What Is Dust?

Dust consists of tiny particles of solid matter that can be carried in suspension by air. Dust is usually lifted by the wind from the place it originated and is canied along by air currents until it finally settles,because of gravity, or it comes down with rain. Dust is produced by a wide range of conditions. It may come from soil that is being blown about, from th: exhaust of heavy traffic, from the burning of fuel in homes and industry, and from volcanic activity, forest fires, and ocean spray.

You probably never thought of ocean spray as a producer of dust in the air. But did you know that ocean spray produces about 2.000, 000,000tonnes of salt dust in the air each year? After the water has evaporated in the spray, the chemical elements found in salt are left in the air.

We have all heard about "dust storms". These originate in areas where drought has removed natural vegetation. Such storms put thousands of tones of dust into the air, and this dust may end up somewhere as far as 2,000 miles away! For example, during "the great dust storm that hit the South Western part of the United States in 1933, about 25 tonnes of dust per square mile were deposited in New England. Dust from the desert region of the Sahara has been noted to fall in London!
There is always an amazing amount of dust in the air. It is estimated that about 43,000,000 tonnes of dust settles over the United States every year. About 12,000,000 tonnes is due to human activities.
It was air pollution and unusual weather conditions that caused the dreadful London smogs—today, with a system of smoke-controlled areas, this serious health hazard seefcis to have been overcome.