Air pollution!!!

Some quick facts about air pollution that I know:
Causes acid rain.
Many huge cities that have smog are cities with large factories and industries such as Newark, NJ, NYC, LA, and others.
Air pollution is mainly caused by human activity such as using cars, electricity or anything that has to deal with carbon emissions.
Air pollution was first founded my Leonardo Da Vinci in the 15th Century,blue haze from trees.
The 1952 London Smog crisis was when air pollution became a more dominant problem.

Facts that I didn't know:

Long-term health effects can include chronic respiratory disease, lung cancer, heart disease, and even damage to the brain, nerves, liver, or kidneys. Continual exposure to air pollution affects the lungs of growing children and may aggravate or complicate medical conditions in the elderly. It is estimated that half a million people die prematurely every year in the United States as a result of smoking cigarettes.
http://www.lbl.gov/Education/ELSI/pollution-main.html

The U.S. is responsible for more green house gas pollution than South America, Africa, the Middle East, Japan and Asia – all put together. http://environment.nationalgeographic.com/environment/global-warming/pollution-overview.html