Most major air pollutants are invisible, although large amounts of them concentrated in areas such as cities can be seen as smog. One often visible air pollutant is particulate matter, especially when the surfaces of buildings and other structures have been exposed to it for long periods of time or when it is present in large amounts. Natural sources include volcanic ash, pollen, and dust blown by the wind. Coal and oil burned by power plants and industries and diesel fuel burned by many vehicles are the chief sources of man-made particulate pollutants, but not all important sources are large scale. The use of wood in fireplaces and wood-burning stoves also produces significant amounts of particulate matter in localized areas, although the total amounts are much smaller than those from vehicles, power plants, and industries.
Wind can carry pollutants hundreds of miles from their origin.
The distance air pollutants travel depends on how high in the atmosphere they go. If the pollutants don't rise very high, they are deposited close to their source. However, pollutants that are lifted high into the atmosphere may travel thousands of miles before they drop back to Earth. By tracing the movement of radiation released during the accident at the Chernobyl nuclear power plant, students will see how air pollution, like particulate matter, can become a global issue. Students may work individually or in groups.