Environmental Engineering Reference
In-Depth Information
7.8.11 Sulfur Dioxide
Sulfur dioxide (SO 2 ) is released naturally through volcanic eruptions. Anthropogenically,
significant sources of sulfur dioxide include automobile exhaust, the burning of coal, and
some industrial processes (USEPA 2008c). Sulfur dioxide is a component of smog. Other
components of smog include ozone, carbon monoxide, particulate matter (PM), VOCs, and
nitrous oxides (USEPA 2008c). The basic structure of sulfur dioxide varies slightly (Pradyot
2003) (Figure 7.29).
Figure 7.30 shows an example of smog. When released into the atmosphere, sulfur diox-
ide often reacts with water vapor and eventually forms sulfuric acid (H 2 SO 4 ). When pre-
cipitation occurs with a pH lower than that of natural rain (5.6) it is considered acid rain
(USEPA 2008c). Figure 7.31 is a diagram showing acid rain development.
According to USEPA (2008c), acid rain and smog are serious environmental problems
affecting large parts of the United States, especially heavily urbanized areas. A total of 21
out of the 27 U.S. urban areas listed in Table 2.4 experience acid rain. Figure 7.32 shows the
areas of the United States having levels of smog capable of causing an adverse health affect
in humans (USEPA 2008c).
7.8.12 Particulate Matter
PM is also known as particle pollution. PM is a complex mixture of very small particles
and liquid droplets. Particle pollution consists of a number of components, including the
following (USEPA 2009i):
• Acids
• Nitrates
+
+
S
S
S
-
-
O
O
O
O
O
O
FIGURE 7.29
Basic molecular structure of sulfur dioxide.
Layer of
smog
FIGURE 7.30
Smog in an urban area. (Photo by Daniel T. Rogers.)
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