Airborne reduced nitrogen: Ammonia emissions from agriculture and other sources

Natalie Anderson, Ross Strader, Cliff Davidson

Research output: Contribution to journalReview articlepeer-review

192 Scopus citations


Ammonia is a basic gas and one of the most abundant nitrogen-containing compounds in the atmosphere. When emitted, ammonia reacts with oxides of nitrogen and sulfur to form particles, typically in the fine particle size range. Roughly half of the PM2.5 mass in eastern United States is ammonium sulfate, according to the US EPA. Results from recent studies of PM2.5 show that these fine particles are typically deposited deep in the lungs and may lead to increased morbidity and/or mortality. Also, these particles are in the size range that will degrade visibility. Ammonia emission inventories are usually constructed by multiplying an activity level by an experimentally determined emission factor for each source category. Typical sources of ammonia include livestock, fertilizer, soils, forest fires and slash burning, industry, vehicles, the oceans, humans, pets, wild animals, and waste disposal and recycling activities. Livestock is the largest source category in the United States, with waste from livestock responsible for about 3 × 109 kg of ammonia in 1995. Volatilization of ammonia from livestock waste is dependent on many parameters, and thus emission factors are difficult to predict. Despite a seasonal variation in these values, the emission factors for general livestock categories are usually annually averaged in current inventories. Activity levels for livestock are from the USDA Census of Agriculture, which does not give information about animal raising practices such as housing types and grazing times, waste handling systems, and approximate animal slurry spreading times or methods. Ammonia emissions in the United States in 1995 from sources other than livestock are much lower; for example, annual emissions are roughly 8 × 108 kg from fertilizer, 7 × 107 kg from industry, 5 × 107 kg from vehicles and 1 × 108 kg from humans. There is considerable uncertainty in the emissions from soil and vegetation, although this category may also be significant. Recommendations for future directions in ammonia research include designing experiments to improve emission factors and their resolution in all significant source categories, developing mass balance models, and refining of the livestock activity level data by eliciting judgment from experts in this field.

Original languageEnglish (US)
Pages (from-to)277-286
Number of pages10
JournalEnvironment international
Issue number2-3
StatePublished - Jun 2003
Externally publishedYes


  • Ammonia
  • Ammonium nitrate
  • Ammonium sulfate
  • Animal waste
  • Emission factors
  • Emission inventory
  • Fertilizer
  • Livestock

ASJC Scopus subject areas

  • General Environmental Science


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