Atmospheric Radiation Measurement Climate Research Facility US Department of Energy

htdma > Humidified Tandem Differential Mobility AnalyzerInstrument Type(s) > Baseline • Guest

The humidified tandem differential mobility analyzer (HTDMA) is part of the aerosol observing system (AOS).

It measures how aerosol particles of different initial dry sizes grow or shrink when exposed to changing relative humidity (RH). It uses two different mobility analyzers (DMA) and a humidification system to make the measurements.

One DMA selects a narrow size range of dry aerosol particles, which are exposed to varying RH conditions in the humidification system. The second (humidified) DMA scans the particle size distribution output from the humidification system.

Scanning a wide range of particle sizes enables the second DMA to measure changes in size or growth factor (growth factor = humidified size/dry size) due to water uptake by the particles. A condensation particle counter (CPC) downstream of the second DMA counts particles as a function of selected size in order to obtain the number size distribution of particles exposed to different RH conditions.


  • Fixed
  • AMF1
  • AMF2
  • AMF3


Islam M, N Meskhidze, A Satheesh, and M Petters. 2022. "Turbulent Flux Measurements of the Near‐surface and Residual‐layer Small Particle Events." Journal of Geophysical Research: Atmospheres, 127(17), e2021JD036289, 10.1029/2021JD036289.

Oxford C, R Chakrabarty, and B Williams. 2022. "Evaluation of assumptions made by Hygroscopic Tandem Differential Mobility Analyzer inversion routines." Journal of Aerosol Science, 162, 105955, 10.1016/j.jaerosci.2022.105955.

Zhang J, Y Wang, S Spielman, S Hering, and J Wang. 2022. "Regularized inversion of aerosol hygroscopic growth factor probability density function: application to humidity-controlled fast integrated mobility spectrometer measurements." Atmospheric Measurement Techniques, 15(8), 10.5194/amt-15-2579-2022.

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Research Highlight


Petters M. 2021. "Revisiting matrix-based inversion of scanning mobility particle sizer (SMPS) and humidified tandem differential mobility analyzer (HTDMA) data." Atmospheric Measurement Techniques, 14(12), 10.5194/amt-14-7909-2021.

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