About 800 years ago, King Edward I of England (1272 - 1307) imposed a death penalty on anyone found burning coal (the high sulfur type), because it created noxious fumes and an "intolerable smell." During Queen Elizabeth I's (1558 - 1603) reign, she created laws to stop people from burning coal in London, but coal was so cheap that no one paid much attention. In the 17th century, John Evelyn wrote two books about pollution (about smoke pollution in London and about plans to save woodlands).

Serious problems started in the 1800s with the coal-burning factories of the Industrial Revolution era. During this time, much home-based hand manufacturing shifted to large-scale factory production. One consequence was a great increase in pollution emitted into our skies (see Figure 2). The introduction of motor vehicles in the 1900s increased atmospheric pollution greatly.

Figure 2. Modern day industrial air pollution. click for copyright

In the 1970s, the U.S. passed legislation to curb sources of air pollution and set standards for air quality. In 1987, more than 20 nations signed an agreement to limit CFC (chlorofluorocarbon) production and work towards eliminating them altogether. In 1989, major car manufacturers and oil companies funded a $40 million research study to help find ways to reduce emissions. In 1990, Congress passed the Clean Air Act, which requires industry and individuals to take additional steps to clean the air in our cities.

Clean air contains only the gases and water vapor needed to keep the Earth's environment healthy. Pollutants are substances, or even energy, that contaminate our air and harm living things (and some non-living ones, too). A high concentration of pollutants in the air is called air pollution.

There are literally hundreds of pollutants that float around in the air that we breathe. Some come from natural sources, but most come from human activity. Air pollutants consist of numerous particulates, fibers, mists, molds, bacteria and gases. They can be found outdoors and indoors. Climatic conditions and emission sources dictate the magnitude and variety of air pollutants found outdoors. Most major air pollutants are invisible, but large amounts of them can be seen as smog when they are concentrated in areas such as cities. (See Air Pollution Unit, Lessons 2 and 3, for details about visible and invisible air pollutants.)

Indoor air pollution is becoming a large concern for environmental engineers because the majority of the public's time is spent indoors. Indoor air pollutants include: pesticides, dust, fibers, furnishings, radon, fungi, chemicals, cleaning supplies and animal dander. (Refer to Air Pollution Unit, Lesson 9, for more information.)

Some people also consider sound pollution a type of air pollution because sound waves travel through the air. Outdoor sources include loud jet engines, construction equipment, huge trucks and other forms of transportation, etc. Indoor sources include music, TVs, mixers, dishwashers, washing machines, etc. Bright outdoor lights are also considered a source of air pollution, especially to astronomers.

Outdoor Sources — The burning of fossil fuels is one of the main causes of air pollution. Smoke and fumes containing carbon dioxide and sulfur dioxide from power stations and factories are the worst offenders. Car exhaust is another primary source of air pollution. It contains both invisible gases (carbon dioxide, carbon monoxide, hydrocarbons and nitrogen oxides) and particles. Many consumer products (hair spray, paint, cleaners) release high levels of volatile organic compounds (VOCs) into the atmosphere. Other substantial sources of outdoor air pollution include gas stations, industry, agriculture and forestry.

Volcanic eruptions, a natural outdoor source of air pollution, often spew gases and ash into the atmosphere. Forest fires also release dust and smoke into the air.

Indoor Sources — Indoor air pollutants can be created within a building or drawn inside from outdoor sources. Indoor sources include: foundations, equipment (malfunctioning HVAC systems, emissions from office equipment/labs), furnishings (new carpet that releases formaldehyde and burnt Teflon pans), dust-producing or water-damaged materials, unsanitary trash emissions, insects and pests, food preparation areas, cleaning materials, pets and people (smoking). Some of the most common outdoor air pollutants that are brought inside are: smog, bacteria and mold spores, vehicle exhaust, exhaust fumes, pollen and dust, algae (from standing water) and smoke.

The cumulative effect of air pollution destroys our environment and poses health threats to humans and other living organisms. Air pollution can make people sick, make things dirty, damage buildings and our ecosystem, change the weather, trap heat and make the air warmer than it should be, chew holes in the atmosphere and mix with clouds to form poisonous acid rain.

Air pollutants may cause a variety of adverse human health effects ranging from minor (rashes, eye/nose irritation, headaches, fatigue, shortness of breath, coughing, sneezing and dizziness) to major effects (cancer, breathing complications/asthma, kidney failure, liver damage and birth defects). The degree of the health effects depends on the magnitude and frequency of exposure to the pollutants.

Environmental effects are also numerous. For example, sulfur dioxide emissions combine with water particles and fall to the Earth in the form of acid rain or snow. This destroys the food and nutrients for fish and other aquatic life in oceans, lakes and streams. It damages trees, other plants and even some buildings. CFCs transform and destroy the ozone layer, which increases the Earth's exposure to ultraviolet radiation and can cause crop failures, skin cancer and other environmental/health disasters.

The water cycle usually cleans the air of pollutants naturally. Currently, however, there are two problems with this: the water cycle is unable to clean contaminants as quickly as they are added, and high concentrations of pollutants contribute to acid rain (see Figure 3).

Figure 3. The air pollution cycle. Pollution enters the water cycle and contaminates our natural resources. click for copyright

How do we get people to keep the air clean? The government passes strict legislation to control the amount of by-products released by industrial companies and modes of transportation. These air quality standards are designed to protect the health and welfare of people, plants and animals, and protect structures, monuments, water resources, etc. The U.S. Environmental Protection Agency (EPA) set national standards for six specific air pollutants that tend to reach unsafe levels. These six pollutants are: carbon monoxide (from vehicles), nitrogen oxides (from power plants), lead (from metal refineries), sulfur dioxide (from coal-burning power plants), particulate matter and tropospheric (low-level) ozone (not to be confused with upper-level ozone — also called stratospheric ozone — which helps filter out harmful rays from the sun).

On a more personal level, adjustments can be made to help improve the air. For example, one can reduce fuel use by joining a car pool, taking the bus/train, riding a bike or walking. In general, reducing energy use (especially in our homes) can be an important contribution to improving air quality. Also, some people choose to buy and use more environmentally-friendly products such as non-aerosol hair spray and non-toxic cleansers.

Oxygen is a colorless, tasteless and odorless gas that forms about 21% of the Earth's atmosphere. All living things need the oxygen in the air to survive. Without the oxygen gas available in non-polluted air, the Earth would not have any living organisms.

Humans cannot live without oxygen for more than a few minutes. Because air is essential to our survival, our bodies are constantly interacting with it. Air enters our bodies through our mouths and noses. Inhalation is the process of breathing air through the mouth and nose into our lungs. Once air enters the lungs, cells take the oxygen from the air and distribute it throughout the body. Once the cells have finished with the oxygen, our body exhales and pushes out the remaining air (and the carbon dioxide by-product) from our lungs.

Air supports other biological activities as well. Air allows us to hear (objects move the air around them and these air waves cause our eardrum to vibrate). Air allows us to see (light travels through air very quickly). Air allows us to smell (carries tiny particles that make up odors).

Air is also necessary in many non-biological activities. Air helps distribute heat and water around the world. We can tell that air is at work when objects (leaves, branches, flags, clouds) are moving, and when thunder is crashing. There are many other objects that rely on air to move, too. An airplane uses air to help it take off from the runway, a bird needs it to fly, a sailboat needs it to move in the water, and a hot air balloon uses it to rise off the ground. Other uses for air include heating and cooling, recreation, energy and pollination.

What will the world be like if we do not develop some solutions to our air pollution problems? Even today, if people travel to places where there is not as much oxygen/air (tops of mountains, underwater) or no air at all (space) they must take air with them. This could become an everyday experience if we continue to neglect and mistreat this essential natural resource.

Read more about air pollution in the attached Air Pollution Reading and Health Effects Reading.

• Mexico City is one of the world's most polluted cities. When pollution is really bad, birds have been known to drop dead out of the sky.
• Every day, each of the world's 11 billion cattle gives off one pound of methane (produced in their gut as they digest food). How much methane is produced every year? (Answer: 274 billion pounds or 137 million tons.) Methane is also produced in large quantities by rotting vegetation in landfills.
• The average person takes about 20,000 breaths a day.
• Even though plants make oxygen, which is essential to live, people have destroyed almost two-thirds of the original forests on Earth.