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Centre for Atmospheric Science

Knudsen Effusion Mass Spectrometer

KEMS Schematic
Figure 1. Schematic of the KEMS instrument.
KEMS Photograph
Figure 2. Photograph of the KEMS instrument.

Knudsen Effusion Mass Spectrometry (KEMS) is an established vapour pressure measurement technique capable of measuring vapour pressures from 101-10-8 Pa (e.g. for ceramic solutions and metal alloys at high temperature). SOA components are likely to have vapour pressures around 10-4 Pa, measurable at ambient temperature, well inside the range measurable by KEMS.

A KEMS system has been build by Dr Murray Booth. It consists of temperature controlled Knudsen effusion cell, suitable for controlled generation of a molecular beam of the sample organic compounds in a vacuum chamber, coupled to a quadrupole mass spectrometer. The system is calibrated using the mass spectrometer signal from a sample of known vapour pressure, a load-lock allows the ioniser filament to be left on, then a new sample of unknown vapour pressure can be measured .



Booth et al., Atmos. Meas. Tech., 2, 355–361, 2009