The instrument is similar in function to the related Aerosol Mass Spectrometer, but is optimised for long-term monitoring, with a lower specification of mass spectrometer and no sizing capability. Aerosol are drawn into the instrument through an aerodynamic lens and concentrated using differential pumping, before being vaporised at 600 °C on a tungsten surface. The vapours are then analysed using 70 eV electron ionisation and a quadrupole mass spectrometer.