Environmental Engineering Reference
In-Depth Information
history of bronchitis, emphysema, or heart disease. Apparently, individuals with a previous history
of respiratory and cardiac diseases are predisposed to the impact of air pollution.
The 1952 London pollution episode induced the British Parliament to pass a Clean Air Act in
1956. This act focused on the manner and quality of coal burned in Great Britain. This act, and the
fact that Great Britain shifted much of her fuel use from coal to oil, “cleaned” the air considerably
over the British Isles. The ubiquitous London fog became a much rarer event; and when it occurs,
it may be truly a natural phenomenon, rather than of anthropogenic cause as it was often in
the past.
In the United States the first Clean Air Act was passed by Congress in 1963. Subsequently, the
Clean Air Act was amended in 1970, 1977, and 1990. Other countries followed suit by enacting
their own clean air acts and various legislation and regulations pertaining to reducing air pollution.
As a consequence, the air quality in most developed countries is improving steadily, although what
is gained in reducing emissions from individual sources is often negated by the ever-increasing
number of sources, especially automobiles.
We classify air pollutants in two categories: primary and secondary. Primary pollutants are
those that are emitted directly from the sources; secondary ones are those that are transformed by
chemical reactions in the atmosphere from primary pollutants. Examples of primary pollutants are
sulfur dioxide, nitric oxide, carbon monoxide, organic vapors, and particles (inorganic, organic,
and elemental carbon). Examples of secondary pollutants are higher oxides of sulfur and nitrogen,
ozone, and particles that are formed in the atmosphere by condensation of vapors or coalescence
of primary particles. We shall later explain some of the processes that lead to the transformation of
primary to secondary pollutants.
Most developed countries prescribe the maximum amount of pollutants that can be emitted
from the sources. These are called
emission standards
. For large sources, the emission standards are
usually set at a level that, after dispersion in the air within a reasonable distance, the pollutants will
not cause significant human health or environmental effects. For small sources, such as automobiles,
the emission standard may be set so as to prevent health effects from the cumulative emissions of
all sources.
In order to protect human health and biota, most countries also prescribe maximum tolerable
concentrations in the air. These are called
ambient standards
. The emission and ambient standards
are legal parameters, published in laws and decrees. If these standards are exceeded, the causative
sources can be punished or penalized, or their licences can be revoked.
9.2.1
U.S. Emission Standards
In the United States, emission standards have been promulgated for stationary and mobile sources.
The Clean Air Act Amendments of 1970, 1977, and 1990 require the Environmental Protec-
tion Agency (EPA) to promulgate emission standards, called New Source Performance Standards
(NSPS) and National Emission Standards for Hazardous Air Pollutants (NESHAP). Emission
standards are specific to certain industrial categories, such as power plants, steel plants, smelters,
refineries, pulp and paper mills, chemical manufacturing, and so on, as well to mobile sources—that
is, automobiles, trucks, aircraft, and ships. The maximum allowable emission rates are prescribed
for a variety of pollutants including SO
2
,NO
x
(the sum of NO and NO
2
), CO, particulate matter
(PM), lead, mercury, arsenic, copper, manganese, nickel, vanadium, zinc, barium, boron, chromium,
selenium, chlorine, HCl, benzene, asbestos, vinyl chloride, pesticides, radioactive substances, and
many other inorganic and organic pollutants.
