CRS Report for Congress
EPA's Tier 2 Emission Standards for
New Motor Vehicles: A Fact Sheet
David M. Bearden
Environmental Information Analyst
Resources, Science, and Industry Division
The Clean Air Act Amendments of 1990 established “Tier 1” standards to limit
tailpipe emissions from new motor vehicles. The law also required the Environmental
Protection Agency (EPA) to determine if stricter controls would be necessary by model
year (MY) 2004 to assist states in attaining or maintaining the National Ambient Air
Quality Standards. EPA also was required to assess the availability and cost-effectiveness
of technologies necessary to control emissions. In a report submitted to Congress in
August 1998, EPA concluded that tougher standards are necessary and that essential
technologies are available and cost-effective.1 As a result, EPA finalized stricter “Tier 2”
standards on February 10, 2000.2 The new standards will be phased in beginning in
MY2004 and will require all new passenger cars and light trucks up to 8,500 pounds, and
all new heavier passenger vehicles up to 10,000 pounds (including large sport-utility
vehicles), to demonstrate full compliance by MY2009. To improve the efficiency of
emission control technologies, oil refiners also will be required to limit gasoline sulfur
levels to an average of 30 parts per million (ppm) nationwide beginning in 2005, roughly

90% less than the current national average of 340 ppm.

The new Tier 2 standards will require vehicle manufacturers to reduce tailpipe
emissions of carbon monoxide (CO), formaldehyde (HCHO), nitrogen oxides (NOx), non-
methane organic gases (NMOG), and particulate matter (PM). However, manufacturers
will have the flexibility to average the NOx emissions of their vehicle fleets to demonstrate
compliance with the standards instead of certifying each vehicle according to the same
stringency. The standards will require the most reductions in emissions of NMOG and
NOx to help control the formation of ground-level ozone pollution. Relative to the Tier
1 standards, the fleet average standard for NOx will require vehicle manufacturers to
reduce overall tailpipe emissions by 88% to 95%. The standards also will require at least
an 80% reduction in PM emissions but will require less stringent reductions in CO
emissions. The standard for HCHO is a new requirement that is intended to reduce
emissions of carcinogenic pollutants. The table on page 2 compares the current Tier 1
standards, which became effective in MY1994, to the new Tier 2 standards that will be
phased in beginning in MY2004.

1EPA. Office of Air and Radiation. Tier 2 Report to Congress. July 31, 1998. 55 p.
2EPA. Federal Register. February 10, 2000. p. 6698-6870.
Congressional Research Service ˜ The Library of Congress

Comparison of Tier 1 and Tier 2 Tailpipe Emission Standards for Motor Vehicles
Intermediate Useful Life (grams/mile) aFull Useful Life (grams/mile) a
Vehicle Type/WeightNMHC/NMHC/
.250 3.4 .40 .08 n/a .310 4.2 .60 .10 n/a
.320 4.4 .70 .08 n/a .400 5.5 .97 .10 n/a
.390 5.0 1.10 n/a n/a .560 7.3 1.53 .12 n/a
c n/a n/a n/a n/a n/a n/a n/a .07 n/a n/a
d n/a n/a n/a n/a n/a n/a n/a .20/.30 n/a n/a
e n/a n/a n/a n/a n/a .280 7.3 .90 .12 .032
f, g.125/.1603.4/4.4.40n/a.015/.018.156/.2304.2/
f, g.075/.1403.4.20n/a.015.090/.1804.
g .100/.125 3.4 .14 n/a .015 .125/.156 4.2 .20 .02 .018
.075 3.4 .11 n/a .015 .090 4.2 .15 .02 .018
.075 3.4 .08 n/a .015 .090 4.2 .10 .01 .018
.075 3.4 .05 n/a .015 .090 4.2 .07 .01 .018
n/a n/a n/a n/a n/a .070 2.1 .04 .01 .011
n/a n/a n/a n/a n/a .055 2.1 .03 .01 .011
n/a n/a n/a n/a n/a .010 2.1 .02 .01 .004
n/a n/a n/a n/a n/a .000 0.0 .00 .00 .000
intermediate useful life standards set a benchmark for the amount of pollutants that a vehicle is expected to emit after being driven
to emit after 100,000
of vehicle use. The Tier 2 standards increase the full useful life benchmark to 120,000 miles. If a manufacturer voluntarily chooses

1 vehicles are subject to the testing procedure for NMHC, but Tier 2 vehicles will be subject to the testing procedure for NMOG.

pollutants are closely related hydrocarbon compounds that can combine with NOx in the presence of sunlight to form ground-level
manufacturer will have the flexibility to select any set, or “bin”, of emission standards when certifying different models of vehicles,
x emissions.
the phase-in period, the interim fleet average for LDVs and LLDTs will be .30 grams/mile and will expire at the end of
x = nitrogen oxides