Environmental Impacts of Air Pollution

Fresh air and clean water have been for centuries regarded as the key ingredients to a long and healthy life. Air and water are two elements that actually enter easily into living cells and represent their important structural elements that keep their metabolism going.

Sadly enough, with the rise of the industrial development, access to the clean air and water has become a luxury. And not only for us. Even plants and wild animals living in distant ecosystems suffer greatly of the negative impacts of air pollution.

Air pollutants can travel long distances and do not respect any boundaries or regions of a special ecological significance. Harmful particles emitted from power plants, cars or mining sites are easily carried hundreds of miles away from their original source and then pollute pristine natural areas.

Throughout the years, scientists have observed numerous examples of this worrisome phenomenon.

For example, endangered Florida Panthers in Everglades National Park suffer of poor reproductive success due to high levels of airborne mercury. How did mercury get to Everglades? Particles of this heavy metal are blown to the park from coal-burning power plants and waste incinerators located in larger cities around.

Similarly, plants in Great Smoky Mountains National Park suffer of leaf injuries due to the increased levels of ground-level ozone (a human-made pollutant). This pollution largely affects the functioning of the whole ecosystem by decreasing capacity of plants to sequester carbon and retain water in their bodies [1].

Above mentioned examples only lightly tap on the surface of this problem, which is bigger than you may think. Keep on reading to learn more about the full scope of the environmental impacts of air pollution that are affecting our world on the daily basis.

How does air pollution affect the environment?

All particles released into the atmosphere react with other atmospheric compounds and form aerosols (a suspension of small particles or liquid droplets in air). Examples of naturally-occurring aerosols are fog, mist and clouds; examples of aerosols originating from our activity are smoke or haze.

As you can tell from watching the clouds drifting across the sky, aerosols can be easily carried by wind long distances and then fall on the land or water surface either with the precipitation or by the deposition from the air.

Combined with high concentrations of air pollutants emitted from our industrial centers, aerosols introduce through the deposition many unwanted chemicals into ecosystems.

This leads to following effects:

Acid rain

Under normal conditions, pH of rainwater is around 5.6. Yes, rainwater is naturally acidic due to the presence of carbon dioxide in the atmosphere [2].

However, the combustion of fossil fuels emits nitric oxide and sulfur dioxide, also acidic substances, into the atmosphere. Both of these air pollutants react with airborne water molecules and decrease rainwater pH, leading to the formation of acid rain.

According to the Washington University, pH of acid rainwater can drop as low as 1.8 [3]. To get a better idea: pure lemon juice has pH around 2 – imagine how acidic this rain must be then.

Such a change in the rain acidity comes with many negative effects on the environment, including:

• Acidification of water bodies, making them inhospitable for fish. Water acidity leads to body deformities, gill damages and lowers success rate of reproduction. Sensitive fish species are trout and salmon.
• Damage to plant leaves and needles, reducing the ability of plants to photosynthesize.
• Changes of soil chemistry, which affects plant metabolism and nutrient cycling – making plants (especially trees) nutrient deprived and vulnerable to diseases [4].

In 1990s many forests across Europe suffered a great damage caused by acid rains. For example, more than 50 percent of trees in the Black Forest, Germany, died and over 60 percent of the beech and yew trees in Great Britain showed signs of acid rain exposure [8].

Eutrophication of water bodies

Eutrophication occurs where an overabundance of plant nutrients (nitrogen, phosphorus) accumulates in freshwater bodies and causes an overgrowth of algae in water. The excessive algae growth is dangerous for other aquatic organisms, because once the algae die, their decomposition depletes oxygen from water. The affected water body then cannot support other life and turns into a dead zone.

While algal blooms have always been naturally occurring in nature, nitrogen emissions from transport and power plants introduce excessive nitrogen loads into our already scarce freshwater resources. This leads to permanently raised nutrient content, making the natural recovery of the affected ecosystem extremely difficult.

For example, long-term monitoring of the nitrogen levels in the Chesapeake Bay showed that 27 percent of excessive nutrients stem from the atmospheric deposition [2].

Introduction of toxins to the food chain

Combustion of fossil fuels, mining for natural resources, waste incineration, intensive agriculture and other industrial activities emit daily large number of pollutants into the air. These include toxic heavy metals that have been listed by the World Health Organization (WHO) as ‘Chemicals of major public concern’ – arsenic, cadmium, lead and mercury.

To make this toxic cocktail even more “breathable,” intensive agriculture releases high levels of organic contaminants into the air, which mainly originate from the application of various pesticides.

When all these pollutants get deposited on the vegetation, into the soil, or surface waters, animals feeding and drinking from these sources ingest harmful chemicals as well. Repeatedly. Every time they feed, they take in more and more of these persistent air pollutants. Toxic elements then start to accumulate in their body tissues.

This is the pathway of air pollutants into the food chain.

Later when herbivores get eaten by predators (or us), accumulated toxins are passed further on. The problem is that their concentrations can be very high since they have been gradually building up in the organism of the prey animal, and may lead to acute poisoning of the predator. This is a process known as biomagnification.

High levels of airborne mercury found in bodies of Florida Panthers from Everglades National Park is an example of biomagnification. High concentrations of mercury enter panthers’ bodies because they mostly feed on raccoons and alligators whose primary source of nutrition is fish [5].

Fish and shellfish easily accumulate mercury in their body tissues and represent the most significant source of mercury contamination in the food chain (even many cases of mercury poisoning in humans are related to eating fish) [6].

Mercury poisoning results in changed behavioral patterns, infertility, disruptions in endocrine system and eventually leading to the death of animals [6].

Ozone depletion

Ozone naturally occurs in the upper atmosphere, where it acts as a shield that helps to protect the earth from sun’s UV-A and UV-B rays. Unfortunately, some of human-made chemicals have greatly damaged the ozone layer throughout the last century. Chlorofluorocarbons (CFCs), hydrofluorocarbons, and halons, used as refrigerants and in aerosol sprays since 1930s, were later identified as the main ozone-depleting chemicals.

Even though the Montreal Protocol has banned further production of these substances in 1987, in certain cases, they are still being used in coolants, foaming agents, fire extinguishers, solvents, pesticides, and aerosol propellants.

And that’s not the only problem…

A new study from 2018 discovers that emissions of chlorofluorocarbons have not stalled over the years as expected. Instead, they keep rising. According to the authors of the study, these “unexpected” emissions originate from decommissioned old buildings and fridges, or are an accidental by-product in chemical manufacture. But surprisingly the biggest portion comes from the illegal chlorofluorocarbons production in East Asia.

This is not good news for terrestrial or aquatic ecosystems, because harmful effects of ozone depletion come in many forms that are highly damaging to all life forms. Exposure of living organisms to UV radiation increases the incidence of skin cancer, cataracts, impaired immune system, metabolic disorders and reduces survival rates of offspring.

Reduced plant growth and minimized crop yields

As important as ozone is in the upper atmosphere, as damaging it can become in the lower atmosphere.

Ground-level ozone is recognized as one of the main air pollutants that is formed when volatile organic compounds (contained in paints) react with nitrogen oxides (coming mainly from transport) in the presence of sunlight and higher temperatures.

Long-term exposure of vegetation to the ground-level ozone results in visible leaf injuries when ozone actually burns (oxidizes) plant tissues, reduced growth of tree seedlings, and increased susceptibility to diseases, pests and other environmental stressors (e.g. extreme weather events).

Affected plants are weak and do not grow well. According to the scientific research in Great Smoky Mountains National Park, trees exposed to high ozone levels grew only to 60 percent of their full potential. Reduced growth is often accompanied with lower yields and high mortality levels among plants [6].

Ground-level ozone is, therefore, considered one of the main contributors to forest destruction and poses a threat to future food security.

Commonly grown crops such as soybean, cotton, corn and wheat show reduced yields under the prolonged ground-level ozone exposure. According to computer model projections, ozone pollution might decrease production of these crops by up to 26 percent in the next decade [7].

Decreased carbon sequestration

Through the process of photosynthesis, plants draw carbon dioxide from the air, and use carbon to develop their bodies while releasing oxygen back into the atmosphere. Trees especially have a great capacity to store large amounts of carbon in their majestic bodies throughout the lifetime. That is why forests are some of the greatest carbon sinks on earth.

However, ground-level ozone exposure reduces the ability of a plant to metabolize carbon dioxide. Quite logically, this is also linked to the smaller growth of a plant (mentioned above), as it cannot effectively utilize carbon to grow its body.

This is certainly an alarming fact, considering that our activities emit high amounts of carbon dioxide into the atmosphere where it acts as a strong pollutant itself. In fact, carbon dioxide is such a potent air pollutant that it has begun to change climate of the whole planet.

By adding to the equation even ground-level ozone, we inadvertently reduce capacity of plants to sequester this excessive carbon dioxide, which only magnifies the impacts of climate change.

Loss of soil fertility and lower water content

When plants do not properly metabolize carbon dioxide after their prolonged exposure to ground-level ozone, soil fertility declines as well. Under normal conditions, plants draw carbon dioxide from the air and then use some carbon as a structural element to build their bodies. But they do not use all of it.

The unused carbon is sent through their roots to the soil where it provides for soil microbes, including beneficial soil bacteria, fungi and viruses, that are responsible for decomposition of organic matter and nutrient cycling – extremely important actions to secure soil health and productivity [9].

When plants metabolize less carbon dioxide, carbon distribution to the soil ceases. With the lack of carbon, numbers of beneficial soil microbes plummet, resulting in the loss of soil fertility.

Another problem caused by elevated ozone levels is the weakening of the ability of plants to control water evaporation from their bodies. Affected plants keep losing water faster than healthy plants. This in turn leads to their increased water uptake from the soil, reducing soil moisture and changing water availability for other living organisms [2].

Haze

Haze is produced when sunlight hits concentrated particles of airborne pollutants, such as sulfur dioxide and nitrogen oxide, emitted from power plants, industrial facilities or produced by the smoke from wildfires.

Haze-causing particles can be carried by the wind large distances away from where the pollutants were produced. For example, Indonesian peatland fires cover every year neighboring countries in thick haze and negatively impact local ecosystems and health of people and animals.

In 2006, researchers in Borneo observed that Bornean white-bearded gibbons cease to sing their special “couple-bonding and territorial songs” when haze suffocates their habitat. Scientists believe that the cause of this behavior are respiratory problems, affecting the overall health and reproduction success of these primates.

Impacts of haze on plants are also profound. When the thick blanket of haze blocks the sunlight, plants cannot properly photosynthesize and finish their growth.

Prolonged periods of the decreased visibility harm insects as well. Many of which are crucial for local ecosystems, like pollinators. As observed in Singapore in 2015, insect activity has significantly dropped during the critical period of smoky days [10].

Global climate change

Due to excessive burning of fossil fuels and extensive changes in the land cover by deforesting large areas to make space for cities or farms, immense quantities of greenhouse gases such as carbon dioxide and methane are released into the air.

Greenhouse gases facilitate an increase in global temperatures by trapping the heat in the atmosphere, and their ever-increasing concentrations have gradually started to change the planet’s climate.

Climate change is manifested through many negative events, including:

• stronger storms
• floods
• searing summer heats
• droughts
• destructive wildfires
• increased risk of disease and pest infestations
• sea level rise
• ocean acidification
• and many more…

These events are disturbing for the natural balance of ecosystems and affect living organisms that have to promptly adapt to sudden changes and weather extremities.

One example of a species that is losing the battle against changing climate are polar bears in the Arctic. Polar bears depend upon the formation of the Arctic sea ice to successfully hunt for seals, walruses or beluga whales.

But in the past years, the Arctic has been losing its ice cover fast, making it very difficult for polar bears to access their premium hunting grounds during summer months when the ice is pretty much gone. During the months when the ice retreats, many bears struggle to find sufficient food sources to survive, leaving scientists worried about the future of this species.

Sadly, examples of environmental destruction start to become the “new normal” in our period of time. Air pollution together with climate change influence our health, quality and access to natural resources, our ability to grow food and benefit from sharing the planet with millions of other living creatures who help to establish the planet’s balance.

Perhaps by understanding the connection between the pollution that our activities produce and its impacts on nature, we can make changes that are necessary to prevent it and live in harmony with nature, passing a more sustainable world on to future generations.