Jacobson M.Z. Atmospheric Pollution

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supplier and an oil company agreed to put solar panels in 50,000 homes currently

without electricity. Homeowners would have to buy cards to activate the panels.

The Constitution of South Africa is somewhat unique among constitutions in that it

guarantees everyone the right (a) “to an environment that is not harmful to their health

or well-being” and (b) “to have the environment protected for the beneﬁt of present

and future generations through reasonable legislative and other measures.” In October

1997, a White Paper on Environmental Management called for South Africa’s

Department of Environment Affairs and Tourism to regulate and combat air pollution,

particularly from coal and fuel burning, vehicles, mining, industrial activity, and incin-

erators. Although emission regulations have resulted, they have not been enforced

strictly to date.

8.2.18. Australia

Air pollution problems are less severe in Australia than they are in many other coun-

tries, particularly because

Australian cities are less populated and have fewer sources

of pollution than do more polluted cities. Australia is also surrounded by oceans, so it

does not receive much transboundary air pollution. The sulfur contents of coal and oil

in Australia are lower than those in other countries. Coal-ﬁred power plants are also

located away from urban areas. As a result, sulfur dioxide mixing ratios in Australian

cities are relatively low. Sydney and Melbourne occasionally have bad air pollution

days, particularly in summer and autumn.

Automobiles are the largest source of air pollution in Australia. Catalytic convert-

ers were required starting in 1986. Because cars that use the converter cannot run on

lead, lead concentrations in the air subsequently decreased. Lead is expected to be

phased out of gasoline completely by 2002,

at which time automobile emission stan-

dards for particulates, nitric oxide, carbon monoxide, and hydrocarbons will be

strengthened. Australia is planning to give ﬁnancial incentives to industry to convert

commercial vehicles to clean fuels by 2015.

8.3. SUMMARY

In this chapter, regulation of and trends in urban air pollution were discussed with

respect to several countries. Until the 1950s, air pollution in the United States w

as not

addressed at the national level. Increased concern over photochemical smog and fatal

London-type smog events in the United States encouraged Congress to implement the

Air Pollution Control Act of 1955 and the United Kingdom to implement the U.K.

Clean Air Act of 1956. The U.S. Act provided funds to study air pollution and provid-

ed for technical assistance to states, many of which had already enacted air pollution

legislation, but it did not regulate air pollution at the federal level. The U.S. Congress

ﬁrst regulated stationary sources of pollution through the Clean Air Act of 1963. This

Act led to the Motor Vehicle Air Pollution Control Act of 1965, which was the ﬁrst

federal legislation controlling emission from motor vehicles. The Air Quality Act of

1967 divided the country into Air Quality Control Regions, speciﬁed the development

of Air Quality Criteria for certain pollutants, and required states to submit State

Implementation Plans for combating air pollution. In landmark legislation, Congress

passed the Clean Air Act Amendments of 1970. This act required the newly created

U.S. EPA to develop National Ambient Air Quality Standards for certain pollutants

238 ATMOSPHERIC POLLUTION: HISTORY, SCIENCE, AND REGULATION

identiﬁed as being unhealthful and speciﬁed that the U.S. EPA set performance

standards for new sources of air pollution. Regulations under CAAA70 led to the 1975

invention of the catalytic converter, the most important device to date for limiting

emissions from automobiles. The Clean Air Act Amendments of 1990 led to controls

of many hazardous air pollutants not controlled under earlier legislation. The Clean

Air Act Revision of 1997 led to revised ozone and particulate standards. State and fed-

eral air pollution legislation resulted in a remarkable improvement in urban air in the

United States. Strong legislation by the European Union and several industrialized

countries has also led to improved air quality. Although legislation has been enacted in

many developing countries, legislation in several of those countries is relatively new,

has not been enforced, or has not been sufﬁciently strong. As such, air pollution in

many cities of the world has worsened. Some of the most polluted cities in the world

today include Mexico City, New Delhi, Beijing, Cairo, Sao Paolo, Shanghai, Jakarta,

Bangkok, Tehran, and Calcutta.

8.4. PROBLEMS

8.1. Suppose you drive a gasoline engine car 15,000 miles per year.

(a) How many kilograms per year of hydrocarbons and carbon monoxide

would your car have emitted in 1968 versus today if your car exactly met

federal emission standards in both years? (Use intermediate useful life

emission standards for the present year.)

(b) If each of 10 million cars in your city were driven 15,000 miles per year,

how many tons per day of carbon monoxide would have been emitted in

1968 versus today?

8.2. Explain how the three-way catalyst works.

8.3. The United Kingdom Alkali Act of 1863 resulted in new control technologies

for converting hydrochloric acid from soda-ash factory chimneys to reusable

forms of chlorine, and the Clean Air Act Amendments resulted in the develop-

ment of the catalytic converter. If air pollution control regulation leads to

improved technologies, why is tough air pollution legislation generally so difﬁ-

cult to pass?

8.4. Identify any one-hour California state or federal standards, health advisories,

or smog-alert levels exceeded by NO

(g) or O

(g) in Fig. 4.10(a) and (b).

8.5. What are two possible explanations for the improvements in Los Angeles air

pollution between 1975 and today, as shown in Fig. 8.2?

8.6. Today, what criteria pollutants exceed U.S. federal standards the most? Which

exceed the standards the least?

8.7. Although more people in the United States are exposed to levels of CO(g) than

above the federal standard (Fig. 8.1), exposure to PM

is of greater con-

cern in terms of health effects. Why?

INTERNATIONAL REGULATION OF URBAN SMOG SINCE THE 1940s 239

8.8. Match each city below with an air pollution related characteristic of the city.

(a) Cairo (1) Heavy reliance on alcohol-fuel burning

(b) Santiago (2) High sulfur dioxide and soot concentra-

tions in the air

power

(d) Los Angeles (4) Severe lead air pollution problem

(e) Beijing (5) Experienced a devastating smog event in

1952

(f) New Delhi (6) Heavy particulate pollution, particularly

from soil erosion

(g) Paris (7) Lack of funding limits enforcement of

air pollution laws

(h) Sao Paolo (8) Most dangerous city (in terms of air pol-

lution) worldwide for children, 1999

(i) Moscow (9) Ozone levels exceeded 0.6 ppmv in the

1950s

(j) London (10) Car sales limited by law to slow rise in

vehicle emissions

240 ATMOSPHERIC POLLUTION: HISTORY, SCIENCE, AND REGULATION

INDOOR AIR POLLUTION

ecause people spend most of their time indoors, it is useful to examine the

composition and quality of indoor air. Because people’s time is often divided

between home and work, it is important to examine air quality in both resi-

dences and workplaces. Sources of indoor air pollution include outdoor air and indoor

emissions. Outdoor air contains the constituents of smog, but some of these con-

stituents dissipate quickly indoors because of the lack of ultraviolet (UV) radiation to

reproduce them indoors. Major indoor sources of pollution include stoves, heaters,

carpets, ﬁreplaces, tobacco smoke, motor vehicle exhaust from garages, building mate-

rials, and insulation. Whereas indoor air pollution in the United States is regulated in

workplaces, it is not regulated in residences. In this chapter, characteristics, sources,

and regulation of indoor air pollution are discussed.

9.1. POLLUTANTS IN INDOOR AIR AND THEIR SOURCES

In the United States, about 89 percent of people’s time is spent indoors, 6 percent is

spent in vehicles, and 5 percent is spent outdoors (Robinson et al., 1991). Another

study found that in nonindustrialized countries, people in urban areas spend 79 percent

of their time indoors and those in rural areas spend 65 percent of their time indoors

(Smith, 1993). Because people breathe indoor air more than outdoor air, an examina-

tion of indoor air is warranted.

Table 9.1 identiﬁes major pollutants in indoor air and their primary sources. Many

of the pollutant gases in indoor air are also found in outdoor air. Outdoor pollutants

enter indoor air by inﬁltration, natural ventilation, and forced v

entilation.

Inﬁltration

242

Table 9.1. Important Indoor Air Pollutants and Their Emission Sources

Gases

Carbon dioxide Metabolic activity, combustion, garage exhaust, tobacco smoke

Carbon monoxide Boilers, gas or kerosene heaters, gas stoves, wood stoves,

ﬁreplaces, tobacco smoke, garage exhaust, outdoor air

Nitrogen dioxide Outdoor air, garage exhaust, kerosene and gas space heaters, wood

stoves, gas stoves, tobacco smoke

Ozone Outdoor air, photocopy machines, electrostatic air cleaners

Sulfur dioxide Outdoor air, kerosene space heaters, gas stoves, and coal appliances

Formaldehyde Particleboard, insulation, furnishings, paneling, plywood, carpets,

ceiling tile, tobacco smoke

Volatile organic compounds Adhesives, solvents, building materials, combustion appliances,

paints, varnishes, tobacco smoke, room deodorizers, cooking,

carpets, furniture, draperies

Radon Diffusion from soil

Aerosol particles

Allergens House dust, domestic animals, insects, pollens

Asbestos Fire-retardant materials, insulation

Fungal spores Soil, plants, foodstuffs, internal surfaces

Bacteria, viruses People, animals, plants, air conditioners

Polycyclic aromatic hydrocarbons Fuel combustion, tobacco smoke

Other Resuspension, tobacco smoke, wood stoves, ﬁreplaces, outdoor air

Pollutant Emission Sources

Sources: Spengler and Sexton (1983), Nagda et al. (1987).

is natural air exchange through cracks and leaks, such as through door and window

frames, chimneys, exhaust vents, ducts, plumbing passages, and electrical outlets.

Natural ventilation is air exchange resulting from the opening or closing of windows

or doors to enhance the circulation of air. Forced ventilation is the air exchange

resulting from the use of whole-house fans or blowers (Masters, 1998). Next, the

pollutants in Table 9.1 are discussed brieﬂy.

9.1.1. Carbon Dioxide

Carbon dioxide [CO

(g)] is present in background air and produced indoors from

breathing and combustion. It does not pose a health problem until its mixing ratio

reaches 15,000 ppmv, much higher than its background mixing ratio of 370 ppmv

Mixing ratios and health effects of carbon dioxide are discussed in Section 3.6.2.

9.1.2. Carbon Monoxide

Carbon monoxide [CO(g)], produced outdoors by automobile and other fossil-fuel

combustion sources, is emitted indoors by boilers,

heaters, stoves, ﬁreplaces, ciga-

rettes, and in-garage cars. In the absence of indoor sources, mixing ratios of CO(g)

indoors are usually less than are those outdoors (Jones, 1999). In the presence of

indoor sources, indoor mixing ratios of CO(g) can reach a factor of four or more times

those outdoors. Mixing ratios and health effects of carbon monoxide are discussed in

Section 3.6.3.

9.1.3. Nitrogen Dioxide

Nitrogen dioxide [NO

(g)] is produced chemically from oxidation of nitric oxide

[NO(g)] and is emitted in small quantities indoors. Sources of NO(g) and NO

(g)

indoors include in-garage cars, kerosene and gas space heaters, wood stoves, gas

stoves, and cigarettes. In the absence of indoor sources, indoor mixing ratios of

(g) are similar to those outdoors (Jones, 1999). High short-term mixing ratios of

(g) occur during the operation of NO

(g)-producing appliances. Because UV

sunlight does not penetrate indoors, the photolysis of NO

(g) and subsequent produc-

tion of ozone is not a concern in indoor air. The health effects of NO

(g) are discussed

in Section 3.6.8.

9.1.4. Ozone

Ozone [O

(g)], produced photochemically outdoors following photolysis of nitrogen

dioxide, is rarely produced indoors because UV sunlight, required for its production, is

usually unavailable indoors. The major indoor source of ozone is outdoor air.

Photocopy machines and electrostatic air cleaners emit sufﬁcient UV radiation to pro-

duce ozone indoors. In residences and most workplaces, however, ozone mixing ratios

indoors are almost always less than are those outdoors. The indoor to outdoor ratio of

ozone ranges from 0.1:1 to 1:1, with typical values of 0.3:1 to 0.5:1 (Finlayson-Pitts

and Pitts, 1999). Ozone is lost indoors by reaction with wall, ﬂoor, and ceiling sur-

faces; reaction with indoor gases; and deposition to ﬂoors. Health effects of ozone are

discussed in Section 3.6.5.

INDOOR AIR POLLUTION 243

9.1.5. Sulfur Dioxide

Sulfur dioxide [SO

(g)], emitted outdoors during gasoline, diesel, and coal combus-

tion, is emitted indoors during combustion of kerosene in space heaters. In the absence

of indoor sources, indoor SO

(g) mixing ratios are typically 10 to 60 percent those of

outdoor air (Jones, 1999). Once indoors, SO

(g) does not chemically degrade quickly

in the gas phase because the hydroxyl radical [OH(g)], required to initiate its break-

down, is not produced indoors. Because the e-folding lifetime of the hydroxyl radical

is about 1 second, OH(g) brought indoors from the outside disappears quickly. Losses

of SO

(g) include deposition to wall and ﬂoor surfaces, dissolution into liquid water

(e.g., in bathtubs and sinks), and dissolution into aerosol particles containing liquid

water. The health effects of sulfur dioxide are discussed in Section 3.6.6.

9.1.6. Formaldehyde

Formaldehyde [HCHO(g)], produced during bio-

mass burning and chemical reaction outdoors, is

emitted from particleboard, insulation, furnishings,

paneling, plywood, carpets, ceiling tile, and tobacco

smoke indoors. Formaldehyde mixing ratios indoors

are usually greater than are those outdoors. In out-

door air, its major breakdown processes are

photolysis by UV sunlight and reaction with HO

(g)

and OH(g). UV sunlight and OH(g) are not present

indoors, but HO

(g) sometimes is, and it is the most

likely indoor chemical breakdown source of

formaldehyde. Formaldehyde is also removed by

deposition to the ground and reaction with wall,

ﬂoor, and ceiling surfaces. Health effects of

formaldehyde are discussed in Section 4.2.6.

9.1.7. Radon

Radon (Rn) is a radioactive but chemically unreac-

tive, colorless, tasteless, and odorless gas that forms

naturally in soils. Its decay products are believed to

be carcinogenic and have been measured in high

concentrations near uranium mines and in houses (particularly in their basements)

overlying soils with uranium-rich rocks (Nazaroff and Nero, 1988). Radon plays no

role in acid deposition, stratospheric ozone, or outdoor air pollution problems.

Because of its indoor effects, radon is considered a hazardous pollutant in the United

States under the 1990 Clean Air Act Amendments (CAAA90).

Sources and Sinks

The ultimate source of radon gas is the solid mineral uranium-238 (

238

U), where

the 238 refers to the isotope, or number of protons plus neutrons in the nucleus of an

uranium atom. Of all uranium on Earth, 99.2745 percent is

238

U, 0.72 percent is

235

and 0.0055 percent is

234

238

U has a half-life of 4.5 billion years.

Radon formation from uranium involves a long sequence of radioactive decay

processes. During radioactive decay of an element, the element spontaneously emits

244 ATMOSPHERIC POLLUTION: HISTORY, SCIENCE, AND REGULATION

Figure 9.1. Antoine Henri Becquerel (1871–

1937).

(9.1)

INDOOR AIR POLLUTION 245

238

218

234

230

226

222

214

210

206

4.5x10

24 d

1.2 min

2.5x10

8x10

1620 yr

3.8 d

3 min

27 min

30 min

0.00016 s

22 yr

5 d

138 d

radiation in the form of an alpha () particle, a beta () particle, or a gamma () ray. An

alpha particle is the nucleus of a helium atom, which is made of two neutrons and two

protons (Fig. 1.1). It is the least penetrating form of

radiation and can be stopped by a thick piece of

paper. Alpha particles are not dangerous unless the

emitting substance is inhaled or ingested. A beta

particle is a high-velocity electron. Beta particles

penetrate deeper than do alpha particles, but less than

do other forms of radiation, such as gamma rays. A

gamma ray is a highly energized, deeply penetrating

photon emitted from the nucleus of an atom during

nuclear ﬁssion (such as in the sun’s core), but also

sometimes during radioactive decay of an element.

Radioactive decay was discovered on March 1,

1896, by French physicist Antoine Henri

Becquerel (1871–1937; Fig. 9.1). To obtain his dis-

covery, Becquerel placed a uranium-containing

mineral on top of a photographic plate wrapped by

thin, black paper. After letting the experiment sit in a

drawer for a couple of days, he dev

eloped the plate

and found that it was fogged by emissions (Fig. 9.2)

that he traced to the uranium in the mineral. He

referred to the emissions as metallic phosphores-

cence. What he had discovered was radioactive

decay. He repeated the experiment by placing coins

under the paper and found that their outlines were

traced by the emissions. Two years later, British

physicist Ernest Rutherford (1871–1937; Fig. 9.3)

found that uranium emitted two types of particles,

which he named alpha and beta particles.

Rutherford later discovered the gamma ray as well.

Equation 9.1 summarizes the radioactive decay

pathway of

238

U to

206

Pb. Numbers shown are half-

lives of each decay process.

When it decays to produce radon,

238

U ﬁrst

releases an alpha particle, producing thorium-234

(

234

Th), which decays to protactinium-234 (

234

Pa),

releasing a beta particle.

234

Pa has the same number

of protons and neutrons in its nucleus as does

234

Th,

but

234

Pa has one less electron than does

234

Th,

Figure 9.2. First evidence of radioactivity, along

with Becquerel’s notes (American Institute of

Physics Emilio Segrè Visual Archives, William

G. Myers Collection).

Figure 9.3. Ernest Rutherford (1871–1937).

giving

234

Pa a positive charge.

234

Pa decays further to uranium-234 (

234

U), then to

thorium-230 (

230

Th), then to radium-226 (

226

Ra), then to radon-222 (

222

Rn).

Whereas radon precursors are bound in minerals (Lyman, 1997),

222

Rn is a gas and

can escape through soil and unsealed ﬂoors into houses, where its mixing ratio builds

up in the absence of ventilation.

222

Rn has a half-life of 3.8 days. It decays to poloni-

um-218 (

218

Po), which has a half-life of three minutes and decays to lead-214 (

214

Pb).

218

Po and

214

Pb, referred to as radon progeny, are electrically charged and can be

inhaled or attach to particles that are inhaled (Cohen, 1998). In the lungs or in the

ambient air,

214

Pb decays to bismuth-214 (

214

Bi), which decays to polonium-214

(

214

Po).

214

Po decays almost immediately to lead-210 (

210

Pb), which has a lifetime of

22 years and usually settles to the ground if it has not been inhaled. It decays to

bismuth-210 (

210

Bi), then to polonium-210 (

210

Po), then to the stable isotope, lead-206

(

206

Pb), which does not decay further

Concentrations

Outdoor concentrations of radon are generally low and do not pose a human health

risk. Because of the lack of ventilation in many houses, indoor concentrations can

become thousands of times lar

ger than outdoor concentrations (Wanner, 1993). Indoor

concentrations depend on the abundance of radon in soil and the porosity of ﬂoors.

Nero et al. (1986) found mean indoor concentrations of

222

Rn in 552 homes as 56 Bq

(becquerels) m

3

, where a becquerel is a the number of disintegrations of atomic

nuclei per second. A variety of other studies found indoor concentrations of 46 to

116 Bq m

3

(Jones,

1999). Marcinowski et al. (1994) estimated that about 6 percent of

U.S. homes contained radon concentrations in excess of U.S. EPA levels considered

safe (148 Bq m

3

). Radon levels in homes can be reduced by installing check valves in

drains, sealing basement walls and ﬂoors, and installing fans in crawl spaces (to speed

mixing of outside air with radon-laden air under the house).

Health Effects

222

Rn, a gas, is not harmful itself, but its progeny,

218

Po and

214

Pb, which enter the

lungs directly or on the surfaces of aerosol particles, are believed to be highly car-

cinogenic (Polpong and Bo

vornkitti, 1998). Any activity increasing the inhalation of

aerosol particles enhances the risk of inhaling radon progeny; thus, the combination

of radon and cigarette smoking is expected to increases lung cancer risks above the

normal risks associated with smoking (Hampson et al., 1998). Whereas several stud-

ies argue that a link exists between high radon levels and enhanced cancer rates

(Henshaw et al., 1990, Lagarde et al., 1997), other studies argue that no such link

exists (Etherington et al., 1996).

9.1.8. Volatile Organic Compounds

Volatile organic compounds (VOCs) are organic compounds that have relatively low

boiling points (50 to 260C). Because of the their low boiling points, VOCs often

evaporate from materials containing them. Sources of VOCs indoors include adhe-

sives, solvents, building materials, combustion appliances, paints, varnishes, tobacco

smoke, room deodorizers, cooking, carpets, furniture, and draperies. More than 350

VOCs with mixing ratios greater than 1 ppbv have been measured in indoor air

(Brooks et al., 1991). Carpets alone emit at least 99 different VOCs (Sollinger et al.,

1994). Some common VOCs in indoor air include propane, butane, pentane, hexane,

246 ATMOSPHERIC POLLUTION: HISTORY, SCIENCE, AND REGULATION

n-decane, benzene, toluene, xylene, styrene, acetone, methylethylketone, and

limonene, among many others. VOC mixing ratios indoors can easily exceed those

outdoors by a factor of ﬁve (Wallace, 1991). Many VOCs are hazardous. The health

effects of some VOCs are described in Table 3.16.

9.1.9. Allergens

Allergens are particles such as pollens, foods, or microorganisms that cause an

allergy, which is an abnormally high sensitivity to a substance. Symptoms of an

allergy include sneezing, itching, and skin rashes. Indoor sources of allergens are

dust-mite feces, cats, dogs, rodents, cockroaches, and fungi. Pollens, mostly from

outdoor sources, originate from trees, plants, grasses, and weeds. An omnipresent

source of indoor allergens is dust mites. Dust mites grow to adult size of about 250

to 350 m from an egg in about 25 days (D’Amado et al., 1994). Their feces range

in size from 10 to 40 m. A gram of dust may contain up to 100,000 feces. The

allergen in dust-mite feces is a protein in the intestinal-enzyme coating of the feces

(Jones, 1999). Allergens in airborne dust-mite feces may exacerbate symptoms in

85 percent of asthmatics (Platts-Mills and Carter, 1997). In cockroaches, the

sources of allergens are body parts and feces. Cat allergens are present in the saliva,

dander, and skin of the cat. Dog allergens are found in the saliva and dander of the

dog. Allergens from cats, dogs, and cockroaches can trigger rapid asthmatic

responses.

9.1.10. Asbestos

Asbestos is a class of natural impure hydrated sili-

cate minerals that can be separated into ﬂexible

ﬁbers (Fig. 9.4). Asbestos is chemically inert, does

not conduct heat or electricity, and is ﬁre resistant.

Its ﬁre-resistant properties were known by French

emperor Charlemagne (742–814), who would

amuse his guests at dinner parties by wiping his

mouth with a napkin made of asbestos, throwing the

napkin into the ﬁreplace, then retrieving the

unburned napkin to their surprise. Until the 1970s,

asbestos was used widely in the construction indus-

try as an electrical and thermal insulator, particularly

in pipe and boiler insulation, cementboard, thermal tiles, paint, and wallpaper (Maroni

et al., 1995; Jones, 1999). Today, new asbestos production is banned in many coun-

tries, but much of the asbestos installed in buildings before the bans took place still

exists.

People who were most likely to be exposed to asbestos in the past were miners,

insulation manufacturers, and insulation installers. From the 1950s to 1990, the town

of Libby, Montana, was the center of a vermiculite (clay mineral) mining operation.

Unknown to the miners, the vermiculite was laden with asbestos. Between the early

1980s and 2000, 192 people from the town of 2,700 died and 375 others were diag-

nosed with asbestos-related lung problems. Some miners inadvertently exposed their

families to asbestos when they brought their clothes, carrying asbestos-laden dust, into

their homes. Today, miners and those who remove asbestos from buildings are the

INDOOR AIR POLLUTION 247

Figure 9.4. Unmilled Chrysotile asbestos. Photo

by Robert Grieshaber.