NPL have been closely involved with the development of standard methods for PM₁₀ and PM_2.5 measurement, and with the field evaluation of many monitoring instruments on behalf of CEN, Defra and DTI.

The reference methods, based on the manual weighing of filters, are clearly unsuited to real-time automated data production that can be disseminated to the public in the same way as for gaseous pollutants. Commonly used automatic methods across Europe include Tapered Element Oscillating Microbalances (TEOM), which measure the increasing mass of a filter by its effect on the resonant frequency of a vibrating support; beta attenuation monitors, which measure the increasing amount of material on a filter by its absorption of electrons emitted by a weak beta-source; and optical monitors, which can gauge the size of individual particles from signals scattered from a light beam and integrate this into a total volume of particles.

All of these instruments give different results from the reference method to varying degrees in differing circumstances, and have many variations. A variation of the TEOM called the Filter Dynamic Measurement System (FDMS) is currently receiving a great deal of attention in the UK.

The picture shows the inlet heads of many instruments being evaluated at NPL as part of a trial to determine which of them was Equivalent to the EU reference method, within the definition set out for this purpose.

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