Ammonia: A "Two-Faced Gas" From Pungent Odor to Industrial Pillar
I. What is ammonia?
Ammonia (chemical formula NH₃) is a colorless gas with a strong, pungent odor. It has a molecular weight of 17.03 and is lighter than air (air has a density of 1, while ammonia has a relative density of about 0.59), so it will rise after a leak.
Key physical properties :
| nature | numerical values |
| boiling point | -33.5℃ |
| Melting point | -77.7℃ |
| Solubility in water | Approximately 700 volumes of ammonia can be dissolved in 1 volume of water (at 20°C). |
| Explosion Limit | 16% - 25% (volume fraction in air) |
Ammonia is highly soluble in water, which is one of its most notable properties. At room temperature and pressure, one volume of water can dissolve approximately 700 volumes of ammonia gas, making ammonia's solubility in water far greater than that of other common gases. An aqueous solution of ammonia is called ammonia water, and it is weakly alkaline, which is why moist red litmus paper turns blue upon contact with ammonia gas .
II. Where does ammonia come from? — Natural sources and the Industrial Revolution
2.1 Ammonia in nature
Ammonia is one of the most common gases in nature, found in air, water, and soil. Its main natural sources include:
The decomposition of plants and animals : After proteins decompose, nitrogen-containing organic matter such as amino acids and urea is produced, which further decomposes to produce ammonia.
Animal excrement : Urea in urine decomposes under the action of urease to produce ammonia.
Lightning, volcanoes, wildfires : these natural phenomena can also produce small amounts of ammonia.
Nitrogen fixation : Some legumes have a symbiotic relationship with rhizobia, which allows them to fix atmospheric nitrogen into ammonia.
2.2 Ammonia in the human body
Ammonia is also produced in the human body. Ammonia in the body mainly comes from three pathways:
Catabolism of amino acids in tissues
Breakdown of amino acids in kidney cells
Urea hydrolysis and putrefaction in the intestine
Ammonia is toxic to the human body, so the liver converts it into urea, which is then excreted in urine. When liver function is severely impaired, elevated blood ammonia levels can lead to hepatic encephalopathy, a critical condition that requires close monitoring in clinical practice.
2.3 The Industrial Revolution: The Birth of the Haberforce
Although ammonia exists in nature, natural sources are far from meeting human needs. In the late 19th century, European agriculture was heavily reliant on Chilean nitrate (sodium nitrate) as a source of nitrogen fertilizer, a resource now threatened with depletion. The scientific community faced a major challenge: how to produce ammonia from the inexhaustible nitrogen (N₂) in the atmosphere?
A nitrogen molecule consists of two nitrogen atoms linked by a strong N≡N triple bond , making it extremely chemically stable and almost unreactive under normal conditions. This is precisely why plants cannot directly utilize atmospheric nitrogen.
In 1909, German chemist Fritz Haber achieved a breakthrough in the laboratory—successfully synthesizing ammonia from nitrogen and hydrogen under high temperature and pressure conditions of approximately 200 atmospheres and 500°C, using osmium as a catalyst. Subsequently, German engineer Carl Bosch scaled up this process, developing iron-based catalysts and process flows suitable for industrial production. This is the world-changing Haber-Bosch Process .
The reaction equation is:
N₂ + 3H₂ ⇌ 2NH₃
In 1913, Germany's first synthetic ammonia plant was built and put into operation, with an annual output of 7,000 tons. Haber and Bosch were awarded the Nobel Prize in Chemistry in 1918 and 1931, respectively.
Today, the world produces approximately 187 million tons of ammonia annually, ranking ninth in chemical production. About 85% of this is used in agricultural fertilizer manufacturing, supporting the food supply for roughly half the world's population. In this sense, the Haber process is one of the greatest inventions in human history.
III. Wide range of uses for ammonia
Ammonia is an extremely important chemical raw material with a wide range of applications:
Agriculture : Production of nitrogen fertilizers (urea, ammonium nitrate, ammonium phosphate, etc.), with approximately 85% of ammonia used in this field.
Refrigeration : Liquid ammonia is a highly efficient and environmentally friendly refrigerant, widely used in large cold storage facilities and food processing.
Chemical raw materials : used in the manufacture of nitric acid, hydrazine, cyanide, amino acids, amines, etc.
Household cleaning products such as glass cleaner contain ammonia.
Pharmaceuticals and dyes : as intermediates
Explosives manufacturing : Ammonium nitrate is both a fertilizer and a raw material for explosives.
Water treatment : pH adjustment
Marine fuel : Green ammonia is being studied as a low-carbon marine fuel.
IV. The Hazards of Ammonia
Ammonia is a double-edged sword. It has a wide range of uses, but its dangers should not be ignored.
4.1 Toxicity – Harm to the Human Body
Ammonia is a toxic substance that has multiple mechanisms of harm to the human body:
Irritation : It has a strong irritant and corrosive effect on the skin, eyes, and respiratory mucous membranes.
Tissue damage : It absorbs water from skin tissue, denatures tissue proteins, and disrupts cell membrane structure.
Respiratory tract damage : Paralyzes respiratory cilia, damages mucosal epithelial tissue, and reduces resistance to disease.
Blood toxicity : After entering the bloodstream, it binds to hemoglobin, impairing oxygen-carrying function.
Fatal risk : Inhalation of high concentrations can lead to pulmonary edema and even cardiac arrest via the trigeminal nerve reflex.
Symptoms of acute poisoning include tearing, sore throat, chest tightness, difficulty breathing, dizziness, nausea, vomiting, and fatigue. Severe cases may develop pulmonary edema and acute respiratory distress syndrome.
Hazard Comparison : The toxicity of ammonia is far lower than its explosion hazard—the occupational exposure limit (TWA) is only 20 mg/m³ (approximately 28 ppm), while the lower explosive limit is as high as 15% (approximately 150,000 ppm). The difference is more than 5,000 times. Therefore, in industrial monitoring, ammonia is usually prioritized for monitoring as a toxic gas rather than a flammable gas.
4.2 Environmental Hazards
Soil acidification : Ammonia deposition leads to a decrease in soil pH.
Eutrophication : Nitrogen compounds enter water bodies, leading to excessive algal growth.
Biodiversity loss : Species adapted to high nutrient levels crowd out other species; wetland lichens and mosses are extremely sensitive to ammonia.
PM2.5 formation : Ammonia reacts with sulfuric acid and nitric acid to form ammonium salts, which are important precursors to PM2.5. In some parts of the United States, ammonia produced by livestock farming can contribute 5%-20% of atmospheric PM2.5.
4.3 Fire and Explosion Hazards
Pure ammonia is not easily flammable, but it is explosive when mixed with air, with an explosion limit of 16%-25% (volume fraction) and the most easily ignited concentration being 17%.
4.4 The Dark Side of Haberfa
Nitrogen is not only a nutrient for plants, but also an important component of explosives . Ammonium nitrate is both a highly efficient nitrogen fertilizer and a raw material for explosives.
Chemical weapons in World War I : Haber himself actively promoted the use of poisonous gases such as chlorine in warfare. In the Second Battle of Ypres in 1915, the German army used chlorine gas for the first time, causing serious casualties to the Allies.
Beirut Explosion : The historical fact that approximately 2,750 tons of ammonium nitrate stored at the port of Beirut, Lebanon, exploded in August 2020, killing more than 200 people and injuring thousands, reminds us that technology itself is neutral; whether it brings benefit or harm depends on how humanity uses it.
V. Sources of Indoor Ammonia Pollution
Besides industrial exposure, ammonia pollution can also exist in indoor air, mainly from:
Construction : Concrete additives contain a large amount of ammonia compounds, which are slowly released into the wall as temperature and humidity change.
Interior decoration : Some decoration materials decompose and release ammonia.
Cleaning products : Use of ammonia-containing cleaners
Human metabolism : The human body also produces a small amount of ammonia.
Conclusion
Ammonia, a seemingly simple compound, reflects the complex nature of technological development.
It is a hero that feeds the world —without Haberfa, half the world’s population would not have enough food; it is also a threat to the environment and health —high concentrations of ammonia can be deadly, and ammonia emissions from agricultural sources are damaging ecosystems; and behind it lies the shadow of war and destruction —from poison gas to explosions, ammonia is intertwined with the history of human violence.
When we smell that pungent odor, we should perhaps realize that it's not just the smell of a chemical substance, but also a microcosm of modern industrial civilization, the agricultural revolution, and the existential dilemmas of humanity. Understanding ammonia is understanding one aspect of the complex world we depend on for survival.