Radial DMA

• Full Name: Radial Differential Mobility Analyzer

• Short Name or Acronym: RDMA

• Measurements Provided: size distribution and concentration of aerosol particles ~7 to 200 nm diameter in 64 size bins, 10 sps

• Manufacturer or Builder of the Instrument: Constructed at RAF from a mix of commercial and custom fabricated components

• Operational Status:

  • not on request list but could be available if requested

• General Description:

  • RDMA is a continuous flow instrument that measures aerosol particle electrical mobility distributions that correspond to particles ~7 nm to ~200 nm diameter. The exact size range depends on flow rate, voltages, air pressure and temperature. The air sample passes through an ion source where the aerosol particles acquire an electrical charge. Particles with the correct charge and mobility are selected in a parallel-plate precipitator, where a voltage is imposed between the plates. Thse particles are counted with a CN counter. The selected size changes continuously by ramping the voltage through a large range, ~30 to 6000 volts over ~160 s period. RDMA requires an air sample inlet and piping.

• Measurement Characteristics:

  • Overall estimate of uncertainty:
  • Response time: each up/down voltage scan cycle takes ~160 sec and produces two size distributions
  • Precision: 64 size bins in logarithmic increasing sequence, 7 to 200 nm diameter
  • Other measurement characteristics (comments on signal/noise, bias limits, etc):
    • Sampling is affected by particle diffusion losses, size-dependent charging efficiency, splash/breakup artifacts at the inlet tip, and humidity.

• Lead Contact: Dave Rogers

Documentation

• Descriptive Publications
• Documentation of the Processing Algorithm(s): See the Technical Note on Processing Algorithms at this URL (fix when available)