James Westphal, age 7, of Waukee, Iowa, for his question:

WHAT IS SMOKE?

You'll find smoke when finely divided solid particles become suspended or mixed in a gas. It is usually caused by particles of carbon from the burning of fuels.

A mixture of fog and smoke is called smog. Smoke and smog is bad for the health and most dangerous when a weather condition called an inversion traps a lot of it in the air we breathe.

Smoke causes large economic losses by blackening buildings, corroding metals and damaging plants. It.has been estimated that the annual loss because of smoke in the United States is about $1 billion.

Not all smoke is bad. Colored smoke is used in military signals. And controlled smoke is used to cure certain meats. Also, a smoke called smudge is used in some orchards during the winter to prevent freezing of fruit.