Facts About Smog

The word "smog" is a combination of the words "smoke" and "fog." It originally referred strictly to a combination of exactly those two things. Nowadays, however, the word "smog" refers more loosely to any mixture of air pollutants, including gas and fine particles, that congregate in the air, usually around populated areas. Smog can cause health problems and is a serious environmental issue.

Causes

• Traditionally smog came from the smoke produced by burning coal in factories and house stoves. That is what caused the smog that Victorian London was infamous for. In modern times, smog is "photochemical air pollution" caused by the burning of fuel in factories and power plants (as well as other industrial production), and using volatile substances such as gasoline and paint, which release light-blocking chemicals into the atmosphere.

Components

• One of the two main components of smog is particulate matter. Tiny particles, so small and light that they float in the air, are what give smog its brownish, gray, or white color. The particulates come from motor vehicle exhaust and factory emissions. They are smaller than 10 micrometers, and some are as fine as 2.5 micrometers. When those particles are warmed by sunlight, vapors are released, creating the other main component of smog, "ground-level ozone."

Smog in the U.S.

• In the United States, most of the worst cities for smog are in California, including Los Angeles, Bakersfield, Fresno, and Sacramento. Outside of California, other U.S. cities on the high-smog list include Birmingham, AL; Salt Lake City; Detroit; Chicago; Cleveland; Houston; and Dallas. Pittsburgh tops the list for short-term particle pollution.

  Title 42, Chapter 85 of the United States Code, created with the Clean Air Act of 1970, regulates emissions for airplanes, motor vehicles and industries in part to curb smog.

Smog Around the Globe

• Around the world, many of the worst cities for smog are also, obviously, the most populous. Many of them are in China, including Beijing, Hong Kong, and Shanghai. Other smoggy cities in the world include: Mexico City, Mexico; Kabul, Afghanistan; Tehran, Iran; Sao Paulo, Brazil; Cairo, Egypt; Athens, Greece; Dhaka, Bangladesh; and New Dehli, India.

  Smog is more than just an eyesore. In Tehran, 1,600 people were hospitalized for exposure during one particularly bad day, Dec. 10, 2005.

Health Effects

• Acute symptoms of adverse smog exposure include irritation to the eyes, nose and throat. The eyes may become red and watery. The nose may itch or run. The throat may become parched and scratchy. Long-term exposure may worsen existing heart and lung conditions, and in the worst cases may shorten one's life span. Smog is thought to be one of the causes of lung cancer. People are advised to stay indoors on high smog days.