Elsevier

Journal of Aerosol Science

Volume 92, February 2016, Pages 38-52
Journal of Aerosol Science

Performance comparison of two thermodenuders in Volatility Tandem DMA measurements

https://doi.org/10.1016/j.jaerosci.2015.10.002Get rights and content
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Highlights

  • Thermophoretic losses are deeply dependent on thermodenuder design.

  • Significant variation in particle volatilization amid instruments was observed.

  • Differences among devices varied with the aerosol studied and temperatures used.

  • Both thermodenuders allow to withdraw similar conclusions on particle mixing state.

Abstract

Volatility Tandem Differential Mobility Analysers (VTDMAs) are widely used for determining the volatile and refractory fractions and thus the mixing state of aerosols particles. A three-channel VTDMA consisting of two thermodenuders (TDs) with distinct designs (i.e., the NanoTD, having a straight tube design, and a coiled TD; cTD) and a by-pass line was built and fully characterized. Both TDs were tested using laboratory-generated aerosol particles (single compound and core–shell particles) as well as atmospheric aerosols observed at an urban background station. The NanoTD exhibited high particle penetration efficiency and negligible thermophoretic losses, making it advantageous for ultrafine particle analysis, especially in environments with low particle concentration. The cTD allows longer particle residence time for the same flow rate, resulting in higher particle volatilization in some cases. Higher particle losses in this TD, both thermophoretic and diffusional, pose a limitation when dealing with low particle concentrations.

The difference in the performance between the thermodenuders was only noticed at intermediate temperatures, at which particle volume loss becomes more pronounced. These temperatures vary among aerosols, since the volatilization rate depends on the chemical complexity and size of the particles sampled. Differences in the aerosol volume fraction remaining after heating with the two TD designs exhibited a maximum of 20% for single-compound particles and 12% for urban background aerosols. Measurements using core–shell particles yielded differences of up to 21% in particle volatilization, independently of particle size, when comparing the system using either of the two TD designs. Similar results were obtained with the two TD designs at higher operating temperatures (e.g., 230 °C), indicating that at this temperature most of the material on the particles was evaporated.

Keywords

Aerosol volatility
Nanoparticles
Thermodenuder
VTDMA

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