The Chilbolton Facility for Atmopsheric and Radio Research's aerosol particle concentration measurements are provided by a 164DM environmental dust monitor manufactured by Grimm Aerosol Technik. A Lufft WS500 weather station is incorporated into the instrument to provide co-located meteorological measurements. Alternatively, particle mass concentrations can be produced as PM1, PM2.5 and PM10 measurements. The instrument measures the size and number density of aerosol molecules by using a 0.5m vertical inlet to suck ambient air into a measurement chamber. The scattering of a laser beam transmitted through the chamber is used to deduce size and concentration information. It is operated continuously on the roof of a cabin at a height of 8m above ground at the Chilbolton Observatory site. Measurements are taken every 60s, providing aerosol particle concentration (counts/m3) in 31 size bins in the range 0.265-34.0 um, air temperature, relative humidity, air pressure, wind speed and wind direction. The instrument is calibrated every 18 months by the manufacturer