Air Pollution: Earth's Slow Poisoning

Air pollution is a pressing issue that significantly impacts the Earth and its ecosystems. It refers to the release of harmful substances into the Earth's atmosphere, including gases, solid particles, and liquid droplets. These pollutants, such as sulfur dioxide, nitrogen oxides, and carbon monoxide, are primarily produced by human activities like burning fossil fuels and industrial processes. The effects of air pollution are wide-ranging, from damaging human health to harming the natural environment. It contributes to climate change by trapping heat in the atmosphere, leading to rising temperatures, melting ice sheets, and extreme weather conditions. Additionally, air pollution affects ecosystems by damaging habitats, water sources, and plant and animal life. The release of pollutants also leads to reduced visibility and the formation of acid rain, which further impacts both human-made structures and natural environments.

Air pollution impacts human health

Air pollution is a mix of hazardous substances from both human-made and natural sources. It is the presence of one or more contaminants in the atmosphere, such as dust, fumes, gas, mist, odour, smoke or vapour, in quantities and durations that can be injurious to human health. According to the World Health Organization (WHO), air pollution is responsible for nearly seven million deaths worldwide each year.

The main pathway of exposure from air pollution is through the respiratory tract. Breathing in these pollutants leads to inflammation, oxidative stress, immunosuppression, and mutagenicity in cells throughout our body, impacting the lungs, heart, and brain, among other organs, and ultimately leading to disease. Almost every organ in the body can be impacted by air pollution. Due to their small size, some air pollutants can penetrate into the bloodstream via the lungs and circulate throughout the entire body, leading to systemic inflammation and carcinogenicity. Fine particulate matter (PM2.5) is of particular concern, as it can be inhaled deeply into the lung tissue and has been linked to serious health problems.

Health problems in children and adults can occur due to both short- and long-term exposure to air pollutants. The levels and duration of exposure that can be considered 'safe' vary by pollutant and the related disease outcomes. Maternal exposure to air pollution is associated with adverse birth outcomes, such as low birth weight, pre-term birth, and small for gestational age births. A growing body of evidence also suggests that air pollution may affect diabetes and neurological development in children. Older people, children, and those with pre-existing health conditions are more sensitive to the health impacts of air pollution.

Pollutants with the strongest evidence for public health concern include particulate matter (PM), carbon monoxide (CO), ozone (O3), nitrogen dioxide (NO2), and sulphur dioxide (SO2). Ground-level ozone, often referred to as smog, is created when pollutants emitted by cars, power plants, industrial boilers, refineries, and other sources chemically react in the presence of sunlight. Vehicle emissions, fuel oils, and natural gas used to heat homes, as well as by-products of manufacturing and power generation, are the primary sources of human-made air pollution.

It damages natural ecosystems

Air pollution can have detrimental effects on natural ecosystems. Pollutants in the air can be toxic to sensitive plants and trees, while pollutants in rainfall can damage habitats by depositing acid or excess nutrients. Water bodies such as rivers and lakes are also susceptible to the effects of air pollution.

One of the most significant forms of air pollution for natural ecosystems is the deposition of reactive nitrogen compounds, such as ammonia and nitrogen oxides. This deposition can occur through direct contact between polluted air and plants, a process known as "dry deposition", which typically happens close to pollution sources. It can also occur when pollution is dissolved in precipitation (rain and snow) and falls onto sensitive sites, known as "wet deposition", which can occur at long distances from the pollution source.

Ammonia, a byproduct of agricultural activities such as livestock housing and fertiliser use, is the biggest contributor to nitrogen deposition. Nitrogen oxides, produced by road transport and some industries, are another significant source. These pollutants can lead to excessive nitrogen levels in terrestrial and aquatic ecosystems, causing eutrophication. In water bodies, eutrophication is characterised by algal blooms and reduced oxygen availability. In sensitive terrestrial ecosystems, excessive nitrogen deposition can drive the loss of sensitive species, alter ecosystem structure and function, and increase the growth of species that thrive in high-nitrogen environments.

Atmospheric nitrogen deposition can also have indirect effects on ecosystems. For example, peatlands that sequester carbon can be damaged by ammonia and nitrogen deposition, reducing their effectiveness in combating climate change. Additionally, nitrogen deposition can alter plant communities, affecting the ecosystem's biodiversity and function.

Sulphur dioxide, produced by burning fuels like coal, is another pollutant that negatively impacts vegetation. It can lead to excess acid levels in lakes and streams, damaging trees and forest soils. Ground-level ozone is also detrimental, reducing growth rates and yields of agricultural crops, forests, and plants, and affecting their biodiversity and ecosystem services.

It contributes to climate change

Air pollution is causing the climate to change, and climate change is also causing air quality to change. The recent increase in greenhouse gas pollution is trapping excess heat and causing the climate to warm. This is known as the greenhouse effect.

Greenhouse gases, such as carbon dioxide, prevent heat from escaping the Earth's atmosphere. They are a natural part of the Earth's atmosphere, but their increasing amounts since the early 1900s are causing the planet to warm. This warming is caused by vehicle exhaust, pollutants from smokestacks at factories and power plants, emissions from agriculture, and other sources.

Ozone in the troposphere is a greenhouse gas and a health hazard. It is a significant contributor to warming in the Arctic, where it is transported during the winter and spring months. The Arctic is warming faster than any other region on Earth due to positive feedback loops, where warming melts snow and ice, changing the Earth's surface and leading to more warming.

Black carbon, a particulate pollutant from combustion, also contributes to warming the Earth. It is released from burning wood or fossil fuels and absorbs most of the sunlight that hits it. Wildfire smoke, which contains black carbon, increases the risk of respiratory diseases and has been linked to premature births. Climate change has led to more frequent and longer-lasting wildfires, which impair visibility, disrupt outdoor activities, and spread pollution downwind to other regions.

Additionally, climate change can cause earlier and longer springs and summers, higher carbon dioxide concentrations, and changes in precipitation patterns. These changes can increase ground-level ozone and particulate matter, worsening existing air pollution and decreasing indoor air quality.

It affects water bodies

Air pollution has a significant impact on the Earth's water bodies, particularly the oceans. The process by which pollutants are deposited into water bodies is called atmospheric deposition. Pollutants enter the water through various pathways, including direct dumping and exhaust emissions from vessels, as well as the absorption of airborne carbon dioxide (CO2) by seawater.

One of the most pressing concerns is the acidification of water bodies caused by air pollution. Atmospheric deposition of nitrogen and sulfur, as well as carbon dioxide, can lead to a decrease in pH levels, making the water more acidic. This has been observed in smaller water bodies, where increased acidity can cause the disappearance of crustaceans, insects, and some plankton species. If the pH drops below 5.0, drastic changes in the plankton community occurs, leading to a dominance of less desirable species and potential reductions in fish populations. This effect would be even more drastic in smaller lakes, rendering the area devoid of fish and covered in undecayed material.

Air pollutants such as nitrogen, mercury, combustion emissions, pesticides, and heavy metals can settle into water bodies, damaging aquatic ecosystems and posing risks to public health. These pollutants can enter water bodies through atmospheric deposition or when hazardous chemicals fall as dust or are washed into waterways by rain, a process known as acid precipitation. The effects of acid precipitation can be immediate and lethal to aquatic organisms, as seen in the case of "acid shock" caused by the sudden release of acidic snowmelt in the spring.

Additionally, air pollution can indirectly harm water bodies by affecting the soil. Acid precipitation can alter soil chemistry, reducing its ability to retain essential nutrients, minerals, and elements. This, in turn, affects plant growth and water quality as these nutrients are transported and leached into water bodies.

Furthermore, air pollution contributes to water pollution through the improper disposal of solid waste and toxic chemicals. Industrial waste, chemical processes, and agricultural runoff can introduce pollutants such as lead, mercury, chromium, and pesticides into water bodies, contaminating them and disrupting aquatic ecosystems. Sewage and toxic waste can promote algae growth, leading to eutrophic "dead zones" where aquatic life cannot survive due to oxygen depletion.

It reduces visibility

Air pollution is detrimental to the planet and human health. It is caused by the release of pollutants into the air, which can come from a variety of natural and manmade sources. Natural sources include windblown dust and soot from wildfires, while manmade sources include motor vehicles, industrial fuel burning, and manufacturing operations.

One of the most noticeable effects of air pollution is the reduction of visibility. This has been recognized since the 16th century, when urban smogs caused by smoke and sulphur dioxide led to extreme losses in visibility, sometimes down to just a few meters. Today, this issue persists, and many visitors to scenic areas and national parks are unable to see the views they expect due to a veil of white or brown haze in the air. This haze is caused by air pollution, which is carried by the wind and can travel hundreds of miles from its source. The average visual range in eastern parks in the US has decreased from 90 miles to 15-25 miles, while in the west, it has decreased from 140 miles to 35-90 miles.

Haze is formed when sunlight encounters tiny pollution particles in the air. Some light is absorbed by these particles, while other light is scattered before it reaches an observer. The more pollutants there are in the air, the more light is absorbed and scattered, reducing the clarity and color of what we see. This is particularly noticeable during "photochemical episodes," which occur in conditions of strong sunshine and low windspeeds.

Particulate matter pollution, which includes haze-causing particles, is a major cause of reduced visibility in parts of the United States. Some of these particles are directly emitted into the air, while others are formed when gases emitted into the air form particles as they are carried away from the source of the pollutants. These particles can also have serious health effects, including increased respiratory illness, decreased lung function, and even premature death.

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