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Ammonia: Threats to the Environment & Human Health

Iowa has some of the highest concentrations of ammonia in the lower atmosphere in the United States. Ammonia is a nitrogen-containing compound with the chemical formula NH3, and it is emitted almost exclusively by agricultural sources, including livestock production (67%) and nitrogen fertilizer use (29%).

Land and Water Deposition
Much atmospheric ammonia is redeposited from the air to nearby land and water, a process called nitrogen deposition (see Vitousek et al. 1997). Ammonia binds with other pollutants and changes from a gas to a solid particle form. In this process, it changes into ammonium, or NH4, as shown in the map below.


Nitrogen deposition harms terrestrial ecosystems, including Iowa’s native prairies and oak savannahs, by reducing biodiversity and favoring invasive plants.

Nitrogen in Iowa’s waterways—some of which comes from airborne particles—finds its way downstream, eventually contributing to the Gulf hypoxia zone or “Dead Zone,” a coastal area in the Gulf of Mexico that is starved for life-supporting oxygen. You can view the hypoxic zone and learn more about it here. [].

Ammonia and fine particulate matter
Increasingly ammonia (NH3) emissions are recognized for their importance in contributing to high concentrations of fine particulate matter, defined as liquid or solid particles, 2.5 micrometers in diameter or smaller, that are suspended in the air. Fine particulate matter penetrates human respiratory systems further than larger particles and is associated with asthma, heart problems, and other illnesses.

The old solution to high levels of particle pollution was to increase the height of emitting industrial smokestacks, but now Iowa and regions downwind from Iowa  are known to have high levels of particle pollution from other sources besides smokestacks, such as from agriculture.  When the source of air pollution is widespread, rather than coming from one certain point such as a smokestack, it’s called “background” or “non-point source” pollution.  Communities with a concentration of pollution emitting smokestacks and with high levels of “background” particle pollution are more likely to experience poor air quality days and violations of air quality standards.


Ammonia and three other categories of “precursors” – compounds that combine to form PM2.5 – are major contributors to background levels of fine particulate pollution in the Upper Midwest. Two of the other categories – sulfur dioxide (SO2) and nitrogen oxides (NOx, including NO and NO2) come from combustion sources, such as gas- and diesel-fueled vehicles, coal-powered energy production and industrial processes, and open burning of wastes. These are subject to regulatory controls under the Clean Air Act, because they are known to contribute to acid rain (sulfuric and nitric acids) and other environmental damage, and to worsen or possibly cause several human health problems. The role of SO2 and NOx varies by season, while ammonia is constantly available.

The bar graph on the left shows that agriculture is by far the largest contributor to non-point emissions of ammonia, and the graph on the right shows which agricultural sectors are of most concern. NOTE: Graphs based on Iowa DNR 2008 Point Source Emissions Inventory & EPA 2008/2005 National Emissions Information Data.Ammonia_from_ag

You can learn more about fine particle pollution at this Iowa Environmental Council web page: [] and at the EPA’s web page: [].

Reducing and controlling ammonia emissions
Actual points of emissions from agricultural sources are many—from manure-fertilized crop land and anhydrous ammonia fertilizers, to livestock confinement buildings and stored manure. Many types of emissions controls are needed. In addition, agricultural interests have successfully resisted most regulatory controls, with some exceptions for manure handling and confinement siting in Iowa. These rules were adopted to prevent nuisance odors and protect surface waters, but they may have positive impacts on exposure to air pollutants. The preference has been for voluntary adoption of identified “best management practices” for fertilizer application and livestock production operations. However, annual air quality data demonstrate that voluntary controls are not sufficient at present to reduce ammonia levels. Monitoring of the Midwestern atmosphere shows a sharp rise in ammonia concentrations starting in the late 1990s (Stensland et al. n.d.; NADP web site [see below])

Current studies provide a strong case for regulation of ammonia emissions to reduce fine particle pollution.  For example, studies of ambient monitor data in Wisconsin (Baek et al. 2010; Stanier et al. 2009) demonstrate that reducing ammonia emissions is “likely to decrease episode concentrations” of fine particles, at least on Midwestern winter days when air quality is poor.

A study for the European Commission (Oenema et al. 2007) addresses the complexity of farming and suggests using a combination of strategies to reduce nitrogen inputs and increase nitrogen use efficiency, such as precisely adjusting applications according to a field’s crop type, soil features, and drainage.

There are also excellent resources from agricultural organizations on effective practices, such as those available from Iowa State and Purdue Universities (Burns 2007; Iowa State University Extension 2004; Reynolds n.d.; Sutton 2008).

Specific practices to reduce airborne ammonia emissions may vary according to the soil type, farm operation design, management requirements and much more. However, complexity should not prevent increased efforts at controlling ammonia emissions. The rewards are better air quality, improved soil and water quality, greater environmental diversity, and improvements in our health.

All sectors should be held accountable for measurable reductions and for working together to seek solutions to Iowa’s air quality problems.  Corporations, small operator/owners, members of affected communities, nongovernmental organizations, and state agencies are needed at the table to work out effective and feasible strategies for reducing ammonia and other emissions.

Increased future emissions of ammonia are anticipated
The Livestock, Environment, and Development Initiative (LEAD), of the United Nations Food and Agriculture Organization predicts, that global meat production will double between about 2005 and 2050. According to LEAD, “we need to halve impacts per unit of output to achieve a mere status quo in overall impact.” If Iowa is a key part of this growth, then ammonia controls are an absolute need in order to prevent higher concentrations of fine particulate matter in the state and in downwind states.


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For more information about ammonia as a contributor to pollution and about practices to reduce ammonia emissions:

Baek, J., G. Carmichael, S. R. Lee, J. Oleson, et al. (2010) “Episodic air pollution in Wisconsin (LADCO Winter Nitrate Study) and Georgia (SEARCH Network) during January-March 2009.”

Burns, R. (2007) “Swine Manure Storage and Handling Practices to Minimize Odors.”

Coe, Dana L., & Stephen B. Reid (2003) “Research and development of ammonia emission inventories for the Central States Regional Air Planning Association.”

Environmental Protection Agency’s web page on hypoxic or “dead” zones:

Iowa Department of Natural Resources, Air Quality Bureau. (2008) “Animal Feeding Operations Field Study: Hydrogen Sulfide and Ammonia Results: Executive Summary.”

Iowa State University Extension. (2004) “Practices to Reduce Ammonia Emissions from Livestock Operations.”

Lake Michigan Air Directors Consortium. (2007) “Source category: Agricultural emissions of ammonia.
This “white paper” provides specific information for the Midwestern states on the types of sources, the estimated amounts emitted, and the effectiveness of several reduction scenarios.

National Academy of Sciences. (2003) “Air Emissions from Animal Feeding Operations: Current Knowledge, Future Needs.”
A free summary is available at the site. The report may be purchased by chapter or in entirety, as a PDF download and/or as a printed copy. Chapters 3, 4, and 5 cover air pollutants, the measurement of emissions, and emissions estimation.

National Atmospheric Deposition Program:
The animated trend map for ammonia covers 1985 to 2005 and shows how ammonia concentrations have increased over the Upper Midwest:

National Atmospheric Deposition Program (2000) “Nitrogen in the Nation’s Rain.”

Oenema, O., D. A. Oudendag, H. P. Witzke, G. J. Monteny, et al. (2007) “Integrated measures in agriculture to reduce ammonia emissions: final report.” Research report. Wageningen, The Netherlands: Alterra, Wageningen University.

Reynolds, M., ed. (n.d.) “Managing livestock manure to protect environmental quality.” Lincoln: University of Nebraska Extension.

Stensland, G. J., V. C. Bowersox, B. Larson, & R. D. Claybrooke (no date) “Comparison of ammonium in USA wet deposition to ammonia emission estimates.”

Stanier, C. S., & the Stanier Group. (2009) “Understanding episodes of high airborne particulate matter in Iowa.”
This analysis of data from the Lake Michigan Air Directors’ Consortium (LADCO) winter nitrate study, along with data from Iowa measurements, demonstrates that ammonia is a “limiting pollutant”: in other words, it occurs in low enough quantities that viable control measures for ammonia will help reduce fine particulate matter levels. This reverses years of thinking that nitrogen oxides, sulfur dioxide, and volatile organic compounds were “limiting” and therefore the most effectively controlled pollutants.

Steinfeld, Henning, et al. (2006) “Livestock’s Long Shadow: Environmental Issues and Options.” Rome: UN FAO LEAD.
This thorough analysis and summary of worldwide livestock contributions to climate change and environmental degradation includes a section (chapter 3) on greenhouse gases and air pollutants, along with control strategies. Other chapters address landscape alteration, water pollution and depletion, biodiversity impacts, and policy directions. Accompanying maps show production of various crops for animal feeding and the distribution of various classes of livestock.

Sutton, A. (2008) “Feed management practices to minimize odors from swine operations.”

Virginia Cooperative Extension (2009) “Ammonia emissions and animal agriculture.”

Vitousek, Peter, et al. (Spring 1997) “Human Alteration of the Global Nitrogen Cycle: Causes and Consequences,” Issues in Ecology
Human changes in the global nitrogen cycle and impacts of nitrogen deposition on terrestrial and aquatic ecosystems. The report can be saved or printed.

Related publications, available on the Internet:

Environmental Health Sciences Research Center, University of Iowa (2002) “Iowa Concentrated Animal Feeding Operations Air Quality Study.”
Known by various shorthand names, such as the “joint report” or “Regents’ report.”

Iowa Department of Natural Resources, Air Quality Bureau. (2006) “Results of the Iowa DNR Animal Feeding Operations Odor Study.”

Related online resources:

Iowa Department of Natural Resources, Air Quality Bureau:
This link takes you to the home page of the Air Bureau, where you will find a map of current air quality conditions.

University Hygienic Lab’s Historical Air Quality Index web page:
The information here is one to several days old, but it is useful for getting an idea about which pollutants are causing problems on which days and at what monitor sites.

US Department of Agriculture’s Agricultural Air Quality Task Force (AAQTF):
The AAQTF meets twice annually to provide a forum for cutting-edge research and lead researchers who are studying agricultural air emissions and control strategies.




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