nderstanding the processes related to particle formation in the atmosphere is crucial in order to quantify more accurately their effect on climate. New particle formation is a global scale phenomenon, through which significant amounts of new particles are introduced in the atmosphere. A main mechanism of new particle formation is ion-induced nucleation, where vapor molecules nucleate on pre-existing atmospheric ions. It follows that in order to understand the mechanism of ion-induced nucleation, research must be focused on the very first steps of formation which normally lay in the sub-2nm size range. The work of this thesis is focused on facilitating the research on new particle formation by advancing the instrumentation state-of-the-art, but also performing experimental work on the dynamics of ion-induced nucleation. @en

The detection efficiency of Condensation Particle Counters (CPCs) reduces drastically as particle size becomes smaller than 2 nm. Increasing the supersaturation in order to enhance the detection efficiency, has limited applicability because the onset supersaturation value of droplet formation by homogeneous nucleation is very close to the heterogeneous onset supersaturation for sub-2 nm particles. In this work we introduce a new method for increasing the detection efficiency of CPCs for sub-2 nm particles, which relies mainly on controlling the spatial distribution of the supersaturation profile by simply modifying the operating temperatures of the CPC. We evaluated the new method by generating monodisperse particles in the size range of 0.98–4.50 nm and used them to characterize a TSI 3025 CPC. We achieved significant increase of the detection efficiency for sub-2 nm particles. Furthermore, we calculated the supersaturation field developed in the condenser tube with a finite element model and used it to determine the detection efficiency according to heterogeneous nucleation theory. These calculations reveal that the observed increase of the detection efficiency can be explained by the manipulation of the spatial distribution of the supersaturation field. The method introduced here can greatly improve the detection efficiency of CPCs and in the meantime further extend their use for particle sizing purposes in the sub-2-nm range.

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Recent advanced in the fields of nanotechnology and atmospheric sciences underline the increasing need for sizing sub-10-nm aerosol particles in a simple yet efficient way. In this article, we develop, experimentally test and model the performance of a High-Pass Electrical Mobility Filter (HP-EMF) that can be used for sizing nanoparticles suspended in gaseous media. Experimental measurements of the penetration of nanoparticles having diameters down to ca 1nm through the HP-EMF are compared with predictions by an analytic, a semi-empirical and a numerical model. The results show that the HPEMF effectively filters nanoparticles below a threshold diameter with an extremely high level of sizing performance, while it is easier to use compared to existing nanoparticle sizing techniques through design simplifications. What is more, the HP-EMF is an inexpensive and compact tool, making it an enabling technology for a variety of applications ranging from nanomaterial synthesis to distributed monitoring of atmospheric nanoparticles.

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Hygroscopic Tandem Differential Mobility Analyzers (HTDMAs) are widely used to measure the water uptake characteristics of aerosol particles. As has been shown experimentally in the past, potential differences in the relative humidity (RH) between the aerosol and the sheath flow of the second Differential Mobility Analyzer (DMA) can lead to erroneous estimates of the apparent hygroscopic behavior of the sampled particles. A prompt phase transition, for example, may become smeared and be erroneously interpreted as non-prompt. Using a particle-tracking model, here we simulate the trajectories and the state of the particles classified in a DMA with non-uniform RH and temperature profiles. Our simulations corroborate earlier observations proving that such an experimental artifact can induce particle growth within the second DMA. Given the importance of maintaining uniform RH and temperature inside the second DMA of HTDMA systems and the limitations of existing RH and temperature sensors, we further provide suggestions for their operation.@en