Environmental Engineering Reference
In-Depth Information
required that Secretary do so. Beginning with the 1968 model year, federal
standards set hydrocarbon emissions at no more than 275 parts per million
(ppm) and put the acceptable level of carbon monoxide at 1.5 percent of
total emissions. By the 1970 model year these were required to drop to 180
ppm and 1.0 percent, respectively.The federal Clean Air Act, passed in 1970,
mandated a 90 percent reduction in emissions of nitrogen oxide by 1976.
New standards for hydrocarbons and carbon monoxide were even more
ambitious; amendments to the act passed in 1977 required a 96 percent
reduction of these pollutants.
Another set of amendments passed in 1990 gave the automobile indus-
try its current emissions standards, which are now defined in terms of pol-
lutants per mile rather than as percentages of total emissions. Beginning
with the 1994 model year, carbon monoxide was to be limited to 3.4 grams
per mile, hydrocarbons to 0.25 gram per mile, and NOx to 0.4 gram per
mile.There was also a requirement that emissions controls perform accept-
ably for 100,000 miles. Regions currently not in compliance with current
air-quality standards were obliged to meet them according to a specific
schedule or face a possible loss of federal highway construction and main-
tenance funds.
In 1990 the state of California went one step further.The California Air
Resources Board (CARB) decreed that by 1998 2 percent of new cars sold
had to be zero-emissions vehicles (ZEVs), with the ratio rising to 5 percent
in 2000 and 10 percent in 2003. Faced with intense opposition from man-
ufacturers and the absence of a receptive market, in 1996 CARB rescinded
the 1998 and 2000 mandates while retaining the one for 2003. The pro-
gram was further modified in early 2001, when CARB enacted a compli-
cated schedule that granted manufacturers extra credits for such things as
the early introduction of ZEVs and the sale of ZEVs with ranges beyond
50 miles, as well as an award of half a ZEV credit for “partial zero emission
vehicles” such as gasoline-electric hybrids.The program also stipulated that
the ZEV requirements would increase after 2008, rising to 16 percent of
the light vehicle fleet by 2018. 4
Whether these standards will be met is an open question.The only zero-
emissions vehicles available for at least the next decade are battery-powered
electrics. The high cost and limited range of these vehicles makes their
widespread usage problematic, and up to now the few electrics that have
been put on the market have met with a tepid consumer response at best.
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