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leaving in its path a barren and unhealthy environment for all living things.
Working with Federal, State and Local mandated rules, regulations and by
carefully monitoring the emissions, industries have greatly reduced the amount of
pollutant emitted from their industrial sources, striving to obtain an acceptable
level. Because of the mandated industrial emission clean up, many land areas and
streams in and around the cities that were formerly barren of vegetation and life,
have now begun to move back in the direction of nature's intended balance.
Automotive Pollutants
The third major source of air pollution is the automotive emissions. The emissions
from the internal combustion engine were not an appreciable problem years ago
because of the small number of registered vehicles and the nation's small
highway system. However, during the early 1950's, the trend of the American
people was to move from the cities to the surrounding suburbs. This caused an
immediate problem in the transportation areas because the majority of the
suburbs were not afforded mass transit conveniences. This lack of transportation
created an attractive market for the automobile manufacturers, which resulted in
a dramatic increase in the number of vehicles produced and sold, along with a
marked increase in highway construction between cities and the suburbs. Multi-
vehicle families emerged with much emphasis placed on the individual vehicle per
family member. As the increase in vehicle ownership and usage occurred, so did
the pollutant levels in and around the cities, as the suburbanites drove daily to
their businesses and employment in the city and its fringe area, returning at the
end of the day to their homes in the suburbs.
It was noted that a fog and smoke type haze was being formed and at times,
remained in suspension over the cities and did not quickly dissipate. At first this
"smog'', derived from the words "smoke'' and "fog'', was thought to result from
industrial pollution but it was determined that the automobile emissions shared
the blame. It was discovered that when normal automobile emissions were
exposed to sunlight for a period of time, complex chemical reactions would take
place.
It is now known that smog is a photo chemical layer and was developed when
certain oxides of nitrogen (NOx) and unburned hydrocarbons (HC) from the
automobile emissions are exposed to sunlight. Pollution was more severe when
the smog would become stagnant over an area in which a warm layer of air would
settle over the top of a cooler air mass at ground level, trapping and holding the
automobile emissions, instead of the emissions being dispersed and diluted
through normal air flows. This type of air stagnation was given the name
"Temperature Inversion''.
Temperature Inversion
In normal weather situations, the surface air is warmed by the heat radiating
from the earth's surface and the sun's rays and will rise upward, into the
atmosphere, to be cooled through a convection type heat expands with the cooler
upper air. As the warm air rises, the surface pollutants are carried upward and
dissipated into the atmosphere.
When a temperature inversion occurs, we find the higher air is no longer cooler
but warmer than the surface air, causing the cooler surface air to become trapped
and unable to move. This warm air blanket can extend from above ground level to
a few hundred or even a few thousand feet into the air. As the surface air is
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18.11.2005 http://www.chiltondiy.com/content/8687/8687_4_1.html