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40 Lawrence K. Wang et al.

viewed as another significant ozone-depleting compound; (7) stratospheric ozone loss-
es cause a global-mean negative radiative forcing; the ozone-depleting gases (CFCs,
carbon tetrachloride, methyl chloroform, methyl bromide, etc.) have been used exten-
sively in industrial applications, including refrigeration, air conditioning, foam blowing,
cleaning of electronic components, and as solvents; (8) many countries have decided to
discontinue the production of CFCs, halons, carbon tetrachloride, and methyl chloro-
form, and industry has developed many “ozone-friendly” substitutes for protection of
the stratospheric ozone layer; and (9) in the domestic refrigeration industry, HFC134A
and HFC152A have been used as the substitutes for CFC; in commercial refrigeration
industry, HFC134A, HCFC22, HCFC123, and ammonia have been used as the substi-
tute for CFC; and in mobile air conditioning systems, only HFC134A is recommended
as the substitute for CFC.

9.2.2. Photochemical Oxidants
The formation of ozone in the troposphere (lower level) is simplistically illustrated
in Fig. 16. The primary constituents are nitrogen oxides (NO ), organic compounds, and
x
solar radiation. Nitrogen oxide emissions are primarily from combustion sources,
including both stationary and nonstationary types. Coal-burning power plants are the
major stationary source for NO , whereas transportation modes, such as automobiles,
x
trucks, and buses, are the major nonstationary source for NO . Another source for
x
organic compounds is waste-management operations.
When nitrogen oxides and organic compounds are exposed to sunlight, a series of
complex chemical reactions occur to form two principal byproducts: ozone (O ) and an
3
aerosol that, among other things, limits visibility. This mixture of ozone and aerosol is
described as photochemical smog. The respiratory system can be negatively affected
when humans are exposed to ozone. Possible effects include inflammation of the lungs,
impaired breathing, reduced breathing capacity, coughing, chest pain, nausea, and gen-
eral irritation of the respiratory passages. The long-term exposure to ozone could
result in increased susceptibility to respiratory infections, permanent damage to lung
tissue, and severe loss of breathing capacity. The effects of ozone are more severe on
the very young, elderly, and those with pre-existing respiratory conditions than on the
normal, healthy, adult population. It has been shown, however, that young, healthy
individuals who exercise outdoors can also exhibit negative health effects when
exposed to ozone.
Urban areas can be subjected to an oxidizing type of pollution, which is the result of
a chemical reaction of NO and HC in sunlight and produces O , PAN, and other complex
x 3
compounds. This pollution is described as ozone and referred to as photochemical oxi-
dants. Because this pollution is considered a secondary pollutant, transport is a concern.
Ozone is a regional concern because it can impact an area 250 km from the source.
Researchers showed the existence and the extent of impact of ozone on human
health. In 1998, a study examined several hundred deceased persons in Los Angeles
who were victims of automobile accidents but were otherwise healthy. It was found that
about half had lesions on their lungs, which is a characteristic of lung disease in the
early stages. One of the causes for the observed lesions was attributed to the victims’
exposure to the levels of ozone in the Los Angles area.