AIR POLLUTION SOURCES 81
Part 1. Pollutant Emissions (continued)Pollutant types Sources and abundance Abatement and controlB. INORGANIC GASES: The chemistry of the lower
atmosphere is controlled by the reactivity of oxygen.
In the presence of molecular oxygen (O 2 ), the stable
forms of almost all of the elements are oxides, with
the notable exception of nitrogen. Thus, many of the
major pollutants are oxides (i.e., CO, SO 2 , SO 3 , NO,
NO 2 ) and their associated reactive by-products.- Carbon Oxides
Significant amounts of carbon oxides, carbon monoxide
(CO) and carbon dioxide (CO 2 ), are produced by
natural and anthropogenic (man made) sources. CO
is considered a major atmospheric pollutant because
of its significant health effects, whereas, CO 2 is a
relatively non-toxic, normal tropospheric (lower
atmospheric) constituent and is, therefore, not
usually described as a major atmospheric pollutant.
However, anthropogenic emissions of CO 2 are of
significant concern since large amounts of CO 2 may
contribute to global climatic warning.
a. Carbon Monoxide:
Carbon monoxide (CO) is a colorless, odorless,
tasteless gas formed by the incomplete
combustion of fossil fuels and other organic
matter. During combustion, carbon is
oxidized to CO by the following reactions:
2C O 2 ⎯→ 2CO (1)
2CO O 2 ⎯→ 2CO 2 (2)
CO, formed as an intermediate in the
combustion process, is emitted if there is
insufficient O 2 present for reaction (2) to
proceed. CO is produced naturally by
volcanic eruptions, forest fires, lightning and
photochemical degradation of various
reactive organic compounds. Biologically,
CO is formed by certain brown algae,
decomposition of chlorophyll in leaves of
green plants, various micro-organisms and
microbial action in the oceans. Major
anthropogenic sources include transportation,
industrial processing, solid waste disposal
and agricultural burning. it also is present in
high concentrations in cigarette smoke.
Background concentrations of CO average
0.1 ppm, with peak concentrations in the
northern hemisphere during the autumn
months due to the decomposition of
chlorophyll associated with the color change
and fall of leaves. The residence time for CO
in the atmosphere is estimated to be 0.1 to 0.3
years.
Because CO has a higher affinity (approximately
200 greater) for blood hemoglobin than
oxygen, and also tends to remain more tightly
bound, oxygen transport throughout the bodyCO can be removed from the
atmosphere by the actions of soil
micro-organisms which convert it to
CO 2. The soil in the U.S. alone is
estimated to remove approximately
5 108 tons of CO per year, which
is far in excess of the anthropogenic
emission rate. However, little CO is
removed in urban areas since
emissions of CO are large and soil is
scarce. In automobiles, catalytic
convertors are used to reduce CO
emissions by combusting the
exhaust gases over a catalyst. This
catalyst aided reaction combines O 2
with CO to produce CO 2 and water.
Similar after-burner processes are
used in controlling emissions from
stationary sources.(continued)TABLE 7 (continued)
Total National Emissions of Carbon Monoxide, 1940 through 1994 (thousand short tons)Source Category (^19401950196019701980199019931994)
construction 1,198 2,409 2,262 250 368 395 423 453
industrial 780 1,558 1,379 732 970 1,228 1,285 1,340
lawn and garden NA NA NA 4,679 5,366 6,001 6,212 6,276
farm 1,351 2,716 3,897 46 77 63 70 73
light commercial NA NA NA 2,437 2,680 3,254 3,402 3,519
recreational marine vessels 60 120 518 976 1,102 1,207 1,245 1,256
Non-Road Diesel 32 53 65 543 801 841 903 954
Aircraft 4 934 1,764 506 743 966 1,019 1,063
Railroads 4,083 3,076 332 65 96 122 124 124
MISCELLANEOUS 29,210 18,135 11,010 7,909 8,344 11,173 6,700 9,245
Other Combustion 29,210 18,135 11,010 7,909 8,344 11,173 6,700 9,245
forest wildfires 25,130 11,159 4,487 5,620 5,396 6,079 1,586 4,115
TOTAL ALL SOURCES 93,615 102,609 109,745 128,079 115,625 100,650 94,133 98,017
Note(s): Categories displayed below Tier 1 do not sum to Tier 1 totals because they are intended to show major contributors.
1994 emission estimates are preliminary and will be updated in the next report.
Tier 1 source categories and emissions are shaded.
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