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Atmospheric Pollution and Pollutants
Published in Wayne T. Davis, Joshua S. Fu, Thad Godish, Air Quality, 2021
Wayne T. Davis, Joshua S. Fu, Thad Godish
Particle growth may occur as a result of condensation of homogeneous phase reaction products on particle surfaces, condensation of H2O vapor, collisions between particles and subsequent coalescence or adherence, surface adsorption, and heterogeneous chemical reactions. In the last case, both gas-phase and particulate-phase substances participate in chemical reactions (as when SO2 is oxidized to sulfite in an aqueous droplet). The rate of particle growth by this mechanism is limited by chemical reactions at the surface of or within the particle. Collisions with other particles that result in coalescence or adherence also result in particle growth. Associated with this phenomenon is a decrease in particle number and total surface area, whereas the average volume per particle increases. Coagulation produces chain agglomerates in soot and some metal-based particles.
Particle Characterization and Dynamics
Published in Wen-Ching Yang, Handbook of Fluidization and Fluid-Particle Systems, 2003
Investigators have studied the use of electrostatic interactions or electrification of solid particles in measuring various two-phase flow parameters in pneumatic transport, namely, the average particle velocity and the mass flow rate (Gajewski et al., 1990; Gajewski et al., 1991; Klinzing et al., 1987). The effect of electrification on system pressure drop, choking, and saltation velocities, flow patterns, pressure fluctuations, and particle velocity was also investigated in the past (Myler et al., 1985; Ally and Klinzing, 1983, 1985; Smeltzer et al., 1982a,b). It was found that at constant loading, greater electrostatic effects were seen for small particles over large particles because of the high particle number density and thus increased interactions for the smaller particles. Bipolar charging was detected for polyethylene powder with fine particles charging negatively and the coarse particles positively (Cartwright et al., 1985). The material electrification obtained experimentally has also been compared to theoretical values (Gajewski, 1989). Nifuku et al. (1989) found that the electrostatic charge increases, peaks, and decreases with increasing powder concentrations or transport velocities; charge generation was greatly influenced by the powder flow pattern in the pipe.
Expansion of a size disaggregation profile library for particulate matter emissions processing from three generic profiles to 36 source-type-specific profiles
Published in Journal of the Air & Waste Management Association, 2020
Elisa I. Boutzis, Junhua Zhang, Michael D. Moran
Particle concentrations and size distributions can also be expressed in terms of particle number. There are several instruments (and combinations of instruments) that are used for this purpose. Similar to cascade impactors, the Electrical Low Pressure Impactor (ELPI), and Aerodynamic Particle Sizer (APS) separate particles according to aerodynamic diameter (Amaral et al., 2015; McMurry 2000). In the case of the ELPI, particles are charged before passing through a low-pressure cascade impactor. Each particle generates an electrical signal, which is counted when it impacts the appropriate stage. The APS relies on optics to count particles. As particles are accelerated through the instrument, they travel at different rates according to aerodynamic diameter and pass through two laser beams. The scattered light is detected to count particles, and the travel time between the two laser beams is used to calculate the aerodynamic diameter. While the ELPI is able to measure particles ranging from 0.007 to 10 μm in diameter, the APS is limited to larger particles ranging from 0.5 to 20 μm in diameter.
Emission measurements with gravimetric impactors and electrical devices: An aerosol instrument comparison
Published in Aerosol Science and Technology, 2019
Laura Salo, Fanni Mylläri, Marek Maasikmets, Ville Niemelä, Alar Konist, Keio Vainumäe, Hanna-Lii Kupri, Riina Titova, Pauli Simonen, Minna Aurela, Matthew Bloss, Jorma Keskinen, Hilkka Timonen, Topi Rönkkö
In addition to accuracy, other instrument properties to consider when choosing instruments for a measurement setup are price, time resolution, size, measurement output, and how much maintenance is required. Aerosol measurement techniques can be divided into two main groups: offline and online, with the former generally being the more inexpensive method upfront (Dhaniyala et al. 2011). Collecting particles with an impactor or filter are types of offline measurements. Although the instruments are inexpensive, the collected substrates require handling, consuming work hours. Online instruments are generally more expensive, but offer numerous benefits: high time-resolution, instantaneous results and fewer work hours. When it comes to measurement output, mass concentration is commonly used, as particle air quality standards are defined by mass concentration (“Air Quality Standards” 2017). Particle number is also commonly measured, as small particles are not well represented by mass, and particle number emissions are limited for vehicles. When possible, it is better to measure both in order to get a full picture of the emissions.
Experimental determination of the dispersion of ions from a point source in the environment
Published in Environmental Technology, 2019
E. R. Jayaratne, X. Ling, B. Pushpawela, L. Morawska
By introducing compressed air and filtered air at controlled rates, the particle number concentration in the chamber was maintained close to 5000 cm−3 with a CMD of 128 nm. The ionizer was switched on for 5 s. Figure 2 shows the (a) cluster ion concentration (b) particle charge concentration and (c) particle number concentration in real time. The ionizer was switched on soon after time 14:45. The cluster ion concentration immediately increased to about 8.0 × 104 cm−3 when the ionizer was switched on and dropped to about 3.0 × 104 cm−3 as soon as it was switched off. Thereafter, it decreased to background in about 8 min, with a steady linear decrease rate of 4.9 × 103 ions cm−3 min−1. The particle charge concentration also began to increase soon after the ionizer was switched on, but did not attain its maximum value of about 1.2 × 104 ions cm−3 for at least 3 min. It then decreased linearly over time at a rate of about 300 ions cm−3 min−1. During this 8 min period, the particle number concentration fell linearly from 5.0 × 103 cm−3 at a rate of decrease of about 90 particles cm−3 min−1. It is interesting to note that the particle charge concentration exceeded the particle number concentration, suggesting that many of the particles were carrying more than a single electron.