Humidified Tandem Differential Mobility Analyzer (HTDMA)

Model 3100


Most particles in the atmosphere take up water when exposed to increasing relative humidity – this often explains the poor visibility during the early morning hours when the relative humidity is high and particles have swollen in size and more effectively scatter solar radiation. When we inhale particles they also grow into water droplets, how large they grow determines where they deposit in our respiratory systems. Brechtel developed the first commercial version of the Humidified Tandem Differential Mobility Analyzer (HTDMA) so researchers who wanted to explore the complexities of particle water uptake no longer had to build their own instruments, instead they could rely on our 20 plus years of experience with HTDMAs to invest in a solution that would let them focus on their science and not the tool.

If your work requires real-time particle size and relative humidity dependent water uptake and number size distribution measurements, the HTDMA may be the solution for you.

  • Fully automated and field tested
  • Comprehensive, easy-to-use software with experiment scheduler module
  • Large particle performance: up to 2 microns!
  • Rapid RH and particle size changes
  • Fast response barrier-free diffusion-based humidifier
  • Integrated and automated aerosol generation system (optional)
  • Rack mount kit (optional)


  • Characterized in peer-reviewed literature
  • Easily integrated with chemical composition measurement devices
  • Years of continuous field deployment
  • Backed by over 20 years of HTDMA measurement experience

Technical Specs

HTDMA Tech Specs

parameter value
DMA polydisperse flow rate 0.2-2.0 lpm
DMA sheath flow rate 2.5-10.0 lpm
Relative humidity range 2-93 % RH
RH control stability at 80% RH (1σ) 0.5% RH
Time to reset RH set point by 10% <180 seconds
Time to reach 93% RH from 2% <300 seconds
Time to reach 80% RH from 2% <300 seconds
DMA particle diameter sizing range 0.01-2.0 μm
CPC particle diameter size range 0.005-2.0 μm
CPC counting range 0.001-10u cm⁻³
Operating pressure range 200-1000 mb NOTE¹
Operating temperature range 15-35°C
SEMS footprint size 18.9 x 13 in/48x33 cm
HSEMS footprint size 15 x 22.85 in/38x58 cm
Height 25.2 in/64 cm
Total weight 150 lb/68 kg
HTDMA instrument power 240 watts
Pump power required (@230vac) 650 watts
Operating voltage 100-230 VAC
Note 1 Only with SEMS-Exp options

Copyright ©2017 All specifications are subject to change without notice. BMI assumes no responsibility for inaccuracies in this document or for any obligation to update information in this document. BMI reserves the right to change, modify, transfer or otherwise revise this publication without prior notice.

*Some products may be shown with optional accessories, which are sold separately. Items shown may not be to scale.

Applications and Solutions

  • Aerosol climate impact studies
  • Measurement of hygroscopic growth of rapidly evolving aerosol size distributions
  • Cloud condensation nucleus studies
  • Visibility reduction studies
  • Aerosol health impacts
  • Long-term climate and air quality monitoring
  • Process monitoring
  • Tobacco smoke inhalation studies


The HTDMA software runs on Windows PCs integrated into the instrument and features a graphical user interface with point-and-click operation. A real-time display of particle water uptake is available through plots of measured number concentration versus growth factor or physical size. Data are displayed as raw counts, raw concentration and processed concentration. System overview and detailed operating parameter views make it easy to determine if the instrument is operating within specification. Data is inverted on-line using a simplified inversion process for quickly viewing and analyzing results. An easy-to-use data post processing software tool applies the full HTDMA transfer function to invert raw measurement data accounting for the full instrument response function.

The scheduler feature allows you to pre-define the various experiments, including atomizer runs, you wish to perform and leave the HTDMA unattended while it does your work for you!

What’s Included

The HTDMA comes with the following items:

  • Scanning Electrical Mobility Sizer (SEMS, dry sizer with either 1um or 2um DMA,  external pump package and Mixing CPC)
  • Humidified Scanning Electrical Mobility Sizer (HSEMS) with either 1um or 2um DMA, Diffusion-based Humidifier and Mixing CPC
  • Software to control HTDMA operation, configure experiments & instrument, perform & check calibrations and post-process data
  • Software to allow upstream SEMS to run in scanning mode during HTDMA operation
  • Keyboard, monitor, mouse & KVM switch to connect SEMS and HSEMS computers
  • Rugged Wooden shipping container holding both SEMS & HSEMS


The following optional accessories are available:

HTDMA Accessories

Part Number Description
3110 Aerosol pre-humidifier (0.1 to 2 lpm flow)
3105 Thermodenuder
8008 Round Jet Impactor with 0.5 micrometer cut size, 0.6 lpm flow
8009 Round Jet Impactor with 1.0 micrometer cut size, 0.6 lpm flow
9000 Aerosol charge neutralizer (requires Polonium-210 sources)
9001 Aerosol non-radioactive charge neutralizer (available 2018)
9002 Aerosol Soft X-ray Charger
9200 Aerosol Generation System
9202 Automated Aerosol Generation System: includes Model 9200 AGS plus Auto-3 way Valve Chassis
HT-DAIR115 External dry air supply, 115V
HT-DAIR230 External dry air supply, 230V
HT-P115 External vacuum pump, 115V
HT-P230 External vacuum pump, 230V
HT-PPSoft Post-processing software to allow off-line data inversion
RackH Rackmount kit for 3100 HTDMA
HTDMA-Kit Maintenance kit for 3100 HTDMA

Related Products

Contact us to discuss how Brechtel can help you.

  • We have been operating Brechtel’s HTDMA (Model 3002) in the lab and at our field site since 2010 and have found the staff and Fred himself very helpful and sensitive to our needs, even though we are are located in Hong Kong, quite a long distance from California. The timely responses to our needs over the years have been very important to us and we are very satisfied with service provided by Brechtel.

    Chak K. Chan, Ph.D. Professor, Division of Environment and Department of Chemical and Biomolecular Engineering
    Hong Kong University of Science and Technology