of uncertainty associated with their reported values for emission rates may be a reflection of the limited number of observations upon which their reported values are based. Equal weighting should not be given to reported emission rates and derived emission factors when the actual number of observations on which these reported values are based differs significantly among investigators. All other things being equal, reported values for emissions based on a relatively large number of observations should be given greater weight than those derived from relatively few observations.

As presented in this chapter, a wide range of factors can influence air emissions of gases, PM, and other substances from AFOs. Combinations of these factors that will be most useful in pursuing regulatory goals will depend on research-based information about the strength of the relationship between each combination of factors and the rate of emission of a particular pollutant.

Finding 5: Reasonably accurate estimates of air emissions from AFOs at the individual farm level require defined relationships between air emissions and various factors. Depending on the character of the AFOs in question, these factors may include animal types, nutrient inputs, manure handling practices, output of animal products, management of feeding operations, confinement conditions, physical characteristics of the site, and climate and weather conditions.

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