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and have particularly objectionable odors.

Hydrogen sulfide pollution from artificial sources is not as much of an overall air

pollution problem as sulfur dioxide pollution. However, there have been several acute

incidents of hydrogen sulfide emissions resulting in damage to human health and even

fatalities. The most notorious such incident occurred in Poza Rica, Mexico, in 1950.

Accidental release of hydrogen sulfide from a plant used for the recovery of sulfur

from natural gas caused the reported deaths of 22 people and the hospitalization of

over 300.

Hydrogen sulfide at levels well above ambient concentrations destroys immature

plant tissue. This type of plant injury is readily distinguished from that due to other

phytotoxins. More-sensitive species are killed by continuous exposure to around 3000

ppb H2S, whereas other species exhibit reduced growth, leaf lesions, and defoliation.

Damage to certain kinds of materials is a very expensive effect of hydrogen

sulfide pollution. Paints containing lead pigments, 2PbCO 3•Pb(OH)2 (no longer used),

were particularly susceptible to darkening by H2S. A black layer of copper sulfide

forms on copper metal exposed to H2S. Eventually, this layer is replaced by a green

coating of basic copper sulfate such as CuSO4•3Cu(OH)2. The green “patina,” as it is

called, is very resistant to further corrosion. Such layers of corrosion can seriously

impair the function of copper contacts on electrical equipment. Hydrogen sulfide also

forms a black sulfide coating on silver.

Carbonyl sulfide, COS, is now recognized as a component of the atmosphere at a

tropospheric concentration of approximately 500 parts per trillion by volume,

corresponding to a global burden of about 2.4 teragrams. It is, therefore, a significant

sulfur species in the atmosphere.

Both COS and CS2 are oxidized in the atmosphere by reactions initiated by the

hydroxyl radical. The initial reactions are

HO• + COS → CO2 + HS•


HO• + CS2 → COS + HS•


The sulfur-containing products undergo further reactions to sulfur dioxide and,

eventually, to sulfate species.


The chapter summary below is presented in a programmed format to review the

main points covered in this chapter. It is used most effectively by filling in the

blanks, referring back to the chapter as necessary. The correct answers are given at

the end of the summary.

Atmospheric aerosols are 1


. Condensation aerosols are formed by


dispersion aerosols are formed by 3

. As applied to the formation of

atmospheric aerosols, the reaction 2SO2 + O2 + 2H2O → 2H 2SO4 shows4

© 2001 CRC Press LLC

. In general, the proportions of

elements in atmospheric particulate matter reflect5

. The two reactions 2SO2 + O2 + 2H2O →

2H2SO4 and H 2SO4 + 2NaCl(particulate) → 2Na 2SO4(particulate) + 2HCl show

why particulate matter largely from ocean spray origin in a coastal area receiving

sulfur dioxide pollution may show 6

. Insofar as origins of elements in particulate matter

are concerned, soil erosion, rock dust, and coal combustion produce 7

; incomplete combustion of carbonaceous fuels produces 8


marine aerosols and incineration of organohalide polymer wastes produces 9

; and combustion of residual petroleum produces 10


Mineral particulate matter in the form of oxides and other compounds produced

during the combustion of high-ash fossil fuel that can be collected in furnace flues is

. Three adverse respiratory health effects caused by

called 11

inhalation of asbestos are 12

. The toxic metal of greatest concern in the urban

atmosphere is 13

because it 14

. A significant natural source of radionuclides in the

atmosphere is 15

,which initially decays to 16


Another significant source of radioactivity in the atmosphere is 17

and a former source of atmospheric radioactivity was 18

. Three effects of atmospheric particles are 19



The most common health effects of atmospheric particles are on the

. Some of the most common ways to control particulate emissions

are 21

. Carbon monoxide

causes pollution problems in cases of 22


. It is of most concern because of its 23


Automobiles are equipped with 24

to cut down carbon monoxide emissions. It is generally agreed that carbon monoxide

is removed from the atmosphere by 25

. The greatest

pollution concern with carbon dioxide is its role as 26

. The two major sources of atmospheric carbon dioxide are


. Most sulfates enter the


atmosphere from

and most sulfur dioxide from


. The fate of any H2S that does get

into the atmosphere is that it is 30


Sulfur dioxide’s primary health effect is upon the 31


Chronic exposure of plants to sulfur dioxide causes 32

. Sulfur dioxide

processes, of which the

can be removed from stack gas by 33

major types are 34

. The three oxides of nitrogen normally encountered in the

atmosphere are 35

. Nitric oxide (NO)

and nitrogen dioxide (NO2) are collectively designated 36

, most of which enters

the atmosphere as 37

. The most important photo-chemical

reaction of NO2, and one that can lead to photochemical smog formation is 38

© 2001 CRC Press LLC


. Pulmonary








, a condition fatal within 3–5 weeks after exposure. During the combustion of fossil

fuels, 40

is effective in reducing NOx emissions. Sources of

atmospheric ammonia are 41

Much of the

sulfur and nitrogen oxides entering the atmosphere are converted to 42

, which, along with hydrochloric acid arising from

hydrogen chloride emissions, cause 43

. The major

damaging effects of acid precipitation are 44


Two specific gaseous fluorine-containing air pollutants are 45

. Though not directly toxic, the fluorine-containing air

pollutants with the greatest potential for damage to the atmosphere are the 46

. Halons, which are related to

chlorofluorocarbons, are compounds that contain 47

and are used in 48











. The first reaction in this harmful process is











with ozone. The most prominent instance of ozone layer destruction that has been

documented in recent years is 52

. The highly damaging

conse-quence of stratospheric ozone destruction is that it would allow 53

, which would result in 54

. Atmospheric chlorine dissolves in atmospheric water

droplets, yielding 55



Natural sources of hydrogen sulfide are


Answers to Chapter Summary

1. solid or liquid particles smaller than 100 µm in diameter

2. condensation of vapors or reactions of gases

3. grinding of solids, atomization of liquids, aerosol or dispersion of dusts

4. oxidation of atmospheric sulfur dioxide to sulfuric acid, a hygroscopic sub-stance

that accumulates atmospheric water to form small liquid droplets

5. relative abundances of elements in the parent material

6. anomalously high sulfate and corresponding low chloride content

7. Al, Fe, Ca, Si

8. C

9. Na, Cl

10. V

© 2001 CRC Press LLC






































fly ash

asbestosis, mesothelioma, and bronchogenic carcinoma


comes closest to being present at a toxic level



Po and 216Po

the combustion of fossil fuels

the above-ground detonation of nuclear weapons

reduction and distortion of visibility, provision of active surfaces upon which

heterogeneous atmospheric chemical reactions can occur, and nucleation bodies

for the condensation of atmospheric water vapor

respiratory tract

sedimentation, inertial mechanisms, baghouses, scrubbers, electrostatic


concentrated localized pollution


catalytic converters

reaction with hydroxyl radical

a greenhouse gas

burning of fossil fuels and deforestation

marine sources


converted rapidly to SO2

respiratory tract



throwaway and recovery systems

nitrous oxide (N2O), nitric oxide (NO), and nitrogen dioxide (NO2)



NO2 + hν → NO + O

bronchiolitis fibrosa obliterans

low excess air firing

microorganisms, decay of animal wastes, sewage treatment, coke manufacture,

ammonia manufacture, and leakage from ammonia-based refrigeration systems

sulfuric and nitric acids

acidic precipitation

direct phytotoxicity to plants from excessive acid concentrations; phytotoxicity

from acid-forming gases; indirect phytotoxicity, such as from Al3+ liberated from

acidifiedsoil; destruction of sensitive forests, respiratory effects on humans and

other animals; acidification of lake water with toxic effects to lake flora and fauna;

corrosion to exposed structures, electrical relays, equipment, and ornamental

materials; and associated effects, such as reduction of visibility by sulfate aerosols

and the influence of sulfate aerosols on physical and optical properties of clouds.

fluorine gas and hydrogen fluoride

chlorofluorocarbons (CFC)


© 2001 CRC Press LLC










fire extinguisher systems

their potential to destroy stratospheric ozone

Cl2CF2 + hν → Cl• + ClCF 2•

Cl + O 3 → ClO + O2

the Antarctic ozone hole

penetration of high-energy ultraviolet radiation

adverse biological effects, such as increased skin cancer

hydrochloric acid and hypochlorous acid

microbial decay of sulfur compounds and microbial reduction of sulfate


Beim, Howard J., Jennifer Spero, and Louis Theodore, Rapid Guide to Hazardous

Air Pollutants, John Wiley & Sons, New York, 1997.

Ghodish, Thad, Air Quality, 3rd ed., Lewis Publishers/CRC Press, Boca Raton, FL,


Heumann, William L., Ed., Industrial Air Pollution Control Systems, McGraw-Hill,

New York, 1997.

Hocking, Martin B., Handbook of Chemical Technology and Pollution Control,

Academic Press, San Diego, CA, 1998.

Matson, P., Biogenic Trace Gases: Measuring Emissions from Soil and Water,

Blackwell, Carlton South, Australia, 1995.

Maynard, Douglas G., Ed., Sulfur in the Environment, Marcel Dekker, 270 Madison

Ave., New York, 1998.

Mycock, John C., John D. McKenna, and Louis Theodore, Eds., Handbook of Air

Pollution Control Engineering and Technology, Lewis Publishers/CRC Press, Boca

Raton, FL, 1995.

Rogers, John E., and William B. Whitman, Eds., Microbial Production and

Consumption of Greenhouse Gases:

Methane, Nitrogen Oxides, and

Halomethanes, American Society for Microbiology, Washington, D.C., 1991.

Schifftner, Kenneth C. and Howard E. Hesketh, Wet Scrubbers, Technomic

Publishing Co., Lancaster, PA, 1996.

Stevens, Lem B., William L. Cleland, and E. Roberts Alley, Air Quality Control

Handbook, McGraw-Hill, New York, 1998.

Warner, Cecil F., Wayne T. Davis, and Kenneth Wark, Air Pollution: Its Origin and

Control, 3rd ed., Addison-Wesley, Reading, MA, 1997.

© 2001 CRC Press LLC


1. A freight train that included a tank car containing anhydrous NH3 and one

containing concentrated HCl was wrecked, causing both of the tank cars to leak.

In the region between the cars a white aerosol formed. What was it, and how was

it produced?

2. What two vapor forms of mercury might be found in the atmosphere?

3. Analysis of particulate matter collected in the atmosphere near a seashore shows

considerably more Na than Cl on a molar basis. What does this indicate?

4. What type of process results in the formation of very small aerosol particles?

5. Which size range encompasses most of the particulate matter mass in the


6. Why are aerosols in the 0.1–1 µm size range especially effective in scattering


7. Per unit mass, why are smaller particles more effective catalysts for atmospheric

chemical reactions?

8. What is the rationale for classifying most acid rain as a secondary pollutant?

9. Distinguish among UV-A, UV-B, and UV-C radiation. Why does UV-B pose the

greatest danger in the troposphere?

10. Why is it that “highest levels of carbon monoxide tend to occur in congested

urban areas at times when the maximum number of people are exposed?”

11. Which unstable, reactive species is responsible for the removal of CO from the


12. Which of the following fluxes in the atmospheric sulfur cycle is smallest: (a)

Sulfur species washed out in rainfall over land, (b) sulfates entering the

atmosphere as “sea salt,” (c) sulfur species entering the atmosphere from

volcanoes, (d) sulfur species entering the atmosphere from fossil fuels, (e)

hydrogen sulfide entering the atmosphere from biological processes in coastal

areas and on land.

13. Of the following agents, the one that would not favor conversion of sulfur dioxide

to sulfate species in the atmosphere is: (a) Ammonia, (b) water, (c) contaminant

reducing agents, (d) ions of transition metals such as manganese, (e) sunlight.

14. The air inside a garage was found to contain 10 ppm CO by volume at standard

temperature and pressure (STP). What is the concentration of CO in mg/L and in

ppm by mass?

15. Assume that an incorrectly adjusted lawn mower is operated in a garage such that

the combustion reaction in the engine is

C8H18 + 17/2O2 → 8CO + 9H2O

© 2001 CRC Press LLC

If the dimensions of the garage are 5 × 3 × 3 meters, how many grams of

gasoline must be burned to raise the level of CO in the air to 1000 ppm by

volume at STP?

16. A 12.0-L sample of waste air from a smelter process was collected at 25˚C and

1.00 atm pressure, and the sulfur dioxide was removed. After SO2 removal, the

volume of the air sample was 11.50 L. What was the percentage by weight of

SO2 in the original sample?

17. What is the oxidant in the Claus reaction?

18. How many metric tons of 5%–S coal would be needed to yield the H2SO4

required to produce a 3.00–cm rainfall of pH 2.00 over a 100 km2 area?

19. In what major respect is NO2 a more significant species than SO2 in terms of

participation in atmospheric chemical reactions?

20. Match the effect on the right with its most likely source or cause from the left,


A. Sunlight and autos

B. Burning of all types

of fossil fuels

C. Chlorofluorocarbons

D. Burning of coal, especially

1. Global warming

2. Increased acidity in the atmosphere

3. Pollutant oxidants in the lower


4. Destruction of stratospheric ozone

21. Of the following, the most likely to be formed by pyrosynthesis is

A. Sulfate particles

B. Ammonium particles

C. Sulfuric acid mist


E. Ozone in smog

22. Of the following, the true statement related to carbon monoxide in the

atmosphere is

A. It is strictly a pollutant with none coming from natural sources.

B. It is an intermediate in reactions by which methane is removed by

normal atmospheric processes.

C. It is increasing in the atmosphere at a rate of approximately 1 ppm per


D. Although produced by a reaction with hydroxyl radical it does not

react with HO•.

E. Most harmful levels of CO are produced as secondary pollutants.

23. Of the following, the untrue statement regarding the fate of sulfur dioxide in the

atmosphere is

A. It reacts to form particulate matter.

B. It is largely oxidized by reactions occurring inside water aerosol


C. Although acidic, it can react to form an even more acidic species.

D. The presence of hydrocarbons and nitrogen oxides generally

accelerates sulfur dioxide oxidation.

E. It is produced as a stable species during smog-forming conditions.

© 2001 CRC Press LLC

24. Assume that the wet limestone process requires 1 metric ton of CaCO3 to remove

90% of the sulfur from 4 metric tons of coal containing 2% S. Assume that the

sulfur product is CaSO 4. Calculate the percentage of the limestone converted to

calcium sulfate.

25. Of the following, the statement that is untrue is

A. Acid rain is denoted by any precipitation with a pH less than neutral


B. Acid may be deposited as acidic salts and acid gases, in addition to

liquid acid rain

C. Acid rain is a regional air pollution problem as distinguished from local

or global problems.

D. Carbon dioxide makes rainfall slightly acidic

E. Acid rain is often associated with elevated levels of sulfate ion, SO42-.

© 2001 CRC Press LLC


Fundamentals of Environmental Chemistry

Boca Raton: CRC Press LLC,2001





Organic pollutants may have a strong effect upon atmospheric quality. The

effects of organic pollutants in the atmosphere can be divided into two major categories. The first consists of direct effects, such as cancer caused by exposure to

vinyl chloride. The second is the formation of secondary pollutants, especially

photochemical smog, discussed later in this chapter. In the case of pollutant

hydrocarbons in the atmosphere, the latter is the more important effect. In some

localized situations, particularly the workplace, direct effects of organic air

pollutants may be equally important.

Global Distillation and Fractionation of Persistent Organic Pollutants

On a global scale, it is likely that persistent organic pollutants undergo a cycle of

distillation and fractionation in which they are vaporized into the atmosphere in

warmer regions of the Earth and condense and are deposited in colder regions. The

theory of this phenomenon holds that the distribution of such pollutants is governed

by their physicochemical properties and the temperature conditions to which they are

exposed. As a result, the least volatile persistent organic pollutants are deposited

near their sources, those of relatively high volatility are distilled into polar regions,

and those of intermediate volatility are deposited predominantly at mid latitudes.

This phenomeonon has some important implications regarding the accumulation of

persistent organic pollutants in environmentally fragile polar regions and cold

mountainous areas far from industrial sources.

Reactions and Fates of Organic Compounds

Much of the remainder of this chapter deals with the reactions and fates of

organic compounds in the atmosphere, especially in respect to how these processes

lead to the formation of the common air pollution problem of photochemical smog.

© 2001 CRC Press LLC

There are two important points related to what happens to organic compounds in the

atmosphere. The first of these is the importance of photochemical reactions initiated

by the absorption of photons of electromagnetic radiation, usually of wavelengths in

the ultraviolet region just a bit shorter than those of visible light. The energy of these

photons is equal to the product of Planck’s constant, h, and the frequency of the

radiation, ν. Therefore, the product hν is used to represent photons of

electromagnetic radiation in photochemical reactions. The second crucial point

regarding the fates of organic species in the atmosphere is the central role played by

the highly reactive hydroxyl radical represented HO . This is a free radical species

meaning that it has an unpaired electron, which is what the dot in the formula

represents. Hydroxyl radical is involved in virtually all the pathways by which

organic compounds react in the atmosphere and by which photochemical smog is




Natural sources are the most important contributors of organics in the

atmosphere, and hydrocarbons generated and released by human activities consitute

only about 1/7 of the total hydrocarbons in the atmosphere. This ratio is primarily

the result of the huge quantities of methane produced by anaerobic bacteria in the

decomposition of organic matter in water, sediments, and soil:

2{CH2O} (bacterial action) → CO2(g) + CH4(g)


Flatulent emissions from domesticated animals, arising from bacterial decomposition

of food in their digestive tracts, add about 85 million metric tons of methane to the

atmosphere each year. Anaerobic conditions in intensively cultivated rice fields

produce large amounts of methane, perhaps as much as 100 million metric tons per

year. Methane is a natural constituent of the atmosphere and is present at a level of

about 1.4 parts per million (ppm) in the troposphere.

Methane in the troposphere contributes to the photochemical production of

carbon monoxide and ozone. The photochemical oxidation of methane is a major

source of water vapor in the stratosphere.

Atmospheric hydrocarbons produced by living sources are called biogenic

hydrocarbons. Vegetation is the most important natural source of non-methane

biogenic compounds. Several hundred different hydrocarbons are released to the

atmosphere from vegetation sources. Other natural sources include microorganisms,

forest fires, animal wastes, and volcanoes.

One of the simplest organic compounds given off by plants is ethylene, C2H4.

This compound is produced by a variety of plants and released to the atmosphere in

its role as a messenger species regulating plant growth. Because of its double bond,

ethylene is highly reactive with hydroxyl radical, HO•, and with oxidizing species in

the atmosphere. Ethylene from vegetation sources should be considered as an active

participant in atmospheric chemical processes.

Most of the hydrocarbons emitted by plants are terpenes, which constitute a

large class of organic compounds found in essential oils. Essential oils are obtained

when parts of some types of plants are subjected to steam distillation. Most of the

plants that produce terpenes are conifers (evergreen trees and shrubs such as pine

© 2001 CRC Press LLC

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