vvEPA
Air and Radiation EPA420-R-05-014
December 2005
UnTted States NR-001c
Environmental Protection
Agency
Temperature Corrections for
Nonroad Exhaust Emissions
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EPA420-R-05-014
December 2005
for
NR-OOIc
Assessment and Standards Division
Office of Transportation and Air Quality
U.S. Environmental Protection Agency
NOTICE
This technical report does not necessarily represent final EPA decisions or positions.
It is intended to present technical analysis of issues using data that are currently available.
The purpose in the release of such reports is to facilitate the exchange of
technical information and to inform the public of technical developments which
may form the basis for a final EPA decision, position, or regulatory action.
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Purpose
This report documents how the final NONROAD2005 emission inventory model
accounts for the effects of temperature on four-stroke exhaust emissions. RVP and temperature
also affect both vapor displacement, which is covered in NR-013b ("Refueling Emissions for
Nonroad Engine Modeling") as well as diurnal emissions, which are covered in NR-012c
("Nonroad Evaporative Emission Rates").
Background
NONROAD includes effects of ambient temperature on exhaust emissions. The method
used in NONROAD is taken directly from the MOBILESb highway vehicle emission factor
model. Only effects on 4-stroke gasoline engine exhaust hydrocarbons (HC), carbon monoxide
(CO), and oxides of nitrogen (NOx) are included. We are not aware of any data that could be
used to estimate temperature effects on the other pollutants in NONROAD, so no such effects
are currently modeled.
Approach
Temperature Effects on Four-Stroke Exhaust Emissions
The details of the temperature correction method from the MOBILESb model are as
follows:
TCP = EXP [ A * (Tambient -75) ]
where:
TCP = multiplicative Temperature Correction Factor
Tambient = Ambient Temperature, in degrees Fahrenheit
"A" = The coefficient "A" is taken from MOBILESb for "Bag 2" effects on uncontrolled
light-duty gasoline vehicles (LDGV's). "Bag 2" refers to the hot stabilized portion of the
test sequence, so no cold-start effects are present. The value of "A" in the above equation
depends on high or low temperature (relative to 75F) and on pollutant (HC/CO/NOx).
Values for A are:
NR-OOlc December 2005
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"A" Tambient<75 Tambient>75
HC (4-stroke) - 0.00240 +0.00132
CO (4-stroke) +0.00158 +0.00375
NOx (4-stroke) - 0.00892 - 0.00873
These coefficients are applied only to pre-1968 model year vehicles in MOBILE,
including both LDGVs and LDGTs. These coefficients for pre-1968 model year vehicles are
assumed to apply to all nonroad 4-stroke engines. Due to lack of data, there is no attempt in
NONROAD to apply different temperature corrections for different generations of nonroad 4-
stroke engine technologies.
For two-stroke engines, conditions differ significantly from those of on-road motor
vehicles. Therefore, the 4-stroke corrections from MOBILESb are not applied to 2-stroke or
diesel engines in NONROAD. Due to lack of data for these engine types, temperature effects on
exhaust emissions from 2-stroke and diesel engines are not currently included in
NONROAD2005.
NR-OOlc December 2005
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