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Iron is one of the most essential and abundant metals found in the Earths crust. Its importance to civilization is well recognized, having been used since the Bronze Age for tools and weapons, and playing a major part in the industrial revolution. Iron has also long been an important component of the Earths atmosphere, both naturally occurring and through anthropogenic means.
Iron is found in the atmosphere primarily in its natural form, ferrous oxide (FeO). It is typically released into the atmosphere through volcanic activity and wildfires, along with contributions from other sources like aeolian dust, sea spray and incineration. Iron is also released into the atmosphere by human activities, such as emissions from steel production and other industrial processes. Even the natural weathering of rusty metal objects can contribute trace amounts of iron to the environment.
In its natural state, iron in the atmosphere exists as dust, soot and dry particles in suspension in the atmosphere. As these particles travel with the wind and interact with sunlight and water vapor, their surface oxidation can be altered, causing them to combine with oxygen, producing FeO. As the iron undergoes oxidation, it combines with oxygen to form iron oxides (Fe2+ and Fe3+).
Iron in its oxidized form, Fe3+, is water-soluble and can be dissolved in rain or deposited from the air into bodies of water and soils, as well as onto plant surfaces. The presence of Fe3+ in rainwater, for example, can lead to the acidification of surface and ground water, which can lead to potential health problems in humans, such as skin and respiratory irritation.
Iron in its natural oxidized state, Fe2+, has a much higher solubility than Fe3+. Fe2+ can be more easily and efficiently removed from the atmosphere through natural processes such as rainfall, fog and snow. As it falls to Earth and dissolves in water, Fe2+ can bind to other substances, including organic matter, and become less mobile, settle to the bottom of the water body and eventually be buried in the sediment.
Iron in its oxidized form can also be removed from the atmosphere through the process of atmospheric deposition. This process, otherwise known as ‘dry deposition’, occurs when particles containing Fe2+ or Fe3+ in the air come in contact with surfaces like roads, roofs and vegetation and are deposited directly onto the ground.
Iron oxide in its oxidized form, Fe3+, can also be recycled back into the atmosphere is through the process of volatilization, which involves the heating and subsequent evaporation of iron-containing particles. This cycle can be beneficial, as it helps to replenish the atmosphere with needed nutrients, but too much iron can be detrimental to plant growth and human health.
In summary, iron is one of the most essential and abundant metals found on Earth and plays a significant role in the global atmosphere. Its presence in the atmosphere is primarily in its oxidized form, Fe3+ and Fe2+, and can be cycled back into the atmosphere through natural processes such as rainfall, fog and snow or through the process of volatilization. Iron oxides, especially Fe3+, can contribute to acidification of surface and ground water, and therefore can be detrimental to human health. Overall, the understanding of the cycling of iron in the atmosphere is an essential part in tackling global air pollution and understanding our environment.
