April 21, 2008

[MEMORANDUM]{.underline}

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.[^1] 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.[^2]^,^[^3] 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]{.underline}

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.[^4] 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.[^5] The
maximum lead concentration specified by ASTM for 100LL is 0.56 grams per
liter or 2.12 grams per gallon.[^6] 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.[^7]
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)]{.underline} ~=~ 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.[^8] 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.[^9] 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)]{.underline} ~=~ 623 tons Pb

907,180 g/ton

[II. New Methodology for Estimating Airport-specific Pb
Emissions]{.underline}

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)[^10]
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)]{.underline}

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.[^11] 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.[^12] 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.[^13] 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.[^14] 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]{.underline} gPb/LTO[)
(0.95)]{.underline}

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 | Tons Pb        |
|             |                       | NEI          |                |
|             |                       |              | 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           |
+-------------+-----------------------+--------------+----------------+

[^1]: EPA (1998) Locating and Estimating Air Emissions from Sources of
    Lead and Lead Compounds. EPA-454/R-98-006. page 7-8.

[^2]: 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.

[^3]: FAA William J. Hughes Technical Center
    http://www.tc.faa.gov/act4/insidethefence/2006/0609_06_AvFuels.htm

[^4]: DOE Energy Information Administration. Fuel production volume data
    obtained from <http://tonto.eia.doe.gov/dnav/pet/hist/mgaupus1A.htm>
    accessed November 2006.

[^5]: ChevronTexaco (2005) Aviation Fuels Technical Review. FTR-3.

[^6]: 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.

[^7]: 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.

[^8]: 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

[^9]: Terminal Area Forecast available from
    [http://aspm.faa.gov/main/taf.asp]{.underline}

[^10]: EDMS available from
    [http://www.faa.gov/about/office_org/headquarters_offices/aep/models/edms_model/]{.underline}

[^11]: 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_aviation/

[^12]: EPA understands that EDMS 5.0.2 has a limited list of piston
    engines, but these are currently the best data available.

[^13]: U.S. EPA, *Procedures for Emission Inventory Preparation, Volume
    IV: Mobile Sources*, EPA-450/4-81-026d (Revised), 1992.

[^14]: 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.