10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Significantly Improving the Operation and Information Yield of Sensor-Type Instrument Densmo by Introduction of a Scanning Mode
PAXTON JUUTI, Antti Rostedt, Jyrki M. Mäkelä, Jorma Keskinen, Tampere University of Technology, Tampere, Finland
Abstract Number: 1223 Working Group: Instrumentation
Abstract The use of sensors for measuring aerosols has been steadily increasing in the past years. Sensors are typically simple and affordable in construction, which makes them excellent candidates for measurement networks. On the downside, the sensors might operate on only set parameters, yielding less information than they structurally are able to. To remedy this, parameter scanning is quite commonly used route, which can be seen for example in instrument naming schemes.
In this work, we further develop DENSMO (Juuti et al. 2016), an instrument designed to monitor effective density of aerosol nanoparticles, and introduce a voltage scanning mode to significantly improve its capabilities without doing any structural modifications. The operation of DENSMO is based on the principle of classifying the aerosol first with a zeroth order mobility analyzer and then with a low-pressure impactor. This yields information on both the mobility and aerodynamic behavior of the measured particles, resulting in the values of mobility and aerodynamic median diameters, and consequently the effective density. Without scanning the voltage of the mobility analyzer, the geometric standard deviation of the measured aerosols number concentration needs to be known or estimated based on the source. Thus, one source of uncertainty is completely removed from the operation of DENSMO. In addition, the voltage scanning mode enables DENSMO to give a measure of the fractal dimension of the measured aerosol particles. This is due to the fact that now the effective density is measured as a function of the mobility size.
As DENSMO is designed to be used for monitoring of aerosol nanoparticle synthesis, the performance of the scanning mode is evaluated with spherical and agglomerated nanoparticles made from metal and ceramic particles. For the fractal dimension measurements, in addition to the metal and ceramic particles, also liquid oil droplets are used to ensure the lack of fractality in the particles. These measurements are referenced against scanning mobility particle sizer (SMPS) and electrical low pressure impactor (ELPI), which can be used to measure same particle properties and used to calculate the fractal dimension based on the same particle properties. The results show that the operation of DENSMO is significantly improved by the addition of the voltage scanning mode and, given an aerosol that is inside the working range of DENSMO, the measured values are comparable to the ones retrieved from the reference instrumentation.
Juuti, P., Arffman, A., Rostedt, A., Harra, J., Mäkelä, J.M., & Keskinen, J. (2016). Real-time effective density monitor (DENSMO) for aerosol nanoparticle production. Aerosol Science and Technology, 50, 487–496.