WHAT IS SMOG? Smog is a mixture of air pollutants that form smoke and fog in the air. It is generally formed when ground-level ozone, fine particles, and other chemicals react on hot days. Ozone in the upper atmosphere protects the Earth from the sun's harmful ultraviolet rays, but at ground level, ozone is a highly irritating gas. It forms when two primary pollutants -- nitrogen oxides and volatile organic compounds -- react in sunlight and stagnant air. Most nitrogen oxides come from burning fossil fuels, while VOCs are gases that contain carbon, usually emitted by gasoline fumes and solvents, such as those found in some paints. Airborne particles, sometimes called aerosols, are microscopic particles of pollutants that can remain suspended in the air for a considerable length of time. Primary particles include windblown dust and soil, sea spray, pollen, and plant spores.
ABOUT OZONE: Ozone is a minor constituent in our atmosphere; there are about three molecules of ozone per every 10 million air molecules, and yet it plays a vital role in human health. Most ozone (90%) can be found in an upper layer of the earth's atmosphere called the stratosphere. It is beneficial because it absorbs most of the damaging ultraviolet sunlight, which can cause skin cancers, among other conditions. The remaining 10% of ozone can be found in a lower region called the troposphere. Here, it reacts with other molecules to produce smog, which has toxic effects on crops, forest growth, and human health.
SMOG MAKES BREATHING DIFFICULT: Smog can make breathing difficult and can make human beings more susceptible to cardio-respiratory diseases. People already suffering from heart or lung disease are particularly affected. The two main ingredients in smog that affect human health are ground-level ozone and fine airborne particles.