What Is Smog?

The term "smog" was coined in London in 1905 by a member of the Coal Smoke Abatement Society to describe smoke and soot mixed with fog.  Today the term is used informally to describe air that contains a mixture of pollutants that can cause eye irritation and breathing problems. 

The recipe for smog may include ground-level ozone and other materials such as unburned hydrocarbons, oxides of nitrogen, carbon monoxide, sulfur dioxide, ammonia, and particulate matter such as dust, smoke, and droplets of liquid.   Smog's ingredients and levels are constantly changing, as primary pollutants like NOx are released in the morning and converted to ozone by the action of sunlight during the day.

Airborne particles give smog most of its color and affect visibility.  Depending on the type of particles, the air can appear yellowish-brown or even white.  Like ozone, airborne particles can adversely affect plants, plastic, rubber, marble and other materials as well as human health.