Environmental Engineering Reference
In-Depth Information
Atmospheric CO
2
at Mauna Loa Observatory
Scripps Institution of Oceanography
NOAA Earth System Research Laboratory
380
360
340
320
1960
1970
1980
1990
Year
2000
2010
Figure 8.2
Atmospheric concentration of carbon dioxide from 1959 to January 2011 measured by the US
National Oceanic and Atmospheric Administration (NOAA) at the Mauna Loa Observatory in Hawaii.
Tans, 2011.
nonwetland soils, and wildfires (EPA, 2010a). Methane is removed from the atmosphere by
conversion to carbon dioxide via a reaction involving the hydroxyl radical (OH
•
) according to
the following equation (Shoemaker et al., 2010):
•
•
CH
+
OH
→ +
CH
H O
[8.6]
4
3
2
Anthropogenic nitrous oxide is generated by nitrogen fertilization, animal manure, sewage
treatment, and combustion of fossil fuels among others. In nature, nitrous oxide is produced
by microbial action in soil and water and removed from the atmosphere by photolytic action
of sunlight. Table 8.3 lists the main sources of anthropogenic methane and nitrous oxide emis-
sions (EPA, 2010b).
Fluorinated gases (e.g., hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride) are
man-made gases that are emitted from industrial processes in relatively small amounts; how-
ever, their impact is significant because they are powerful GHGs. For this reason, these sub-
stances are sometimes referred to as high global warming potential gases. Many fluorinated
gases, also called hydrofluorocarbons, are used as substitute for ozone-depleting substances
that contain chlorine.
In the food supply chain, hydrofluorocarbons are working fluids in refrigeration and air-
conditioning equipment; and the direct emissions of these compounds is a result of accidental
leaks in pipes, joints, and faulty equipment. An indirect impact of the emission of fluorinated
gases comes from the use of aluminum for the production of packaging material. During the
primary aluminum production, perfluorocarbon compounds (CF
4
and C
2
F
6
) are emitted as by-
products of the smelting process. To a lesser extent, two other indirect impacts come from
transmission and distribution of electricity and from the semiconductor manufacturing that
both use SF
6
(EPA, 2010b).
