Air Quality and Animal Agriculture: The Basics
Agriculture and Air Quality
Air emissions from energy production, manufac- turing, and transportation have been regulated for decades under federal and state law. Increas- ingly, air emission regulations are being extended to animal agriculture. But air emissions from agriculture do not come from smoke stacks or tailpipes and are more diffuse, less visible, and hard to measure. The difficulty of measurement makes implementation of regulations and the choice of abatement technologies particularly challenging. Yet, the impact of emissions from agriculture can have implications for human health and the environment.
Air quality problems occur on a range of spatial scales. Some air quality issues are localized, such as the odor from a swine farm. At the regional or global scale, the emission of methane and carbon dioxide, both known greenhouse gases, contrib- utes to climate change. Air quality regulations are designed to meet air quality standards for specific geographic areas referred to as airsheds (Figure 1). Airsheds are atmospheric units that behave in a coherent fashion with respect to the dispersion of emissions. The size of an airshed depends on the pollutant. For example, fugitive dust, a common emission from a feedlot, will be dispersed by winds within a limited local airshed. This is in contrast with the airshed that applies to methane and carbon dioxide emissions, which would be considered global.
Agriculture and Air Quality
Animal agriculture is a source of several signifi- cant air pollutants, including particulate matter, ozone precursors, greenhouse gases, and odors. Particulates are a mixture of extremely small airborne particles and liquid droplets (aerosols), which are linked to respiratory disease in humans. Particulate matter is measured and reported as a coarse, often visible particle, PM10 (between 10 and 2.5 microns in diameter), and fine particle, PM2.5 (2.5 microns or less in diameter). Particles discharged directly from a source, like dust during feed handling or from poultry barns, are called “primary particles.” In contrast, ammonia emis- sions from animal agriculture are considered “precursors” to PM2.5. Through chemical reac- tions, ammonia can interact with other air emis- sions, such as nitrogen oxide from combustion emissions, creating fine particles that contribute to PM2.5 aerosols. Particles formed by chemical reactions are called “secondary particles.” Animal agriculture’s direct contribution to PM2.5 is rela- tively small, but it does account for three-quarters of ammonia emissions in the United States as a secondary particulate.1 It is noteworthy that the U.S. Environmental Protection Agency (EPA) considers PM2.5 to be a principal cause of haze pollution in the United States. Ground-level ozone is created in the atmosphere by chemical reactions involving nitrogen oxides (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Ozone in the upper atmosphere is “good ozone,” protecting the Earth from the sun’s harmful ultraviolet rays. “Bad ozone” is found at the ground level. Ground-level ozone can cause respiratory problems for humans and animals and affects the productivity of crops and plant health. Animal agriculture is a source of VOC emissions that contribute to ground- level ozone formation.
Greenhouse gases refer to a range of compounds that affect the amount of solar energy that is retained in the Earth’s atmosphere. Primary green- house gases from animal agriculture include methane, nitrous oxide, and carbon dioxide. Accumulation of greenhouse gases in the Earth’s at- mosphere is important due to global warming concerns. Animal agriculture contributes about a quarter of the human-made methane in the atmo- sphere, primarily from cattle digestive processes and manure management.
The most notable air emission from animal agriculture operations at the local level is odor from manure genera- tion, storage, and, ultimately, land ap- plication to farm fields. For some, these odors affect the quality of life and are considered a nuisance.
Under the EPA’s Clean Air Act (CAA), ozone, nitrogen oxides, and particulate matter are all regulated as criteria pol- lutants. Odor is not currently regulated through the CAA. Instead, EPA has tar- geted two known odor-causing gases to be regulated individually: ammonia and hydrogen sulfide. Both gases are regulat- ed by the EPA for other industries due to their toxic nature under the Compre- hensive Environmental Response Com- pensation and Liability Act (CERCLA), also known as Superfund, and the Emergency Planning and Community Right-to-Know Act (EPCRA). As of January 2009, agriculture is required to report under EPCRA to local emergen- cy management authorities if ammonia or hydrogen sulfide emissions attain the reportable threshold level of 100 pounds per day or more. In Pennsylvania most commercial-scale egg-laying farms would be required to report ammonia emissions under the existing definition. Recently, the EPA has suggested that all but the largest animal agriculture operations should be exempted from these require- ments. However, even with exemptions, it is expected that emission reductions will be sought from animal agriculture.
A study conducted by the National Academy of Science looked at air emissions from concentrated animal feeding operations (CAFOs) and “con- cluded that there is no industry wide, scientifically credible way to estimate emissions.” This report was the catalyst for the National Air Emissions Moni- toring Study being conducted during 2008 through 2010 at twenty-two swine, poultry, and dairy farms nationwide with the intent to collect high-quality data on CAFO emissions. The results of this study are expected to guide future regulation of the industry.