How much do livestock farms emit?
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 (100 lbs. per day for EPCRA). In order to ensure compliance with these requirements and create a national methodology for estimating air emissions from AFOs, the U.S. Environmental Protection Agency (EPA) developed the National Air Emissions Monitoring Study (NAEMS) under the Air Consent Agreement with 2,600 participating AFOs. The NAEM Study began in June 2007 measuring air emissions at sites across the U.S. for a two-year period. Sites included dairy, swine, laying hen, and broiler chicken farms. Measurements of air emissions include: particulate matter (dust), ammonia (NH3), hydrogen sulfide (H2S) and volatile organic compounds (VOCs). The EPA will develop and publish air emission estimating methodologies for these types of facilities based on the study findings and other literature. Recently, EPA publically released reports from the NAEM Study Scientific Advisor and team that included a very preliminary assessment of the collected data.
The preliminary data collected during the NAEM Study, along with data from published scientific journals, suggest that there is considerable variation among types of farms (swine, dairy, laying hen, and broiler chicken) and even within a specific type of farm. Preliminary data from the NAEM Study suggest that as few as 107 dairy cows may trigger the need for a farm to report under EPCRA when emissions from both housing and manure storage sources are considered EPCRA (based on NH3 emission threshold: 100 lb/day). The data also suggest that the number may be as high as 4,500 dairy cows. For swine farms, the number of sows onsite 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 onsite before EPCRA reporting is necessary. And for laying hens the number ranges from somewhere between 40,000 and 75,000 hens. Variation in emissions data is contributed to by climate (season) and management practices (animal management, housing type, and manure management) as well as size of the farm.
Air emissions from AFOs depend on manure characteristics and how the manure is managed. Emission rates are generally dependent on several factors: Wet or dry manure management systems, pH and temperature of manure, the presence of an aerobic or anaerobic microbial environment, manure storage time, and the precursors present in the manure (e.g., nitrogen, or sulfur). Higher temperature and longer manure storage 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 nitrous oxide (N2O). Higher pH of manure can result in higher emissions of NH3, while lower pH can raise emissions of H2S. The NAEM Study collected quality-assured emission data and promoted a national consensus on methods and procedures for measuring AFO emissions.
The NAEM Study aimed to collect quality-assured emission data and to promote a national consensus on methods and procedures for measuring AFO emissions. 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 being developed. Given the size of the study and the variations in those data, it may be difficult for EPA to adequately characterize the emissions in what is truly a site-specific manner. However, as EPA reviews the data the agency may recognize sources of emissions that require greater attention. At the earliest that information is not expected to be made available until late 2012. To be proactive, consider your own farm and what you might do to reduce emissions. For assistance in determining where to make changes in your farm management to reduce emissions, visit the National Air Quality Site Assessment Tool.
Special thanks to Zifei Liu and Venkata Vaddella for contributing to this article.