On the Feasibility of a Number Concentration Calibration Using a Wafer Surface Scanner

A Faraday cup aerosol electrometer based electrical aerosol instrument calibration setup from nanometers up to micrometers has been designed, constructed, and characterized. The setup utilizes singly charged seed particles, which are grown to the desired size by condensation of diethylhexyl sebacate. The calibration particle size is further selected with a Differential Mobility Analyzer (DMA). For micrometer sizes, a large DMA was designed, constructed, and characterized. The DMA electrical mobility resolution was found to be 7.95 for 20 L/min sheath and 2 L/min sample flows. The calibration is based on comparing the instrument's response against the concentration measured with a reference Faraday cup aerosol electrometer. The setup produces relatively high concentrations in the micrometer size range (more than 2500 1/cm 3 at 5.3 mm). A low bias flow mixing and splitting between the reference and the instrument was constructed from a modified, large-sized mixer and a four-port flow splitter. It was characterized at different flow rates and as a function of the particle size. Using two of the four outlet ports at equal 1.5 L/min flow rates, the particle concentration bias of the flow splitting was found to be less than ±1% in the size range of 3.6 nm-5.3 mm. The developed calibration setup was used to define the detection efficiency of a condensation particle counter from 3.6 nm to 5.3 mm with an expanded measurement uncertainty (k ¼ 2) of less than 4% over the entire size range and less than 2% for most of the measurement points.

“…to 2.1% at 2 L/min. These bias values are acceptable, as values of several percent have been reported previously (Li et al 2014).…”

Section: Mixer and Flow Splitter Testssupporting

confidence: 79%

Section: Mixer and Flow Splittermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Extending the Faraday cup aerosol electrometer based calibration method up to 5 µm

Järvinen

Keskinen

Yli-Ojanperä

2018

“…One method developed for fluorescence intensity verification can also be used to validate particle concentration and establish traceability (Li et al 2014). Particles size selected by a differential mobility analyzer (DMA) is sampled by an optical particle counter, collected on a wafer, and scanned for number count verification (Linnell et al 2016).…”

Section: Fluorescence Calibration Methodsmentioning

confidence: 99%

Real-time sensing of bioaerosols: Review and current perspectives

Huffman

Perring

Savage

et al. 2019

190

138

Detection of bioaerosols, or primary biological aerosol particles (PBAPs), has become increasingly important for a wide variety of research communities and scientific questions. In particular, real-time (RT) techniques for autonomous, online detection and characterization of PBAP properties in both outdoor and indoor environments are becoming more commonplace and have opened avenues of research. With advances in technology, however, come challenges to standardize practices so that results are both reliable and comparable across technologies and users. Here, we present a critical review of major RT instrument classes that have been applied to PBAP research, especially with respect to environmental science, allergy monitoring, agriculture, public health, and national security. Eight major classes of RT techniques are covered, including the following: (i) fluorescence spectroscopy, (ii) elastic scattering, microscopy, and holography, (iii) Raman spectroscopy, (iv) mass spectrometry, (v) breakdown spectroscopy, (vi) remote sensing, (vii) microfluidic techniques, and (viii) paired aqueous techniques. For each class of technology we present technical limitations, misconceptions, and pitfalls, and also summarize best practices for operation, analysis, and reporting. The final section of the article presents pressing scientific questions and grand challenges for RT sensing of PBAP as well as recommendations for future work to encourage high-quality results and increased cross-community collaboration.

“…WSS are alternatively used to count aerosolized particles by depositing them on a polished flat surface. One study utilizes a WSS as a reference for particle numbers over a range of a few micrometers and evaluates the counting efficiency of an airborne optical particle counter (OPC) at a 3 mm particle diameter (Li et al 2014). The dynamic range of WSS with respect to particle diameter is from a few tens of nanometers to several micrometers.…”

Section: Introductionmentioning

confidence: 99%

A method to deposit a known number of polystyrene latex particles on a flat surface

Tajima

Iida

Ehara

et al. 2019

This study introduces a method to deposit polystyrene latex (PSL) particles on a silicon wafer in a manner that allows their number to be predicted with a high degree of accuracy. A laminar flow growth tube is used to condense supersaturated water vapor on seed aerosol particles that are water-insoluble. After condensation is complete the droplets are accelerated through a nozzle to form an aerosol jet, and the number of droplets in this jet is counted optically. The droplets are then deposited on a flat surface by inertial impaction. The particle number on the surface is predicted by multiplying the droplet number by an experimentally evaluated conversion coefficient of 0.991 ± 0.011 (k ¼ 2). Uncertainty analysis showed with a 95% confidence interval that the particle number on a flat surface is ± 2.0%. The primary application of this method is to make a particle number standard (PNS) wafer whose intended use is to evaluate the counting efficiencies of wafer surface scanners, and this study demonstrates the fabrication of such PNS wafers. A motorized XY-stage moves the surface horizontally to deposit PSL particles along desired paths over a half-inch wafer. The particle number was varied over seven levels ranging from 10 to 10,000. The particle diameter was varied at four levels: 0.814, 0.18, 0.102, and 0.046 mm. In all PNS wafers, the number of deposited particles was counted using optical microscopes. The observed particle numbers were all within the 95% confidence interval of the predicted value.