Air Emissions from Animal Feeding Operations Current Knowledge, Future Needs (2003) / Chapter Skim
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4. Measuring Emissions
4. Measuring Emissions
Pages 74-97
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From page 74... ...
While this approach to regulation may be straightforward for some industrial operations, livestock feeding operations pose especially complicated issues for estimating and measuring air emissions. AFOs are complex physical, chemical, and biological systems.
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From page 75... ...
. These concentrations depend not only on short-term emission rates, but also on meteorological conditions at the time, including wind speed and direction, atmospheric stability, and precipitation.
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From page 76... ...
measured near a dairy wastewater lagoon. Method used was an ultraviolet differential optical absorption spectroscopy technique with a detectability limit of l ppb and a time resolution of 0.6 second.
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From page 77... ...
The mixing ratios of these gases remain stable for years if the cylinders are stored and handled properly, so these mixtures can provide reliable calibration standards with absolute uncertainty well below 10 percent. NIST Standard Reference Materials Calibration gas standards of CH4, NO, and N2O in air or in nitrogen (certified at concentrations of approximately 5 to 40 ppm [parts per million]
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From page 78... ...
The long-term stability of ammonia in compressed gas mixtures has not been demonstrated, but calibration standards can be produced using permeation devices. Samples collected using both denuders and filters can be analyzed by aqueous-phase calorimetry or ion chromatography to measure NH3 and ammonium ion (NH4+)
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From page 79... ...
(2002) recently described a new technique for measuring atmospheric NH3 in real time, using differential optical absorption spectroscopy (DOAS)
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From page 80... ...
Nitric Oxide Nitric oxide is generally measured in situ with instruments based on chemiluminescence. NO at ambient concentrations cannot be reliably stored in grab samples for later analysis; it is too reactive at typical concentrations in ambient air.
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From page 81... ...
The Portable Jerome Hydrogen Sulfide Analyzer (Model 631-X, Arizona Instrument, Phoenix, AZ) has an accuracy of 6-8 percent depending on the concentration of H2S to be measured.
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From page 82... ...
Thus, the nature of PM depends not only on the source, but also on other co-pollutants, chemical reactions, and distance from the source. By comparison, PM from animal feeding operations tends to contain a significant fraction of mechanically generated material such as soil, dried manure, and so forth material that is typically larger than 1 ,um in aerodynamic diameter ("coarse particulate matter".
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From page 83... ...
Complications of current samplers include weight loss from semivolatile materials and weight gain by adsorption of gas-phase substances including water during sampling and handling. Continuous methods that rely on optical techniques must be calibrated for each type of particulate matter, since optical properties are a function of particle size and composition.
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From page 84... ...
A concentration of 100 OU/m3 means that a given volume of odorous air must be diluted with 100 volumes of odor-free air before it reaches the detection threshold. In the recently developed European Standard, the unit of measurement for odor concentration is the European Odor Unit per cubic meter (OUE/m3; European Committee for Standardization, 2002~.
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From page 85... ...
that are inflated in the field using portable wind tunnels or negatively pressurized canisters are commonly used. Odor Concentration Measurements Methods for measuring odor concentrations include sensory methods, analytical methods, and "electronic noses" for specific odorous gases.
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From page 86... ...
detection, including metal oxide semiconductors, field-effect transistors, optical fibers, semiconducting polymers, and piezoelectric quartz crystal devices. These approaches raise the possibility of remote odor monitoring or surveillance networks for individual compounds or odorant mixtures.
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From page 87... ...
The emission rate for a ground-level area source (GLAS; Figure 4-3) may be determined using "flux chambers" or micrometeorological techniques or by measuring upwind and downwind concentrations and back-calculation of flux using dispersion modeling.
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From page 88... ...
Point Sources In theory, measurement of the emission rates of gaseous substances from a mechanically ventilated animal facility requires only the concentration of the substance being emitted and the ventilation rate, but accurate measurement of these two factors is difficult in practice. Ventilation rate is affected by many factors including the length of time the fans operate, fan design, fan speed, fan maintenance, motor startup time, static pressure, outside wind speed, wind direction, and infiltration.
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From page 89... ...
. In the case of poultry, typical ventilation rates range from 0.1 to 10 cubic feet per minute | Source | | samplers | Wind c O~_ Ambient samplers FIGURE 4-4 Schematic illustrating the essential elements associated with the regulation of emissions from agricultural sources that can be characterized as low-level point sources such as tunnel-ventilated AFOs.
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From page 90... ...
Measuring ventilation rates accurately in naturally ventilated houses is extremely difficult due to the dynamics of outside weather and wind conditions. The emission rate for an LLPS (Figure 4.4 and 4-5)
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From page 91... ...
. Emissions of gases or aerosols from area sources are often expressed in terms of fluxes, or mass emission rates per unit area perpendicular to the direction of the flux.
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From page 92... ...
Surface-Layer Scale (102 to 106 m2J At the surface-layer scale, micrometeorological techniques or mass balance methods can be used to measure area source fluxes. Micrometeorological methods include eddy correlation, eddy accumulation and other conditional sampling techniques, and gradient and difference methods.
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From page 93... ...
Eddy Accumulation This method is a variation of the eddy correlation technique which relaxes the requirement for fast chemical sensors by "conditional sampling," in which samples are collected in two or more containers based on the vertical wind velocity component. The sample collection rate is proportional to the vertical wind speed.
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From page 94... ...
Also where turbulence or fast photochemistry strongly influence emissions or ambient concentrations, box methods must be used with caution. Dispersion Modeling In this method, upwind and downwind concentration measurements are made, and the emission rate is back-calculated from a dispersion simulation, usually based on a Gaussian dispersion algorithm, making assumptions regarding the
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From page 95... ...
, can be used either to measure emission rates "directly" or to improve the dispersion characterization in a dispersion model, thus decreasing the uncertainty in that technique. Under certain conditions, direct flux measurements can be made if the tracer release can adequately simulate the emission source (e.g., point releases to mimic a smokestack emission; line source releases to mimic a heavily traveled road)
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From page 96... ...
. SUMMARY Assessment of the health and environmental effects associated with air emissions from animal feeding operations requires a substantial increase in both the accuracy of estimates of emissions of substances of interest and the accuracy of measurements of their concentrations.
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From page 97... ...
The paucity of emission measurements from AFOs is likely due at least in part to a lack of resources available for this research area. The availability of concentration measurement methods is a prerequisite for emission rate determination.
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