April 21, 2008

MEMORANDUM

SUBJECT:	Revised Methodology for Estimating Lead Emissions from
Piston-Engine Aircraft Operating on Leaded Aviation Gasoline 

FROM:  	Marion Hoyer, OTAQ/ASD

Bryan Manning, OTAQ/ASD

Solveig Irvine, OTAQ/ASD

	   	

TO:	 	Lead RIA Docket EPA-HQ-OAR-2008-0253

The purpose of this memorandum is to describe the new methodology EPA
will be using to estimate emissions of lead (Pb) from the consumption of
leaded aviation gasoline (avgas) by piston-engine powered aircraft. 
Previous guidance on EPA’s method for estimating airport-specific lead
inventories is described briefly and is available in other documents. 
Airport-specific lead estimates used in the Draft Lead Regulatory Impact
Analysis (RIA) are those published in EPA’s 2002 NEI.  For the final
RIA, we will use airport-specific lead estimates developed using the
approach described in Section II of this document.  

Background information regarding the use of leaded aviation gasoline in
piston-engine powered aircraft is available in other documents.,  Lead
is not added to jet fuel that is used in commercial aircraft, military
aircraft, or other turbine-engine powered aircraft.      

I.  Airport-specific Emissions of Lead from Piston-engine Aircraft in
the 2002 NEI

To estimate airport-specific lead inventories in the 2002 NEI, we
allocated the national lead avgas inventory to individual airports based
on the percentage of piston-engine operations at each airport.  To
calculate the national avgas lead inventory we multiplied the volume of
leaded avgas produced in the U.S. in 2002 by the concentration of lead
in the avgas and by the fraction of lead emitted from a combustion
system operating on leaded fuel (as discussed later, some lead is
retained in the engine or engine oil).  These parameters are described
below.  The following equation was used to calculate the national avgas
lead inventory:

Avgas lead emitted/year = avgas gal x [Pb] x 0.75

The volume of avgas produced in the U.S. in 2002 was 6,682 thousand
barrels or 280,644,000 gallons.  The concentration of lead in avgas
([Pb] in the above equation) can vary (currently, leaded avgas is
supplied in up to four different formulations that can contain lead
concentrations ranging from 0.14 to 1.12 grams per liter), but by far,
the most common avgas supplied is “100 Low Lead” or 100LL.  The
maximum lead concentration specified by ASTM for 100LL is 0.56 grams per
liter or 2.12 grams per gallon.  A fraction of lead is retained in the
engine, engine oil and/or exhaust system.   EPA has historically used a
value of 25% vehicle retention for lead when it is added to fuel.  For
aviation engines, we identified this value as a likely overestimate of
the amount of lead retained, however, we did not have data specific for
aviation engines at the time the 2002 inventory was finalized.  This
estimate of retention in an engine has been revised as discussed in
Section II below.

For the 2002 NEI, the national estimate of lead emissions from the
consumption of avgas was 

(280,644,000 gal)(2.12 g Pb/gal)(0.75)   =   491.9 tons Pb

907,180 g/ton

The 491.9 tons of lead was allocated to the 3,410 airports located
throughout the U.S. based on the percentage of piston-engine landing and
take-off (LTO) activity at each airport.  The airport-specific estimates
of lead emitted at airports that are being analyzed in the Draft RIA are
presented in Table 1 below.  The LTO data used to allocate lead to
airports can be found in the Terminal Area Forecast (TAF) system, which
is the official forecast of aviation activity at Federal Aviation
Administration (FAA) facilities.  Airport-specific lead emissions
estimates in the NEI include lead emitted during the entire flight
(i.e., not limited to the landing and take-off cycle and local
operations).

EPA understands that allocating lead emissions to airports from
operations outside the landing and take-off cycle overestimates the
local emissions near airports because longer duration (e.g., itinerant)
flights emit lead at altitudes and at distances from the airport as well
as in the local area near the airport.  As described in the following
section of this memo, EPA has developed a new methodology to calculate
airport-specific lead emissions attributable only to the
landing/take-off (LTO) cycle of piston-engine aircraft.  

For future inventories, EPA will use the equation described above to
develop the national inventory for lead emissions from piston-engine
powered aircraft.  The equation will be modified using new information
described below, to account for 5% retention of Pb in the engine/oil of
the aircraft.  The new equation is as follows, applied to 2002 avgas
supply values:

(280,644,000 gal)(2.12 g Pb/gal)(0.95)   =  623 tons Pb

907,180 g/ton

II.  New Methodology for Estimating Airport-specific Pb Emissions 

The new methodology for estimating lead emissions at airports where
piston-engine aircraft operate is referred to here as the
landing/take-off based method (LTO-based method).  Historically,
aircraft gaseous and particulate matter (PM) emissions have been
calculated through the FAA’s Emission and Dispersion Modeling System
(EDMS)  This modeling system was designed to develop emission
inventories for the purpose of assessing potential air quality impacts
of airport operations and proposed airport development projects. 
However, EDMS is currently not set up to calculate lead emissions from
piston-powered aircraft, and thus, it is not a readily available tool
for determining airport lead inventories related to aircraft operations.
 In developing an LTO-based approach to determine piston-engine aircraft
lead emissions, we relied upon the basic methodology employed in EDMS. 
This approach requires as input the activity of piston-engine aircraft
at a facility, fuel consumption rates by these aircraft, the
concentration of lead in the fuel and the retention of lead in the
engine/oil.  The equation used to calculate airport-specific lead
emissions during LTO activity is below, followed by a description of
each of the input parameters.

LTO Pb(tons) = (piston-engine LTO)(avgas gal/LTO)([Pb])(1-Pb retention)

907,180 g/ton

1) Piston-engine LTO:  Most piston-engine aircraft fall into the
categories of either general aviation (GA) or air taxi (AT).  Some GA
and AT activity is conducted by turboprop and turbojet aircraft which do
not used leaded avgas.  There are no national databases that provide
airport-specific landing and take-off activity data for piston-engine
aircraft separately from turbojet and turboprop aircraft.  The fraction
of GA and AT that use piston-engines will vary by airport, however, in
the absence of these data, a national default estimate was derived using
FAA’s GA and AT Activity (GAATA) database.  The 2005 GAATA reports
that approximately seventy-two percent (72%) of all GA and AT LTOs are
piston-engine aircraft which use avgas, and about twenty-eight percent
(28%) are turboprop and turbojet powered which use jet fuel, such as Jet
A.  Therefore, to calculate piston-engine LTO as input for this
equation, the total GA plus AT LTOs are multiplied by 0.72.

2) Avgas use (gal/LTO): Piston-engine aircraft can have either one or
two engines.  EDMS version 5.0.2 contains information on the amount of
avgas used per LTO for some one and two-engine aircraft.  The proportion
of the fleet having one versus two engines was taken from the FAA’s
GAATA Survey CY2005.  Since two-engine aircraft have higher fuel
consumption rates than one-engine, a weighted average LTO fuel usage
rate was established to apply to the population of piston engine
aircraft as a whole.  For the single engine aircraft, the average amount
of fuel consumed per LTO was determined from the six types of single
piston-engine aircraft within EDMS.  This was accomplished by averaging
the one-engine EDMS outputs for fuel consumed per LTO using the EDMS
scenario property of ICAO/USEPA Default - Times in Mode (TIM), with a 16
minute taxi-in/taxi-out time according to EPA’s Procedures for
Emission Inventory Preparation, Volume IV: Mobile Sources, 1992.  This
gives a value of about 16.96 pounds of fuel per LTO (lbs/LTO).  Next,
the average one-engine consumption was divided by the average density of
100LL avgas, 6 pounds per gallon (lbs/gal), producing an average fuel
usage for one-engine piston aircraft of 2.83 gallons per LTO (gal/LTO). 
This same calculation was performed for the two twin-engine piston
aircraft within EDMS, producing an average LTO fuel usage rate for
twin-engine piston aircraft of 9.12 gal/LTO.  

Using these one and two-engine piston aircraft fuel consumption rates, a
weighted average fuel usage rate per LTO was computed by multiplying the
average fuel usage rate for one-engine aircraft (2.83 gal/LTO) by the
fleet percentage of one-engine aircraft LTOs (90%).  Next, the
two-engine piston aircraft average fuel usage rate (9.12 gal/LTO) was
multiplied by the fleet percentage of two-engine aircraft (10%).  By
summing the results of the one- and two-engine usage rates, the overall
weighted average fuel usage rate per LTO of 3.46 gal/LTO is obtained.

3) Concentration of Pb in fuel:  As described above in Section I, the
maximum lead concentration specified by ASTM for 100LL is 0.56 grams per
liter or 2.12 grams per gallon.  Multiplying this lead concentration in
avgas by the weighted average fuel usage rate produces an overall
average value of 7.34 grams of lead per LTO (g Pb/LTO) for piston
engines: 3.46 gal/LTO x 2.12 gPb/gal = 7.34 g Pb/LTO.

4) Retention of lead in engine/oil:  As described in Section I, for
previous inventories of lead emitted from mobile sources, it was
estimated that 25% of the lead emitted from the combustion of a
lead-based fuel was retained in the engine, engine oil and exhaust
system.  This estimate was based on information from motor vehicles that
operated on leaded gasoline.  Recent data collected from aircraft piston
engines operating on leaded avgas suggests that about 5% of the lead
from the fuel is retained in the engine and engine oil.  This new
information is used in calculating airport-specific lead inventories and
will be used to develop future national estimates of lead emitted from
the consumption of leaded avgas.

Applying these factors to the equation above yields the following lead
emission rate per LTO:

Pb(tons) =(#piston-engine LTO)(7.34 gPb/LTO) (0.95)

907,180 (g/ton)

Pb(tons) per piston-engine LTO = 5.53 X 10-6

This LTO-based method for estimating airport-specific lead emissions
provides a more realistic estimate of the lead emitted in the immediate
vicinity of an airport compared with the approach described in Section
I.  However, there are short-comings to this approach that are
potentially significant on an airport-specific basis.  These
short-comings are largely due to the lack of data on airport-specific
piston-engine aircraft activity, the lack of data on single- versus
twin-engine activity on an airport-specific basis and the limited amount
of data on fuel consumption rates for piston-engine aircraft.    

Table 1 provides a comparison of airport-specific lead inventories using
the 2002 NEI approach and the new LTO-based approach for the airports in
the Draft RIA.  For the final RIA, the LTO-based approach will be used
to calculate airport-specific lead emissions.  As discussed earlier,
these airport-specific lead emissions are attributable only to the LTO
cycle of piston-engine aircraft, and not lead emissions from non-LTO
portions of flight (we intend to estimate non-LTO lead emissions in the
future).  

Table 1. Comparison of lead emissions for airports in the draft RIA: 
2002 NEI and the LTO-based method

Airport ID	Airport County, State	Tons Pb 2002 NEI	Tons Pb 

LTO Method

LGB	Los Angeles, CA	1.67	0.93

CPS	St. Clair, IL	0.83	0.47

RDG	Berks, PA	0.71	0.40

MSP	Dakota, MN	0.62	0.39

MGJ	Orange, NY	0.60	0.34

AGC	Allegheny, PA	0.56	0.33

VDF	Hillsborough, FL	0.47	0.26

BKL	Cuyahoga, OH	0.46	0.26

IND	Marion, IN	0.44	0.29

MDW	Cook, IL	0.40	0.24

IGQ	Lake, IN	0.22	0.18

SGS	Dakota, MN	0.25	0.14

TPF	Hillsborough, FL	0.24	0.14

GYY	Lake, IN	0.24	0.13

CSG	Muscogee, GA	0.20	0.12

TOI	Pike, AL	0.20	0.11

EYE	Marion, IN	0.19	0.11

MIE	Delaware, IN	0.17	0.10

JST	Cambria, PA	0.16	0.09

06N	Orange, NY	0.11	0.06

3SY	Marion, IN	0.10	0.05

717	Logan, OH	0.04	0.02

SBD	San Bernardino, CA	0.04	0.02

MIO	Ottawa, OK	0.04	0.02

49T	Dallas, TX	0.02	0.01



 EPA (1998) Locating and Estimating Air Emissions from Sources of Lead
and Lead Compounds. EPA-454/R-98-006. page 7-8.

 EPA (2007) Review of the National Ambient Air Quality Standards for
Lead: Policy Assessment of Scientific and Technical Information. OAQPS
Staff Paper. EPA-452/R-07-013 November 2007. pp 2-8 and 2-9.

FAA William J. Hughes Technical Center 
http://www.tc.faa.gov/act4/insidethefence/2006/0609_06_AvFuels.htm

 DOE Energy Information Administration.  Fuel production volume data
obtained from   HYPERLINK
"http://tonto.eia.doe.gov/dnav/pet/hist/mgaupus1A.htm" 
http://tonto.eia.doe.gov/dnav/pet/hist/mgaupus1A.htm  accessed November
2006.

 ChevronTexaco (2005) Aviation Fuels Technical Review. FTR-3.

 ASTM International (2005) Annual Book of ASTM Standards Section 5:
Petroleum Products, Lubricants, and Fossil Fuels Volume 05.01 Petroleum
Products and Lubricants (I): D 56 – D 3230.

 ASTM International (2005) Annual Book of ASTM Standards Section 5:
Petroleum Products, Lubricants, and Fossil Fuels Volume 05.01 Petroleum
Products and Lubricants (I): D 56 – D 3230.

 U.S. Environmental Protection Agency. (2007b) Airport-specific
emissions of lead from combustion of leaded aviation gasoline. 
http://www.epa.gov/ttn/chief/net/2002inventory.htm

 Terminal Area Forecast available from http://aspm.faa.gov/main/taf.asp

 EDMS available from
http://www.faa.gov/about/office_org/headquarters_offices/aep/models/edms
_model/

 The FAA GAATA is a database collected from surveys of pilots flying
aircraft used for general aviation and air taxi activity.  For more
information on the GAATA, see Appendix A at
http://www.faa.gov/data_statistics/aviation_data_statistics/general_avia
tion/

 EPA understands that EDMS 5.0.2 has a limited list of piston engines,
but these are currently the best data available.

 U.S. EPA, Procedures for Emission Inventory Preparation, Volume IV:
Mobile Sources, EPA-450/4-81-026d (Revised), 1992.

 The information used to develop this estimate is from the following
references:  (a) Todd L. Petersen, Petersen Aviation, Inc, Aviation Oil
Lead Content Analysis, Report # EPA 1-2008, January 2, 2008, available
at William J. Hughes Technical Center

Technical Reference and Research Library at
http://actlibrary.tc.faa.gov/ and (b) E-mail from Theo Rindlisbacher of
Switzerland Federal Office of Civil Aviation to Bryan Manning of U.S.
EPA, regarding lead retained in engine, September 28, 2007.

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