304 ENERGY SOURCES—ALTERNATIVES
and unburnt fuel in vehicular exhausts. Emission factors
for various sources of hydrocarbons are given in Table 10.
Blowby of gasoline vapors from the cylinder into the crank-
case was a large automotive emission source but has been
largely brought under control by positive crankcase ventila-
tion techniques that recycle these vapors back to the combus-
tion chamber. Control of other sources may be provided by
better fuel handling techniques, improved combustor design,
treatment of exhaust gases and reduction of fuel volatility.
The treatment of automotive exhaust gases involves control of
both CO and hydrocarbon emissions using thermal oxidation
in the 1600°F to 1800°F temperature range, or catalytic oxida-
tion with transition metal oxide materials. These catalysts are
generally poisoned by lead additives and offer extra incentive
to eliminate lead additives in fuels.Carbon Dioxide
This gas is inevitably produced in the complete combus-
tion of carbon-bearing fuels. It is not normally thought of as
a pollutant, however, there is some concern over its long-term
effect on the thermal equilibrium of the earth because of the so-
called “greenhouse effect.” Carbon dioxide is a strong absorber
in the long wavelength infrared region of the electromagnetic
spectrum, a region where much of the energy that the earth
loses by radiation to space is concentrated. The CO 2 absorbs
this energy, reradiating it in turn to space at a lower source
temperature. This mechanism effectively reduces the heat loss
from the earth and causes its temperature to increase.
Bolin^20 has reviewed the carbon cycle mechanisms that
are at work in the biosphere. The current annual releaseto the atmosphere of carbon, as CO 2 , attributable to fossil
fuel combustion is about 5 10 9 tons while a total of some
200 10 9 tons have been released to the atmosphere by
combustion processes during the past century. During this
same time period the average concentration of CO 2 in the
atmosphere has increased from 290 to 320 ppm, a change
that accounts for only about^1 / 3 of the total CO 2 emissions.
Apparently, removal processes are effective and include pho-
tosynthesis, solution in ocean waters, and deposition in car-
bonate sediments. One analysis^14 indicates that an increase
in atmospheric CO 2 concentration to 400 ppm, which will
be attained in 1990 if fossil fuel consumption increases
at an annual rate of 5% and if 60% of the CO 2 emissions
remain in the atmosphere, would increase the temperature
of the earth by 1.4°F. The growth of vegetation is stimulated
by high CO 2 levels but, of course, carbon fixed in organic
compounds by photosynthesis is ultimately released again
either by combustion or natural decay processes. Also, to
be considered are the increase of world population and the
energy consumption per capita connected with a consider-
able decrease of surface available for natural vegetation.Water Quality^14The energy activities have an impact on water quality in
several ways. Severe damage is done to the marine environ-
ment in the accidental discharge of oil either from offshore
drilling operations or from oil tankers and other vessels thatTABLE 9
Emission factors for nitrogen oxides^11Average emissions per
unit of fuel burned
Coal
Household and commercial 6 lb/ton
Industry 18 lb/ton
Utility 18 lb/ton
Fuel oil
Household and commercial 12 lb/1000 gal
Industry, tangentially fired unit 40 lb/1000 gal
Utility 105 lb/1000 gal
Natural gas
Household 50 lb/million ft^3
Commercial 100 lb/million ft^3
Industry 230 lb/million ft^3
Utility 390 lb/million ft^3
Gasoline-powered vehicle, urban 1970 183 lb/1000 gal
Diesel-powered bus and truck 370 lb/1000 gal
Aircraft, long range turbofan 5 lb/engine-flighta
Jumbo jet 6 lb/engine-flighta
a Emission during portion of flight at altitudes less than 3500 ft, including
takeoff and landing.TABLE 10
Hydrocarbon emission factors^11Average emissions per
unit of fuel burned
Coal
Household and commercial 3 lb/ton
Industry 1 lb/ton
Utility 0.3 lb/ton
Fuel oil
Household 3 lb/1000 gal
Industry and commercial 3 lb/1000 gal
Utility 2 lb/1000 gal
Natural gas
Household and commercial 8 lb/million ft^3
Utility and industry 40 lb/million ft^3
Gasoline-powered vehicle urban 1970 330 lb/1000 gal
Diesel-powered bus and truck 37 lb/1000 gal
Aircraft, long range turbofan 17 lb/engine-flighta
Jumbo jet 3 lb/engine-flighta
Vehicle gas tank and carburetor 75 lb/1000 gal
Fillingb of automobile tanks 12 lb/1000 gal
Fillingb of service station tanks 12 lb/1000 gal
a Emission during portion of flight at altitudes less than 3500 ft, including
takeoff and landing.
b Assumes splash fill.C005_006_r03.indd 304C005_006_r03.indd 304 11/18/2005 12:05:47 PM11/18/2005 12:05:47 PM