Environmental Engineering Reference
In-Depth Information
research to be a consequence of the industrial production of chlorofluorocarbons. (By international
treaty, these chemicals are being replaced by less harmful ones, and the stratospheric ozone destruc-
tion will eventually be reduced.) But the more ominous global pollutants are infrared-absorbing
molecules, principally carbon dioxide but including nitrous oxide and methane, that are inexorably
accumulating in the atmosphere and promising to disturb the earth's thermal radiation equilibrium
with the sun and outer space. It is currently believed by most scientists that this disequilibrium
will cause the average atmospheric surface temperature to rise, with probable adverse climatic
consequences. Because carbon dioxide is formed ineluctibly in the combustion of fossil fuels that
produce much of current and expected future energy use, and is known to accumulate in the atmo-
sphere for centuries, its continued emission into the atmosphere presents a problem that cannot be
managed except on a global scale. It is a problem whose control would greatly affect the future
course of energy use for centuries to come.
1.3.1
Managing Industrial Pollution
To address the problem of a deteriorating environment, industrialized nations have undertaken
to regulate the emission of pollutants into the natural environment, whether it be air, water, or
land. The concept that underlies government control is that the concentration of pollutants in the
environment must be kept below a level that will assure no harmful effects in humans or ecological
systems. This can be achieved by limiting the mass rate of pollutant emissions from a particular
source so that, when mixed with surrounding clean air or water, the concentration is sufficiently
low to meet the criterion of harmlessness. 13
In the case of multiple sources located near to each other, such as automobiles on a highway
or many factories crowded together in an urban area, the additive effects require greater reduction
per source than would be needed if only one isolated source existed. In industrialized countries
and regions, the cumulative effects of emissions into limited volumes of air or water result in
widespread contamination, with both local and distant sources contributing to local levels.
The ultimate example of cumulative effects is the gradual increase in the global annual average
atmospheric carbon dioxide concentration caused by the worldwide emissions from burning of fossil
fuels and forests. Because the residence time of carbon dioxide in the atmosphere is of the order
of a century, this rise in atmospheric concentration reflects the cumulative emissions over many
prior decades. Unlike urban or regional air pollutant emission reduction, reducing carbon dioxide
emissions will not reduce the ambient carbon dioxide level, only slow its inexorable rise.
The scientific and technological basis for national and international management of environ-
mental pollution is the cumulative understanding of the natural environment, the technology of
industrial processes that release harmful agents into the environment, and the deleterious effects
upon humans and ecological systems from exposure to them. By itself, this knowledge cannot
secure a solution to environmental degradation, but it is a requisite to fashioning governmental
programs for attaining that purpose.
13 In regulatory procedures, it is usually not necessary to prove absolute harmlessness, but only the absence
of detectable harm.
 
 
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