Ammonia: An Air Pollutant? Understanding Its Environmental Impact

Ammonia, a compound of nitrogen and hydrogen, is a by-product of agriculture and industry. It is a highly reactive and soluble alkaline gas that is now recognized as a potentially hazardous air pollutant. Ammonia gas is emitted from agricultural slurry, fertilizer factories, and livestock farming, as well as natural sources like coal mines and seabird colonies. This gas can affect human breathing, cause acidification and eutrophication, and have negative impacts on plant and aquatic life. Despite some efforts to reduce ammonia emissions, it continues to be a challenge for air quality management, especially in densely populated areas.

Ammonia's impact on human health

Ammonia (NH3) is a compound of nitrogen and hydrogen and is one of the most commonly produced industrial chemicals in the United States. It is used in industry and commerce and also exists naturally in humans and the environment. While ammonia is essential for many biological processes, it can have adverse effects on human health when exposure is high.

Ammonia is usually shipped as a compressed liquid in steel containers and is found in many household and industrial-strength cleaning solutions. Most people are exposed to ammonia through inhalation of the gas or vapours, or through skin or eye contact. Exposure to ammonia is almost always unintentional, although 9.2% of household exposure is intentional, occurring mostly in adults.

The US National Institute of Occupational Safety and Health states that the maximum permissible exposure of anhydrous ammonia for an 8-hour workday of 40 hours per week is 25 ppm. The short-term exposure limit, or the concentration at which exposure of longer than 15 minutes is potentially dangerous, is 35 ppm. The concentration at which the gas is immediately harmful to life or health is 300 ppm.

The health effects of ammonia exposure include skin damage, respiratory distress, and severe eye irritation. Ammonia ingestion can cause thermal injury to the surrounding tissues. Inhalation of high concentrations of ammonia can result in acute respiratory distress, with symptoms similar to status asthmaticus, anaphylaxis, and foreign body aspiration.

Ammonia pollution in the atmosphere can also have indirect effects on human health. Gaseous ammonia reacts with other pollutants in the air to form fine particles of ammonium salts, which can affect human breathing. These particles can enter the lungs and bloodstream through inhalation and cause complications including asthma, lung cancer, cardiovascular issues, birth defects, and premature death.

Ammonia's impact on the environment

Ammonia (NH3) is a highly reactive and soluble alkaline gas that plays a significant role in various environmental issues. It is a byproduct of agriculture and industry, with agriculture being the dominant source of emissions. The impact of ammonia on the environment is far-reaching, and efforts to reduce emissions have been met with varying levels of success.

In the atmosphere, ammonia reacts with acid pollutants, such as the products of SO2 and NOX emissions, to form fine ammonium (NH4+) aerosols. These aerosols are classified as fine particulate matter (PM2.5), which can travel long distances and have detrimental effects on both human health and the environment. The small size of PM2.5 particles allows them to enter the human lungs and bloodstream through inhalation, causing complications such as asthma, lung cancer, cardiovascular issues, birth defects, and even premature death.

Ammonia emissions contribute to international transboundary air pollutant issues. While the lifetime of NH3 is relatively short ( <10-100 km), NH4+ can be transported over much longer distances (100-1000 km). This means that NH3 emissions can have impacts on both local and international scales, affecting not only the countries where the emissions originate but also neighbouring regions.

In addition to the atmospheric effects, ammonia also impacts sensitive plant groups such as lichen and moss, as well as habitats such as bogs, peatlands, grasslands, heathlands, and forests. High ammonia concentrations have been linked to various health issues in livestock, including ascites, gastrointestinal irritation, and respiratory disease. Ammonia seeps into aquatic ecosystems from both anthropogenic sources (wastewater, fertilizers, and industrial waste) and natural sources (nitrogen fixation and air deposition). It is toxic to aquatic life, leading to increased fish deaths and decreased biodiversity.

Despite the recognition of ammonia as a hazardous air pollutant, only some countries have taken significant action to reduce their emissions. The European Union, for example, has implemented policies such as the Gothenburg Protocol and the Directive on Integrated Pollution Protection and Control to address ammonia pollution. While NH3 emissions in Europe have fallen since 1990, they have not decreased as much as emissions of other pollutants. This highlights the ongoing challenge of managing ammonia pollution and the need for continued efforts to reduce emissions and mitigate their environmental impacts.

Sources of ammonia emissions

Ammonia (NH3) is a highly reactive and soluble alkaline gas that is emitted from both natural and anthropogenic sources. The main source of ammonia emissions is agriculture, including livestock manure, urine, and the spreading of inorganic fertilisers. In Northern Ireland, 96% of man-made ammonia comes from agricultural sources, with similar proportions observed in other regions.

Livestock farming, particularly dairy and beef production, contributes significantly to ammonia emissions. Cattle, including dairy and non-dairy cattle, are a major source, followed by other livestock such as poultry, pigs, sheep, goats, deer, and agricultural horses. The housing of livestock and the storage and land spreading of livestock manures are significant contributors.

Inorganic fertiliser application is another large source of ammonia emissions from agriculture. The use of urea-based fertilisers, in particular, has been on an upward trend and contributes to higher ammonia emissions. The cost of fertilisers and weather conditions also influence emission levels from this source.

Non-agricultural sources of ammonia emissions include catalytic converters in petrol cars, landfill sites, sewage works, composting of organic materials, and combustion processes. Seabird colonies are also a source, although they contribute smaller amounts to overall emissions. However, in remote and otherwise "clean" areas, they can be the dominant emission source. Domestic pets are another non-agricultural source, accounting for 5% of total ammonia emissions in 2023.

Ammonia emissions have significant environmental and human health impacts. In the atmosphere, ammonia reacts with acid pollutants such as sulfur dioxide (SO2) and nitrogen oxides (NOX) to form fine particulate matter (PM2.5) containing ammonium (NH4+) aerosols. These aerosols can travel long distances and have adverse effects on human health, including respiratory issues, asthma, lung cancer, and cardiovascular problems.

Measuring ammonia in the atmosphere

Ammonia (NH3) is a pungent-smelling, colourless, and toxic gas that is hazardous to human health and the ecosystem. It is a common air pollutant, with natural sources like the burning of coal mines and guano from seabird colonies, as well as human activities like agriculture and industry. As such, it is important to measure ammonia in the atmosphere to understand its impact and inform strategies to mitigate its negative effects.

The measurement of atmospheric ammonia is crucial for assessing its concentration and deposition, which vary based on proximity to industrial and agricultural sources. Ammonia is measured through various methods, including ground-based instrumentation and satellite remote sensing. The earliest detailed measurements of atmospheric ammonia were conducted by Egner and Eriksson over Scandinavia using ground-based techniques. However, their approach did not differentiate between gas-phase NH3 and aerosol NH4+. Subsequently, Junge performed the first measurements of gas-phase NH3 alone over locations in Florida and Hawaii.

Over time, advancements in measurement techniques have led to the development of continuous NH3 measurement methods. One example is the fully automated continuous flow rotating wet denuder by Wyers et al. Regional passive sampler networks, such as the Ammonia Monitoring Network (AMoN) in the US, play a vital role in quantifying ambient ammonia gas concentrations. AMoN employs a cost-efficient and spatially dense approach to provide data for evaluating long-term trends and the impact of emission reduction regulations.

To measure ammonia in the atmosphere, several methods and instruments are utilized. One common technique is the use of filter packs, which consist of an air pump with a Teflon and glass fiber filter. The pump draws in air, and the filters capture ammonia particles. The filters are coated in citric acid, which reacts with the basic ammonia, essentially "gluing" it in place. The filters are then tested with Nessler's reagent, and a spectrophotometer quantifies the ammonia content. Another method is fabric denuders, which rely on passive sampling without the use of a pump, collecting samples based solely on airflow.

In addition to ground-based measurements, satellite remote sensing has provided global quantification of NH3 since 2002. This technology, such as AIRS, CrIS, IASI, TANSO-FTS, and TES, offers valuable insights into NH3 chemistry, transport, and spatiotemporal variations. Furthermore, models like GEOS-Chem (global) and FRAME (UK) are applied to enhance our understanding of atmospheric ammonia. A synergistic approach combining measurements, satellite inference, and modeling is necessary to comprehensively study atmospheric ammonia and its effects on human health and the ecosystem.

Strategies to reduce ammonia emissions

Ammonia (NH3) is a chemical compound composed of one nitrogen (N) and three hydrogen (H) molecules. It is a byproduct of agriculture and industry and is commonly found in gaseous form. Gaseous ammonia emitted into the atmosphere can deposit quickly near its source. However, if it is lofted high above the ground or reacts with acidic gases, its atmospheric lifetime can increase, and it can be transported much further from its source.

Ammonia is a known air pollutant, and its presence in the atmosphere is most commonly measured by collecting samples through methods such as filter packs, fabric denuders, satellite imaging, and rainwater analysis.

As ammonia is a significant contributor to air pollution, it is important to implement strategies to reduce its emissions. Here are some key strategies that can help reduce ammonia emissions:

• Agricultural Practices: The dominant source of ammonia emissions is agriculture, specifically the use of nitrogen-based fertilizers and livestock farming. Conservation agriculture practices can help reduce ammonia emissions. This includes implementing better manure management practices, such as incorporating manure into the soil as quickly as possible to reduce volatilization losses. Surface banding, a technique that deposits liquid manure under vegetation at the soil surface, can also increase contact with the soil and reduce ammonia emissions.
• Reducing Nitrogen Losses: Minimizing nitrogen losses during fertilization is crucial. This can be achieved by covering slurry pits and silos, reducing the exposed surface area of liquid manure in storage, and acidifying slurry to a neutral pH level to reduce ammonia outgassing.
• Feed Management: Optimizing feed utilization in livestock by ensuring they are not fed more protein than necessary can help reduce ammonia emissions. Adjusting feed composition according to the animal's stage of lactation, age, and weight can also decrease emissions.
• Regulatory Measures: Implementing policies and regulations, such as the Gothenburg Protocol and the Directive on Integrated Pollution Prevention and Control in the European Union, can provide a framework for reducing ammonia emissions.
• Transportation and Industrial Sources: While agriculture is the dominant source, transportation and industrial sources also contribute to ammonia emissions. Upgrading to modern petrol cars with improved catalytic converters can help reduce emissions from road transport. Additionally, addressing emissions from fertilizer factories and industrial waste can contribute to overall ammonia reduction strategies.

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