10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Calibration and Ambient Measurements of Sub-3 nm Aerosols
HELINA LIPP, Eduard Tamm, Kalju Tamme, Kaupo Komsaare, Urmas Hõrrak, Heikki Junninen, University of Tartu
Abstract Number: 172 Working Group: Instrumentation
Abstract New particle formation (NPF) is a process where molecular clusters are formed from atmospheric vapours by condensation. The clusters can grow into larger particle sizes and act as cloud condensation nuclei. To investigate NPF in the ambient air it is necessary to use instrumentation that is capable of measuring the smallest formed particles around 1-2 nm in size. For this purpose, we used Airmodus A11 nano Condensation Nucleus Counter system (nCNC-system) containing the Condensation Particle Counter (CPC) in pair with Particle Size Magnifier (PSM) (Vanhanen et al. 2011). The foremost importance is on calibration of the instrumentation for accurate size separation. The instrumentation was calibrated in laboratory conditions and used for detection of nanoparticles in ambient conditions in the Station for Measuring Ecosystem-Atmosphere Relations (SMEAR) in Järvselja, Estonia. SMEAR Estonia (http://smear.emu.ee/) is an environmental research and monitoring complex located in the hemiboreal forest of south-eastern Estonia at Järvselja, which can be described as a remote and rural site with low anthropogenic disturbances (Noe et al. 2015).
Our measurement system (A11 nCNC-system) was calibrated using tungsten nanoparticles, generated in a Carbolite STF tube furnace, where an alumina boat with a piece of tungsten wire was placed. Tungsten was evaporated at furnace temperature of 1100⁰C, the vapour was excreted by the 1.5 l/min nitrogen flow through a nozzle and then turbulently mixed with cold clean air with flow rate of 1500 l/min. Nucleation process gave a polydisperse tungsten aerosol, particles were charged in a bipolaar charger and then a fraction with narrow distribution (quasy-monodisperse fraction) was selected by closed-loop DMA (Differential Mobility Analyzer). The A11 nCNC-system was operated in scanning flow mode together with aerosol electrometer as a reference instrument to find the detection efficiency and calibration coefficients. The calibration provides the PSM flow conditions for instrument detection of tungsten ions with diameters of 3 nm, 2.9 nm, 2.7 nm, 2.5 nm, 2.3 nm, 2.1 nm, 1.9 nm, 1.7 nm, 1.5 nm, 1.3 nm, 1.1 nm and 1 nm, respectively. We used diethylene glycol (DEG) as the working fluid of PSM.
Conducting the field measurements A11 nCNC-system was set up in a cabin so that the PSM inlet, which was a 51 cm long tube, was placed directly through the cabin wall for detection of nanoparticles in ambient conditions. In parallel with A11 nCNC-system the atmospheric aerosols and ions were monitored with NAIS (Neutral cluster and Air Ion Spectrometer) and EAS (Electrical Aerosol Spectrometer) for a complete size distribution of aerosols in hemiboreal forest. In the presentation the results from the ambient measurements will be shown and discussed in details.
This work was supported by European Regional Development Fund project MOBTT42 under Mobilitas Pluss programme and by the Estonian Research Council Projects IUT20-11.
Noe, Steffen M. et al. 2015. “SMEAR Estonia: Perspectives of a Large-Scale Forest Ecosystem– Atmosphere Research Infrastructure.” Forestry Studies 63:56–84. Vanhanen, J. et al. 2011. “Particle Size Magnifier for Nano-CN Detection.” Aerosol Science and Technology 45:533-542, 2011.