The
Catalyst
and
Clean Air
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Lo meet the tougher auto exhaust
limits that went into effect with
the production of 1975 model auto-
mobiles, U.S. manufacturers are using
a catalytic converter system, usually
just called a "catalyst," on most of
their new cars. In this system, the
exhaust passes through catalytic
material in a stainless steel container
so that much of the unburned
hydrocarbons coming from the engine
are converted into harmless carbon
dioxide and water, and carbon
monoxide is changed into carbon
dioxide. The cleaned exhaust is expelled
through a conventional muffler.
The U.S. Environmental Protection
Agency has received many inquiries
about the catalyst. This leaflet has
been prepared to answer the questions
most frequently asked.
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How much does a catalyst cost?
Catalyst installed in 1975 model cars cost
the purchaser about $60 to $100. Since
there is no change in emission control
requirements for 1976 model cars, the cost
of the catalyst is expected to be about the
same as in the 1975 models. Properly
maintained and not abused, most catalysts
are designed to operate for 50,000 miles.
Replacement cost is expected to range from
$40 to $100 or so; in some cars it is possible
to replace only the catalytic materials, while
in others the entire unit must be replaced.
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Does the catalyst increase
gasoline consumption?
No. In fact most vehicles equipped with
catalysts show a marked improvement in
gasoline mileage over the 1974 models. Many
of the measures used by manufacturers
to meet emission control standards from 1968
through 1974 involved engine adjustments
which resulted in lower fuel economy. With
the catalyst these adjustments often are not
necessary and fuel economy is approximately
what it was for uncontrolled cars.
Don't catalysts require special,
expensive gasolines?
All cars equipped with catalysts require
unleaded gas. Most cars manufactured since
1971 are designed so that they can run on
unleaded gas. Currently, unleaded regular
gasoline is priced at about one cent more per
gallon than the leaded regular grade. This
additional cost is more than offset in
most catalyst-equipped cars by the improved
fuel economy and the longer life of
components, such as spark plugs and
exhaust systems, resulting from use of
unleaded gasoline.
What happens to my car
if the catalyst fails?
There would be no change in engine
performance from a malfunctioning catalyst
but there would be a substantial increase
in the amounts of hydrocarbons and carbon
monoxide in the exhaust.
Is the catalyst a fire hazard?
A catalyst-equipped vehicle with an engine
operating properly is no more of a fire hazard
than vehicles without catalysts. But when
an engine has defective ignition, i.e. one or
more spark plugs not firing, it is possible
for the catalyst to get hotter than an ordinary
muffler. To avoid any such problem you
should make sure that your engine is always
properly maintained. EPA has asked the
industry to add catalyst over-temperature
warning systems to their cars, and that
suggestion is being considered.
Why does EPA require catalysts?
EPA does not require catalysts. The Clean
Air Act puts a limit on how much pollution
there can be in auto exhaust. The law leaves
it up to the individual auto manufacturer
to decide how to make cars that won't
exceed those limits. EPA tests vehicles to be
certain that whatever system is used, pollution
levels are at or below what the law requires.
Does the catalyst produce more
sulfuric acid mist?
In some cases, yes. Gasoline usually contains
some sulfur, either as a natural impurity
or as a sulfur compound additive. When
gasoline is burned this sulfur is oxidized into
sulfur dioxide gas. In cars without catalysts
most of this sulfur dioxide passes through
the exhaust system into the air where
it quickly disperses and, in a span of several
days, reacts to form various sulfates including
perhaps sulfuric acid. Some catalyst
emission control systems, however, change
some of the sulfur dioxide into sulfuric acid
within the exhaust system.
How serious is this problem?
Present indications are that automotive
sulfuric acid is not an immediate major health
problem. But as more and more catalyst-
equipped cars come into use, it may become
necessary to limit the amount of sulfuric
acid in auto exhausts. Research is underway
to determine the exact quantities of sulfuric
acid being emitted by catalyst-equipped cars
and to learn how these emissions accumulate
or disperse in the atmosphere. >
What is EPA doing to avoid adverse
health effects from catalysts?
EPA will adopt a sulfuric acid emission
standard for new automobiles at a level which
will avoid any significant increase in health
risk from automotive sulfate emissions.
That standard is expected to take effect
with the 1979 model year, the earliest date at
which manufacturers can be expected to
have developed arid tested low sulfate '
automotive systems. EPA has postponed
for a year the stronger hydrocarbon and
carbon monoxide control requirements
scheduled for 1977 model cars. The stricter
standards would lead auto makers to install
a more effective catalyst which in turn might
produce more sulfuric acid. EPA .also
suggested that Congress consider further
delays in the emission standards to provide
time for the auto industry vfcft develop sulfuric
acid emission control technology.
Using leaded gasoline
will "kill" the catalyst.
Wouldn't this solve
the sulfuric acid problem?
Such action would also increase the amounts
of hydrocarbons and carbon monoxide in
the exhaust by anywhere from 100 to
300 percent. The amount of sulfuric acid now
in the exhaust is not judged to be harmful
to human health. EPA believes that a
1979 sulfuric acid emission standard will
protect public health from this pollutant
while preserving the benefits of controlling
hydrocarbons and carbon monoxide.
Some catalysts have at times
produced a "rotten egg" smell.
Why? §
Catalysts burn pollutants in the presence §
of excess air. If, for some reason, there is not <$
as much air available as is needed some of q;
the sulfur dioxide in the exhaust stream can-i
be converted into hydrogen sulfide, which ^
has that particularly objectionable odor. o
This odor usually indicates that engine &
maintenance is needed. 'nl ,
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Is hydrogen sulfide g
a health problem? g :
Like any toxic chemical, hydrogen sulfide g {
becomes increasingly toxic as exposure pq £
increases. It is very doubtful, however, that
automotive exhausts could form enough
hydrogen sulfide to create a health risk. The
presence of a strong odor does not by itself
indicate a high concentration of the gas.
The odor of hydrogen sulfide is so pungent
that it can be smelled in minute concentrations
far below any danger level.
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