AND EFFECT OF AIR POLLUTANTS
pollution occurs in many forms but can generally be thought of as gaseous and
particulate contaminants that are present in the earth's atmosphere. Gaseous pollutants include sulfur dioxide (SO2), nitrogen oxides
(NOx), ozone (O3),
carbon monoxide (CO), volatile organic compounds (VOC), hydrogen sulfide (H2S),
hydrogen fluoride (HF), and various gaseous forms of metals. These pollutants
are emitted from large stationary sources such as fossil fuel fired power
plants, smelters, industrial boilers, petroleum refineries, and manufacturing
facilities as well as from area and mobile sources. They are corrosive to
various materials which causes damage to cultural resources, can cause injury
to ecosystems and organisms, aggravate respiratory diseases, and reduce
Particulates come in
both large and small or "fine" solid forms. Large particulates include substances such as dust, asbestos fibers, and
lead. Fine particulates include sulfates (SO4) and nitrates (NO3).
Important sources of particulates are power plants, smelters, mining
operations, and automobiles. Asbestos and lead affect organisms, while sulfates
and nitrates not only cause health problems, but also contribute to acid rain
or acid deposition and a reduction in visibility. Particulate matter, a term
sometimes used instead of particulates, refers to the mixture of solid
particles and liquid droplets found in the air.
Toxic air pollutants are a
class of chemicals which may potentially cause health problems in a significant way. The sources of toxic air pollutants
include power plants, industries, pesticide application, and contaminated
windblown dust. Persistent toxic pollutants, such as mercury, are of particular
concern because of their global mobility and ability to accumulate in the food
chain. More research is needed to fully understand the fate and effects of
mercury and the many other toxic pollutants.
Primary pollutants are those
that are emitted directly into the air from pollution sources. Secondary
pollutants are formed when primary pollutants undergo chemical changes in
the atmosphere. Ozone is an example of a secondary pollutant. It is formed when
nitrogen oxides (NOx) and volatile organic compounds (VOCs) are
mixed and warmed by sunlight. Ozone (O3) is a major component of
what is often referred to as smog. The ozone which is present in the
troposphere, or the atmosphere that is close to the ground, should not be confused
with beneficial ozone that is located in the stratosphere or upper atmosphere.
This beneficial ozone in the stratosphere helps protect the earth from harmful
ultraviolet light from the sun.