet. It passes into a chamber where the degree of scattering of a laser beam is used to quantify the aerosols. A weather station to measure temperature, relative humidity, atmospheric pressure and wind speed is also mounted on the instrument.

Many other sensors at Chilbolton, such as the lidars and the AERONET sun photometer, are sensitive the aerosols. As well as being useful in their own right, the ground-level measurements provided by the optical particle counter can be used to better quantify the remote aerosol measurements from the lidars and sun photometer.

The optical particle counter was manufactured by GRIMM Aerosol Technik GmbH (Germany). It was deployed at Chilbolton Observatory in 2013.

Technical specifications of the optical particle counter