1. Baku, Azerbaijan
Surrounded by Iran, Georgia, Russia and Armenia on the Caspian Sea, Azerbaijan has long been an oil hub. As a consequence, Baku, the capital, suffers from life-threatening levels of air pollution emitted from oil drilling and shipping.
2. Dhaka, Bangladesh
Located in southern Asia, between Burma and India, Dhaka, the capital of Bangladesh battles with the constant threat of water pollution. Surface water is often thick with disease and pollutants from the use of commercial pesticides. With an estimated 150 million people living in a relatively small area, cleaning up the problem won't be easy.
Madagascar, located off of the southeastern coast of Africa in the Indian Ocean, makes this year's list with its capital city, Antananarivo. Well known for its variety of unique flora and fauna, Madagascar has often been referred to as the world's eighth continent, but the effects of the human population are quickly leaving their footprint.
4.Port au Prince, Haiti
The country's politically inspired violence and corruption are well documented. Equally dangerous: its air and water. Serving as one of the main ports on the island of Hispaniola, Port au Prince is central to Haiti's economic development. A lack of pollution controls, however, contributes to the widespread environmental problems confronting the Haitian city.
5. Mexico City, Mexico
Mexico City, the capital of Mexico, and the capital of North American air pollution, estimates unhealthy ozone emissions nearly 85% of the year. Mexico's geographical location--in the center of a volcanic crater and surrounded by mountains--only serves to lock in the air pollution, causing smog to sit above the city.