AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Tandem Mobility-Mass Measurements of Bipolar Ions Generated in a Po-210 alpha Radiation Source
ANNE MAISSER, Jikku Thomas, Carlos Larriba-Andaluz, Siqin He, Christopher Hogan Jr., University of Minnesota
Abstract Number: 150 Working Group: Aerosol Physics
Abstract Aerosol measurements, especially of particles in the nanometer size range, commonly rely on electrostatic manipulation and measurement. Therefore, particles need to be charged in a controlled way prior to their measurement. A common charging technique is the exposure of particles to ions generated by weak radiation (alpha-, or beta- radiation). The radiation ionizes the gas via electron loss and attachment of the electrons to neutral gas molecules. This leads to equal concentrations of positively and negatively charged ions. As pointed out by previous studies (Steiner et al.) the physical and chemical properties of the ions generated in this manner can vary between experiments; the composition depends upon gas composition and is also influenced by impurities evaporating from tubing walls. To better characterize such ions, we applied differential mobility analysis-mass spectrometry (DMA-MS, with a SEADM P5 DMA and a time of flight mass spectrometer) to measure the ion mass and mobility of Po-210 generated charger ions. Charger ions of both polarities were chemically identified. We used density function theory calculations (DFT) for minimum local energy structure determination of the identified molecules and a non-specular scattering model (Larriba et al.) to calculate mobilities for DFT structures. This enabled direct comparison of the mass-mobility relationship calculated to that found experimentally. Subsequently, the bipolar charge distribution was calculated applying Brownian dynamic simulations (Gopalakrishnan et al.) for varying ion distribution input parameters to determine the dependency of the particle charge state on the ion population.
Steiner, G., Jokinen, T., Junninen, H., Sipila, M., Petaja, T., Worsnop, D., Reischl, G.P., & Kulmala, M. (2014). Aerosol Science and Technology, 48, 261-270.
Larriba, C., Hogan, C.J., The Journal of Physical Chemistry A, 117, 3887-3901
Gopalakrishnan, R., Meredith, M.J., Larriba-Andaluz, C., Hogan, C.J., (2013), Journal of Aerosol Science, 63, 126-145