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Many of the world's large cities today have bad air quality. Even 2,000 years ago, the Romans were complaining about the bad air in their cities. At that time, the air was thick with smoke from fires and the smell of sewers. Air pollution has been a danger to human health and Earth's many ecosystems for a long time.
Even "clean" air is not really clean. It has many pollutants (things that pollute the air) from natural sources. These pollutants include dust, sea salt, volcanic ashes and gases, smoke from forest fires, pollen, and many other materials. In fact, there are many more natural pollutants than pollutants that humans make. However, humans have adapted to most of these natural pollutants.
Types of air pollution
Air pollutions are usually described as either primary pollutants or secondary pollutants. Primary pollutants are pollutants that are put directly into the air by humans or natural sources. Examples of primary pollutants are exhaust fumes (gas) from cars, soot from smoke, dust storms and ash from volcanic eruptions (as seen in the picture on the left).
Secondary pollutants are pollutants that are made from chemical reactions when pollutants mix with other primary pollutants or natural substances like water vapor. Many secondary pollutants are made when a primary pollutant reacts with sunlight. Ozone and smog are secondary pollutants. Ozone is a gas that is helpful and takes in harmful rays from the sun. When it is near the ground, though, ozone is a dangerous pollutant that influences the health of all organisms.
Sources of human-made air pollution
Human-made air pollution comes from many things. Most air pollution made by humans today is because of transportation. Cars, for instance, make about 60% of the human-made air pollution. The gases inside car exhaust, like nitrogen oxide, make smog and acid rain.
Industrial air pollution
Many industrial power plants burn fossil fuels to get their energy. However, burning fossil fuels can make a lot of oxides (chemical compounds that have oxygen and other elements inside). In fact, the burning of fossil fuels makes 96% of the sulfur oxides in the atmosphere. Some industries also make chemicals that make poisonous fumes (smoke).
Indoor air pollution
Air pollution is not only on the outside. Homes, schools, and buildings can also have air pollution. Sometimes the air inside a building is even worse than the air outside. Many things which humans use every day can pollute the air. Compounds inside carpets, paints, building materials and furniture also pollute the air, especially when they are new.
In buildings where the windows are tightly shut to stop air leaks, the air inside can be polluted more than the air outside.
Air pollution is a problem everywhere in the world. Local air pollution usually affects big cities. Air pollution becomes a worldwide problem when local pollution moves away from where it came from. For example, winds carry air pollution made in the middle of the western part of the United States to Canada, like acid precipitation.
Acid precipitation is precipitation, like rain, sleet, or snow, that contains acids from air pollution. When fossil fuels are burned, they let out oxides into the air. When these oxides mix with water in the atmosphere, they make acid, which fall as precipitation. Acid precipitation can kill living things, like fish and trees, by making the place where they live too acidic. Acid rain can also damage buildings made of limestone and concrete.
Other global concerns because of air pollution include the greenhouse gases and the hole in the ozone layer in the stratosphere. The Earth's ozone layer is supposed to protect people from the Sun's harmful ultraviolet rays, but in the 1970s, scientists found out that some chemicals let out into the atmosphere makes the ozone turn into oxygen, which means that more ultraviolet rays reach the Earth. During the 1980s, scientists found that the ozone layer above the South Pole had thinned by 50 to 98 percent.
On March 17, 1992, in Mexico City, all children under the age of 14 could not go to school because of air pollution. This does not often happen, but being exposed to air pollution every day can make people have many health problems. Children, elderly (old) people, and people with allergies especially, can have a lot of problems because of air pollution. Studies from the University of Birmingham showed that deaths because of pneumonia and air pollution from motor vehicles like cars are related.
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- Air quality science and general information
- UNEP Urban Issues
- European Commission > Environment > Policies > Air >Air Quality.
- UNEP Partnership for Clean Fuels and Vehicles
- Air quality modelling
- Stuff in the air Standard air quality modelling procedure for industrial sources.
- Wiki on Atmospheric Dispersion Modelling. Addresses the international community of atmospheric dispersion modellers — primarily researchers, but also users of models. Its purpose is to pool experiences gained by dispersion modellers during their work.
- Air Dispersion Modeling Conversions and Formulas One of six technical articles devoted to air quality and air pollution dispersion modeling.
- Effects on human health