China
Africa
Explore chapters and articles related to this topic
Inertial Samplers: Biological Perspectives
Published in Christopher S. Cox, Christopher M. Wathes, Bioaerosols Handbook, 2020
Although the samplers described above collect without dividing the catch into different particle size fractions, the principle of collecting by impaction means that size discrimination is possible (Chapter 8). Air can be drawn through a series of slits sequentially diminishing in size so that air velocity increases from one stage to the next. Particles of sufficient mass will be deposited on the upper stage, while smaller particles capable of remaining in the airstream at a lower velocity will leave the airstream at higher velocities to be impacted onto the collection surfaces. This type of sampler is known as the cascade impactor. May19 described the first prototype that separated particles into four size fractions. Operating at 17.5 L min-1, particles are deposited onto glass microscope slides coated with adhesive. This cascade impactor is no longer available commercially but has been superceded by a seven-stage version, operated at 10 or 20 L min-1, known as the “ultimate cascade impactor,” that again collects particles onto glass microscope slides (Figure 9.3).20
Particulate matter
Published in Abhishek Tiwary, Ian Williams, Air Pollution, 2018
The standard cascade impactor cannot normally be used to measure particles smaller than about 0.3 μm because the high air speeds needed for deposition cause unacceptable pressure drops and impact forces. The size range has been extended with the electrostatic low pressure impactor (ELPI), in which reduced air pressure (and hence a larger value for C) enables deposition of particles down to around 30 nm. Even this is not small enough to include the mode of the number distribution produced by engines running on low-sulphur fuel. One disadvantage is that the low air pressure (about 8 kPa at the final stage) increases the evaporation from semi-volatile particles. The ELPI also charges the particles electrostatically and measures the rate of particle deposition from the current flow to each stage. Hence it can be used in real time rather than having to wait for a weighable deposit to accumulate on each stage. However, these image and space charges themselves generate a new force on the particles which may change their deposition characteristics. In the micro-orifice uniform deposit impactor (MOUDI), which is another equipment using the same principle, the particles are deposited on rotating substrates to avoid re-entrainment, and the mass is determined gravimetrically.
Measurement of gases and particles
Published in Abhishek Tiwary, Jeremy Colls, Air Pollution, 2017
The standard cascade impactor cannot normally be used to measure particles smaller than about 0.3 μm because the high air speeds needed for deposition cause unacceptable pressure drops and impact forces. The size range has been extended with the electrostatic low pressure impactor (ELPI), in which reduced air pressure (and hence a larger value for C) enables deposition of particles down to around 30 nm. Even this is not small enough to include the mode of the number distribution produced by engines running on low-sulphur fuel. One disadvantage is that the low air pressure (about 8 kPa at the final stage) increases the evaporation from semi-volatile particles. The ELPI also charges the particles electrostatically and measures the rate of particle deposition from the current flow to each stage. Hence it can be used in real time, rather than having to wait for a weighable deposit to accumulate on each stage. However, these image and space charges themselves generate a new force on the particles which may change their deposition characteristics. In another version of this principle, the micro-orifice uniform deposit impactor (MOUDI), the particles are deposited on rotating substrates to avoid re-entrainment, and the mass is determined gravimetrically.
The use of transmission electron microscopy with scanning mobility particle size spectrometry for an enhanced understanding of the physical characteristics of aerosol particles generated with a flow tube reactor
Published in Aerosol Science and Technology, 2023
Emma C. Tackman, Devon N. Higgins, Devan E. Kerecman, Emily-Jean E. Ott, Murray V. Johnston, Miriam Arak Freedman
Notably, spreading represented by increases in particle diameter after impaction were similar for samples generated using the two different methods of impaction (i.e., cascade impactor and NAS). Here, dry ammonium salt particles are assumed to have an adequately high viscosity, or stiffness, so that they are able to recover after deformation during the impaction process to the same degree, regardless of impaction velocity (Morris et al. 2016; O’Brien et al. 2014). The range of percent differences between SMPS- and TEM-measured ammonium sulfate particle diameters was wider than expected for size-selected particles of only one component, but consistent between the two experimental schemes both in sign and magnitude. The NAS at the University of Delaware used a biased substrate where oppositely charged particles are impacted through electrostatic precipitation, giving the total range of percent differences between +0% and +30%. The cascade impactor used at the Pennsylvania State University sorted particles by inertia, where the particles in a gas stream are forced to take a series of sharp turns; particles above the cutoff size of each stage are deposited onto a substrate while those below are small enough to carry on through the turn. This process provided a range of percent differences from +7% to +19% (Table 1), falling within the spreading range derived from NAS-impacted samples. While electrostatic precipitation is a softer impaction method than cascade impaction, these data indicate that the two methods are interchangeable in this situation.
A matrix-free fixed-point iteration for inverting cascade impactor measurements with instrument's sensitivity kernels and hardware
Published in Inverse Problems in Science and Engineering, 2021
Laura Valtonen, Sampo Saari, Sampsa Pursiainen
This article focuses on the mathematical modelling and inversion of cascade impactor aerosol measurements. An aerosol is a finely divided mixture consisting of gaseous media and mixed liquid or solid particles. Aerosol particles are formed when liquids or solids are fined or when the gas forms particles, e.g. in burning processes. Aerosols include, for example, smoke, clouds and street dust. Today, aerosol research is an important part and growing of research on air pollution, public health, nanotechnology, medicine, atmospheric, radiological health and respiratory toxicology [1,2]. A cascade impactor separates particles contained by a sample of air or gas into known mass or size ranges. Several different measurement techniques might be needed to cover the full range [3]. Aerosol particle mass distribution is generally log-normal, meaning a significant portion of all aerosol particles belong to a specific mass and size class [1]. In the measurement process of the cascade impactor, air-containing particles pass through impactor stages, where particles collide with impactor plates. The speed of the air increases gradually making the particles of different sizes accumulate to altogether 12 different stages. Each stage is sensitive to a specific size range according to a given kernel function [4,5].
Production of bromelain aerosols using spray-freeze-drying technique for pulmonary supplementation
Published in Drying Technology, 2020
M. N. Lavanya, R. Preethi, J. A. Moses, C. Anandharamakrishnan
The in-vitro aerosol performance was explained in terms of emitted dosage (ED), mass mean aerodynamic diameter (MMAD) and fine particle fraction (FPE) using Westech eight-stage non-viable cascade impactor (Westech Scientific Instruments, Bedfordshire, UK) at a flow rate of 28.3 L/min for 4 s. The eight-stage cascade impactor was constructed in a way that particles with higher size get deposited in the upper stage due to higher inertia and impact, while particles with lesser particle size receive insufficient inertia and hence get carried to the next stage.[41] Hence, it is explained that smaller particle size can reach the alveoli region.