Ammonia (NH3) feeds and pollutes the world.1 The synthesis of ammonia underpins all nitrogen fertilizers, and without their applications it would be impossible to feed, at current levels, nearly half of today’s 8 billion people. China could not feed 40% of its population without nitrogen fertilizers.2 This makes ammonia one of the most important materials humans have ever developed.
Ammonia is also a major pollutant that degrades the health of ecosystems and people. Ammonia reacts with other atmospheric chemicals to form fine particulate matter (PM2.5), one of the most impactful pollutants on human health. In the United States and Europe, ammonia accounts for 30% and 50% of PM2.5, respectively.3 Ammonia that runs off into water bodies leads to eutrophication, a form of algae growth that has harmful effects on aquatic life and public water supply. Ammonia deposited on soils can increase acidity, which can reduce biodiversity and the availability of essential nutrients for plants.
Ammonia is not a greenhouse gas, but it plays an important indirect role in climate change. The manufacture of ammonia via the Haber-Bosch process uses natural gas (methane) as a feedstock and accounts for 1.8% of global greenhouse gas emissions.4 Ammonia deposited on soils fuels microbial processes that can produce nitrous oxide (N₂O), a potent greenhouse gas.5
Global emissions of ammonia tripled between 1960 and 2022. The overwhelming majority of this increase occurred in agriculture. The 1960s marked the beginning of the Green Revolution, particularly in Asia and Latin America, where high-yield crop varieties were cultivated using fertilizer-intensive production methods, supported by government and international subsidies. The Haber-Bosch process matured and rapidly spread around the world. Nitrogen fertilizer application to soils increased from 19 million metric tonnes in 1961 to 109 million metric tons in 2022.6
Manure is second to soils in ammonia emissions. Urea (found in urine) from livestock is quickly converted to ammonia and carbon dioxide by the enzyme urease, which is present in feces and soil. Another manure source is ammonia volatilization which involves the transformation of ammonium ions (NH₄⁺) in manure into ammonia, which can then escape into the atmosphere. These processes are mediated by temperature pH, moisture content, wind, and manure management methods.
Wastewater is a third major source of ammonia emissions, originating from the decomposition of nitrogen-containing organic matter. Major sources include domestic sewage, industrial effluents, and agricultural runoff.
China has caused about 23% of ammonia emissions since 1750, almost twice the contribution of India (13%). The top five emitters (China, India, the United States, Russia, and Brazil account for 53% of all-time emissions.
Soils and manure dominate ammonia emissions in most countries, but there are notable differences between nations. India has an unusually large share of ammonia emissions released from soils (62%), which can be attributed to several factors. The country heavily relies on urea for nitrogen fertilizers, which is highly prone to volatilization—the process by which ammonia gas escapes from soils into the atmosphere. This problem is exacerbated by the Indian government’s heavy subsidization of fertilizers, which often leads to overuse by farmers. Additionally, India employs intensive cropping systems with multiple harvests per year (such as rice-wheat rotations), which not only increase the total amount of fertilizer applied but also alter soil chemistry in ways that produce more ammonia.
The United States has a remarkably small fraction of ammonia emissions from wastewater compared to other leading emitters such as India and China. This difference primarily stems from the pervasive implementation of advanced wastewater treatment technologies with nitrification-denitrification processes that convert ammonia into nitrate or nitrogen gas. These processes significantly reduce the amount of ammonia released into the air or discharged in effluent. While open sewers, septic tanks, and uncovered treatment ponds—which allow ammonia to volatilize directly into the atmosphere—are common in many countries, most United States wastewater systems are enclosed, limiting ammonia volatilization. Furthermore, the United States has strong, well-enforced regulations that set strict discharge limits for nitrogen compounds, whereas such laws are less common and often poorly enforced in many low- and middle-income countries.
Ammonia emissions continue to rise in many low and middle income countries (LMICs), such as Nigeria, Indonesia, Pakistan, and India. There are a variety of drivers at work here. Rapid agricultural expansion fueled by population growth leads to higher cropping intensity, especially of nitrogen-intensive crops like rice and wheat. Livestock numbers are rising rapidly in many of those same countries to demand for meat, dairy, and eggs. Management of the resulting increase in manure is often rudimentary at best in most LMICs resulting in large ammonia emissions. LMICs have weak or no regulations limiting ammonia emissions in most LMICs, and environmental enforcement is often weak. The same conditions prevail in wastewater treatment.
Ammonia has been called Cinderella of air pollution because it has received much less attention than other pollutants, such as carbon dioxide, sulfur dioxide, nitrogen oxides, ozone, and particulate matter.7 But rising ammonia emissions and their harmful effect on climate, water, soils, air quality, and human health justify strong action to reduce admissions
Managing fertilizers, livestock, wastewater, and manure presents the greatest potential for reducing anthropogenic ammonia emissions. Incorporating manure and fertilizer into the soil—rather than applying them on the surface—can significantly lower emissions. Tertiary treatment of wastewater, which removes nitrogen, phosphorus, and other nutrients, also offers substantial potential for ammonia reduction, particularly in low- and middle-income countries (LMICs) where such treatment is often absent.
However, the widespread adoption of ammonia abatement measures faces numerous technical, economic, behavioral, and policy barriers. Many farmers lack access to low-emission technologies such as slurry injection systems, or are unable to afford the high upfront costs. There is also limited awareness of the environmental impacts of ammonia and of available mitigation practices. In many regions, government regulations are weak or nonexistent, and subsidies frequently promote fertilizer use that exacerbates ammonia emissions.
1 Erisman, Jan Willem. “How Ammonia Feeds and Pollutes the World.” Science 374, no. 6568 (November 5, 2021): 685–86. https://doi.org/10.1126/science.abm3492.
2 Smil, Vaclav. “The Modern World Can’t Exist Without These Four Ingredients. They All Require Fossil Fuels.” TIME, May 12, 2022. https://time.com/6175734/reliance-on-fossil-fuels/.
3 Wyer, Katie E., David B. Kelleghan, Victoria Blanes-Vidal, Günther Schauberger, and Thomas P. Curran. “Ammonia Emissions from Agriculture and Their Contribution to Fine Particulate Matter: A Review of Implications for Human Health.” Journal of Environmental Management 323 (December 1, 2022): 116285. https://doi.org/10.1016/j.jenvman.2022.116285.
4 The Royal Society, “Ammonia: zero-carbon fertiliser, fuel and energy store,” February 2020, Link
5 Esquivel-Elizondo, Sofia, Blake Walkowiak, Stavroula S. Sartzetakis, and Brian Buma. “Climate Impact of Direct and Indirect N2O Emissions from the Ammonia Marine Fuel Value Chain.” Environmental Science & Technology, May 2, 2025. https://doi.org/10.1021/acs.est.4c13135.
6 Hannah Ritchie, Max Roser, and Pablo Rosado (2022) – “Fertilizers” Published online at OurWorldinData.org, https://ourworldindata.org/fertilizers, accessed May 3, 2025
7 Sutton, Mark A., Netty van Dijk, Peter E. Levy, Matthew R. Jones, Ian D. Leith, Lucy J. Sheppard, Sarah Leeson, et al. “Alkaline Air: Changing Perspectives on Nitrogen and Air Pollution in an Ammonia-Rich World.” Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 378, no. 2183 (September 28, 2020): 20190315. https://doi.org/10.1098/rsta.2019.0315.
