HEALTH EFFECTS:
Smog is a problem in a number of cities and continues to harm human health. Ground-level ozone, sulfur dioxide, nitrogen dioxide and carbon monoxide are especially harmful for senior citizens, children, and people with heart and lung conditions such as emphysema, bronchitis, and asthma. It can inflame breathing passages, decreasing the lungs' working capacity, and causing shortness of breath, pain when inhaling deeply, wheezing, and coughing. It can cause eye and nose irritation and it dries out the protective membranes of the nose and throat and interferes with the body's ability to fight infection, increasing susceptibility to illness. Hospital admissions and respiratory deaths often increase during periods when ozone levels are high.
According to the American Heart Association, chronic exposure to air pollution has been linked to heart disease and stroke. The EPA says that exposure to smog can also affect your immune system's ability to fight off bacterial infections.
(SOURCES: http://en.wikipedia.org/wiki/Smog#Health_effects, http://www.fitsugar.com/235601)
Top 5 places with the most Smog:
1. Mexico City,
Mexico
2. Sao Paulo, Brazil
3. Cairo, Egypt
4. New Delhi, India
5. Shanghai, China