Q: What exactly is haze?

A: Haze is usually defined as fine particles of dust or smoke that are dispersed through portions of the atmosphere, says Brent McRoberts of Texas A&M University. "These particles are so small that they cannot be felt or seen individually with the naked eye," he explains. "These particles tend to decrease visibility in the area, and because of the way they refract light, can give a tint to the sky that can appear as brown, green, grey or other colors. Under stagnant air conditions, the air can be trapped in valleys or canyons and produce a layer of haze that can stretch for miles."

Q: Where can haze occur?

A: Just about anywhere, and in recent years, some of the worst cases have occurred in Latin American and in Southeast Asia, McRoberts says. "Forest fires and brush fires in some areas of the world produce hazy conditions that can be seen from space. The thick smoke can wander over huge portions of the Earth, including parts of the United States. Because haze is basically bad air, it can be very hazardous to human health, especially to people who have difficulty breathing. Long-term exposure can produce lung and eye diseases and that's why a concerted effort has been made to make sure that logging companies and others are aware of the risks associated with haze," he points out.

Weather Whys is a service of the Department of Atmospheric Sciences at Texas A&M University.

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