84 AIR POLLUTION SOURCES
Part 1. Pollutant Emissions (continued)Pollutant types Sources and abundance Abatement and control
coal and crude oils for electric power and
heating. The sulfur content of refined
petroleum is usually quite low. At the high
temperatures of combustion, the sulfur in
these fuels is converted to SO 2 by the
reaction:
S O 2 SO 2 (3)
Background levels of SO 2 are very low, about
1 ppb. In urban areas maximum
concentrations vary from less than 0.1 to over
0.5 ppm. SO 2 itself is a lung irritant and is
known to be harmful to people who suffer
from respiratory disease. However, it is the
sulfuric acid aerosol formed from the
oxidation of SO 2 and SO 3 that causes the most
damaging health effects in urban areas. The
sulfuric acid aerosol is formed by the
following reactions which in the atmosphere
are photochemically and catalytically
accelerated:
2SO 2 O 2 2SO 3 (4)
SO 3 H 2 O H 2 SO 4 (5)
The sulfuric acid aerosols formed are usually
less than 2 microns in diameter and can quite
effectively penetrate the innermost passages
of the lung, known as the pulmonary region.
This is the region where O 2 is exchanged with
CO in the blood. Sulfuric acid aerosols irritate
the fine vessels of the pulmonary region,
causing them to swell and block the vessel
passages. Severe breathing impairment may
occur. The effect is cumulative, with older
people suffering the most severe respiratory
problems.
SO 2 can also severely damage crops such as
spinach, turnip, beets, alfalfa and oats. Trees
such as the white pine, white birch and
trembling aspen, as well as, ornamental plants
such as gladiolus, tulip and sweet pea, can
also be damaged.which are far from the source of the
pollutant.
The sulfuric acid aerosol is washed
out in either rain or snowfall and
increases the acidity of local waters
downwind from the plant. This
condition is known as acid rain.
Another approach to SO 2 abatement is
to substitute low sulfur coal, sulfur
free coals (produced by screening
crushed coal) and other sulfur free
fuels for high sulfur to low sulfur
fuels. This can be seen in urban
areas where coal has largely been
displaced by petroleum and natural
gas. An alternative approach is to
remove the SO 2 from the stack gases
of the plant by using chemical
scrubbers. In the chemical scrubber,
the stack gas is passed through a
slurry of limestone (calcium
carbonate, CaCO 3 ) which removes
the SO 2 and produces calcium
sulfite which can be collected and
disposed of. More commercially
valuable abatement processes
include catalytic oxidation to
produce usable sulfuric acid and
reaction with alkalized alumina
which allows the recovery of usable
sulfur.TABLE 8
Total National Emissions of Sulfur Dioxide 1940 through 1994 (thousand short tons)Source Category 1940 1950 1960 1970 1980 1990 1993 1994
FULE COMB. -ELEC. UTIL. 2,427 4,515 9,264 17,398 17,469 15,898 15,191 14,869
Coal 2,276 4,056 8,883 15,799 16,073 15,227 14,546 14,312
bituminous 1,359 2,427 5,367 9,574 NA 13,365 12,199 11,904
subbituminous 668 1,196 2,642 4,716 NA 1,425 1,796 1,854
anthracite and lignite 249 433 873 1,509 NA 438 551 555
Oil 151 459 380 1,598 1,395 639 612 523
residual 146 453 375 1,578 NA 629 602 512
FULE COMB. -INDUSTRIAL 6,060 5,725 3,864 4,568 2,951 3,106 2,942 3,029
Coal 5,188 4,423 2,703 3,129 1,527 1,843 1,661 1,715
bituminous 3,473 2,945 1,858 2,171 1,058 1,382 1,248 1,289
subbituminous 1,070 907 574 669 326 29 26 26
anthracite and lignite 645 571 272 289 144 81 72 75(continued)C001_006_r03.indd 84C001_006_r03.indd 84 11/23/2005 9:42:38 AM11/23/2005 9: