Environmental Implications of a Massive Oil Spill and

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would enter the mixed layer of the atmosphere (between ground level and
3,000 to 5,000 feet altitude1 over arid areas). There is a natural lid on the
spread of these constituents to higher altitudes; the height range of 3,000 to
5,000 feet is a rough average that would be modified by both meteorology
and geography. Particles in the mixed layer would generally stay there for
a few days (perhaps as long as a week, and depending on whether or not it
rains) before depositing to the ground, and hence the areas affected would
not be very large.

In the daytime, heating by the sun would cause the plume to be mixed
fairly rapidly -* the rising plume would drop back to ground level within a
few miles. At night, there might well be clear space underneath the plume;
immediately downwind areas would not be greatly influenced. Under these
conditions, the highest surface concentrations would be observed in the
early morning, when the elevated plume is first mixed to the ground.

If the fire were large and energetic enough, or during stormy periods, the
plume could rise through the mixed layer into the "free troposphere
(between 5,000 and about 30,000 feet altitude). The plume would then
meander for a period of weeks, becoming striated but retaining its visible
identity for perhaps a thousand miles or more. At such long ranges,
however, the plume would be widely spread and quite diluted.

It does not appear possible for a fire of this kind to generate enough energy
to inject particles into the stratosphere (above 39,000 feet) unless aided by
severe storms. Storms of sufficient intensity to cause this effect occur near
the equator, but not at Middle Eastern latitiides. bth~er than by intense
equatorial storms, stratospheric injection of surface material occurs only
with the most vigorous volcanic eruptions (such as those of Mt. Agung, el
Chichon, M~ Redoubt, etc.) and with such events as atmospheric-tests of
nuclear weapons. Even nuclear explosions are not always energetic enough
to penetrate into the stratosphere.

In conclusion, it would be likely that the pfume would be confmed to the
mixed layer and the free troposphere. The plume might be detectable for a
thousand miles or more depending on the size and intensity of the fire.
Effects on sunsets and sunrises might be evident for several thousand miles.
Over the intervening distance, the plume would slowly disperse into the
surrounding air, large particles would soon fall out and the plume's visible
identity would slowly be lost. The residence time of particles in the free
troposphere is such that long-term accumulations beyond one or two weeks


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