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Air Pollution Monitoring
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
If we add an electron to each particle and then apply an electric field, the resultant electrostatic force takes the place of gravity, measuring the drift (“mobility”) of the particle then provides a direct measure of the aerodynamic diameter, even of ultrafine particles. Summing up the rate of arrival of the electrons, i.e., the electric current, in a Faraday cup electrometer can then give us a number density of fine or ultrafine particulate (cf. Dekati or Grimm Aerosol Technik). Scanning the applied voltage and looking at the current as a function of arrival time gives us a number spectrum as a function of aerodynamic diameter (“differential mobility analyzer”) down to diameters of a few nanometers.
Particle Size Analyzers: Practical Procedures and Laboratory Techniques
Published in Christopher S. Cox, Christopher M. Wathes, Bioaerosols Handbook, 2020
The EAA consists of three main components (Figure 8.26a): a unipolar diffusion charger, the mobility analyzer and a Faraday-cup electrometer detector. Gas-borne particles pass through the diffusion charger at a flow rate of 4 L min-1, where they acquire a well-defined electrostatic charge that depends on the number of ions encountered during the time spent within the charger (ion product), as well as on particle size. The charged particles pass to the tubular mobility section, which consists of a central electrode surrounded by a core of clean (sheath) gas (Figure 8.26b). The aerosol flow is introduced so as to surround the sheath gas in laminar flow; any aerosol leaving the mobility analyzer is collected on the filter of the electrometer and the electrostatic charge measured as the current drains to earth potential. Initially, the analyzer is operated with the central electrode at low voltage, so that all the aerosol collects on the electrometer filter. As this voltage is increased in a series of well-defined steps, progressively fewer particles penetrate through the mobility section, and the electrometer current falls to zero (Figure 8.26c). The measured decrease in electrometer current between two successive settings of electrode voltage can be related to the particle number concentration associated with a particular size band through a deconvolution technique (Kapadia123). The EAA has the capability to discriminate size bands in the range 0.013 to 0.75 μm diameter; this range can be extended to 0.004 μm, but the performance of the instrument below 0.013 μm is uncertain. Over the normal operating range, a size distribution may be obtained within 2 minutes if the aerosol source is stable. It should be noted that the density and viscosity of the sheath and aerosol gases should be the same for the size separation process to work correctly.
Characteristics of Scanning Flow Condensation Particle Counter (SFCPC): A rapid approach for retrieving hygroscopicity and chemical composition of sub-10 nm aerosol particles
Published in Aerosol Science and Technology, 2023
Kewei Zhang, Zhengning Xu, Xiangyu Pei, Fei Zhang, Hang Su, Yafang Cheng, Zhibin Wang
A soft X-ray charger (Model 3088, TSI Inc.) was used to achieve steady-state charge distribution for the WOx particles. The ES generated particles were neutralized by the build-in soft X-ray. After particle generation, the aerosol flow was diluted with the make-up flow at 1 L min−1 for ES-generated particles and 2 L min−1 for WOx particles. A nano-DMA (Model 3086, TSI Inc.) was applied for sizing particles with a sheath-to-aerosol flow ratio of 10, where the aerosol flow rate and sheath flow rate in nano-DMA were 3 L min−1 and 30 L min−1, respectively. Then the monodispersed aerosol flow was split to the SFCPC and a faraday cup electrometer (EM, Model 3068B, TSI Inc.), which was used as a total particle counter. Both the EM and SFCPC were operated at a flow rate of 1.5 L min−1. The schematic of the setup used for SFCPC measurements is shown in Figure S1. The default saturator temperature Ts, growth tube temperature Tg and aerosol flow rate Qa of WCPC are 15 °C, 75 °C, and 300 cm3 min−1, respectively. WCPC with these standard settings could activate ∼2 nm AS particles (Wlasits et al. 2020), which was still difficult to generate by ES. To study the correlation between S and Qa in a broad size range, the ΔT of SFCPC was reduced by setting the Ts at 35 °C. For the measurements of κ values in 3.5–8 nm, Qa and Ts were regulated to generate sufficient S to activate particles (Figure S2).
Repeatability and intermediate precision of a mass concentration calibration system
Published in Aerosol Science and Technology, 2019
Jordan Titosky, Ali Momenimovahed, Joel Corbin, Kevin Thomson, Greg Smallwood, Jason S. Olfert
A Faraday cup is a device which captures particles; where the charge induced by the charged particles is measured with an electrometer. The combination of the Faraday-cup, electrometer, and flow controller is often called an aerosol electrometer. Particle capture inefficiencies or leakage current caused by the Faraday cup may result in erroneous currents measured by the electrometer. A method to determine the instrumental bias of the Faraday cup by measuring an accepted standard is not known. The repeatability and intermediate precision of the two aerosol electrometer systems were determined by comparing the simultaneous measurement of a stable charged particle source.
Size characterization and detection of aerosolized nanoplastics originating from evaporated thermoplastics
Published in Aerosol Science and Technology, 2022
Peter Josef Wlasits, Andrea Stoellner, Gregor Lattner, Klara Maggauer, Paul Martin Winkler
Following size selection, the flow of aerosol was symmetrically split up and fed into a Faraday Cup Electrometer (Aerosol Electrometer Model 3068B, TSI Inc.) and a Condensation Particle Counter. The FCE was mainly used as a backup detector for particle diameters smaller than 5 nm as well as for settings yielding high particle number concentrations (<4·105 cm−3). Measurements of the particle number size distributions were performed using a TSI 3776 UCPC. During these measurements the inlet flow rates of the particle detectors (QFCE and QCPC) were kept at 1.5 L·min−1.