Brian Barton
Atmospheric deposition is the transfer of air pollutants (gases or particles) to the Earth's surface. It can be a primary source of pollutants to aquatic and terrestrial environments, including forests and coastal ecosystems. Atmospheric deposition can occur through dry and wet deposition, with the former including particulates, gases, and droplets, and the latter including rain, snow, hail, fog, and freezing rain. While atmospheric deposition is recognised as a source of nonpoint source pollution, it may be considered distinct from traditional nonpoint sources as it can originate from a point source of air pollution, such as a factory.
| Characteristics | Values |
|---|---|
| Definition | Atmospheric deposition is the transfer of air pollutants (gases or particles) to the Earth’s surface. |
| Forms | Atmospheric deposition may be in a wet form (rain, snow, hail, fog, and freezing rain) or in a dry form (particulates, gases, and droplets). |
| Sources | The largest sources are point sources such as coal- and oil-burning electric utilities and large industries that together account for about 53% of nitrogen emissions. Automobiles, trucks, buses, and other forms of transportation account for approximately 38% of nitrogen emissions. Atmospheric deposition of nitrogen onto land, freshwaters, and estuaries is also caused by the use of N fertilizers in agriculture and sewage wastewater. |
| Effects | Atmospheric deposition is a primary source of pollutants to terrestrial and aquatic environments. The health of people, animals, and the ecosystem can be adversely affected by the atmospheric deposition of pollutants. Atmospheric deposition of sulfur and nutrients may contribute to the acidification and eutrophication of various water bodies. |
| Prevention | The Clean Air Status and Trends Network (CASTNET) provides long-term monitoring of regional air quality to determine trends in atmospheric concentrations and deposition of nitrogen, sulfur, and ozone. |
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What You'll Learn
- Atmospheric deposition is a primary source of pollutants
- Pollutants are deposited on surfaces or washed out via rain/snow
- Point sources of nitrogen pollution are large and small industries
- Atmospheric deposition is the second most important source of nitrogen pollution
- Atmospheric deposition is a determinant factor for tree growth and forest health
Atmospheric deposition is a primary source of pollutants
Atmospheric deposition is the transfer of air pollutants (gases or particles) to the Earth's surface. It can occur through dry deposition, where pollutants are deposited directly onto surfaces, or wet deposition, where pollutants are washed out of the atmosphere by rain or snowfall. Atmospheric deposition is a significant source of pollutants, including gases, particulates, metals, and nutrients, which can have detrimental effects on aquatic and terrestrial ecosystems, as well as human health.
The sources of atmospheric deposition are diverse. In the context of nonpoint-source pollution, atmospheric deposition is recognised as an important contributor of nitrogen to major watersheds. Commercial fertiliser is the dominant source of nitrogen in the Western United States due to intensive agriculture, while atmospheric deposition is the second most important source. In contrast, in the Northeastern United States, where agriculture is less intensive, atmospheric deposition is the dominant source of nitrogen in most watersheds. Automobiles, trucks, buses, and other forms of transportation also contribute significantly to atmospheric deposition, accounting for approximately 38% of nitrogen emissions.
The effects of atmospheric deposition on the environment are determined by the amount and mixture of pollutants deposited. For example, the deposition of sulfur and nutrients may contribute to the acidification and eutrophication of water bodies. Atmospheric deposition of oxidized and reduced forms of nitrogen can also cause environmental changes beyond acidification, such as eutrophication of water bodies from the deposition of reduced nitrogen (ammonia/ammonium). Furthermore, pollutants deposited on the Earth's surface can be moved from their original sites through groundwater fluxes, surface runoff, and soil erosion, further exacerbating their impact.
Additionally, atmospheric deposition can impact human health and ecosystems located far from the original source of pollution. Pollutants released from point sources such as factories can remain aloft for extended periods, travelling great distances before being deposited. This long-range transport and the presence of multiple sources of pollutants make it challenging to identify and regulate atmospheric deposition as a nonpoint source of pollution. Nevertheless, it is crucial to recognise the significant role of atmospheric deposition in pollutant transfer and its potential impacts on the environment and human well-being.
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Pollutants are deposited on surfaces or washed out via rain/snow
Atmospheric deposition is a significant contributor to nonpoint source pollution. Nonpoint source pollution is caused by rainfall or snowmelt moving over and through the ground, picking up and carrying away natural and human-made pollutants, and depositing them into bodies of water. Atmospheric deposition can occur in two ways: wet deposition and dry deposition.
Wet deposition, commonly known as acid rain, is the process by which acidic particles and gases are washed out of the atmosphere by rain, snow, fog, or hail. Acid rain is formed when sulfur dioxide (SO2) and nitrogen oxides (NOx) are emitted into the atmosphere, typically from the combustion processes of power plants and industries, and then react with water molecules to produce acids. These acids fall to the ground mixed with precipitation and can have harmful effects on the environment, including lakes, streams, forests, soils, and aquatic life. Acid rain can also be washed off surfaces by rainfall, leading to acidic water that flows over the ground and harms plants and wildlife.
Dry deposition, on the other hand, occurs when pollutants are deposited on surfaces without the presence of moisture. These pollutants may include acidic particles, gases, or larger particles formed during atmospheric transport. While dry deposition is challenging to measure, it can have significant impacts on the environment. For example, pollutants deposited on surfaces such as water bodies, vegetation, and buildings can affect aquatic ecosystems, plant health, and infrastructure. Additionally, when these accumulated pollutants are washed off surfaces by rainfall, they contribute to the formation of acidic water, further exacerbating the environmental impact.
The sources of atmospheric deposition can be either point sources or nonpoint sources. Point sources refer to specific locations from which pollutants are discharged, such as coal- and oil-burning electric utilities, large industries, and vehicles. In contrast, nonpoint sources contribute pollutants from multiple and widespread locations, making it challenging to identify a single discharge point. While atmospheric deposition from point sources is significant, it is important to recognize that the long-range transport of pollutants and multiple sources involved can ultimately lead to nonpoint source pollution.
The impact of atmospheric deposition on water quality and ecosystems is a growing concern. In the United States, atmospheric deposition is a dominant source of nitrogen in certain regions, particularly in areas with intensive agriculture and greater rainfall and atmospheric pollution. Additionally, scientists have found that atmospheric inputs are responsible for a significant portion of the trace elements, such as lead and mercury, that enter the Great Lakes. Addressing atmospheric deposition and its contribution to nonpoint source pollution requires a comprehensive approach, including monitoring, controlling emissions, and implementing best management practices to minimize the release of pollutants into the atmosphere.
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Point sources of nitrogen pollution are large and small industries
Nitrogen pollution is a pressing issue, with over 3.2 million tons of nitrogen deposited in the United States each year. Point sources of nitrogen pollution are varied and include large and small industries, as well as publicly and privately owned wastewater treatment plants. These industries, through their combustion processes, discharge nitrogen directly into streams, making them distinct point sources.
Large industries, such as coal- and oil-burning electric utilities, are major contributors, accounting for about 53% of nitrogen emissions. This is primarily due to the combustion processes of power plants, which release nitrogen into the atmosphere, leading to atmospheric deposition. This deposition can occur through wet or dry processes, with rain, snow, and other forms of precipitation being the dominant mechanisms in certain regions, such as the Northeastern United States.
Small industries also play a role in nitrogen pollution as point sources. These can include various industrial facilities that discharge pollutants through smokestacks, dispersing them over long distances. While the pollutants may have originated from a single point source, they can be transported over vast distances and deposited in diverse locations, blurring the lines between point and non-point sources.
In addition to industrial sources, wastewater treatment plants, both publicly and privately owned, are considered point sources. These plants can struggle to effectively remove nitrogen, leading to discharges into waterways. Furthermore, industries such as transportation, agriculture, and fossil fuel burning contribute significantly to nitrogen pollution, with vehicles alone accounting for approximately 38% of nitrogen emissions.
To address nitrogen pollution, it is essential to recognize the complex interplay between point and non-point sources. While point sources are relatively easier to regulate, non-point sources, such as commercial fertilizers and animal manure in agriculture, are more challenging due to their diffuse nature. However, by understanding the specific sources and developing targeted pollution-prevention plans for individual watersheds, effective control programs can be implemented to mitigate the environmental impacts of nitrogen pollution.
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Atmospheric deposition is the second most important source of nitrogen pollution
Atmospheric deposition is a significant contributor to nitrogen pollution, particularly in the Western United States, where it is the second most important source of nitrogen pollution. This is due to the intensive use of commercial fertilizers in agriculture, which is the dominant source of nitrogen in the region. Atmospheric deposition is also a primary source of nitrogen in remote headwater areas and western watersheds devoted to forestry.
Atmospheric deposition occurs when pollutants are released into the atmosphere, often through smokestacks at industrial facilities. These pollutants can remain aloft for extended periods, travelling great distances and impacting ecosystems far from their origin. When these pollutants are deposited onto surfaces through dry deposition or washed out of the atmosphere via rain or snowfall (wet deposition), they contribute to nitrogen pollution.
Nitrogen (N) is an essential element for all life forms, playing a critical role in plant tissues and proteins. However, the excessive availability of reactive nitrogen can have detrimental effects on ecosystems. Atmospheric deposition of reactive nitrogen compounds can lead to eutrophication of surface waters, causing unsightly and harmful algal and aquatic plant growth. This process restricts recreational uses of lakes and slows down rivers and streams.
Additionally, atmospheric deposition of nitrogen contributes to acidification and the accumulation of excess nutrients, negatively impacting terrestrial and marine ecosystems. The increase in reactive nitrogen emissions is a result of human activities, particularly industrialization, which has significantly increased nitrogen deposition. This has led to a 20% increase in total nitrogen deposition, with an estimated 3.2 million tons of nitrogen deposited in the United States annually.
To address this issue, targeted observational experiments are necessary to enhance our understanding of nitrogen deposition's chemical processes. By studying the impact of atmospheric deposition on marine ecosystems, we can better manage and mitigate the negative consequences of nitrogen pollution.
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Atmospheric deposition is a determinant factor for tree growth and forest health
Atmospheric deposition is a significant factor in the growth of trees and the overall health of forests. It is a key component of the nutrient cycles of terrestrial ecosystems. Atmospheric deposition can be a source of essential nutrients for forests, such as nitrogen, phosphorus, and potassium. These nutrients are vital for tree growth and forest productivity.
Nitrogen deposition, for instance, has been shown to increase forest carbon uptake. According to a study, nitrogen deposition currently increases the forest carbon sink by 276–448 Tg C yr−1, with approximately 60% retained in tree wood and 40% in the soil. This increase in carbon uptake is likely due to the fertilizing effect of rising atmospheric CO2 levels. However, the modulation of this effect by changes in sulphur and nitrogen deposition remains unclear and requires further investigation.
Atmospheric deposition can also be a source of pollution, particularly in the form of nonpoint source pollution. Industrial facilities often discharge pollutants such as hydrocarbons and metals into the atmosphere through smokestacks. These airborne pollutants can remain aloft for extended periods, travelling great distances and impacting ecosystems far from their source. While the pollutants may originate from a point source, their long-range transport and multiple sources make them a nonpoint source of pollution when deposited on land or washed out of the atmosphere by precipitation.
The impact of atmospheric deposition on tree growth and forest health is complex and influenced by various factors, including temperature, moisture, and soil conditions. For example, in a study of European forests, it was found that changes in tree growth were associated with interactions between climate and atmospheric deposition drivers. Additionally, the availability of nitrogen from atmospheric deposition may be influenced by factors such as temperature and moisture variability, as suggested by the negative relationship observed between Δ18Ow, sSdep, and aSdep in another study.
In summary, atmospheric deposition significantly influences tree growth and forest health. It provides essential nutrients that sustain forest productivity and increase carbon uptake. However, it can also contribute to pollution when harmful substances are deposited on land or washed out by precipitation. The complex interplay between atmospheric deposition, climate, and other environmental factors continues to be the subject of ongoing research, with the goal of improving our understanding of its effects on tree growth and forest ecosystems.
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Frequently asked questions
Atmospheric deposition is the transfer of air pollutants (gases or particles) to the Earth’s surface.
Atmospheric deposition may be in a wet form as rain, snow, hail, fog, and freezing rain or in a dry form as particulates, gases, and droplets. The largest sources are point sources such as coal- and oil-burning electric utilities and large industries that together account for about 53% of nitrogen emissions.
Point sources of pollution discharge pollutants directly into streams at a single point. Non-point sources of pollution, on the other hand, contribute pollutants to receiving rivers and streams at multiple widespread locations.
Atmospheric deposition is a primary source of pollutants to terrestrial and aquatic environments. Although pollutants may originate from a point source of air pollution such as a factory, the long-range transport and multiple sources of the pollutant make it a non-point source of pollution.
