ESTIMATING SMOG PRECURSOR
EMISSIONS FROM IDLING VEHICLES
IN THE CHICAGO METROPOLITAN
AREA
Riyaz Shipchandler
Jim Janssen
Gary Miller*
Illinois Sustainable Technology Center
Institute of Natural Resources Sustainability
University of Illinois at Urbana-Champaign
October, 2008
Submitted to the
Metropolitan Mayors Caucus
177 North State Street, Suite 500
Chicago, Illinois 60601
*
Corresponding author: Dr Gary Miller, Acting Director of the Illinois Sustainable Technology Center. He can be
reached by phone at (217) 333-8940 or by email at gmiller@istc.illinois.edu .
1
Estimating emissions from idling vehicles can be helpful in securing organizational support for
idling reduction programs. The development of these programs is discussed in a companion
paper entitled, Idling Reduction Programs for the Chicago Metropolitan Area . Section I of this
paper provides an overview of smog precursor emissions in the Chicago region, and Section II
shows how emission calculations can be tailored to specific situations, such as determining
emissions from idling vehicles near a school.
I: OVERVIEW OF EMISSIONS FROM IDLING VEHICLES
Determining the total quantity of emissions produced from idling vehicles in the Chicago
metropolitan area is difficult due to the lack of scientific data. However, using reasonable
assumptions, idling emissions can be estimated.
A. Vehicle Emissions
Vehicles are a significant source of air pollution. In fact, emissions from on-road vehicles are
estimated to be the largest source of anthropogenic (man-made) smog precursors in the Chicago
region according to the Illinois Environmental Protection Agency (Figure 1).1 In 2002, on-road
vehicles emitted 578 tons per day of smog precursors in the Chicago metropolitan area or 31.4%
of total anthropogenic emissions. Heavy-duty trucks, passenger vehicles and light duty trucks
(pickup trucks, SUV's, vans, minivans, etc. ) emitted 240, 181 and 153 tons per day of smog
precursors, respectively. Therefore, reducing emissions from vehicles (either while moving or
idling) can lead to a significant improvement in air quality.
B. Idling Emissions
Determining emissions from idling vehicles is tricky because of the lack of scientific data on the
length of time that various classes of vehicles idle. However, with reasonable assumptions,
idling emissions can be estimated.
The American Transportation
Research Institute conducted a
survey of companies representing
55,000 trucks. The survey showed
that sleeper cabs idle an average of
28 hours per week (1,456 hours
annually) and day cabs idle an
average of 6 hours per week (312
hours annually)2. Trucks often
idle while waiting for shipments to
be loaded or unloaded and to run
heating, air conditioning,
communication or entertainment
devices. Some trucks are equipped with technologies to reduce idling, such as direct-fired
heaters, battery powered air conditioners and auxiliary power units/ generator sets. Assuming
that a gallon per hour of fuel is consumed during idling and that diesel fuel costs $5 per gallon,
then idling costs an average of $7,280 and $1,560 per year for sleeper cabs and day cabs,
respectively.
1
Smog Precursor Emissions in the Chicago area
9 On-road vehicles were responsible for 578
tpd (31.4%) of total anthropogenic
emissions
9 Eliminating truck idling could reduce smog
precursor emissions by 21.9 tpd.
9 Reducing passenger vehicle idling by 5
minutes per day per could reduce
emissions by 25.5 tpd.
Figure 1: Ozone Precursor Emissions in the Chicago Region for 2002 Figure 1: Ozone
Precursor Emissions in the Chicago Region for 2002 Figure 1: Ozone Precursor
Emissions in the Chicago Region for 2002 Figure 1: Ozone Precursor Emissions in
the Chicago Region for 2002Metre
Figure 1: Smog Precursor Emissions in the Metropolitan Chicago Area for 2002.
Based on the results from the American Transportation Research Institute's survey, it is
estimated for the Chicagoland area that 21.9 tons per day of smog precursors are emitted from
idling trucks or 9% of the total smog precursor emissions from heavy-duty trucks. A similar
estimate can be made for passenger vehicles. If all passenger vehicles (passenger cars and light
duty trucks) in the Chicagoland area reduced idling by 5 minutes per day, then total smog
precursor emissions would be cut by 25.5 tons per day (6% of total emissions from passenger
vehicles). These estimates show that reducing idling can have a significant impact on air quality.
Complete assumptions and calculations for these estimates are shown in Appendix B.
II. ESTIMATING EMISSION AND GASOLINE USAGE FROM IDLING VEHICLES
Emissions from idling vehicles can be estimated using the data and formulas given in this
section. The sample calculations at the end of the section demonstrate that the estimates can be
tailored to the focus of the idling reduction program depending on the types and number of
vehicles concerned.
For these estimates, an emission factor methodology should be used. A generalized formula is
shown below.
Emissions = Number of vehicles x Idle Time x Emission Factor
The United States Environmental Protection Agency Office of Mobile Sources has conducted
tests to determine emission factors for various vehicles (Table 1)3. The emission factors
2
represent national averages for all vehicles as of July 1, 1998. Emissions from idling vehicles
are affected by a number of factors including fuel formulation, local temperature and pressure,
and vehicle age and condition. However, these emission factors can be used for general
estimating purposes.
Table 1: Emission Factors
Summer Emissions
Winter Emissions
(g
)
VOC
(
CO NOx
VOC CO NOx
/hr) (g/hr) (g/hr
g/hr) (g/hr) (g/hr)
Passenger Cars (Gasoline)
21.1 371 6.16 16.1 229 4.72
Light-Duty Trucks (Gasoline)
30.7 487 7.47 24.1 339 5.71
Heavy-Duty Trucks (Gasoline) 44.6 682 11.8 35.8 738 10.2
Passenger Cars (Diesel)
3.63 10.1 6.66 3.53 9.97 6.50
Light-Duty Trucks
(Diesel) 4.79 11.5 6.89 4.63 11.2 6.67
Heavy-Duty Trucks (Diesel) 12.6 94.6 56.7 12.5 94.0 55.0
Motorcycles
20.1 388 2.51 19.4 435 1.69
Notes:
• g/hr = grams per hour
Passenger vehicles weigh up to 6,000 lbs.
-up trucks, minivans, passenger vans and SUV's ) weigh up to
uel Usage
umed by idling vehicles has been estimated to be:
Passenger Vehicles: 0.5 gallons per hour
Like emi
mber of factors including fuel formulation,
cal temperature and pressure, and vehicle age and condition.
•
• Light-duty trucks (pick
8,500 lbs.
• Heavy-duty vehicles weigh greater than 8,501 lbs.
F
The fuel cons
Heavy Duty Trucks: 1 gallon per hour4
5
ssions, fuel consumption is affected by a nu
lo
3
SAMPLE PROBLEM 1: IDLING EMISSIONS AT A SCHOOL
PROBLEM STATEMENT
Calculate the VOC emissions from idling vehicles at a school on a summer day. Assume that
there are:
• 50 gasoline powered passenger cars that each idle for 15 minutes
• 10 diesel-powered school buses that each idle for 15 minutes
• 2 gasoline-powered, light-duty maintenance trucks that each idle for 20 minutes
ANSWER
I. Emission Factor
Use Table 1 on page 3 to determine emission factors
Gasoline-powered passenger cars: 16.1 g/hr
Diesel-powered school buses (heavy duty trucks): 12.5 g/hr
Gasoline-powered light-duty trucks: 24.1 g/hr
II. Calculations
Passenger Cars
VOC Emissions =
# of
Vehicles
x
Idling
Time
x
Emission
Factor
=
50 15 min 16.1 g hr
day hr 60 min
= 201.3 g / day
School Buses
VOC Emissions =
# of
Vehicles
x
Idling
Time
x
Emission
Factor
=
10 15 min
12.5 g hr
day hr 60 min
= 31.3 g / day
4
Maintenance Vehicles
VOC Emissions =
# of
Vehicles
x
Idling
Time
x
Emission
Factor
=
2 20 min 24.1 g hr
day hr 60 min
= 16.1 g
Total Emissions
=
(201.3 + 31.3 + 16.1) g
lbs
day
453.593 g
= 0.55 lb of VOC emissions /day
Note: Conversion factors are shown in italics
5
SAMPLE PROBLEM 2: EMISSIONS AND FUEL USAGE FROM IDLING
PASSENGER VEHICLES
PROBLEM STATEMENT
Estimate the VOC, NOx and fuel savings that would occur if all passenger vehicles in the
Chicagoland area reduced their idling time by 5 minutes per day.
ANSWER
I. Number of Vehicles
According to the U.S. Department of Transportation's Research and Innovative Technology
Administration, there were 135,399,345 registered passenger vehicles in the United States in
2006.6
According to the U.S. Census Bureau, 2.8% of the United States population lives in the
Chicagoland area.
7,8
Assume that 2.8% of the registered passenger vehicles in the country are in
the Chicagoland area.
Passenger vehicles in the Chicagoland area = 135,399,345 * 0.028
= 3,791,182
II. Emission Factor
Determine emission factors from Table 1 on page 3. Assume that all passenger vehicles are
powered by gasoline. Only a small percentage of passenger cars in the country run on diesel.
The summer and winter emission factors for NO
x
and VOC have been averaged.
NO
x
: 5.44 g/hr
VOC : 18.6 g/hr
Gasoline: 0.5 gallons per hour
III. Calculations
NOx
NO
x
Emissions =
# of
Vehicles
x
Idling
Time
x
Emission
Factor
=
3,791,182 5 min5.44 g
hr lbs ton
day hr 60 min453.593 g2000 lbs
= 1.89 tons/ day
6
VOC
VOC Emissions =
# of
Vehicles
x
Idling
Time
x
Emission
Factor
=
3,791,182 5 min18.6 g
hr lbs ton
day
hr 60 min453.593 g2000 lbs
= 6.5 tons / day
Total Smog Precursors
= 1.89 + 6.5 (tons/day)
= 8.395 tons/day
Gasoline
Gasoline Usage =
# of
Vehicles
x
Idling
Time
x
Emission
Factor
=
3,791,182
5 min
0.5 gal
hr
day
hr
60 min
= 158,000 gallons of gasoline per day
Note: Conversion factors are shown in italics.
7
SAMPLE PROBLEM 3: EMISSIONS FROM TRUCKS IN THE CHICAGO AREA
PROBLEM STATEMENT
Estimate the daily VOC and NOx emissions from trucks in the Chicago area.
ANSWER
I. Number of Vehicles
According to the U.S. Census Bureau, there were 62,400 sleeper trucks and 229,1000 day trucks
registered in Illinois in 2002.9
Also according to the U.S. Census Bureau, 65% of the Illinois's population lives in the
Chicagoland area.10 Assume that 65% of the registered trucks in the state are in the
Chicagoland area.
Cab with sleepers: 62,400 * 0.65 = 40,560
Cabs without sleepers: 229,1000 * 0.65 = 148,915
II. Idling Time
According to the American Transportation Research Institute, on average, sleeper trucks idle 28
hours per week and day cabs idle 6 hours per week.
III. Emission Factor
Determine the emission factors for heavy-duty diesel vehicles using Table 1 on page 3. The
summer and winter emission factors for NO
x
and VOC have been averaged to determine a year-
round factor.
NO
x
Emissions: 55.85 g/hr
VOC Emissions: 12.55 g/hr
IV. Calculations
Sleeper Cabs
NO
x
Emissions =
# of
Vehicles
x
Idling
Time
x
Emission
Factor
=
40,560 28 hr 55.85 g
wk lbs ton
wk
hr
7 days 453.593 g 2000 lbs
= 10.0 tons / day
8
VOC Emissions =
# of
Vehicles
x
Idling
Time
x
Emission
Factor
=
40,560 28 hr 12.55 g
wk lbs ton
wk
hr
7 days 453.593 g 2000 lbs
= 2.2 tons / day
Day Cabs
NO
x
Emissions =
# of
Vehicles
x
Idling
Time
x
Emission
Factor
=
148,915 6 hr 55.85 g
wk lbs ton
wk
hr
7 days 453.593 g 2000 lbs
= 7.9 tons / day
VOC Emissions =
# of
Vehicles
x
Idling
Time
x
Emission
Factor
=
148,915 6 hr 12.55 g
wk lbs ton
wk
hr
7 days 453.593 g 2000 lbs
= 1.8 tons / day
Total Smog Precursors
= 10.0 + 2.2+ 7.9 + 1.8 (tons/day)
= 21.9 tons/day
9
10
ENDNOTES
1
Illinois Environmental Protection Agency. Illinois Base Year Ozone Inventory for 2002:
Draft. Springfield, IL: IL Environmental Protection Agency, 2006. [cited July 17, 2008].
Available from World Wide Web: < http://www.epa.state.il.us/air/sip/il-base-o3-inventory-
2002.pdf >.
2
U.S. Department of Transportation, Research and Innovative Technology Administration,
Bureau of Transportation Statistics. National Transportation Statistics. Washington D.C.: U.S.
Department of Transportation, 2008 . Table 1-11. [cited July 17, 2008]. Available from World
Wide Web: <http://www.bts. gov/publications/national_transportation_statistics> .
3
U.S. Environmental Projection Agency Office of Mobile Sources. Idling Vehicle Emissions. Ann Arbor,
MI: United States Environmental Projection Agency, 1998. [cited July 17, 2008]. Available from World
Wide Web: <http://www.epa. gov/otaq/consumer/f98014.pdf >.
4
U.S. Environmental Protection Agency Region 1. Idling [Online]. Boston, MA: U.S. Environmental
Protection Agency Region 1, 2008. Updated May 30, 2008. [cited July 17, 2008]. Available from World
Wide Web: < http://www.epa. gov/region1/eco/diesel/idling.html>.
5
ASME Florida Section. Virtual Mythbusters by American Society of Mechanical Engineers Florida
Section [Online]. Florida: American Society of Mechanical Engineers Florida Section, undated. [cited 7
July 2008]. Available from World Wide Web:
<http://sections. asme.org/florida/ASME%20Fla%20Section%20Virtual%20Mythbusters.html >.
6
U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of
Transportation Statistics. National Transportation Statistics. Washington D.C.: U.S. Department of
Transportation, 2008 . See Table 1-11. [cited July 17, 2008] Available from World Wide Web:
< http://www.bts.gov/publications/national_transportation_statistics/> .
7
U.S. Census Bureau, Population Division. County Population Estimates [Online]. Washington, D.C.:
U.S. Census Bureau, 2008. Last Modified: March 20, 2008. [cited July 17, 2008]. Available from World
Wide Web: < http://www.census.gov/popest/counties/CO-EST2007-01.html>.
8
U.S. Census Bureau, Population Division. National and State Population Estimates [Online].
Washington, D.C.: U.S. Census Bureau, 2008. Last Modified: June 26, 2008. [cited July 17, 2008].
Available from World Wide Web: <http://www.census.gov/popest/states/NST-ann-est. html>.
9
U.S. Census Bureau, 2002 Economic Census Vehicle Inventory and User Survey (Illinois) . Washington
D.C.: U.S. Census Bureau, 2004. [cited July 17, 2008]. Available from World Wide Web:
<http://www.census.gov/svsd/www/vius/2002.html>.
10
U.S. Census Bureau, Population Division. County Population Estimates [Online]. Washington, D.C.:
U.S. Census Bureau, 2008. Last Modified: March 20, 2008. [cited July 17, 2008]. Available from World
Wide Web: < http://www.census.gov/popest/counties/CO-EST2007-01.html>.
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