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Design and Characterization of Triple-Tube, Laminar-Flow Condensation Nano Spot-Collector: Application to Microscopy and Spectroscopic Analysis of Aerosols
ORTHODOXIA ZERVAKI, Braden Stump, Patricia Keady, Pramod Kulkarni, Dionysios D. Dionysiou, HELD-NIOSH
Abstract Number: 518
Working Group: Instrumentation and Methods
Abstract
We describe performance evaluation of an aerosol nano spot-collector designed for direct electron or optical microscopy, and laser spectroscopic analysis of nanoparticles and aerosols in the size range 5 nm to 5 μm. The instrument uses water-based laminar-flow condensational growth of particles, followed by gentle impaction for dry spot sample collection directly onto an electron microscopy stub or grid. The spot sample collector was designed for a small logistical footprint while maintaining a high flow rate required to achieve good sampling statistics for microscopy analysis. It uses three parallel laminar flow growth tubes, each with a sample flow rate of 0.4 L/min, providing a total sample flow rate of 1.2 L/min. The laminar flows merge into one flow and exit through a converging nozzle to allow impaction collection on a substrate. The aerosol stream passes through a three-temperature stage growth tube to achieve the desired water vapor supersaturation profile and exit dew point. Experiments were conducted to determine the size-dependent collection efficiency, particle wall losses, uniformity of spot deposit, surface density distribution for particles, and aerosol concentration effects of the three-tube nano spot-collector. Particles as small as 5 nm could be activated as seed condensation nuclei and grow up to 3 µm droplets. During dry collection, the droplets impact onto the warm surface of a SEM stub or a TEM grid forming a spot deposit of approximately 1-mm diameter. The resulting spot particle samples were analyzed using electron microscopy, infrared, and Raman chemical imaging to quantify the size distribution of aerosol and the analyte concentration. Spot samples were analyzed to probe the preservation of the particle size distribution of sampled aerosol.
Keywords: Aerosol nano spot-collector; nanoparticles, condensation growth; supersaturation; aerosol microscopic analysis