Chapter 8
Air Pollution – Inorganic Gases
8.1 INTRODUCTION
This chapter considers four of the major gaseous air pollutants: sulfur dioxide
(SO 2 ), nitrogen dioxide (NO 2 ), ozone (O 3 ), and carbon monoxide (CO). The
importance of these gaseous air pollutants is emphasized by the fact that they
are four of the six ‘‘Criteria Air Pollutants’’ regulated by the U.S.
Environmental Protection Agency (EPA). The other two criteria air pollutants
are volatile organic compounds (VOCs) and lead (Pb). VOCs are discussed in
Chapter 11, while Pb is included in Chapter 12.
8.2 SULFUR DIOXIDE
SO 2 and sulfur trioxide (SO 3 ) are the two sulfur oxides (SO x ) that are
important air pollutants. This chapter focuses on SO 2 because it is far more
important than SO 3 as an air pollutant. In fact, based on the quantities emitted
into the atmosphere, SO 2 is considered the most dangerous of all gaseous
pollutants.
8.2.1 SOURCES OF SO 2
Atmospheric SO 2 arises from both natural and anthropogenic sources. Sulfur
compounds are emitted naturally through volcanic action, sea salt over the
oceans, and decomposition of organic matter (mostly as hydrogen sulfide,
H 2 S). Most anthropogenic emissions of sulfur (S) to the atmosphere (about
95%) are in the form of SO 2 . The main human activities that cause SO 2
emission include combustion of coal and petroleum products, petroleum
refining, and nonferrous smelting. In the U.S., about 95% of the total emission
is from industry and stationary sources.
The S content of coal ranges from 0.3 to 7%, and it is present in both
organic and inorganic forms, whereas in oil the content ranges from 0.2 to
1.7%, and the S is in organic form. The most important S-containing
compound in coal is iron disulfide or pyrite (FeS 2 ). When heated to high
temperatures, pyrite is oxidized through the reactions shown below:
FeS 2 þ 3O 2 ! FeSO 4 þ SO 2
ð8:1Þ
4FeS 2 þ 11O 2 ! 2Fe 2 O 3 þ 8SO 2
ð8:2Þ
[16:53 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-008.3d]
Ref: 4365 MING-HO YU Chap-008 Page: 111 111-134
111
Air Pollution – Inorganic Gases
8.1 INTRODUCTION
This chapter considers four of the major gaseous air pollutants: sulfur dioxide
(SO 2 ), nitrogen dioxide (NO 2 ), ozone (O 3 ), and carbon monoxide (CO). The
importance of these gaseous air pollutants is emphasized by the fact that they
are four of the six ‘‘Criteria Air Pollutants’’ regulated by the U.S.
Environmental Protection Agency (EPA). The other two criteria air pollutants
are volatile organic compounds (VOCs) and lead (Pb). VOCs are discussed in
Chapter 11, while Pb is included in Chapter 12.
8.2 SULFUR DIOXIDE
SO 2 and sulfur trioxide (SO 3 ) are the two sulfur oxides (SO x ) that are
important air pollutants. This chapter focuses on SO 2 because it is far more
important than SO 3 as an air pollutant. In fact, based on the quantities emitted
into the atmosphere, SO 2 is considered the most dangerous of all gaseous
pollutants.
8.2.1 SOURCES OF SO 2
Atmospheric SO 2 arises from both natural and anthropogenic sources. Sulfur
compounds are emitted naturally through volcanic action, sea salt over the
oceans, and decomposition of organic matter (mostly as hydrogen sulfide,
H 2 S). Most anthropogenic emissions of sulfur (S) to the atmosphere (about
95%) are in the form of SO 2 . The main human activities that cause SO 2
emission include combustion of coal and petroleum products, petroleum
refining, and nonferrous smelting. In the U.S., about 95% of the total emission
is from industry and stationary sources.
The S content of coal ranges from 0.3 to 7%, and it is present in both
organic and inorganic forms, whereas in oil the content ranges from 0.2 to
1.7%, and the S is in organic form. The most important S-containing
compound in coal is iron disulfide or pyrite (FeS 2 ). When heated to high
temperatures, pyrite is oxidized through the reactions shown below:
FeS 2 þ 3O 2 ! FeSO 4 þ SO 2
ð8:1Þ
4FeS 2 þ 11O 2 ! 2Fe 2 O 3 þ 8SO 2
ð8:2Þ
[16:53 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-008.3d]
Ref: 4365 MING-HO YU Chap-008 Page: 111 111-134
111