Air pollution and cars were first linked in the early 1950’s by a California researcher who determined that traffic was to blame for the smoggy skies over Los Angeles. At the time, typical new cars were emitting nearly 13 grams per mile hydrocarbons (HC), 3.6 grams per mile nitrogen oxides (NOx), and 87
grams per mile carbon monoxide (CO).
Since then, the Federal Government has set standards to bring down levels of these pollutants, and the auto industry has responded by developing new emission control technologies. The current Federal certification standards for exhaust emissions from cars are 0.25 gram per mile HC, 0.4 gram per mile NOx,and 3.4 grams per mile CO. The standard for evaporative HC emissions is 2 grams per test. The improvements came about in a series of steps:
Read more
http://www.epa.gov/oms/consumer/12-miles.pdf
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