What's Smog?

pollution, smog, pollutants — Smog was a term originally describing a fusion of smoke and fog.

(Image credit: Viktor Fiker | Dreamstime)

Ever been flying over a major city and noticed that murky brown layer of air hovering below? Well, that’s smog.

The word “smog” is a fusion of “smoke” and “fog,” and was originally used to describe the haze that enshrouded coal-burning London at the turn of the 20th century. The burning of large amounts of coal in an area results in a thick, cloudy mixture of smoke and sulfur dioxide.

Latest Videos From

Watch full video here:

Particulate matter (PM) can be produced naturally (for example, by forest fires) or by burning fossil fuels. When people breathe in particulates, they penetrate into the lungs, but just how far in they go depends on their size. PM 10 (which is 10 micrometers in diameter, or the width of a cotton fiber) cannot penetrate as far as PM 2.5 (2.5 micrometers in diameter). The EPA sets standards for both types of PM. Because particulate matter scatters sunlight, smog also reduces visibility in the skies it pollutes.

Andrea Thompson is an associate editor at Scientific American, where she covers sustainability, energy and the environment. Prior to that, she was a senior writer covering climate science at Climate Central and a reporter and editor at Live Science, where she primarily covered Earth science and the environment. She holds a graduate degree in science health and environmental reporting from New York University, as well as a bachelor of science and and masters of science in atmospheric chemistry from the Georgia Institute of Technology.