Modification and laboratory evaluation of a TSI ultrafine condensation particle counter (Model 3776) for airborne measurements

<p>A butanol-type ultrafine condensation particle counter (UCPC, Model 3776, TSI, Inc., Shoreview, MN, USA), which can achieve a 50% detection efficiency diameter (<i>d</i>₅₀) of 2.5 nm using a capillary-sheath structure, was modified and tested in the laboratory for airborne measurements. The aerosol flow rate through the capillary is a key factor affecting the quantification of aerosol particle number concentrations. A pressure-dependent correction factor for the aerosol flow rate was determined using a newly added mass flow meter for the sheath flow and the external calibration system. The effect of particle coincidence in the optical sensing volume was evaluated using an aerosol electrometer (AE, Model 3068B, TSI, Inc.) as a reference. An additional correction factor for the coincidence effect was derived to improve the quantification accuracy at higher concentrations. The particle detection efficiency relative to the AE was measured for mobility diameters of 3.1–50 nm and inlet absolute pressures of 101–40 kPa. The pressure dependence of the <i>d</i>₅₀ value, asymptotic detection efficiency, and shape of the particle detection efficiency curve is discussed, along with simple theoretical calculations for the diffusion loss of particles and the butanol saturation ratio in the condenser.</p> <p>© 2017 American Association for Aerosol Science</p

Inkjet Aerosol Generator as Monodisperse Particle Number Standard

<div><p>The AIST-inkjet aerosol generator (IAG) can generate highly monodisperse solid or liquid aerosol particles in the particle diameter range from 0.3 to 20 μm at precisely known particle generation rates. The device has been developed for evaluating the counting efficiencies of optical and condensation particle counters. Particle generation efficiency of the IAG is defined as the number of aerosol particles generated by one voltage pulse sent to an inkjet head. The 95% confidence interval of the efficiency were 0.998 ± 0.006 within the 0.4 to 10 μm particle diameter range. The efficiencies remained close to unity when the droplet generation rates were within 20–500 s⁻¹ and 100–900 s⁻¹ using ultrapure-water and isopropyl alcohol (IPA) as the solvent of the inkjet solution, respectively. The operating aerosol flowrate range of the IAG is currently 0.5 and 1.0 L/min. The coefficients of variations (C.V.) of the size distributions were 2 to 3% indicating the generated particles were highly monodisperse. The generated particle sizes were defined as the volume equivalent diameter, <i>D</i>_ve. The uncertainty analysis on the factors affecting <i>D</i>_ve indicated that 95% confidence interval of the D_ve is expected to be ±5%. The uncertainty of <i>D</i>_ve was entirely caused by the uncertainty of the average mass of a droplet. The reproducibility of particle sizes within 0.5 to 10 μm was evaluated using an aerodynamic particle sizer. The C.V. of the measured particle sizes were less than 6% and 4% when NaCl particles and ionic liquid droplets were generated, respectively.</p><p>Copyright 2014 American Association for Aerosol Research</p></div

Aerosol-to-liquid collection: A method for making aqueous suspension of hydrophobic nanomaterial without adding dispersant

<p>This article introduces an aerosol-based technique to make aqueous suspension of hydrophobic nanomaterial without adding dispersant. The method is intended for making a test-sample for evaluating the toxicities of nanomaterial by intra-tracheal administration. The method can wet the surface of hydrophobic nanomaterial within a few seconds. After the wetting process five to ten minutes of sonication assisted with manual stirring can fully disperse the hydrophobic nanomaterials in water. Two types of TiO₂ nanomaterial were used in this study; Tayca JMT-150IB whose surfaces are coated with negatively charged hydrophobic functional group, and P25 whose surfaces are naturally hydrophilic. Nanomaterials are aerosolized by a dry-method and become micrometer-sized agglomerates. Then supersaturated water vapor is condensed onto these airborne agglomerates by using a growth tube collector. The collected suspension (CS) of hydrophobic nanomaterial (JMT-150IB) is prepared in two steps; airborne agglomerates are collected onto a flat surface then transferred to liquid-water and subsequently sonicated for complete dispersion. This method works equally well for making the CS of hydrophilic nanomaterial. Size distribution measurements of the CS show that airborne agglomerates of TiO₂ dissociate into smaller units of agglomerates once they are captured into water, and the sizes of the agglomerates are in the nanometer to sub-micrometer range. Light scattering technique is used to show that a short sonication process can reproduce the particle number concentration of the CS after long storage.</p> <p>Copyright © 2017 American Association for Aerosol Research</p

Aerosol Charge Fractions Downstream of Six Bipolar Chargers: Effects of Ion Source, Source Activity, and Flowrate

<p>Bipolar diffusion charging is used routinely in aerosol electrical mobility size distribution measurements. In this study, aerosol charge fractions produced by six bipolar chargers (neutralizers) were measured using a tandem differential mobility analyzer system. Factors that were studied include the type of ion source (²¹⁰Po, ⁸⁵Kr, ²⁴¹Am, and soft X-ray), source activity, charger design, and aerosol flowrate. It was found that all six types of neutralizers achieve stationary state charge distributions when the source activity is sufficiently high. For ²¹⁰Po neutralizers with an initial radioactivity of 18.5 MBq (0.5 mCi), stationary state charge distributions are achieved when the source is less than 3.25 years old (residual activity no less than 0.0527 MBq). Stationary state was achieved for ⁸⁵Kr neutralizers having residual radioactivity greater than 70 MBq. Source activities of ²⁴¹Am and soft X-ray neutralizers are discussed. Aerosol charge fractions for six neutralizers remain reasonably invariant over a wide range of flowrates. The positive charge fractions achieved by the soft X-ray neutralizer are higher than those by the other five neutralizers using radioactive sources while negative charge fractions for all neutralizers studied are all in a similar range. This study also raises questions about bipolar charging fractions used for data inversion in some scanning mobility particle spectrometer (SMPS) systems, and underscores the need to better understand bipolar charging to achieve more accurate measurements of particle size distributions.</p> <p>Copyright 2014 American Association for Aerosol Research</p