What Emissions are of Interest and Why? 

Odors often appear at the top of farm air pollution complaints lists. Farm odors are comprised of over 200 different chemicals.

Ammonia (NH₃) is a gas emitted from farms because of the relatively inefficient conversion of feed nitrogen (20-40% conversion efficiency) into animal product (meat, egg, and/or milk). Deposition of NH₃ can lead to over enrichment of nutrients and cause eutrophication of surface waters. Ammonia gas can react in the atmosphere with other gases to form fine particulates.

Hydrogen sulfide (H₂S) is produced by decomposition of animal manure whenever there are sulfur compounds, anaerobic conditions and sufficient moisture. It is an extremely toxic and irritating gas at high levels, and has a generally objectionable rotten egg odor.

Particulate matter (PM) or dust, is of interest because of its health and environmental concerns. The PM emitted from farms is highly complex in size, physical properties, and composition.

Greenhouse gases (GHG) in the atmosphere can delay heat on the Earth's surface from being lost to space like the glass walls of a greenhouse do (‘greenhouse’ effect), and contribute to global climate change. The GHGs that are emitted from activities related to animal agriculture include CO₂, CH₄, and N₂O.

Potential Importance of Livestock Air Emissions at Different Spatial Scales (Adapted from NRC, 2003)

The effects of airborne pollutants from livestock air emissions differ in their potential severity and the spatial scales. For example, the effects of odor are of interest mainly at local level, while NH₃ has relevant impacts mainly on a regional-scale perspective.

Emissions	Global & Regional	Local & Property Line	Primary Effects of Concern
Odor	Insignificant	Major	Nuisance, quality of life
VOC	Significant	Minor	Odorous, ozone formation
NH3	Major	Minor	Atmospheric deposition
H2S	Insignificant	Significant	Odorous, health
PM	Insignificant	Significant	Health, haze
GHGs	Significant	Insignificant	Global climate change
Rank order from high to low importance is major, significant, minor, and insignificant.

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