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Erosion by Wind: Source, Measurement, Prediction, and Control
Published in Brian D. Fath, Sven E. Jørgensen, Megan Cole, Managing Soils and Terrestrial Systems, 2020
Brenton S. Sharratt, R. Scott Van Pelt
Fugitive dust in suspension is often the most visible evidence of active wind erosion. Passive HMF samplers can be used to trap particles in suspension, but these samplers are inefficient at trapping dust due to resuspension of small particles within the sampling chamber. The suspension component of HMF is most often measured with aspirated sampling devices. Optical sensors such as the DustTrak (Figure 11), E-sampler, or Grimm particle sampler aspirate the sediment-laden air past a light source that measures the optical occlusion caused by the suspended sediment. Optical sensors have been used with saltation impact sensors to examine the linkage between saltation and fine dust emissions.[52] The Tapered Element Oscillating Microbalance (TEOM), as shown in Figure 12, aspirates the sedimentladen air, filters the particulates, and periodically weighs the collected dust. The TEOM is a USEPA-approved device for measuring real-time PM10. Filter-based samplers, such as the low-volume or high-volume sampler, are also used to measure dust in suspension. These samplers aspirate air at a known rate through a preweighed hydrophobic filter, thus providing a time-integrated measure of dust in suspension.
Air Pollution: Monitoring
Published in Brian D. Fath, Sven E. Jørgensen, Megan Cole, Managing Air Quality and Energy Systems, 2020
PM is usually determined using active filter method by gravimetry as the reference method.[36] In this method, the air is passed through a filter that stops particles above 10 pm (PM10) or 2.5 pm (PM2.5). Measurements are made over a period of 24 hr or longer. The filters are collected and the adsorbed particles are measured in the laboratory. Other methods use beta ray absorption or tapered element oscillating microbalance (TEOM) of PM. In beta gauge instruments, which are used for real-time measurements of particulate emissions from stationary sources, the mass of the sample deposited on the filter tape is automatically measured by beta ray attenuation. The measurement is made first on a blank, then on the particulate-laden filter. The range is 2–4000 mg/m3 without interference or effect from color, size, or atomic mass of the dust.
Particulate matter
Published in Abhishek Tiwary, Ian Williams, Air Pollution, 2018
The other variant of this principle is known as the tapered element oscillating microbalance (TEOM, commonly pronounced tee-om, Figure 3.20). The particles are collected continuously on a filter mounted on the tip of a glass element that oscillates in an applied electric field. Again the natural frequency falls as mass accumulates on the filter. This device has been chosen for PM10 measurements in the UK Automated Urban Network, largely because it was the only gravimetric method capable of the required 1-h time resolution when the network was set up in the early 1990s. Although the method is specific to mass loading, there has been a significant systematic error. In order to maintain the constancy of the base resonant frequency while humidity is fluctuating, the oscillating element was maintained at a temperature of 50°C. This temperature is high enough to evaporate volatiles from some particles, resulting in a long-term gradual loss of mass. In specific experiments in which pure ammonium nitrate aerosol was sampled, serious volatilisation losses were experienced which were greatly reduced when the substrate was maintained at 30°C rather than 50°C.
Effective density of airborne particles in a railway tunnel from field measurements of mobility and aerodynamic size distributions
Published in Aerosol Science and Technology, 2018
A tapered element oscillating microbalance (TEOM from Thermo Fischer Inc., Waltham, MA, USA) equipped with a PM10 inlet was used to determine PM10 level (mass concentration of particles of 10 µm aerodynamic diameter and less) every 1 min. The sample flow rate was set to 3 L/min. The TEOM is a gravimetric-based method of directly measuring particle mass concentration. It was equipped with a filter dynamics measurement system (FDMS) to reduce mass loss if the particles are composed of volatile components. According to the manufacturer, the minimum detection limit is 5 µg/m3. For PM10 measurement, the TEOM has been approved by the United States Environmental Protection Agency (USEPA) with an accuracy of 10% (Cowen et al. 2001; Alberta Environment 2009). According to a Swedish standard on measuring systems (Svensk standar 2014), the TEOM is reliable that different pieces of TEOM gives stable performance with only a few percent deviation between each other.
Online measurement of PM from residential wood heaters in a dilution tunnel
Published in Journal of the Air & Waste Management Association, 2022
George Allen, Barbara Morin, Mahdi Ahmadi, Lisa Rector
The Thermo Scientific (Franklin, MA) Tapered Element Oscillating Microbalance (TEOM™) is a continuous true mass measurement method that has been widely used for ambient PM measurements (Patashnick and Rupprecht 1991; Rupprecht, Meyer, and Patashnick 1992). It is an online inertial ultra-microbalance with a resolution of 0.01 micrograms. The TEOM was developed initially for mass measurement in the zero-gravity conditions of space (Patashnick and Rupprecht 1977). PM is collected on a filter mounted on the tip of a hollow tapered glass tube (element), and the change in the element’s oscillating frequency is measured as the filter accumulates mass. The change in frequency from the filter mass loading is converted to a change in mass over an interval using the element’s calibration constant (K0), which is empirically determined by weighing a clean TEOM filter of known mass. The measured mass divided by the sampled volume over the interval equals the PM concentration for that interval. For a stable mass measurement, the TEOM filter must be maintained at a fixed temperature at least a few degrees C above the temperature of the instrument’s environment and also higher than the dewpoint of the sample stream. Unless the filter temperature is sufficiently elevated to prevent the collection of semi-volatile mass (SVM), such as nitrate, organic carbon, and unbound water, the dynamic nature of SVM can result in large and rapid positive and negative transient filter mass changes and thus large changes in reported concentrations (Allen 1998; Li et al. 2012). For this reason, early versions of the TEOM for ambient PM measurement heated the filter to 50°C, but this often resulted in an under-measurement of PM2.5 compared to the regulatory data from a Federal Reference Method (FRM) sampler (Allen et al. 1997). Over time, enhancements were made to the TEOM method to address this ambient PM measurement issue, such as the Sample Equilibration System (SES) that used a dried sample at 30°C to minimize loss of dry SVM (Meyer et al. 2000) and the Filter Dynamic Measurement System (FDMS) differential approach that measures the dry SVM indirectly in near real-time (Grover et al. 2005; Jaques et al. 2004).