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Differential Mobility Analyser


SETUP PROCEDURE

  • The yellow tube is for the sheath air inlet at the top of the DMA.
  • The black tube is for the excess air outlet. This eventually goes back into the inlet.
  • The grey tube is the electrical connection.
  • The red wire is the high voltage supply.

Attach all of the above to their appropriate points on the DMA.

Remove the nozzle of the impactor to check it is the correct device for the DMA in use, and check that it is clean.

INSTRUMENT LIMITATIONS

The instrument will NOT work if the impactor is dirty/blocked, the flow rate is wrong etc.

The charges on aerosol particles will vary. The charge distributions are modelled in the software, and attempts are made to control the charge distribution using the neutraliser. Nevertheless, particles of opposite charge will go to a different electrode - so only those particles of the relevant size AND CHARGE will exit via the central rod. Neutral particles travel straight through the DMA and exit as sheath air. Also, particles may not necessarily have the same size of charge, and this will affect their mobility, even if they are of the correct size to be selected.

There is an ambient humidity operating limit of 95% not condensing - otherwise there may be spark discharge within the high voltage DMA.

The sampling relative humidity may also be ~95% but this may be dependent on the specific gas mixture samples.

The long classifier (DMA) is designed for the particle range 10 - 1100nm (considered particularly suitable for environmental purposes).

The SMPS+C is not designed to be operated when the ambient temperature is greater than 30C. There is a separate adapter for high temperature use but this requires more energy.

Earth Observation Data Group, Department of Physics, University of Oxford. Page last updated: @21:11 GMT 13-Apr-2014