Air pollution is defined as contaminants in the air that can harm human health, animals, plants or property. Nitrogen oxides are common air pollutants that can irritate lungs and damage lung tissue with both short and long term exposure. They also harm vegetation and materials. Sulfur dioxide is another common pollutant emitted from coal burning. It irritates the respiratory system and harms plants. Ozone acts as a powerful respiratory irritant that can lead to shortness of breath, chest pain and wheezing.