Acid rain is a serious environmental problem around the world, particularly affecting Asia, Europe, and large parts of the U.S. and Canada. The acidic pollutants such as SO2 and NOx are emitted into the environment by combustion of fossil fuels.
Most of the sulfur in any fuel combines with oxygen and forms SO2 in the combustion chamber. This SO2 when emitted into the atmosphere slowly oxidizes to SO3. SO3 is readily soluble in water in the clouds and forms H2SO4 (sulfuric acid).
Most of the NOx that is emitted is in the form of NO. This NO is oxidized in the atmosphere to NO2. NO2 is soluble in water and forms HNO3 (nitric acid).
Sunlight increases the rate of most of the SO2 and NO reactions. The result is a mild solution of sulfuric acid and nitric acid. "Acid rain" is a broad term used to describe several ways that acids fall out of the atmosphere. A more precise term is acid deposition, which has two parts: wet and dry.
Prevailing winds blow the compounds that cause both wet and dry acid deposition across state and national borders, and sometimes over hundreds of miles. Please watch the 1:22 presentation below to learn more about the process of acid deposition.
Acid rain is measured using a pH scale.
pH is a measure of hydrogen ion concentration, which is measured as a negative logarithm. In other words, acids produce hydrogen ions and alkalis produce hydroxyl ions, so pH is the power of a solution to yield hydrogen ions [H+].
The pH scale ranges from 0 to 14 and indicates how acidic or basic a substance is.
The lower a substance's pH, the more acidic it is. Each whole pH value below 7 (the neutral point) is ten times more acidic than the next higher value.
The higher a substance’s pH, the more basic or alkaline it is.
Pure water has a pH of 7.0. Normal rain is slightly acidic because carbon dioxide dissolves into it, so it has a pH of about 5.5. As of the year 2000, the most acidic rain falling in the US has a pH of about 4.3.
Below is a video demonstration that replicates the effect of acid rain on plant life. In this video, beans are placed in: a) water, b) slightly acidic water and c) acidic water, and their growth is observed over a period of three days. Please watch the following 5:35 video:
Acid rain results in many negative consequences. Place your mouse over the image below to see the effects of acid deposition.
Acid rain does not usually kill trees directly. Instead, it is more likely to weaken trees by:
Quite often, injury or death of trees is a result of these effects of acid rain in combination with one or more additional threats. Click on the hot spots in the image below to see the effects of acid rain on the forest:
Acid rain causes acidification of lakes and streams and contributes to damage of trees at high elevations (for example, red spruce trees above 2,000 feet) and many sensitive forest soils. Several regions in the U.S. were identified as containing many of the surface waters sensitive to acidification. They include the:
Some types of plants and animals can handle acidic waters. Others, however, are acid-sensitive and will be lost as the pH declines. View the image of the fish, shellfish, and insects below to see what pH levels they can tolerate:
Acid rain and the dry deposition of acidic particles contribute to the corrosion of metals (such as bronze) and the deterioration of paint and stone (such as marble and limestone). These effects seriously reduce the value to society of buildings, bridges, cultural objects (such as statues, monuments, and tombstones), and cars.
Sulfates and nitrates that form in the atmosphere from sulfur dioxide (SO2) and nitrogen oxides (NOx) emissions contribute to visibility impairment, meaning we can't see as far or as clearly through the air.
Sulfate particles account for 50 to 70 percent of the visibility reduction in the eastern part of the United States, affecting our enjoyment of national parks, such as the Shenandoah and the Great Smoky Mountains.
Through the Acid Rain Program, SO2 reductions will be completed to improve visual range at national parks located in the eastern United States. Based on a study of the value national park visitors place on visibility, these reductions are expected to be worth over a billion dollars annually by the year 2010.
In the western part of the United States, nitrates and carbon also play roles, but sulfates have been implicated as an important source of visibility impairment in many of the Colorado River Plateau national parks, including the Grand Canyon, Canyonlands, and Bryce Canyon.
Acid rain looks, feels, and tastes just like clean rain. The harm to people from acid rain is not direct. Walking in acid rain, or even swimming in an acid lake, is no more dangerous than walking or swimming in clean water. However, the pollutants that cause acid rain also damage human health.
You can do the following to protect the environment:
Ozone (O3) is a triatomic oxygen molecule gas that occurs both in the Earth’s upper atmosphere and at ground level. Ozone can be good or bad, depending on where it is found: It is a bluish gas that is harmful to breathe. Therefore, it is bad at the ground level.
The presentation below shows the process of ozone depletion. Ozone depletion is caused by chlorofluorocarbons (CFCs) and other ozone-depleting substances. Please watch the following 1:16 video.
Ozone is constantly produced and destroyed in a natural cycle, as shown in the figure below. However, the overall amount of ozone is essentially stable. This balance can be thought of as a stream's depth at a particular location. Although individual water molecules are moving past the observer, the total depth remains constant. Similarly, while ozone production and destruction are balanced, ozone levels remain stable. This was the situation until the past several decades. Please watch the following 1:32 video about ozone destruction.
Large increases in stratospheric chlorine and bromine, however, have upset the balance of the Ozone. In effect, they have added a siphon downstream, removing ozone faster than natural ozone creation reactions can keep up. Therefore, ozone levels fall.
Since ozone filters out harmful UVB radiation, less ozone means higher UVB levels at the surface. The more the ozone is depleted, the larger will be the increase in incoming UVB radiation. UVB has been linked to:
Although some UVB reaches the surface even without ozone depletion, its harmful effects will increase as a result of this problem.
Ozone-Depleting Substance(s) (ODS) are:
Recent studies by NASA and others have indicated that about 40 percent of the ozone in the Antarctica has been destroyed and that about 7 percent of ozone is destroyed from the Arctic Circle. The destruction of ozone is also called “Ozone Hole."
Ozone hole does not mean that there is no ozone in the region. The ozone hole is defined as the area having less than 220 dobson units (DU) of ozone (concentration) in the overhead column (i.e., between the ground and space).
The image below shows the reduction in ozone concentration over Antarctica. This hole in the Antarctica is unfortunately allowing more Australians to be exposed to UV radiation. However, if this kind of ozone destruction ever takes place in the Arctic zone, more humans (in the Northern Hemisphere) would be exposed to higher levels of UVB radiation.
A Dobson Unit is the measure of the amount or thickness of ozone in the atmosphere. It is based on a measurement taken directly above a specific point on the Earth's surface. One Dobson unit refers to a layer of ozone that would be 0.001 cm thick under conditions of standard temperature (0 degree C) and pressure (the average pressure at the surface of the Earth). The Dobson unit was named after G.M.B. Dobson, who was a researcher at Oxford University in the 1920s. He built the first instrument (now called the Dobson meter) to measure total ozone from the ground.
The size of the Southern Hemisphere ozone hole as a function of the year is shown in the figure below. The graph compares the size of the hole over a twenty-year period, from 1980 to 2010. It can be seen that the size increased each year. Each year, in the spring, the ozone hole is at its largest.
Effects of ozone depletion can result in 1) increased cases of skin cancer, 2) skin damage, 3) cataracts and other eye damage, and 4) immune suppression.
The incidence of skin cancer in the United States has reached epidemic proportions. One in five Americans will develop skin cancer in their lifetime, and one American dies every hour from this devastating disease.
Medical research is helping us understand the causes and effects of skin cancer. Many health and education groups are working to reduce the incidence of this disease, of which 1.3 million cases have been predicted for 2000 alone, according to The American Cancer Society. The figure below shows the sources of ozone depleting substances.
Melanoma, the most serious form of skin cancer, is also one of the fastest growing types of cancer in the United States. Many dermatologists believe there may be a link between childhood sunburns and melanoma later in life. Melanoma cases in this country have more than doubled in the past 2 decades, and the rise is expected to continue.
Nonmelanoma skin cancers are less deadly than melanomas. Nevertheless, left untreated, they can spread, causing disfigurement and more serious health problems. More than 1.2 million Americans will develop nonmelanoma skin cancer in 2000 while more than 1,900 will die from the disease. There are two primary types of nonmelanoma skin cancers.
These two cancers have a cure rate as high as 95 percent if detected and treated early. The key is to watch for signs and seek medical treatment.
Other UV-related skin disorders include actinic keratoses and premature aging of the skin.
Protect yourself against sunburn. Minimize sun exposure during midday hours (10 am to 4 pm). Wear sunglasses, a hat with a wide brim, and protective clothing with a tight weave. Use a broad spectrum sunscreen with a sun protection factor (SPF) of at least 15. To be safer, 30 is better.
Cataracts are a form of eye damage in which a loss of transparency in the lens of the eye clouds vision. If left untreated, cataracts can lead to blindness. Research has shown that UV radiation increases the likelihood of certain cataracts. Although curable with modern eye surgery, cataracts diminish the eyesight of millions of Americans and cost billions of dollars in medical care each year.
Instructions: Place your mouse over the image below to see the effect cataracts can have on vision. (Note: This video has no audio.)
Other kinds of eye damage include pterygium (i.e., tissue growth that can block vision), skin cancer around the eyes, and degeneration of the macula (i.e., the part of the retina where visual perception is most acute). All of these problems can be lessened with proper eye protection from UV radiation.
Scientists have found that overexposure to UV radiation may suppress proper functioning of the body's immune system and the skin's natural defenses. All people, regardless of skin color, might be vulnerable to effects including impaired response to immunizations, increased sensitivity to sunlight, and reactions to certain medications.
Your “Power” in Protecting the Environment from Ozone Depletion
In 1987, the Montreal Protocol, an international environmental agreement, established requirements that began the worldwide phase out of ozone-depleting CFCs (chlorofluorocarbons). These requirements were later modified, leading to the phase out in 1996 of CFC production in all developed nations.
Ozone is a secondary pollutant that forms from the primary pollutants such as Volatile Organic Compounds (Hydrocarbons) and nitrogen oxides (NOx) in the presence of sunlight. Its formation is mainly from the automobile emissions.
Below is a demonstration on how ozone forms at the ground level (note ground level ozone is also known as “bad” ozone). Please watch the following 5:29 video:
As previously mentioned, the formation of ozone is mainly from automobile emission. A typical profile of pollutants in the air of major cities is well repeatable and is shown in the figure below. Note how the formation changes over the course of a day:
Ozone, by itself, is damaging to health and also to the environment. Ozone triggers a variety of health problems even at very low levels and may cause permanent lung damage after long-term exposure. Ozone also leads to the formation of smog or haze, causing additional problems such as a decrease in visibility as well as damage to plants and ecosystems.
As we have learned, volatile Organic Compounds (Hydrocarbons) combine with nitrogen oxides (NOx) in the presence of sunlight to form ozone.
In turn, sunlight and hot weather cause ground-level ozone to form in harmful concentrations in the air. As a result, it is known as a summertime air pollutant.
Many urban areas tend to have high levels of "bad" ozone, but even rural areas are also subject to increased ozone levels because wind carries ozone and pollutants that form it hundreds of miles away from their original sources.
View the graph below to compare the major sources of NOx and VOC that help to form ozone.
Several groups of people are particularly sensitive to ozone—especially when they are active outdoors—because physical activity causes people to breathe faster and more deeply. In general, as concentrations of ground-level ozone increase, more and more people experience health effects, the effects become more serious, and more people are admitted to the hospital for respiratory problems. When ozone levels are very high, everyone should be concerned about ozone exposure.
Click on the hotspots in the image below to find out what you can do to protect the environment.
Links
[1] http://www.flickr.com/photos/mafleen/292293822/lightbox/
[2] http://www.flickr.com/photos/mafleen/
[3] http://creativecommons.org/licenses/by-nc-sa/2.0/
[4] http://www.flickr.com/photos/goldyohio/5110977636/lightbox/
[5] http://www.flickr.com/photos/goldyohio/
[6] http://www.flickr.com/photos/39544517@N08/4677323288/lightbox/
[7] http://www.flickr.com/photos/39544517@N08/
[8] http://creativecommons.org/licenses/by-nc/2.0/
[9] http://www.epa.gov/ozone/science/process.html
[10] http://ozonewatch.gsfc.nasa.gov/
[11] http://www.nasa.gov/
[12] https://cfpub.epa.gov/airnow/index.cfm?action=ozone_health.index