Environmental Engineering Reference
In-Depth Information
partly because of government regulations and partly because of improve-
ments by the auto companies. The introduction of partially or completely
electric vehicles should accelerate the downward trend.
In 2004, about one-third of Americans lived in an area with unhealth-
ful short-term levels of PM
2.5
pollution.
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Nearly 20 percent live in an
area with unhealthful year-round levels. The worst American cities for
particle pollution are Pittsburgh and Los Angeles. In December 2008,
California enacted measures to force trucks to use fi lters to reduce diesel
soot emissions by 85 percent, estimating that they would save about 600
lives per year.
Ozone
Ozone is an extremely reactive gas molecule composed of three oxygen
atoms, in contrast to normal oxygen gas, which contains two oxygen
atoms. It is formed by chemical reactions in the air near the ground from
two gases that are generated from burning fossil fuels: nitrogen oxides
and hydrocarbons. The hydrocarbons are commonly termed VOCs:
volatile (easily evaporated) organic compounds. When the nitrogen com-
pounds and VOCs come in contact with heat and sunlight, they combine
to form ozone, the main component of the near-ground substance we
call smog. Smog is thus a secondary pollutant; it does not come belching
out of smokestacks or car exhausts. Smog is harmful to breathe because
it attacks lung tissue. It is capable of causing infl ammation in the lung
at lower concentrations than any other gas. Those most affected are the
elderly, children, people who work or exercise outdoors, and those with
existing lung diseases such as emphysema and chronic bronchitis.
The current federal allowable amount of ground-level ozone is 75
parts per billion; one-third of the U.S. population lives in counties that
exceed this standard.
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However, we are making signifi cant progress in
smog reduction. Studies indicate that a decrease of 10 parts per billion
ozone saves more than 3,700 lives annually and increases life expectancy
by 2.7 years.
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Smog is a particularly serious problem for the 20 million asthma suf-
ferers in the United States.
12
Every day, 40,000 people miss school or
work because of asthma, 30,000 people have an asthma attack, 5,000
people visit the emergency room and account for one-quarter of all such
visits, 1,000 people are admitted to the hospital, and 11 people die. In
the smoggy San Joaquin Valley of California, 15 percent of the children
have asthma, and Fresno, the valley's largest city, has the third highest
rate of asthma in the country. On bad days, some schools hoist a red
