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of people worldwide who enjoy the benefits provided by cars
and trucks also suffer the miseries of traffic pollution.
advances in automotive technology are helping to stem the
tide of pollution and recent U.S. research into the effectiveness
of one particular anti-pollution automotive component has
uncovered one of the planetâ€™s greatest environmental
success stories which may have far-reaching global implications
for as markets for new cars expand.
The device in question is the catalytic
converter, which cleans gases passing through vehiclesâ€™ exhaust
Engineers estimate that during the last
11 years 130 million catalytic converters used in the U.S.
have eliminated automotive pollutants that-if unchecked and
unabated-could have covered the country with a toxic blanket
of carbon monoxide more than 500 feet deep.
The carbon monoxide was captured from exhaust
streams by catalytic converters and converted into harmless
Engineers say that between 1975 and 1996,
emissions control technology cleaned automotive exhaust streams
in the U.S. of about 195 million tons of carbon monoxide;
nearly 42 million tons of hydrocarbons; and at least 37 million
tons of oxides of nitrogen. The carbon monoxide, at standard
pressure and temperature (one atmosphere at 32 degrees Fahrenheit)
and 100 parts per million concentration (the toxic level)
would pile 512 feet high over the 50 states.
The U.S. Environmental Protection Agency
(EPA) data shows that due to emission controls, vehicles
now sold in the U.S. emit 96 per cent less carbon monoxide,
98 per cent less hydrocarbons, and 90 per cent less oxides
of nitrogen than vehicles sold in the early 1970s.
The improvement in air quality is continuing,
as new vehicles are equipped with the latest emission control
technology and older cars are scrapped. Currently, 85 per
cent of automotive air pollution in the U.S. comes from the
oldest 50 per cent of vehicles on the road.
Catalytic converters typically consist
of a ceramic or metal honeycombed monolith substrate that
carries precious metal catalysts. The coated substrate is
wrapped in an intumescent mat that expands when heated, securing
and insulating the substrate which is packaged in a stainless
steel shell and fitted into the engine exhaust system.
As exhaust gases pass over the catalysts,
they promote chemical reactions that convert pollutants into
harmless gases and water. Hydrocarbons combine with oxygen
to become carbon dioxide; oxides of nitrogen react with carbon
monoxide to produce nitrogen and carbon dioxide; and with
hydrogen to produce nitrogen and water vapour.
The catalyst formulation, which promotes
a faster chemical reaction at a lower temperature, is usually
a mixture of the noble metals platinum, palladium and rhodium,
and sometimes other catalysts such as the rare earth ceria.
A catalytic converter is not a stand-alone
cure-all for emissions control. Unleaded fuel is required.
And to operate properly, a converter is fitted as part of
an engine management subsystem - an integrated set of specific-purpose
emission control components. plesk