Browsing by Subject "LAMINAR-FLOW"

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  • Attoui, Michel; Kangasluoma, Juha (2019)
    Tetraheptylammonium bromide (THABr), tetrabutylammonium bromide (TBABr) and tetraethylammonium bromide (TEABr) dissolved in methanol or water methanol mixtures (similar to 1 mM) produce via positive electrospray atomization and high resolution classification electrical classification standard clean ions (monomer and dier) which are singly charged. THABr is hydrophobic and insoluble in water, TBABr and TEABr are hygroscopic and water soluble (0.6 and 2.8 kg/L respectively). These ions are used to study the effect of hygroscopicity on the activation of aerosol particles in the sub 2 nm range via the detection efficiency measurement of a boosted ultrafine TSI condensation particle counter (3025A). Water solubility of particles seems to play a role in the activation and growth with butanol vapor in the CPC (condensation particle counter) independently of the size.
  • Kangasluoma, Juha; Hering, Susanne; Picard, David; Lewis, Gregory; Enroth, Joonas; Korhonen, Frans; Kulmala, Markku; Sellegri, Karine; Attoui, Michel; Petäjä, Tuukka (2017)
    In this study we characterized the performance of three new particle counters able to detect particles smaller than 3 nm during the Helsinki condensation particle counter (CPC) workshop in summer 2016: the Aerosol Dynamics Inc. (ADI; Berkeley, USA) versatile water condensation particle counter (vWCPC), TSI 3777 nano enhancer (TSI Inc., Shoreview, USA) and modified and boosted TSI 3010-type CPC from Universite Blaise Pascal called a B3010. The performance of all CPCs was first measured with charged tungsten oxide test particles at temperature settings which resulted in supersaturation low enough to not detect any ions produced by a radioactive source. Due to similar measured detection efficiencies, additional comparison between the 3777 and vWCPC were conducted using electrically neutral tungsten oxide test particles and with positively charged tetradodecylammonium bromide. Furthermore, the detection efficiencies of the 3777 and vWCPC were measured with boosted temperature settings yielding supersaturation which was at the onset of homogeneous nucleation for the 3777 or confined within the range of liquid water for the ADI vWCPC. Finally, CPC-specific tests were conducted to probe the response of the 3777 to various inlet flow relative humidities, of the B3010 to various inlet flow rates and of the vWCPC to various particle concentrations. For the 3777 and vWCPC the measured 50% detection diameters (d50s) were in the range of 1.3-2.4 nm for the tungsten oxide particles, depending on the particle charging state and CPC temperature settings, between 2.5 and 3.3 nm for the organic test aerosol, and in the range of 3.2-3.4 nm for tungsten oxide for the B3010.
  • Frye, Maike; Taddei, Andrea; Dierkes, Cathrin; Martinez-Corral, Ines; Fielden, Matthew; Ortsäter, Henrik; Kazenwadel, Jan; Calado, Dinis P.; Ostergaard, Pia; Salminen, Marjo; He, Liqun; Harvey, Natasha L.; Kiefer, Friedemann; Mäkinen, Taija (2018)
    Tissue and vessel wall stiffening alters endothelial cell properties and contributes to vascular dysfunction. However, whether extracellular matrix (ECM) stiffness impacts vascular development is not known. Here we show that matrix stiffness controls lymphatic vascular morphogenesis. Atomic force microscopy measurements in mouse embryos reveal that venous lymphatic endothelial cell (LEC) progenitors experience a decrease in substrate stiffness upon migration out of the cardinal vein, which induces a GATA2-dependent transcriptional program required to form the first lymphatic vessels. Transcriptome analysis shows that LECs grown on a soft matrix exhibit increased GATA2 expression and a GATA2-dependent upregulation of genes involved in cell migration and lymphangiogenesis, including VEGFR3. Analyses of mouse models demonstrate a cell-autonomous function of GATA2 in regulating LEC responsiveness to VEGF-C and in controlling LEC migration and sprouting in vivo. Our study thus uncovers a mechanism by which ECM stiffness dictates the migratory behavior of LECs during early lymphatic development.
  • Enroth, Joonas; Kangasluoma, Juha; Korhonen, Frans; Hering, Susanne; Picard, David; Lewis, Greg; Attoui, Michel; Petäjä, Tuukka (2018)
    Condensation particle counter (CPC) technology has continued to evolve, with the introduction of several new instruments over the last several years. An important aspect in the characterization of these instruments is the measurement of their time response. Yet there is no standardly accepted approach for this measurement. Here we evaluate different classically used methods for determining CPC time response, and present the potential pitfalls associated with these approaches. Further, we introduce a new simple definition for the term response time, E, which is based on the first-order systems response, while providing a practical definition by corresponding to approximate to 95% change in concentration. We also present results for various commonly used CPCs, and for the Airmodus A11 nano Condensation Nucleus Counter (nCNC) system, the TSI 3777+3772 Nano Enhancer system, and Aerosol Dynamics Inc.'s (ADI) new versatile water condensation particle counter.Copyright (c) 2018 American Association for Aerosol Research
  • Kangasluoma, Juha; Cai, Runlong; Jiang, Jingkun; Deng, Chenjuan; Stolzenburg, Dominik; Ahonen, Lauri R.; Chan, Tommy; Fu, Yueyun; Kim, Changhyuk; Laurila, Tiia M.; Zhou, Ying; Dada, Lubna; Sulo, Juha; Flagan, Richard C.; Kulmala, Markku; Petaja, Tuukka; Lehtipalo, Katrianne (2020)
    Interest in understanding gas-to-particle phase transformation in several disciplines such as at-mospheric sciences, material synthesis, and combustion has led to the development of several distinct instruments that can measure the particle size distributions down to the sizes of large molecules and molecular clusters, at which the initial particle formation and growth takes place. These instruments, which include the condensation particle counter battery, a variety of electrical mobility spectrometers and the particle size magnifier, have been usually characterized in lab-oratory experiments using carefully prepared calibration aerosols. They are then applied, alone or in combination, to study the gas-to-particle transition in experiments that produce particles with a wide range of compositions and other properties. Only a few instrument intercomparisons in either laboratory or field conditions have been reported, raising the question: how accurately can the sub-10 nm particle number size distributions be measured with the currently available instrumentation? Here, we review previous studies in which sub-10 nm particle size distributions have been measured with at least two independent instruments. We present recent data from three sites that deploy the current state-of-the-art instrumentation: Hyytiala, Beijing, and the CLOUD chamber. After discussing the status of the sub-10 nm size distribution measurements, we present a comprehensive uncertainty analysis for these methods that suggests that our present understanding on the sources of uncertainties quite well captures the observed deviations be-tween different instruments in the size distribution measurements. Finally, based on present understanding of the characteristics of a number of systems in which gas-to-particle conversion takes place, and of the instrumental limitations, we suggest guidelines for selecting suitable in-struments for various applications.