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Integrating Nephelometer Measurement of Scattering Coefficient and Fine Particle Concentrations
Published in James P. Lodge, Methods of Air Sampling and Analysis, 2017
Primary calibration of the integrating nephelometer is performed by using the scattering coefficient of filtered, particle-free air for the zero calibration and the previously measured scattering coefficient of a high density refrigerant gas for the span calibration. Because the scattering coefficient is a function of wavelength and the different models of commercially available integrating nephelometer have differing spectral sensitivity, it is necessary to use reference values specific to the instrument being used. These values should be further adjusted to the actual temperature and pressure in the sample volume. Reference values for the two most common models of integrating nephelometer have been published (24,41) or may be obtained from the manufacturer. After the primary calibration is established, the measured scattering coefficient of an internal optical path (if provided) may be used as a secondary mechanical span calibration.
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Published in Splinter Robert, Illustrated Encyclopedia of Applied and Engineering Physics, 2017
[biomedical, fluid dynamics, geophysics, thermodynamics] The stationary or portable analytical instrument that can be applied to measure and analyze the light-scattering coefficient of atmospheric and laboratory aerosols to determine the concentration of suspended particulates in a liquid or gas colloid. The nephelometer specifically gauges the stray light outside the path of incidence, hence determining the scattering cross section. Specific applications are in drug solubility screening, and other general nephelometric measurements. The biomedical use relates specifically to immunological assay analysis, the principles of nephelometry rely on the reactions between antibodies and antigens. Antibodies in this realm are specific proteins of the immune system, whereas the antigens are the foreign proteins that can be a threat. Antibodies are very specific and selective in their association with particular antigens and will bind strongly to it (see Figure N.17).
Factors determining the distribution of animals and plants in freshwaters
Published in Nick F. Gray, Water Science and Technology: An Introduction, 2017
The type and concentration of suspended solids control the turbidity and transparency of water. Suspended solids are insoluble particles or soluble particles too large to dissolve quickly, which are too small to settle out of suspension under the prevailing turbulence and temperature. Suspended solids consist of silt, clay, fine particles of inorganic and organic matters, soluble organic compounds, plankton and microorganisms. These particles vary in size from 10 nm to 0.1 mm in diameter. In practice, suspended solids are measured as the fraction of these solids retained on a filter paper with a pore size of 0.45 mm. Particles less than 1 μm can remain in suspension indefinitely and are known as colloidal solids (Section 18.3). These fine solids impart a cloudy appearance to water known as turbidity which is caused by the scattering and absorption of the incident light by the particles present. This affects the transparency or visibility within the water. Turbidity can be caused naturally by surface run-off due to heavy rain or by seasonal biological activity. Turbidity is also caused by pollution and as such can be used to monitor effluents being discharged to sewers or surface waters, and can be closely correlated with other physico-chemical parameters. Turbidity is measured using nephelometry, which is the measurement of light scattering by the suspended solids. Results are expressed in nephelometric turbidity units (NTU). Owing to problems of flocculation and settlement of particles, as well as precipitation if the pH alters during storage, turbidity should be measured in the field whenever possible.
An intercomparison of aerosol absorption measurements conducted during the SEAC4RS campaign
Published in Aerosol Science and Technology, 2018
B. Mason, N. L. Wagner, G. Adler, E. Andrews, C. A. Brock, T. D. Gordon, D. A. Lack, A. E. Perring, M. S. Richardson, J. P. Schwarz, M. A. Shook, K. L. Thornhill, L. D. Ziemba, D. M. Murphy
An integrating nephelometer (model 3563, TSI, Shoreview, MI, USA)1 reported bscat at red, green and blue wavelengths. The nephelometer measures aerosol scattering by illuminating the sample air from all incident angles and measuring the total scattered light (using a photomultiplier tube) over a narrow range of scattered angles (relative to the sample cell geometry). The known Rayleigh scattering coefficients of pure gases are used to calibrate the scattering signal, and the scattering signal due to aerosol alone is obtained by subtracting the instrumental background due to gas phase Rayleigh scattering and the light scattered from the walls of the sample cell. The instrumental background is determined by periodically filtering the sampling stream. The nephelometer data were corrected for instrument nonidealities (e.g., truncation) using methods described by Anderson and Ogren (1998). Using the methodology of Sherman et al. (2015), the accuracy for 10 s and 1 min scattering data were found to be approximately 12% and 9%, respectively.
Functionality of turbidity measurement under changing water quality and environmental conditions
Published in Environmental Technology, 2022
Jani Tomperi, Ari Isokangas, Tero Tuuttila, Marko Paavola
Turbidity is, however, a difficult parameter to measure absolutely because many factors affect the turbidity reading. The most common method for measuring turbidity nowadays is an optical sensor. Optical sensor works by emitting a beam of light and detecting the amount of light that reaches the detector. The more particles present in the liquid, the more the light will be scattered, absorbed and diminished. Scattered light can be measured by nephelometry or turbidimetry methods. The angle between light source and detector is 90° for nephelometry or 180° for turbidimetry, i.e. in turbidimetry the intensity of light transmitted through the medium is measured and in nephelometry the light scattered 90° is measured. However, the optical design (the placement and design of the detector) of the turbidimeter will affect the turbidity reading. Turbidity instruments of different design commonly do not yield identical or equivalent results and therefore turbidity values measured with different turbidity meters, for example based on nephelometry or turbidimetry, are not directly comparable. In addition, bubbles, gases, sensor fouling such as biological growth, or scratches on the optical surface of the instrument produce a bias when light beams are blocked. The degree of scattered light is dependent on the amount and the properties of (i.e. size, shape, density and colour) the suspended particles (e.g. algae, clay or sand). When there are wide variations in the composition of particle properties, precise turbidity measurements are likely impossible. Organic material has different optical properties compared with inorganic material and therefore optical measures as turbidity scatter light differently for organic particles which cause substantial uncertainties. Waters are coloured mostly due to the suspended particles or dissolved compounds, for example, the decomposition of organics, metallic salts or coloured clays. Water colour value is found to be pH dependent and can affect a turbidity measurement. Also, measuring turbidity under static (sampling and laboratory measurement) or dynamic (in situ continuous measuring) conditions will affect the turbidity readings. Dynamic measurement techniques more accurately reflect the dynamic nature of the particle movement within the water body, but static measurements do not account for particle settling. Measuring turbidity directly within the water source is preferable because of problems with representative sampling, the settling of solids, temperature and pH changes, and interferences such as condensation or scratches on sample cuvettes. The temperature of the sample changes during the transport to a laboratory and causes differences between the laboratory and in situ measurements. [1,10–12]