Air pollution is caused by solid and liquid particles and certain gases that are suspended in the air. These particles and gases can come from car and truck exhaust factories dust pollen mold spores, volcanoes and wildfires. The solid and liquid particles suspended in our air are called aerosols. Any particle that gets picked up into the air or is formed from chemical reactions in the air can be an aerosol. Many aerosols enter the atmosphere when we burn fossil fuels such as coal and petroleum and wood. These particles can come from many sources including car exhaust factories and even wildfires. Some of the particles and gases come directly from these sources but others form through chemical reactions in the air. Aerosols can come from other places too such as ash from an erupting volcano. Dust pollen from plants and mold spores are also examples of aerosols. Certain gases in the atmosphere can cause air pollution. For example in cities a gas called ozone is a major cause of air pollution. Ozone is also a greenhouse gas that can be both good and bad for our environment. It all depends where it is in Earths atmosphere. Breathing in polluted air can be very bad for our health. Long term exposure to air pollution has been associated with diseases of the heart and lungs cancers and other health problems. That why it important for us to monitor air pollution.