Acid rain and smog formation

PRINCIPLE OF ACID RAIN AND SMOG FORMATION

The term acid rain refers to what scientists call acid deposition. It is caused by airborne acidic pollutants and has highly destructive results.

Scientists first discovered acid rain in 1852, when the English chemist Robert Angus invented the term. From then until now, acid rain has been an issue of intense debate among scientists and policy makers.

Acid rain, one of the most important environmental problems of all, cannot be seen. The invisible gases that cause acid rain usually come from automobiles or coal-burning power plants. Acid rain moves easily, affecting locations far beyond those that let out the pollution. As a result, this global pollution issue causes great debates between countries that fight over polluting each other’s environments. For years, science studies the true causes of acid rain. Some scientists concluded that human production was primarily responsible, while others cited natural causes as well. Recently, more intensive research has been done so that countries have the information they need to prevent acid rain and its dangerous effects.

The levels of acid rain vary from region to region. In third world nations without pollution restrictions, acid rain tends to be very high. In Eastern Europe, china, and the Soviet Union, acid rain levels have also risen greatly. However, because acid rain can move about so easily, the problem is definitely a global one.

HOW DOES ACID RAIN FORMS?

Power stations, factories and cars all burn fuels and therefore they all produce polluting gases. Some of these gases (especially nitrogen oxides and sulphur dioxide) react with the tiny droplets of water in clouds to form sulphuric and nitric acids. The rain from these clouds then falls as very weak acid - which is why it is known as "acid rain".  The release of sulphur dioxide can also occur naturally when a volcano erupts.

Diagram: Exhaust from vehicle as one of the major source of gases implicated in acid rain

Acid deposition primarily results from the transformation of sulphur dioxide (SO₂) and Nitrogen oxides (NO_x) into dry or moist secondary pollutants such as sulphuric acid (H₂SO₄), ammonium nitrate (NH₄NO₃) and nitric acid (HNO₃). The transformation of SO₂ and NO_x to acidic particles and vapours occurs as these pollutants are transported in the atmosphere over distances of hundreds to thousands of kilometers. Acidic particles and vapours are deposited via two processes - wet and dry deposition. Wet deposition is acid rain, the process by which acids with a pH normally below 5.6 are removed from the atmosphere in rain, snow, sleet or hail. Dry deposition takes place when particles such as fly ash, sulphates, nitrates, and gases (such as SO₂ and NO_x), are deposited on, or absorbed onto, surfaces. The gases can then be converted into acids when they contact water.

		Acid rain is mostly caused by the following substances that are released into the atmosphere.
		Chlorofluorocarbons (CFCs): CFCs are the chemicals that are used in industry, refrigeration, air conditioning systems, and consumer products. Whenever CFCs are released into the air, they reduce the stratospheric ozone layer. The stratospheric ozone layer protects Earth’s surface from the harmful rays of the sun.
		Hazardous air pollutants (HAPS): HAPS are released into the air by sources such as chemical plants, dry cleaners, printing plants, and motor vehicles (cars, trucks, buses, and planes). HAPS can cause serious health problems like cancer, birth defects, nervous system problems, and deaths that are all due to people accidentally letting them go into the air.
		Lead: Lead is released by house and car paint as well as the manufacturing of lead batteries, fishing lures, certain parts of bullets, some ceramic ware, water pipes, and fixtures. In young children, lead can cause nervous system damage and learning problems.
		Nitrogen oxides: Nitrogen Oxides are released into the air by burning fuels such as gasoline and coal. When nitrogen oxides combine with VOCs, they can cause breathing difficulty in people who have asthma, coughs in children, and general illness in your respiratory system.
		Ozone: Ozone is released by motor vehicles, industries, burning coal, gasoline, and other fossil fuels, and in the chemicals that are in hairspray and paints. When ozone is close to the ground (ground level ozone) it can cause chest pain, irritated respiratory tract, or persistent cough, can make you unable to take deep breaths, and can make you more likely to get lung infections.
		Particulate matter (PM): PM, little particles of pollution, is released by cars, trucks, and buses that are burning diesel fuel, fertilizers, pesticides, road construction, steel making, mining, and turning on fire places and wood stoves. When PMs mix with air particles and get breathed in by something, they get stuck in the lung tissue. There they can cause increased respiratory disease and lung damage.
		Sulfur dioxides: Sulfur dioxides are released by burning coal, paper production, and melting metal. Sulfur dioxide can harm vegetation, harm metals, and cause lung problems, which include breathing problems and permanent lung damage.
		Carbon dioxide: Carbon dioxide is released by burning coal, oil, and natural gas. If you inhale carbon dioxide, then since it is toxic, it can cause you to have to breathe more than usual, unconsciousness, and other serious health problems.
		Carbon monoxide: Carbon monoxide is released by burning gasoline, oil, and wood. When carbon monoxide enters your body, it goes into the bloodstream. When this happens, it will slow down the delivery of oxygen to the rest of the body, causing dizziness, headaches, and fatigue.
Air Pollutant			% that mobile sources contribute to acid rain	% that other sources contribute to acid rain
Volatile organic compound			37%	63%
Nitrogen oxide			49%	51%
Carbon monoxide			81%	19%
Particulate matter			27%	73%

The table above shows that the biggest air pollutant that mobile sources contribute to acid rain is carbon monoxide. Of all of the carbon monoxide releases that contribute to acid rain, 81% of them come from mobile sources. The biggest other source is particulate matter, little particles of pollution that are released into the air by cars, trucks, and buses that are burning diesel fuel, fertilizers, pesticides, road construction, steel making, mining, and turning on fire places and wood stoves. 73% of the non-mobile sources that contribute to acid rain are caused by the release of particulate matter. The table above shows how much mobile and other sources of pollution can make acid rain more of a problem. Seeing that carbon monoxide and particulate matter are the leading sources of pollution, by cutting down on these, acid rain will not be as much of a problem.

Diagram: causes of acid rain: How Automobile and industrial exhausts get into the atmosphere

THE EFFECTS OF ACID RAIN

The problem of acid rain is rapidly spreading. Because it is mainly caused by industrial processes, automobiles, and power plants, those countries that are developed have the most severe acid rain problems. However, as the underdeveloped nations begin to industrialize, acid rain will increase greatly.

Determining just how much the planted is being hurt by acid rain is very difficult because the ecosystems that it affects are so diverse and complex. Many ecosystems are affected by acid rain. Bodies of water, such as lakes and rivers, see many of their inhabitants die off due to rising acidity levels.

Acidic water also ruins plant nutrients, hurting plants’ ability to survive and to give life to organisms. Human-made products are also experiencing degradation from acid rain. Cars can lose their finishes, and outdoor statues are beginning to rust.

Acid rain’s effects are destructive and long lasting. Though scientists have studied lakes, streams, and many other natural ecosystems to prove its negative effects, acid rain continues to be produced and is increasing in many parts of the world.

o       Effect on the forests of the world

The impact of acid rain on trees ranges from minimal to severe, depending on the region of the country and on the acidity of the rain. Acid rain, acid fog and acid vapour damage the surfaces of leaves and needles, reduce a tree's ability to withstand cold, and inhibit plant germination and reproduction. Consequently, tree vitality and regenerative capability are reduced.

Trees are also harmed by acid rain. In Germany, the forests are believed to be dying because acid rain is harming them. Scientists say that acid rain damages the waxy outer coating that protects the leaves. When this happens, it allows the acid to seep into the tree. Instead of water changing from a liquid to a gas inside the leaves, gas is taking the place of the water. This prevents the plant from taking in carbon dioxide to perform photosynthesis, and the plant will eventually die.

Acid rain, acid fog, and acid vapor also damage forests by damaging the surface of the leaves and needles. This makes it harder for the trees to withstand the cold and will cause the tree to die. Acid rain also harms the soil that the trees are growing in by taking most of the valuable nutrients away from the soil. Acid rain also leaves a lot of aluminum in the soil, which can be harmful to the trees that grow there.

The atmosphere deposits a lot of toxic metals into the forests because acid rain contains metal. Some of these metals are lead, zinc, copper, chromium, and aluminum. When there is acid rain, the rain releases these metals. This is believed to stunt the growth of many trees and plants. This also stunts the growth of mosses, algae, nitrogen-fixing bacteria, and fungi that are needed to help the forest grow. Forests need these because they eat the harmful things that will kill the trees, such as bad bacteria. Acid rain hurts trees because they cannot grow any more.

Acid rain also depletes supplies of important nutrients (e.g. calcium and magnesium) from soils. The loss of these nutrients is known to reduce the health and growth of trees.

Prolonged exposure to acid rain causes forest soils to lose valuable nutrients. It also increases the concentration of aluminum in the soil, which interferes with the uptake of nutrients by the trees. Lack of nutrients causes trees to grow more slowly or to stop growing altogether. More visible damage, such as defoliation, may show up later. Trees exposed to acid rain may also have more difficulty withstanding other stresses, such as drought, disease, insect pests and cold weather.

The ability of forests to withstand acidification depends on the ability of the forest soils to neutralize the acids. This is determined by much the same geological conditions that affect the acidification of lakes. Consequently, the threat to forests is largest in those areas where lakes are also seriously threatened - in central Ontario, southern Quebec, and the Atlantic provinces. These areas receive about twice the level of acid rain that forests can tolerate without long-term damage. Forests in upland areas may also experience damage from acid fog that often forms at higher elevations.

Acid rain is having harmful effects both on people and on the natural ecosystems of the world. Scientists today are convinced that acid rain is severe in many areas, and that it is having an adverse effect on the environments of those locations.

Effect of acid rain on aquatic life

Acid rain is very harmful to the environment. Acid rain damages everything over a period of time because it makes the living things in the environment die. Acid rain affects the life in the water as well as the life on land. It is almost worse in water than on land because the fish that are in the water need the water to breathe. When the water gets polluted, then the fish get sick and end up dying.

All rainwater contains some level of acidity. Acidity is measured by pH, which stands for potential of hydrogen. The pH scale measures the amount of acid in a substance. PH is measured on a scale from 0-14, with 7 being neutral. The lower the number is on the pH scale, the more acidic that substance is. Normal rainwater has a pH of 5.6. When the pH level of rainwater goes below 5.6, it is considered acid rain.

All of the sea life will die when the water that they swim in gets to be too acidic. For example, all fish will die when the water goes below a pH of 4.5. Most of the frogs and insects that live around the water will also die when the water reaches a pH of 4.5. With a pH of 5.5, all of the bottom-dwelling bacterial decomposers, animals that eat the remains of the food that other animals don’t want, will begin to die. When these decomposers die, they leave the un-decomposed food on the bottom of the water. This pollutes the water by making the water dirty for all of the fish to swim in. All fresh water shrimp die when there gets to be a pH of 6.0. Aquatic plants will grow the best when the water is a pH between 7.0 and 9.2. If acid rain gets to be more of a problem, then all of the sea life will eventually be gone.

Some of the lakes that were once acidic are recovering, but many more are not recovering. Of the 202 lakes that were chosen to be studied in the early 1980s; only 33% of them have become less acidic.

Effect of acid rain on our health

Acid rain affects us in many different ways. One major way is our health. Breathing and lung problems in children and adults who have asthma and in children have been linked to acid air pollution. Everything that we eat, drink, and breathe has at one time come in contact with acid deposits. This could threaten our health by making us become sick.

TACKLING THE ACID RAIN MENACE

Modern science has proven that acid rain is a dangerous and highly destructive problem. As a result, various ways to limit acid rain have been invented and some are now being used.

Debate over acid rain and ways of preventing it have raged between environmentalists and corporations. Businesses such as power companies and car makers oppose controlling acid rain because they fear the effects on their profits.

But in some cases, industries have attempted to curb acid rain production. The Northern State Power company began working to reduce acid rain in the 1980s, and has invested over a billion dollars to that end. There are many ways that industries can reduce acid rain production. They can use coal with a low sulphur content, they can remove the sulphur from the smoke their plants release, and they can limit processes known to generate high levels of acid rain.

Policy makers and environmental experts are now looking into the best methods to limit acid rain.

Environmentalists advocate the installation of sulphur cleaning scrubbers in factories, washing sulphur out of coal, and finding new methods of burning coal. Though power plant operators are looking for less expensive solutions to the problem.

Another way that a lot of our pollution is caused is by creating electrical energy. When electricity is created, fuels are usually burned, and this causes the pollution, which causes acid rain. The generation of electric power produces more pollution than any other industry in the United States. Burning coal and other fossil fuels causes most of our pollution. This is why in some places around the world, acid rain is monitored very closely. In 1998, data shows that by using electricity, the pollution that comes with it was responsible for 67% of the sulfur dioxide emissions that caused acid rain that year. Every time that you turn on the lights, that causes the pollution that causes acid rain. Even doing little things that you may think don’t cause pollution sometimes really do.

Individuals can also stop the pollution in many ways. Some of the ways are:

In Your Home

	Only run the dishwasher with a full load
	Only run the washing machine with a full load
	Turn off the lights in empty rooms or when you will be away from home
	Turn off the hot water tank when you will be gone for a long period of time
	Turn down the heat at night and when you will not be home for the night
	Don’t use your air conditioner as much
	Install fluorescent light bulbs instead of incandescent light bulbs
	Try to reduce, reuse, and recycle as often as you can
	Try not to burn a fire as often as you usually do

Transportation

	When you are going to work, you could walk, ride your bike, or take a bus
	Car-pool to a place with someone else
	For alternate fuels, try ethanol, propane, or natural gas
	Take the train or a bus for long trips
	Limit the amount of long trips you take in your car
	Make sure that your vehicle’s air conditioning system isn’t leaking
	Try not to overflow the gas tank

SMOG FORMATION

Modern smog is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine with the primary emissions to form photochemical smog. Smog is also caused by large amounts of coal burning in an area caused by a mixture of smoke, sulfur dioxide and other components.

Coinage of the term "smog" is generally attributed to Dr. Henry Antoine Des Voeux in his 1905 paper, "Fog and Smoke" for a meeting of the Public Health Congress. The July 26, 1905 edition of the London newspaper Daily Graphic quoted Des Voeux, "He said it required no science to see that there was something produced in great cities which was not found in the country, and that was smoky fog, or what was known as 'smog.' The following day the newspaper stated that "Dr. Des Voeux did a public service in coining a new word for the London fog." "Smog" also appears in a January 19, 1893, Los Angeles Times article and is attributed to "a witty English writer.

Smog formation is also attached to the aforementioned gases. SO₂ can react with water vapour and other chemicals in the air to form very fine particles of sulphate. These airborne particles form a key element of smog and are a significant health hazard. Fine particles lodge deep within the lungs and can cause inflammation and tissue damages. Seniors and persons with heart and respiratory diseases are particularly vulnerable. Recent studies show strong links between high levels of airborne sulphate particles and increased hospital admissions and higher death rates.

Urban smog also forms a haze in the air that reduces the visibility of distant objects. The areas that are most affected are the Windsor-Quebec corridor in eastern Canada and British Columbia's Lower Fraser Valley. It also implicated in Nigeria and other developing countries where scenery and buildings are often obscured.

Sulphur dioxide can react with water vapour and other chemicals in the air to form very fine particles of sulphate. These airborne particles form a key component of urban smog and are now recognized as a significant health hazard.

Smog can cause particulate matter (PM) to lodge deep within the lungs, where they cause inflammation and damage to tissues. These particles are particularly dangerous to the elderly and to people with heart and respiratory diseases. Recent studies have identified strong links between high levels of airborne sulphate particles and increased hospital admissions for heart and respiratory problems, increased asthma-symptom days, as well as higher death rates from these ailments.

The air pollution health effects pyramid is a diagrammatic presentation of the relationship between the severity and frequency of health effects, with the mildest and most common effects at the bottom of the pyramid, e.g., symptoms, and the least common but more severe at the top of the pyramid, e.g., premature mortality. The pyramid demonstrates that as severity decreases, the number of people affected increases.

Smog is a serious problem in many cities and continues to harm human health. Ground-level ozone, sulfur dioxide, nitrogen dioxide and carbon monoxide are especially harmful for senior citizens, children, and people with heart and lung conditions such as emphysema, bronchitis, and asthma.^[5] It can inflame breathing passages, decrease the lungs' working capacity, cause shortness of breath, pain when inhaling deeply, wheezing, and coughing. It can cause eye and nose irritation and it dries out the protective membranes of the nose and throat and interferes with the body's ability to fight infection, increasing susceptibility to illness. Hospital admissions and respiratory deaths often increase during periods when ozone levels are high.

The U.S. EPA has developed an Air Quality Index to help explain air pollution levels to the general public. 8 hour average ozone mole fractions of 85 to 104 nmol/mol are described as "Unhealthy for Sensitive Groups", 105 nmol/mol 124 nmol/mol as "unhealthy" and 125 nmol/mol to 404 nmol/mol as "very unhealthy".^[7] The "very unhealthy" range for some other pollutants are: 355 μg m⁻³ - 424 μg m⁻³ for PM10; 15.5 μmol/mol - 30.4 μmol/mol for CO and 0.65 μmol/mol - 1.24 μmol/mol for NO₂.

The Ontario Medical Association announced that smog is responsible for an estimated 9,500 premature deaths in the province each year.

A 20-year American Cancer Society study found that cumulative exposure also increases the likelihood of premature death from a respiratory disease, implying the 8-hour standard may be insufficient.

Areas affected

Beijing air on a day after rain (left) and a smoggy day (right)

Smog can form in almost any climate where industries or cities release large amounts of air pollution, such as smoke or gases. However, it is worse during periods of warmer, sunnier weather when the upper air is warm enough to inhibit vertical circulation. It is especially prevalent in geologic basins encircled by hills or mountains. It often stays for an extended period of time over densely populated cities or urban areas, such as London, Atlanta, Houston, Phoenix, Las Vegas, New Delhi, New York, Cairo, Los Angeles, Sacramento, São Paulo, Mexico City, Santiago of Chile, Toronto, Milan, Athens, Beijing, Shanghai, Manila, Hong Kong, Seoul, the Randstad or Ruhr Area and can build up to dangerous levels.

Curbing the smog menace

Since sulfur dioxide, nitrogen dioxide and carbon monoxide are implicated in smog formation, measures that are recommended above for the prevention of the release of these gases into the atmosphere should be employed.