A deep dive on the environmental impacts of air pollution

Image provided by NASA via Unsplash

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TL;DR: Air pollutants—ranging from greenhouse gases and ozone to aerosols like black carbon—affect not only human health but also ecosystems, the water cycle, and the global climate. They contribute to acid rain, ocean acidification, ozone depletion, and shifts in Earth's albedo, affecting climate change and disrupting biodiversity. While some pollutants temporarily mask global warming, lasting solutions require comprehensive emission reductions.

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Air pollution is both widespread and varied. While many air pollution emissions—mostly man-made—harm human health, air pollution’s effects on the environment and climate are equally concerning. 

Wildlife faces many of the same challenges that air pollution poses for humans. Animals often suffer from air pollution’s adverse health effects and national parks can experience the same visibility issues that cities face from smog and particulate matter. However, air pollution’s effects on the environment extend beyond these examples, affecting ecosystems in multiple ways.

How air pollution affects the hydrologic (water) cycle

The hydrologic cycle refers to the continuous circulation of water through the atmosphere and along the ground. Air pollution affects the hydrologic cycle in the form of acid rain and ocean acidification. 

Acid rain

Acid rain is caused by two air pollutants: sulfur dioxide (SO₂) and nitrogen oxides (NO_x), both of which are usually emitted by man-made sources. NO_x, in particular, is commonly emitted by cars and contributes to photochemical smog, while SO₂ emissions often come from electric power generators. When SO₂ and NO_x react with the water in the atmosphere, they form sulfuric and nitric acids, respectively. These acids then fall to the ground in the form of rain, or other acid deposition, such as snow, hail, fog, or even sometimes as dry deposition, such as dust. 

Acid deposition has negative impacts on various ecosystems. When acid rain flows through soil, it causes aluminum to leach out from the dirt and into water runoff. Then, when the acid rain flows into bodies of water, it increases the water’s acidity and aluminum levels, harming many of the fish and wildlife that live there and reducing biodiversity. 

Acid rain can leach away certain nutrients from the soil, damaging plant health. However, nitrogen oxides and ammonia can also cause nitrogen deposition, leading to the over-enrichment of soil and the eutrophication of bodies of water. The overabundance of nitrogen harms certain plants and promotes algae growth, reducing biodiversity and disrupting ecosystems. Sulfur dioxide also has a harmful effect on vegetation, and acid fog can strip nutrients from plants such as evergreen trees directly without entering the soil. 

Ocean acidification

Ocean acidification refers to a gradual reduction in the pH of the ocean. It is sometimes called “climate change’s equally evil twin.” This phenomenon mainly occurs because of the increasing levels of carbon dioxide (CO₂) in the atmosphere from anthropogenic activities such as the burning of fossil fuels and land use changes like deforestation. 

Roughly 30% of the carbon dioxide released into the atmosphere is absorbed by the ocean. Since the industrial era, the ocean has absorbed about 525 billion tons of CO₂ and currently absorbs about 22 million tons per day. Carbon dioxide causes a series of chemical reactions that make the ocean’s water more acidic, harming many forms of aquatic life. In the last 200 years, the ocean has already grown acidic faster than any other known change in ocean chemistry in the last 50 million years. 

Although the effects of ocean acidification on aquatic life are largely unknown, it may cause many species to go extinct and greatly disrupt the delicate ecosystems and biodiversity of the ocean as we know it. Acidic waters make it difficult for certain species, such as clownfish, to detect predators. CO₂ increases the amount of hydrogen ions and decreases the amount of carbonate ions in the water. Carbonate ions are vital components in seashells and coral skeletons. Their decrease directly harms shellfish, corals, and other species that rely on them. 

How ozone affects the environment

Ozone (O₃) can be either helpful or harmful to the environment depending on where it is located. Ozone in the upper atmosphere (stratospheric ozone) is naturally occurring and reduces the amount of damaging UV radiation that reaches the Earth’s surface. Ozone at ground level (tropospheric ozone) is more harmful. It forms from the chemical reaction between volatile organic compounds and nitrogen oxides, two anthropogenic air pollutants. 

Ground-level ozone and the environment

Tropospheric ozone harms the environment by reducing photosynthesis in plants. This air pollutant is absorbed through tiny pores on the bottom of leaves called stomata. Ozone can damage the stomata, or even cause them to close, making it more difficult for plants to take in the carbon dioxide they need to survive. Ozone can also damage the parts of leaf cells that make the necessary sugars. 

In addition, ground-level ozone can slow plant growth, and make plants more vulnerable to disease, insect damage, and other threats. These negative effects have led to billions of dollars in crop loss. The National Center for Atmospheric Research has created “ozone gardens” in which ozone-related plant damage can be studied and viewed in action.

Stratospheric ozone and the environment

Stratospheric ozone protects Earth from UVB radiation. Unfortunately, certain air pollutants such as chlorine and bromine can deplete stratospheric ozone. Many anthropogenic emissions of chlorofluorocarbons, hydrochlorofluorocarbons, methyl chloroform, carbon tetrachloride, halons, and methyl bromide, release these ozone-depleting chemicals into the upper atmosphere. These emissions come from refrigeration and propellant devices and processes. 

In addition to causing millions of deaths and negatively affecting human and animal health, UVB radiation at the Earth’s surface impacts various ecosystems. UVB radiation can cause crop and forest damage, affecting both the physiological and developmental processes of plants.

In marine ecosystems, UVB radiation harms phytoplankton, directly reducing their numbers. It also harms fish, crabs, amphibians, shrimp, and other marine animals in their early stages of development and decreases their reproductive capacity.

How air pollution impacts global warming and climate change

Climate change refers to long-term changes in average weather patterns of Earth’s local, regional, and global climates. This term encompasses both global warming and its broader consequences on weather and climate. 

Global warming refers specifically to the long-term heating of the Earth’s surface which has been observed since the 1850s. Since the 1950s, the current heating trend has clearly been the result of human activity. 

Global warming is already causing profound effects around the world. These effects include severe weather such as droughts and extreme rainfall. Flooding will become a greater concern. Both wildfires and hurricanes will become more frequent and severe. Sea levels will rise and Arctic ice will melt. Ecosystems will be disrupted as animals and plants struggle to adapt to new climate conditions. These climate change impacts extend to human health, agriculture, and infrastructure. 

Greenhouse gases

Greenhouse gases trap heat in the atmosphere. They absorb energy and slow the rate at which that energy escapes into space. This insulating effect contributes to global warming. The primary greenhouse gases are carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), and fluorinated gases. Each of these gases has different global warming potentials depending on their radiative efficiency and lifetimes in the atmosphere. 

Human activities are largely responsible for the increase in greenhouse gases in the atmosphere over the last century and a half. The transportation sector, through the burning of fossil fuels, is the largest source of direct greenhouse gas emissions. However, many other sectors—such as electricity production, and the residential, commercial, and agricultural sectors—also play a role.

Other gases and air pollutants also contribute to climate change both directly and indirectly. For instance, ground-level ozone and water vapor trap heat and contribute to global warming, while nitrogen oxides and carbon monoxide indirectly amplify the warming effects of other gases. 

The albedo effect

Certain air pollutants can have a more nuanced effect on climate change due to the albedo effect. Albedo refers to the fraction of light that is reflected by a body or surface. The Earth’s global albedo helps determine how much of the sun’s energy is reflected back out into space. A higher albedo means more reflectivity and therefore less energy and heat are absorbed. A lower albedo has the opposite effect, increasing global warming. 

For instance, the presence of ice caps decreases global warming because they increase the Earth’s albedo. However, the melting of the ice caps accelerates global warming because their absence reduces the earth’s albedo. 

Aerosols refer to microscopic particles that are suspended in the atmosphere. They can be either liquid or solid and are often a form of air pollution. Many aerosols, such as black carbon or sulfate particles, are produced by the same sources that emit carbon dioxide. These particles affect the climate in different ways depending on whether they reflect sunlight or absorb heat. 

Aerosols formed from atmospheric reactions involving nitrogen dioxide and sulfur dioxide increase the Earth’s albedo and thus produce a profound cooling effect. This effect is so great that high-albedo aerosols may currently cool the planet by about half a degree Celsius as estimated by the Intergovernmental Panel on Climate Change. Without them, the effects of global warming would potentially be much worse, making it necessary to reduce both CO₂ and aerosol air pollution rather than just focusing on one. 

Rather than solving the problem, these aerosols mask it—leaving the potential for greater fallout in the future. The solution to global warming lies in reducing CO₂ emissions, not in increasing aerosol air pollution.

Aerosols of black carbon, on the other hand, reduce the Earth’s albedo. Black carbon, also known as soot, is a kind of particulate matter that results from fires and incomplete combustion. Not only does atmospheric black carbon block sunlight from reaching ground level—damaging plants and ecosystems—but its dark color and ability to absorb solar heat also allow it to warm the air.

Although black carbon only has an atmospheric lifetime of a few weeks, its warming effect is 460-1,500 times stronger than CO₂ per unit mass. Black carbon also plays a role in reducing the albedo of glaciers and ultimately causing them to shrink, leading to more global warming. 

Looking forward

Tackling air pollution protects both human health and the environment. Yet, the first step in reducing air pollution is understanding it. Learn how you can monitor many of these air pollutants and build your own solution with Clarity Movement.