Ammonia is made whenever nitrogen atoms bond with hydrogen atoms, forming the molecule NH₃. This happens through several different processes: massive industrial plants, bacteria in soil, reactions inside your own body, and even lightning strikes. The method responsible for the vast majority of the world’s ammonia supply is a century-old industrial technique that combines nitrogen gas from the air with hydrogen gas under extreme heat and pressure.
The Haber-Bosch Process
Almost all commercial ammonia comes from the Haber-Bosch process, widely considered one of the most important inventions of the 20th century. The basic recipe is simple: take nitrogen from the atmosphere (which is about 78% nitrogen) and react it with hydrogen gas. The equation is N₂ + 3H₂ → 2NH₃. Two molecules of ammonia come out for every molecule of nitrogen that goes in.
The challenge is that nitrogen molecules are extremely stable. The two nitrogen atoms are locked together by a triple bond, one of the strongest bonds in chemistry. Breaking it requires enormous energy input. Industrial plants achieve this by running the reaction at temperatures between 300 and 600 °C and pressures 100 to 350 times normal atmospheric pressure. An iron-based catalyst helps speed the reaction along without being consumed by it. Ruthenium-based catalysts also work well, though iron remains the industry standard.
The hydrogen feedstock typically comes from natural gas (methane), which is split apart using steam in a process called steam methane reforming. This is why ammonia production consumes 1 to 2% of the world’s total energy supply and generates significant carbon emissions. The vast majority of that ammonia goes straight into nitrogen-based fertilizers that support global agriculture.
Bacteria That Fix Nitrogen From the Air
Long before humans invented factories, certain soil bacteria and microorganisms were already making ammonia. These organisms, called diazotrophs, use a specialized enzyme called nitrogenase to pull nitrogen gas directly from the atmosphere and convert it into ammonia. Nitrogenase is the only enzyme in nature capable of doing this.
The biological approach works completely differently from the industrial one. Instead of cracking the nitrogen triple bond apart all at once with brute-force heat and pressure, nitrogenase weakens it gradually. The enzyme adds hydrogen atoms to the nitrogen molecule one at a time through a series of electron and proton transfers. Intermediate compounds like diazene and hydrazine may form along the way before the final product, ammonia, is released. The process requires a significant amount of cellular energy: 16 molecules of the cell’s energy currency (ATP) are consumed for every molecule of nitrogen converted.
Some of these nitrogen-fixing bacteria live freely in soil, while others form partnerships with plants. Legumes like soybeans, peas, and clover host nitrogen-fixing bacteria in nodules on their roots. The bacteria supply the plant with usable nitrogen in the form of ammonia, and the plant supplies the bacteria with sugars. This is why farmers rotate crops with legumes: the bacteria naturally replenish nitrogen in the soil.
Your Body Makes Ammonia Constantly
Ammonia production happens in every tissue in your body as a byproduct of breaking down proteins and other nitrogen-containing compounds. When your cells metabolize amino acids (the building blocks of protein), they strip off nitrogen-containing groups in a process called deamination. The amino acid is first converted into a molecule called glutamate, which then releases free ammonia.
This is a problem, because ammonia is a potent neurotoxin. Even modest elevations can cause brain swelling, seizures, and altered consciousness. Normal blood ammonia levels in adults fall between 10 and 80 micrograms per deciliter. Your liver handles the cleanup: it captures circulating ammonia and converts it into urea through a series of reactions called the urea cycle. Urea is far less toxic and dissolves easily in water, so your kidneys filter it out and you excrete it in urine. When the liver is severely damaged, as in advanced cirrhosis, it loses the ability to clear ammonia efficiently, and dangerous levels can build up in the blood.
Decomposing Organic Matter
The sharp smell near a compost pile, a feedlot, or a cat’s litter box is ammonia being released from decomposing organic material. Enzymes produced by soil bacteria and fungi break down nitrogen-rich compounds in waste. Urease, one of the key enzymes involved, splits urea (found in animal urine) into carbon dioxide and ammonium, which readily converts to ammonia gas. Proteases break down proteins into amino acids, and those amino acids are further broken down to release even more ammonia.
This natural recycling process is an essential part of the nitrogen cycle. The ammonia released into soil can be taken up by plants directly or converted by other bacteria into nitrates, another form of nitrogen that plants absorb through their roots. On the downside, large-scale livestock operations and composting facilities can release enough ammonia gas to become an air quality and environmental concern.
Lightning Strikes
Lightning creates ammonia in small but meaningful quantities. The energy in a lightning bolt (electrons carrying 1 to 10 electron-volts of kinetic energy per particle) is enough to break apart the stable nitrogen and oxygen molecules in the atmosphere. Along the plasma channel of a lightning strike, these shattered molecules form highly reactive fragments called radicals. When nitrogen radicals meet hydrogen from water vapor at the air-water interface, they combine through intermediate steps to form ammonia, which dissolves into rainwater as ammonium.
Before biological nitrogen fixation evolved, lightning may have been one of the primary ways nitrogen was converted into a form usable by early life on Earth. Today, lightning-produced nitrogen compounds are a minor contributor compared to biological and industrial sources, but the process remains an active part of the global nitrogen cycle.
Green Ammonia Production
Because traditional ammonia manufacturing relies on natural gas and extreme conditions, researchers are developing ways to make ammonia using renewable energy instead. The most promising approach uses electricity from solar, wind, or hydropower to split water into hydrogen and oxygen through electrolysis, then combines that hydrogen with nitrogen separated from the air. If the entire process runs on renewable electricity, the resulting “green ammonia” has essentially no carbon footprint.
A more ambitious route skips the hydrogen step entirely. Electrochemical nitrogen reduction uses electricity to directly convert nitrogen gas and water into ammonia at or near room temperature. This mimics, in a sense, what nitrogenase does in bacteria. The technology is still in early stages and currently produces ammonia at rates far below what industry needs, but it represents a fundamentally different way of making the same molecule: mild conditions, no fossil fuels, and a much smaller environmental impact.