Nitrogen oxides and sulfur dioxide are gases released from burning fossil fuels for energy. These gases get mixed up with other chemicals in the atmosphere and come back to hurt the environment as acid rain. Most of us are aware of acid rain. However, not all realize the severe effects of acid rain on the environment.
This article explains everything you need to know about the acid rain phenomenon. We also included measures that have been done or we can do to mitigate this issue.
On the pH scale, acidity and alkalinity are measured on a scale of 0 to 14, of which 7 is the neutral point. Acidity is indicated with pH numbers from 7 to 0. The lower the number, the more acidic a substance is.
Acid rain is any form of precipitation or dry deposition with acidic components beyond normal3. Normal rain typically has a slightly acidic pH of 5.6 due to carbon dioxide dissolving in it to form carbonic acid, a weak acid. The pH of acid rain is between 4.0 to 4.5, but it can drop as low as 3.0.
Acid rain comes in wet or dry forms. The wet deposition includes rain, snow, hail, sleet, and fog, while dry deposition includes acidic particles and gases. Scientists use the term acid deposition to refer to any of them, but acid rain is a more popular expression.
When sulfur dioxide and nitrogen oxides react with oxygen and other atmospheric elements, they form sulfuric and nitric acids. Then sulfuric acid and nitric acid mix with atmospheric moisture or particulate matter, falling to the ground as acid rain or acid particles.
The chemicals responsible for causing acid rain can occur naturally from volcanic eruptions1, lightning, natural fires, and decaying vegetation. However, the emissions from natural sources produce a lower deposition pH of no less than 5.2.
The major sources of acid deposition are human activities, especially those related to burning fossil fuels. They include emissions from motor vehicles and heavy equipment, manufacturing industries, power plants, and smelting metal iron ores.
To monitor this event, the National Trends Network (NTN) measures acid rain acidity by collecting rain samples from over 250 monitoring sites throughout America. The Clean Air Status and Trends Network (CASTNET) is responsible for measuring dry deposition, which, unlike wet deposition, is more challenging to estimate.
Although acid rain is less talked about than climate change, it has real and immediate consequences for affected regions. Acid deposition not only has ecological effects, but it can also have adverse impacts on human health.
Acid rain leaches aluminum bound to soil particles. Aluminum, in its dissolved form, is toxic to plants and animals.
Acid rain also removes essential nutrients from the soil, such as calcium, potassium, and magnesium. The lack of nutrients can negatively affect the health of plants and soil organisms.
In some areas, the soil is thick. It has a high buffering capacity due to naturally occurring limestone that helps to neutralize acid rain. However, the buffering capacity is low in places where the soil is thin, such as the northeast of the United States. The harmful effects of acid precipitation are more visible there.
A direct consequence of poor soil health is poor agricultural yield. Acid particles can cover the leaves of plants and affect photosynthesis. Aluminum toxicity will also reduce the ability of plants to take up water.
Small organic farms that depend on rainfall for irrigation would be most affected. Their crops will perform poorly due to the acidic soil and water.
Also, if the locals know of an acid rain problem, they may be less willing to shop at the farmers market. They will reach for imported foods, and the local economy will suffer.
When acid rain falls into streams, rivers, and lakes, their chemistry is altered, putting the survival of aquatic life at risk. Also, the aluminum from the soil and water runoff enters surface water and damages fish gills.
Acidic waters reduce fish populations. Research showed that fish species reduced from five to one when lakes with pH 6 and 7 were compared to those with pH 4 to 4.5. Most fish eggs can not hatch at pH 5, most fish eggs cannot hatch, and even adult fish may die as acidity increases.
There are some lakes so acidic they have no fish. Acid rain also contains nitrogen, an excess of which is partially responsible for declining fish and shellfish populations in some aquatic environments.
Many forests, especially those at higher elevations, are filled with dead or dying trees due to acid deposition. Acid deposits strip the soil of essential nutrients and raise soil aluminum levels, which makes the trees unable to absorb water.
Acidic fog and clouds contain greater amounts of acid than rain and snow. They can remove nutrients from trees at high elevations, leaving them with dead or brown leaves. Stripped of leaves and needles, the trees are less able to absorb vital sunlight.
The loss of nutrients, lack of sunlight, and excess aluminum make the affected forests less resistant to diseases, pests, droughts, freezing temperatures, and other environmental stressors.
All creatures have a limit to the amount of acidity they can adapt to. Some can tolerate acidic waters better compared to others. However, because of the interdependency between organisms in an ecosystem, a threat to one is a threat to all.
Take the food chain, for example. Frogs can survive at a pH of 4.0, but the mayflies they feed on begin to die out at pH 5.5.
There's also the issue of episodic acidification, where water bodies experience high acidity levels periodically. It happens due to melting snow. The episodes can stress the ecosystem, resulting in death or injury to many acid-sensitive organisms.
Dry deposition, at its mildest, will cause eye irritation. Nitrogen oxides, together with hydrocarbon emissions, can cause ground-level ozone. That can set off respiratory health issues like bronchitis, pneumonia, and lung damage.
Sulfur dioxide and nitrogen oxides can also form fine sulfate and nitrate particles easily entering the lungs2. Those particles worsen asthma and increase the risks of lung diseases and heart attacks.
High acidity in wetlands can accelerate the formation of neurotoxic methylmercury. The toxin moves up the food chain from plankton to fish to humans. Acidic water can also leach metals into the home water supply system from the soil, resulting in severe illnesses.
Acid rain, as dry or wet deposition, contributes to water pollution through eutrophication. Normal rain is slightly acidic and contains some nutrients, including nitrogen, but acidic water has even more. Nitrogen pollution leads to excess algae growth, reducing oxygen available to fish and other aquatic animals.
Air pollution and acid deposition are intertwined as they originate from the same sources and follow similar paths. Ground-level ozone formed by oxides of nitrogen and hydrocarbons is one of the most common forms of air pollution.
Particles of nitrogen oxides and sulfur dioxide can cause smog. Smog reduces visibility, making it difficult to enjoy our environment. More importantly, it can adversely affect human health.
Acid rain damage extends to man-made structures, especially marble and limestone ones. Limestone and marble primarily contain calcium carbonate, which dissolves easily with sulfuric and nitric acids.
The dry deposition has a corrosive effect on marble and limestone buildings. It also corrodes metal and paint. Even sheltered stone buildings are unsafe as sulfur dioxide reacts with limestone, causing it to flake off.
Concerning construction, dry deposition does more damage than wet deposition. Damage from acid deposition increases the cost of maintenance due to frequent repairs. Historical monuments, sculptures, and tombstones may also lose fine details.
Winds often carry acidic particles and gases miles away from the points they generate. So, acidic deposition can severely affect even rural areas far from industrial areas.
Furthermore, when acid rain reaches the earth, it enters into water systems, water bodies, and groundwater. That way, the contaminants flow from place to place.
So, whether you live in a bustling city or a countryside village with no factories, acid rain might still affect you.
Therefore, individuals, industry directors, policymakers, and government officials need to work together to drive emission controls. We can do that by reducing our reliance on fossil fuels to generate electricity and looking for clean, renewable energy sources.
There is evidence that proves that measures to reduce polluted air are effective. The EPA implemented several programs to reduce power plant emissions. They include the Acid Rain Program and the Clean Air Interstate Rule.
Those programs have helped reduce sulfur dioxide by 93% and nitrogen oxides by 87%. That, in turn, has resulted in significant decreases in acid rain across the nation. The standard indicator for acid rain, wet sulfate deposition, decreased by 68% in 2019.
Also, the conditions of freshwater ecosystems in the eastern United States have significantly improved.
Despite the giant strides taken to reduce acid deposition, some parts of North America are yet to recover fully. Years of acid precipitation have weakened the capacity of the soil to neutralize acids. Therefore, those regions are susceptible to acid rain damage, even at reduced levels.
You may not be a scientist or have the power to make emission control laws, but you can still do something about acid rain. They include
Acid rain occurs when sulfuric acid and nitric acid mix with atmospheric moisture or dust. It causes an imbalance in the pH of ecosystems, endangering biodiversity and harming human health.
Burning fossil fuels for various energy needs is the major contributor to acid rain. Consequently, a lasting and far-reaching solution would be to reduce or stop fossil fuel consumption.
Jen’s a passionate environmentalist and sustainability expert. With a science degree from Babcock University Jen loves applying her research skills to craft editorial that connects with our global changemaker and readership audiences centered around topics including zero waste, sustainability, climate change, and biodiversity.
Elsewhere Jen’s interests include the role that future technology and data have in helping us solve some of the planet’s biggest challenges.
Fact Checked By:
Isabela Sedano, BEng.