How Much is Emitted?


Accurate quantification of each livestock air emissions and evaluation of their impacts is not an easy task, because:
(1) air emissions from individual farms can vary depending on many factors, such as the species, the number of animals, animal size, animal age, type of feed, manure handling and storage systems, ventilation methods, design and age of structures, farm management and mitigation practices, and climate;
(2) direct measurements of livestock air emissions are expensive and difficult considering the many uncontrollable factors that may affect measurements, and industry-wide, standard methods to accurately estimate livestock air emissions are still under development; and
(3) scientific understanding of livestock air emissions and their effects requires the expertise of many disciplines (animal nutrition, agricultural engineering, waste management, atmospheric chemistry, meteorology, air monitoring, toxicology, etc.), and there are very limited research quantifying these effects.

Many local, state, and federal agencies rely on emission factors to develop emission inventories. EPA defines emission factor as the mass of the pollutants emitted per animal unit (AU) per year and they are usually derived from calculations based on measured data. The emission factor for a livestock operation represents the sum of the annual mean emission rates from housing, manure storage/treatment and land application. Emission factors are based on average annual conditions and typically a composite of various animal sizes and types for a particular animal species.