for objective measurement techniques to correspond to subjective human response.

  • A standardized unit of measurement of odor concentration should be adopted in the United States.


The method selected for measuring emissions will depend on the type of emission and whether it is from a point source (e.g., an exhaust vent from a mechanically ventilated building; Figure 4-2) or an area source (e.g., a waste lagoon; Figure 4-3).

The emission rates for low-level point sources (LLPSs; Figure 4-2) may be determined by measuring concentrations (mass per unit volume) and volumetric flow rates (volume per unit time) at the emitting points and multiplying the two measurements. The emission rates will be expressed as mass per unit time. An alternative procedure consists of measuring the ambient concentrations upwind and downwind (off-property) and back-calculating the emission rate using dispersion modeling. The Air Pollution Regulatory Process (APRP) addresses off-property impacts on the public. For criteria pollutants, EPA regulations stipulate that the 24-hour downwind concentration should not exceed the NAAQS at the property line or at the nearest occupied residence.

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. The units of flux will be mass per unit area per unit time.

FIGURE 4-2 Schematic illustrating the essential elements associated with measurement of emissions from agricultural sources that can be characterized as low-level point sources such as cotton gins, feed mills, grain elevators, and oil mills.

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