In the city, air pollution may be caused by cars, buses and airplanes, as well as industry and construction. Air pollution in the country may be caused by dust from tractors plowing fields, trucks and cars driving on dirt or gravel roads, rock quarries and smoke from wood and crop fires. Ground-level ozone is the major part of air pollution in most cities. Ground-level ozone is created when engine and fuel gases already released into the air interact in the presence of sunlight. Ozone levels increase in cities when the air is still and the sun is bright and the temperature is warm.
Air pollution can irritate the eyes, throat and lungs.
Burning eyes, cough and chest tightness are common with exposure to high levels of air pollutants. However, responses to air pollution vary greatly in people. Some people may notice chest tightness or cough, while others may not notice any effects. Because exercise requires faster, deeper breathing, it may increase the symptoms. People with heart disease, such as angina, or with lung disease, such as asthma or emphysema, may be very sensitive to exposure to air pollution and may notice symptoms when others do not.