Air Emissions and Animal Agriculture

How much is emitted?

 Air emissions from animal feeding operations are a concern in many communities. How much of different pollutants do these farms emit?

Animal Feeding Operations (AFOs) are subject to permitting requirements under the Clean Air Act (CAA) as well as reporting requirements under the Emergency Planning and Community Right-to-Know Act (EPCRA) if their emissions reach specified thresholds. In order to ensure compliance with these requirements and create a national methodology for estimating AFO air emissions, EPA developed the National Air Emissions Monitoring Study (NAEMS) under the Air Compliance Agreement with 2,600 participating AFOs. The NAEMS began in June 2007 to measure air emissions at sites across the U.S. for a two-year period. Sites included dairy farms, swine farms, laying hens farms and broiler chicken farms. Measurements of air emissions include: particulate matter (dust), ammonia (NH3), hydrogen sulfide (H2S) and volatile organic compounds (VOC). Within 18 months of the study’s completion in 2010, EPA will develop and publish air emission estimating methodologies for these types of facilities. Recently, the EPA released preliminary findings from the NAEMS to the public.

The preliminary data collected during the NAEMS, along with data from published scientific journals suggest that there is considerable variation between types of farms (swine, dairy, laying hen and broiler chickens). Data provided in the preliminary NAEMS report suggests that as few as 107 dairy cows may trigger the need for a farm to report under EPCRA. The data also suggest that the number may be as high as 4,500 dairy cows. Variation is contributed to by climate and management practices (animal management, housing type and manure management) as well as size of the farm. For swine farms, the number of sows on-site that trigger reporting under EPCRA may be as few as 200 sows or as many as 3,950. For swine finishing sites, as few as 5,411 head may require that farms report or as many as 7,500 may be on-site before EPCRA reporting is necessary. For laying hens, the number ranges from anywhere between 40,000 and 75,000 hens.

Air emissions from AFOs depend on manure characteristics and how the manure is managed. Emission rates are generally dependent on several factors: wet versus dry manure management systems, pH/temperature of manure, the presence of an aerobic or anaerobic microbial environment, manure storage time, the precursors present in the manure (e.g., nitrogen or sulfur). Higher temperature and longer manure residence time can increase emissions significantly. Wet manure handling systems usually have higher emissions of VOC, H2S and methane (CH4), while dry manure handling systems have higher emissions of particulate matter and N2O. Higher pH of manure can result in higher emissions of NH3, while lower pH can raise emissions of H2S. The NAEMS collected quality-assured emission data and promoted a national consensus on methods and procedures for measuring AFO emissions. Many factors can affect AFO emission rates from an individual farm. Proper management and maintenance practices are key to controlling of air emissions from AFOs.

At this point it is difficult to determine what EPA will do with the data, how it will be interpreted and what factors will be part of the emissions estimating methodologies to be developed. Given the information available and the uncertainties (variation) in those data, it may be difficult to adequately characterize the emissions in what is truly a farm-specific way. However, a close look at the raw data may reveal patterns or sources of emissions that warrant a closer look by EPA to determine if there are types or sizes of operations that require greater attention. That information is not expected to be made available until late 2012.

Last Updated 09/13/2011