by Pamela Meyer et al.

About the author: Pamela Meyer is an epidemiologist working for the air pollution and respiratory health branch of the National Center for Environmental Health in Atlanta, Georgia.

In the course of a day, we breathe 5,000 to 15,000 liters of air. With each breath, we inhale life-sustaining oxygen, which is absorbed in our lungs and carried throughout our body. Air also contains pollutants, including pollen, microbes, particles such as soot and dust, and gases such as carbon monoxide— substances that can harm the human body. Contact with these harmful substances, which are filtered through the lungs and can also irritate the eyes and skin, triggers several defense mechanisms such as coughing, sneezing, and the production of secretions. When these defense mechanisms are overwhelmed, human tissue is damaged or destroyed. Chronic or severe exposure...