1×3TDMA Project

The 1×3 tandem differential mobility analyzer (1×3-TDMA) is a novel instrument developed to investigate the physical state of aerosol particle populations. The primary measurement is the change in particle electrical mobility as a result of the irreversibility of the hygroscopic growth factor. In this way the instrument exploits the hysteresis of phase transitions to infer the physical state of particles (i.e. crystalline or aqueous).

The main difference of this system compared to typical hygroscopicity-TDMA (H-TDMA) systems is that all four DMAs are set to the pass the same sized particle and instead of stepping or scanning the DMA voltage, the RH is scanned.

Figure 1. Schematic diagram of the 1-by-3 tandem differential mobility analyzer (1×3-TDMA) for measurement of the irreversibility of the hygroscopic growth factor.

In the summer of 2007 the instrument was deployed at the Department of Energy Aerosol Radiation Measurement site (DoE - ARM) at the Southern Great Plains (SGP) in Billings, Oklahoma.

An important challenge to the atmospheric chemistry community is to understand and subsequently be able to predict the chemical and the meteorological conditions for which tropospheric particles are aqueous or solid (i.e., their physical phase). In relation to this challenge, the current state of knowledge within the scientific community has a gap on the effect of the organic content of particles on their phase transitions. The goal of our research, through a three-pronged approach of laboratory, field, and modeling work, is to help close this gap. The field campaign focused on sulfate particles, because they are the most significant anthropogenic cooling contribution to global direct radiative forcing, and the effect of SOA organic molecules because of the widespread prevalence of mixed organic-sulfate particles in the atmosphere.

Field observations have clearly established the occurrence of phase transitions in real atmospheric particles, cause-and-effect relationships between particle phase and chemical composition and relative humidity history went largely unexplored in those studies, although importantly the pivotal role of sulfate neutralization was established. Moreover, these earlier deployments, focused principally on GF, were not designed specifically with the present purpose in mind of detecting phase transitions, and the measurement techniques employed were therefore not ideal for the detection of phase transitions. The 1×3 TDMA, which is designed to detect the phase transitions of atmospheric particles, will in fact do a much better job of this task than earlier measurements.

Figure 2. A snapshot of the instrument response to the ambient aerosol at the DoE-ARM SGP site. The bottom left panel shows clear evidence of deliquescence, indicating that there is a significant number of crystalline particles in the test aerosol.

People Involved

• Current Group Members

  • Thomas Rosenorn
  • Scot Martin

Publications

1. T.R. Rosenoern, D. Paulsen, and S.T. Martin, "The 1-by-3 Tandem Differential Mobility Analyzer for Measurement of the Irreversibility of the Hygroscopic Growth Factor," Aerosol Science and Technology, 2009, 43, 641-652. PDF file. Supplement.

2. S.T. Martin, T. Rosenoern, Q. Chen, and D.R. Collins, "Phase Changes of Ambient Particles in the Southern Great Plains of Oklahoma, USA," Geophysical Research Letters, 2008, 35, L22801. PDF file. Supplement.

3. T. Rosenoern, J.C. Schlenker, and S.T. Martin, "Hygroscopic Growth of Multicomponent Aerosol Particles Influenced by Several Cycles of Relative Humidity," Journal of Physical Chemistry A, 2008, 112, 2378-2385. PDF File. Errata.