Abstract
State-of-the-art aerosol nanoparticle techniques all have one feature in common: for analysis they remove the nanoparticles from their original environment. Therefore, physical and chemical properties of the particles might be changed or cannot be measured correctly. To overcome these shortcomings, we apply synchrotron based small angle X-ray scattering (SAXS) as an in-situ measurement technique. Contrasting other aerosol studies using SAXS, we focus on particle concentrations which allow direct comparison to common aerosol nanoparticle analyzers. To this end, we analyze aerosol nanoparticles at ambient pressure and concentrations of slightly above ~106 cm−3. A differential mobility particle sizer (DMPS) is operated in parallel. We find that SAXS enables measurement of the primary particles and the aggregates, whereas the DMPS detects only aggregates. We conclude that in-situ nanoparticle characterization with ultra-low volume fractions of ~10–10 is feasible with SAXS. Our technique opens up a doorway to the in-situ analysis of aerosol nanoparticles under atmospheric conditions.
Highlights
Particle increase Particle fullParticle decrease Valve switchingRelative particle concentration Time stepsmall angle X-ray scattering (SAXS) results
The SAXS experiments were conducted at the Austrian SAXS beamline at ELETTRA, Trieste, Italy[28] and at the ID02 beamline at the European Synchrotron Radiation Facility (ESRF), Grenoble, France[29]
Our study proves that SAXS is suitable to characterize aerosolized nanoparticles even at volume fractions as low as ~10−10
Summary
The intensity of the scattering curve was calibrated with water[35] and scaled to the diameter of the flow tube resulting in an absolute intensity scale in cm−1. The black dots represent the data resulting from the DBS averaging and the red curve a unified fit according to Beaucage[36,37] which is discussed in detail in the Methods section. The fit here is a two-level Beaucage fit, where the first level represents the primary particles and the second level the aggregates. As described in the paper about mass-fractral aggregate SAXS measurements[38], it is possible to measure directly the fractal dimension of aggregates with SAXS, which corresponds to the power-law regime slope ðIðqÞ $ qÀdf Þ in the range between
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