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.

The National Air Emissions Monitoring Study (NAEMS)

Livestock air emissions are subject to permitting requirements under the Clean Air Act as well as reporting requirements under the Emergency Planning and Community Right-to-Know Act (EPCRA) and the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) if their emissions reach specified thresholds. In order to ensure compliance with these requirements and create a national methodology for estimating livestock air emissions, EPA developed the NAEMS under the Air Compliance Agreement with 2,600 participating AFOs. The NAEMS began in June 2007 to measure air emissions at 24 sites (including all major types of swine, dairy and laying hen facilities) in nine states over a two-year period. Measurements of air emissions included: PM, NH₃, H₂S and VOC. Within 18 months of the study’s completion, EPA was to develop and publish air emission estimating methodologies for types of facilities included in this study.

Results of the 2-yr period NAEMS emission data (from animal houses, g/d-head)

Species	NH3	H2S	PM10	VOC
Sow gestation	6.5-29.4	0.3-8.5	0.28-0.48	1.8-7.2
Farrow	1.9-10.0	3.8-7.6	1.17-1.67	10.4-12.1
Finishing swine	6.7-8.4	0.23-0.85	0.18-0.29	0.6-5.5
Dairy	5.0-56.5	0.9-4.9	0-10.3	12-197
Hens - High rise	0.63-1.12	0.001	0.016-0.038	0.03-0.34
Hens - Manure belt	0.28	0.002	0.008-0.025	0.03-0.04
Broilers	0.47-0.54	0.003	0.044-0.045	0.10-0.13

Implications

Air emissions from livestock production are subject to reporting requirements under the Emergency Planning and Community Right-to-Know Act (EPCRA) and the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) if their emissions reach specified thresholds.

Efforts to regulate air emissions from agricultural sources have been confounded by a lack of information. In the past, EPA has generally not enforced the reporting requirement against livestock production. But large livestock operations are vulnerable to citizen suits for failure to comply with reporting under these statutes (NRC, 2003).

As air emissions from livestock production are receiving increasing attention, EPA is keep updating its “CAFO rule” in recent years, which may have significant effects on the U.S. livestock industry (EPCRA effective on CAFO as of Jan 20, 2009). On April 10, 2009, EPA published proposed mandatory GHG reporting rules in the Federal Register (EPA, 2009).

The raw data collected in the NAEMS, along with data from published scientific journals suggest that there is considerable variation among types of farms (swine, dairy, laying hen, and broiler chickens) and even within a specific type of farm. The EPCRA and the CERCLA required reporting of NH₃ and H₂S emissions exceeding 100 lb/day. Based on currently available data (house emissions only), the farm sizes that may trigger the need for a farm to report under EPCRA were estimated as following.

• Sows: 1500-7000 head
• Finishing swine: 5400-6800 head
• Dairy: 800-9100 head
• Beef: 200-600 head
• Layers: 41000-160000 head
• Broilers: 85000-96000 head
• Turkeys: around 46000 head

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