Page 118 - Fundamentals of Air Pollution

88 6. Sources of Air Pollution

TABLE 6-3
Changes in Steel-Making Processes in the United States
Production by specific process (%)
Basic oxygen
Year Bessemer Open hearth Electric furnace Total
1920 21 78 1 0 100
1940 6 92 2 0 100
1960 2 89 7 2 too
1970 1 36 14 48 100
1980 1 22 31 46 100
1990 0 4 37 59 100

possible, but the cost of the control may be prohibitive for the small foundry
which only has one or two heats per week.
2. Nonferrous Metals
Around the turn of the century, one of the most obvious effects of
industry on the environment was the complete destruction of vegetation
downwind from copper, lead, and zinc smelters. This problem was caused
by the smelting of the metallic sulfide ores. As the metal was released in
the smelting process, huge quantities of sulfur were oxidized to SO 2 , which
was toxic to much of the vegetation fumigated by the plume. Present
smelting systems go to great expense to prevent the uncontrolled release
of SO 2 , but in many areas the recovery of the ecosystem will take years
and possibly centuries.
Early aluminum reduction plants were responsible for air pollution be-
cause of the fluoride emissions from their operations. Fluoride emissions
can cause severe damage to vegetation and to animals feeding on such
vegetation. The end result was an area surrounding the plant devoid of
vegetation. Such scenes are reminiscent of those downwind from some of
the uncontrolled copper smelters. New aluminum reduction plants are
going to considerable expense to control fluoride emissions. Some of the
older plants are finding that the cost of control will exceed the original
capital investment in the entire facility. Where the problem is serious,
control agencies have developed extensive sampling networks to monitor
emissions from the plant of concern.
Emissions from other nonferrous metal facilities are primarily metal
fumes or metal oxides of extremely small diameter. Zinc oxide fumes vary
from 0.03 to 0.3 /am and are toxic. Lead and lead oxide fumes are extremely
toxic and have been extensively studied. Arsenic, cadmium, bismuth, and
other trace metals can be emitted from many metallurgical processes.