The American company BRECHTEL manufactures the Humidified Tandem Differential Mobility Analyzer. The HTDMA System is comprised of two SEMS systems and a novel diffusion based humidifier. The first SEMS selects dry particles of known size while the second determines the size of the grown droplets. The HTDMA measures the water uptake (growth factor) of monodisperse particles over a wide range of relative humidities.

·Fully automated growth factor measurements in multiple sampling modes ·Integrated control hardware with easy access to sensor outputs ·Rapid diffusion-based humidification system operating over the 2-93% RH range ·Multiple particle detection options ·Aerosol flow rates of 0.2-1 lpm ·Sheath flow rates 2.5-10 lpm ·Use of ceramic materials as high voltage insulators ·Reduced arcing potential ·Easy-to-use software including multiple sampling modes, data inversion, calibration mode and residence time
The HTDMA allows size-resolved measurements to be made of the wáter uptake properties of aerosols. This information is critical for understanding how particles act as cloud condensation nuclei and how particles grow and deposit within the human respiratory system. HTDMA data have found importantapplications in research on the climate impacts of aerosols.Fully automated and easy-to-use software allows the user to configure the HTDMA to step through a pre-selected series of monodisperse dry particle sizes with multiple RH’s tested at each size. The cycle may be repeated automatically for as long as desired.