10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Validation and Calibration of Particle Sizers with Test Aerosols
TORSTEN TRITSCHER, Thomas Krinke, Andrea Tiwari, Juergen Spielvogel, Francisco Romay, Stephan Große, Andreas Rudolph, Oliver F. Bischof, TSI GmbH
Abstract Number: 1556 Working Group: Instrumentation
Abstract The validity of data obtained with particle counters and sizers depends on their accurate calibration against a known standard that typically is provided by the manufacturer. However, normal use of an instrument may affect the calibration over time, for instance through contamination or drift of sensors controlling the device. The recommended time interval for calibration and the complexity of the calibration procedure may vary from instrument to instrument. For this reason, the user's validation of the instrument performance against the specifications is an important contribution towards assuring long-term measurement consistency.
Globally, several NMIs (National Meteorological Institutes) or standard-setting organizations regulate or recommend test aerosols and complete calibration procedures. We introduce methods to generate aerosols with known properties in the size range of a few nanometers to several micrometers. Here we focus on aerosol generators that can provide aerosol particles fulfilling criteria required for the validation of counters as well as sub- and super-micron sizers without a complex setup. The methods are easy to use and can be conducted by the user.
The aerosol properties need to be adapted to the spectrometer that needs to be verified. Important properties are an adjustable size range and concentration output, monodispersity, output stability, aerosol composition, and handling of the generator including practical aspects of the generator design, such as portability or changing solutions. We introduce and compare the performance of two generators with different test aerosols from the liquid phase.
Portable atomizer aerosol generators like the TSI Model 3079 provide aerosols with particle size distributions in the sub-micrometer size range. A drawback is that they produce very high aerosol concentrations usually above 107 particles/cm3 that require subsequent dilution. The size of the particle mode diameter ranges from 50-200 nm, depending on the oil or salt concentration. A novel Portable Test Aerosol Generator (TSI Model 3073) is introduced that works with a submerged Laskin nozzle to generate the initial droplets. It allows flow and concentration adjustment (flow rate: 0.3 to 4.5 L/min, concentration range 105 to >107 particles/cm3). For operation in the field it can be equipped with a battery pack. The long-term stability and the reproducibility of the aerosol generation has been investigate by measuring the variation of the size distribution over time with a Scanning Mobility Particle Sizer (SMPS). Typical particle materials from solution (sodium chloride, NaCl), liquid (oil) and suspension (Poly-Styrene Latex, PSL) have been studied.
The validation of spectrometers for the micrometer size range, like Optical Particle Counter (OPC) or the Aerodynamic Particle Sizer (APS) require the generation of particles in the size range between 3 is ideal for the validation. The Flow-Focusing Monodisperse Aerosol Generator (FMAG, Model 1520) is a lab-based instrument that produces highly monodisperse aerosol mainly in the supermicron size range. This ability makes the FMAG a valuable tool for verifying the performance of supermicron sizing instruments. The particle size can be adjusted very accurately in the range from 0.7 to 15 µm. We have investigated the high monodispersity and reproducibility for different aerosols and will show our results for particles from solution (NaCl), a liquid (glycerol) and a suspension (PSL). The particle size distributions have been measured by an APS Spectrometer (TSI Model 3321). The dispersion of biological particles such as cells or spores is possible with this generator as well and preliminary results will be shown.
We will present data and instrument specifications detailing the suitability of these two generators for use as on-site validation tools for aerosol sizers and counters.