Encyclopedia of Environmental Science and Engineering, Volume I and II

AIR POLLUTANT EFFECTS 33

reacting with the nitric oxide, the ozone is removed by the

rapid reaction

NO  O 3  NO 2  O 2

Therefore, concentrations of ozone will remain quite small

unless there is a competing reaction for rapid removal of the

nitric oxide.

Many organic compounds can play the role of nitric-

oxide remover in forming photochemical oxidants such as

peroxyacetylnitrate (PAN, CH 3 COO 2 NO 2 ).^ VOCs possess-

ing varying reactivities are able to remove nitric oxide and

thus make possible the buildup of ozone:

VOC  NO → NO 2  organic nitrates

Although ozone is the major component, peroxynitrates, per-

acids, hydroperoxides, aldehydes, and a variety of other com-

pounds are found in photochemical smog. Among the major

sources releasing reactive organic compounds are automobile

engines and tailpipes; gasoline stations; the use of solvents,

paints, and lacquers; and a variety of industrial operations.

Thus, the control of ozone is complicated by the variety of

sources and the distances that can occur between high-ozone

areas and the sources. Suburban and rural areas downwind

of urban sources will often have higher ozone levels than

source areas because of the transport that occurs while ozone

is being formed. Both ozone and PAN cause serious injury to

vegetation, but PAN does so at much lower concentrations.

PARTICULATE MATTER

“Fine particles” are less than 2.5 m in size and require

electron microscopy for detection; nevertheless, they are

much larger than molecules such as ozone and other gas-

eous pollutants, which are thousands of times smaller and

cannot be seen even with electron microscopy. Fine particles

are formed by the condensation of molecules into solids or

liquid droplets, whereas larger particles are mostly formed

by mechanical breakdown of material. “Coarse particles”

are between 2.5 and 10 m in diameter and cannot pene-

trate as readily as fine particles; nevertheless, they have been

found to cause serious deterioration of health. The severity

of effects will vary with the chemical nature of the particles;

however, since their nature can be so varied and difficult to

determine, coarse and fine particles are considered in terms

of what epidemiological studies have shown.

The inhalation of particles has been linked with illnesses

and deaths from heart and lung disease as a result of both

short- and long-term exposures. People with heart disease

may experience chest pain, palpitations, shortness of breath,

and fatigue when exposed to particulate-matter pollutants.

Exposures have been linked to cardiac arrhythmias and

heart attacks. Inhalation of particulate matter can increase

susceptibility to respiratory infections such as asthma and

chronic bronchitis. The EPA has found that nearly 100

million people in the United States live in areas that have

not met the standard for particulate matter with a diameter

less than 2.5 m. It estimates that compliance by 2010 will

prevent 15,000 premature deaths, 75,000 cases of chronic

bronchitis, 20,000 cases of acute bronchitis, 10,000 hospital

admissions for respiratory and cardiovascular disease, and

the loss of 3.1 million days worked.

Emissions from diesel-fuel combustion in vehicles and

equipment are a special problem, especially for those individ-

uals breathing in close proximity to the exhausts. Cars, trucks,

and off-road engines emit more than half a million tons of

diesel particulate matter per year. Emissions of 2.5-m par-

ticles have decreased in the United States from 2.3 million

tons in 1990 to 1.8 million tons in 2003.

SULFUR DIOXIDE

The combustion of sulfur-containing fuels is the main source

of sulfur-dioxide air pollution. The oil and coal burned to

heat homes and water and to produce electrical power are

the main sources that affect the general population, but indi-

viduals who live near metal smelting and other industrial

processes can be heavily exposed. Sulfur-dioxide exposures

are usually accompanied by exposures to particulate matter,

which together exacerbate the effects.

Emissions of sulfur compounds from motor vehicles

have increased in importance as those from oil and coal

burning have been reduced. The diesel fuel used in vehicles

can contain up to 500 ppm by weight of sulfur. California,

which has the unfortunate combination of high emissions

and poor atmospheric ventilation, hopes to reduce the

allowable sulfur content of fuels to 15 ppm by 2007. It

must be noted that California is the only state that is not

preempted by the federal government in controlling pollu-

tion, because its efforts anteceded those of the federal gov-

ernment. Emissions of sulfur dioxide in the United States

decreased from 31 million tons in 1970 to 16 million tons

in 2003.

The defense mechanisms of the lung are challenged by

sulfur dioxide; however, its rapid solution in water irritates

tissues but reduces the concentrations that reach the deeper

parts of the lung. Inhalation of particulate matter together with

sulfur dioxide increases the hazard to the lungs. Asthmatic

children and active adults can experience breathing difficul-

ties in high concentrations of sulfur dioxide, and individuals

with cardiovascular disease can have their symptoms exac-

erbated. The conversion in the atmosphere of sulfur dioxide

into sulfite and sulfate acidic aerosol particles increases its

threat to health.

Sulfur dioxide harms the body’s defense system against

particulate pollution and the ingress of bacteria into the body

through the respiratory system. It also increases the harm-

ful effects of ozone when both of these gases are present.

Asthmatics, the elderly, and those already suffering from

respiratory problems are affected at lower concentrations

than the general population. Studies have shown that in the

1950s and 1960s, when ambient concentrations were some-

times higher than 1 ppm and mixed with particulate matter,

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