Smoke is the result of incomplete combustion of the certain
fuels. This means that if most of our common fuels were able to burn
completely, we would have no smoke!
Most fuel consists of carbon, hydrogen, oxygen nitrogen, a
little sulphur, and perhaps some mineral ash. Now if these fuels would burn complete,
the final product would be carbon dioxide, water vapor, and free nitrogen, all
of which are harmless. If sulphur is preset, small quantities of sulphur
dioxide are also given off, and when this comes in contact with air and
moisture, it becomes a corrosive acid.
For complete combustion, a fuel must have enough air for
full oxidation at a high temperature. These conditions are difficult to obtain,
especially with solid fuels, and the result is smoke. Anthracite and coke can
be burned without producing smoke because they have no volatile matter.
But bituminous coals decompose at rather low temperatures so
that gases and tarry matter are freed; they combine with dust and ash and
produce smoke.
The air in any city is full of suspended solid particles,
but not all of this is smoke. It may contain dust, vegetable matter, and other
materials. All of those gradually settle under the force of gravity. In small
towns or suburbs, probably about 75 to 100 tons of these deposits settle down
per square mile during a year. In a big industrial city, the deposits may be 10
times as great!
Smoke can do a great deal of harm. It damages health,
property, and vegetation. In big industrial towns, it lowers the intensity of
the sunshine, especially the ultraviolet rays which are essential to health.
If the wind didn’t spread the smoke, big industrial towns
would probably have fog every day. In fact, where smoky fog occurs, it often happens
that the death rate goes up for lung and heart diseases.
The effect of smoke on vegetation is especially harmful. It
interferes with the “breathing” of plants and screens off needed sunlight.
Quite often, the acid in the smoke destroys plants directly!
Today, many cities are waging active campaigns to cut down
on smoke or to prevent it from doing damage.
