Environmental Engineering Reference
In-Depth Information
Figure 1.2
A run-of-the-river hydropower plant on the Androscoggin River in Brunswick, Maine (United
States). In the center is the power house, on the right is the dam/spillway, and on the left is a fish ladder to
allow anadromous species to move upriver around the dam. Except when occasional springtime excessive
flows are diverted to the spillway, the entire river flow passes through the power house.
output, compared to fossil-fueled plants. On the other hand, they emit no or few pollutants, while
contributing no net carbon dioxide emissions to the atmosphere. Their capital cost per unit of power
output is higher than that of fossil plants, so that renewable plants may not become economical
until fossil fuel prices rise.
Transportation energy is a major sector of the energy market in both industrialized and devel-
oping nations. Automobiles are a major consumer of transportation energy and emitter of urban air
pollutants. The technology of automobiles has advanced considerably in the last several decades
under regulation by governments to reduce pollutant emissions and improve energy efficiency. Cur-
rent automobiles emit much smaller amounts of pollutants than their uncontrolled predecessors as
a consequence of complex control systems. Considerable gains in energy efficiency seem possible
by introduction of lightweight body designs and electric drive systems powered by electric storage
systems or onboard engine-driven electric generators, or combinations of these.
Air pollutants emitted into the urban atmosphere by fossil fuel users and other sources can
reach levels harmful to public health. Some of these pollutants can react in the atmosphere by
absorbing sunlight so as to form even more harmful toxic products. This soup of direct and indirect
pollutants is termed
smog
. One component of smog is the toxic oxidant ozone, which is not directly
emitted by any source. Because of the chemical complexity of these photochemical atmospheric
reactions, great effort is required to limit all the precursors of photochemical smog if it is to be
reduced to low levels.
Carbon dioxide and other greenhouse gases warm the lower atmosphere by impeding the
radiative transfer of heat from the earth to outer space. Limiting the growth rate of atmospheric
carbon dioxide requires either (a) reducing the amount of fossil fuel burned or (b) sequestering
the carbon dioxide below the earth's or ocean's surface. To maintain or increase the availability
of energy while fossil fuel consumption is lowered, renewable or nuclear energy must be used. Of
course, improving the use efficiency of energy can result in the lowering of fossil fuel use while
