Advances in Aerosol Instrumentation for Atmospheric Science

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.ChemE/Materials for Energy Conversion & Storag

A tunable high-pass filter for simple and inexpensive size-segregation of sub-10-nm nanoparticles

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.ChemE/Materials for Energy Conversion & Storag

Chemical composition and hygroscopic properties of aerosol particles over the Aegean Sea

The chemical composition and water uptake characteristics of sub-micrometre atmospheric particles over the region of the Aegean Sea were measured between 25 August and 11 September 2011 within the framework of the Aegean-Game campaign. High temporal-resolution measurements of the chemical composition of the particles were conducted using an airborne compact time-of-flight aerosol mass spectrometer (cToF-AMS). These measurements were performed during two flights from the island of Crete to the island of Lemnos and back. A hygroscopic tandem differential mobility analyser (HTDMA) located on the island of Lemnos was used to measure the ability of the particles to take up water. The HTDMA measurements showed that the particles in the dominant mode were internally mixed, having hygroscopic growth factors that ranged from 1.00 to 1.59 when exposed to 85% relative humidity. When the aircraft flew near the ground station on Lemnos, the cToF-AMS measurements showed that the organic volume fraction of the particles ranged from 43 to 56%. These measurements corroborate the range of hygroscopic growth factors measured by the HTDMA during that time. Good closure between HTDMA and cToF-AMS measurements was achieved when assuming that the organic species were less hygroscopic and had an average density that corresponds to aged organic species. Using the results from the closure study, the cToF-AMS measurements were employed to determine vertical profiles of a representative aerosol hygroscopic parameter ?mix. Calculated ?mix values ranged from 0.19 to 0.84 during the first flight and from 0.22 to 0.80 during the second flight. Air masses of different origin as determined by back trajectory calculations can explain the spatial variation in chemical composition and ?mix values of the particles observed in the region.ChemE/Chemical EngineeringApplied Science