Calculating Piston-Engine Aircraft

            Airport Inventories for Lead for the

            2011 National Emissions Inventory
&EPA
United States
Environmental Protection
Agency

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                Calculating Piston-Engine Aircraft
                Airport Inventories for Lead for the
                2011  National Emissions Inventory
                           Assessment and Standards Division
                          Office of Transportation and Air Quality
                          U.S. Environmental Protection Agency
&EPA
United States
Environmental Protection
Agency
EPA-420-B-13-040
September 2013

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    Calculating Piston-Engine Aircraft Airport Inventories for Lead for the 2011
                            National Emissions Inventory

                                   September 2013
Section 1. Introduction

       The main purpose of this document is to describe the methods the Environmental
Protection Agency (EPA) used to calculate airport lead (Pb) inventories for the 2011
National Emissions Inventory (NEI).l  These methods focus  on the development of
approaches to estimate piston-engine aircraft activity at airports in the U.S. since the
activity of this fleet is reported to the Federal Aviation Administration (FAA) as general
aviation (GA) or air taxi (AT) activity - categories that also include jet-engine aircraft
activity. The methods described here are largely the same as those used to construct the
2008 NEI.

       Most piston-engine aircraft operations fall into the categories of either GA or AT.
Aircraft used in GA and AT activities include a diverse set of aircraft types and engine
models and are used in a wide variety of applications.  Lead emissions associated with
GA and AT aircraft stem from the use of one hundred octane low lead (100LL)  aviation
gasoline (avgas). The lead is added to the fuel in the form of tetraethyl lead (TEL),
which helps boost fuel octane, prevent engine knock, and prevent valve seat recession
and subsequent loss of compression for engines without hardened valves. Today, 100LL
is the most commonly available type of aviation gasoline in the United States.3  Lead is
not added to jet fuel, which is used in commercial aircraft, most military aircraft, or other
turbine-engine powered  aircraft.

       This document is organized into eight sections.  Section 2 describes the data we
use to calculate the national inventory for the amount of lead released to the air from the
combustion of leaded avgas. Section 3 describes the landing and takeoff data we use to
calculate airport-specific activity.  Section 4  describes how we estimate landing and
takeoff data for the airport facilities that do not report it to the FAA. Section 5 describes
the estimate of landing and takeoff activity occurring at heliports in the U.S.  Section 6
describes the methods used to calculate the airport-specific inventories for lead. Section
7 describes the data that would be needed to  improve the estimates of airport-specific
inventories for lead, and Section 8 describes  the estimates of the amount of lead emitted
in-flight.
1 In this document '2011 NEF refers to the 2011 NEI data, available at:
http://www.epa.gov/ttn/chief/net/201 linventory.html
2 Commercial aircraft include those used for scheduled service transporting passengers, freight, or both.
Air taxis fly scheduled and for-hire service carrying passengers, freight or both, but they usually are smaller
aircraft than those operated by commercial air carriers. General aviation includes most other aircraft (fixed
and rotary wing) used for personal transportation, business, instructional flying, and aerial application.
3 FAA General Aviation and Part 135 Activity Surveys - CY 2010, Table 5.1, '2010 General Aviation and
Air Taxi Total Fuel Consumed and Average Fuel Consumption Rate by Aircraft Type.'

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       In this document, units of tons (i.e., U.S. short tons) are used when discussing the
national and airport-specific lead inventory in order to be consistent with the manner in
which the NEI reports inventories for lead and other pollutants.  The unit of grams is used
in describing the concentration of lead in avgas and in describing emission factors.
Conversion factors are provided for clarity.
Section 2. Calculating the National Avgas Lead Inventory

       Because lead is a persistent pollutant and accumulates in the environment, we
include all lead emissions from piston-engine aircraft in the NEI - emissions occurring
during the landing and takeoff cycle at airports as well as emissions occurring in flight.4
To calculate the national avgas lead inventory, we use information provided by the U.S.
Department of Transportation's (DOT's) Federal Aviation Administration (FAA)
regarding the volume of leaded avgas consumed in the U.S. in 2011.5  The U.S.
Department of Energy's (DOE's) Energy Information Administration (EIA) provides
information regarding the volume of leaded avgas produced in a given year. Prior to the
2008 NEI, EPA used the DOE EIA avgas fuel volume produced to calculate national lead
inventories from the consumption of leaded avgas.  However, since EPA uses DOT
airport activity and aircraft data, we are using the DOT fuel volume  data in the 2011 NEI
to calculate the national lead inventory in order to use a consistent data source.

       To calculate the annual emission of lead from the consumption of leaded avgas,
we multiply the volume of avgas used by the concentration of lead in the avgas and
subtract the small amount of lead that is retained in the engine, engine oil and/or exhaust
system (equation 1). The volume  of avgas used in the U.S. in 2011 was 217,500,000
gallons.6  The concentration of lead in avgas can be one of four levels (ranging from 0.14
to 1.12 grams of lead per liter) as specified by the American Society for Testing and
Materials (ASTM). By far the most common avgas supplied is 100LL.7 The maximum
lead concentration specified by ASTM for 100LL is 0.56 grams per liter or 2.12 grams
per gallon.8 A fraction of lead is retained in the engine, engine oil and/or exhaust system
which we currently estimate at 5%.9
4 U.S. EPA, 2006. Air Quality: Criteria for Lead: 2006; EPA/600/R-5/144aF; U.S. Government Printing
Office, Washington, DC, October, 2006.
5 U.S. Department of Transportation Federal Aviation Administration Aviation Policy and Plans. FAA
Aerospace Forecast Fiscal Years 2013-2033. Tables 23 and 31. Available at:
http://www.faa.gov/about/office_org/headquarters_offices/apl/aviation_forecasts/aerospace_forecasts/2013
-203 3/
6 U. S. Department of Transportation Federal Aviation Administration Aviation Policy and Plans. FAA
Aerospace Forecast Fiscal Years 2013-2033. Tables 23 and 31. Available at:
http://www.faa.gov/about/office_org/headquarters_offices/apl/aviation_forecasts/aerospace_forecasts/2013
-203 3/
7 FAA General Aviation and Part 135 Activity Surveys - CY 2010, Table 5.1, '2010 General Aviation and
Air Taxi Total Fuel Consumed and Average Fuel Consumption Rate by Aircraft Type.'
8 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.
9 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

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       For the 2011 NEI, the national estimate of lead emissions from the consumption
of avgas was 483 tons (see equation 1 below).
               (217.500.000 gal) (2.12 gPb/gal) (0.95)
               	*   10A  /4     ^	  = 483 tons Pb              (1)
                           907,180 g/ton                                         v '
       As described above, DOE's EIA also provides estimates of the annual volume of
leaded avgas produced in a given year. For 2011, the volume of avgas produced in the
U.S. was 5,360 thousand barrels or 225,120,000 gallons.10  Consumption of this volume
of avgas equates to a national lead emissions estimate of 500 short tons.
Section 3. Landing and Takeoff Data Sources and Uses

       Airport-specific inventories require information regarding landing and takeoff
(LTO) activity by aircraft type.n According to FAA records, there are approximately
20,000 airport facilities in the U.S., the vast majority of which are expected to have
activity by piston-engine aircraft that operate on leaded avgas. This section provides an
overview of the FAA data sources used to develop airport-specific LTO inventories; the
method used to adjust older FAA 5010 activity data; and, the method used to avoid
double-counting after FAA data sources were merged.

       FAA's Office of Air Traffic provides a complete listing of operational airport
facilities in the National Airspace System Resources (NASR) database.  The electronic
NASR data report, referred to here as the 5010 airport data report, can be generated from
the NASR database and is available for download from the FAA website. 2 This report is
updated every 56 days.  EPA obtains airport information (including operations) for a
subset of the facilities in the NASR database from FAA's Terminal Area Forecast (TAP)
database that is prepared by FAA's Office of Aviation Policy and Plans.13 The TAP
database currently includes information for airports in FAA's National Plan of Integrated
Airport Systems (NPIAS), which identifies airports that are significant to national air
transportation. Approximately 500 of the airports that are in the TAP database have
either an FAA air traffic control tower or an FAA contract tower where controllers count
operations. The operations data from the control towers is reported to The Operations
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.
10 DOE Energy Information Administration. Fuel production volume data obtained from
http://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=PET&s=MGAUPUSl&f=A. accessed August 2013.
11 An aircraft operation is defined as any landing or takeoff event, therefore, to calculate LTOs, operations
are divided by two. Most data sources from FAA report aircraft activity in numbers of operations which,
for the purposes of calculating lead emissions using the method described in this document, need to be
converted to LTO events.
12http://www.faa.gov/airports/airport_safety/airportdata_5010/
13 http://aspm.faa.gov/main/taf.asp

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                   .14
Network (OPSNET)   which is publically available in the Air Traffic Activity System
(ATADS) database.15  The operations data for the towered airports that is reported in
OPSNET and ATADS is then reported to the TAP database.  The operations data for the
airports in the TAP database that do not have control towers are estimates.16 The
operations supplied in the 5010 airport data report for facilities not reported in the TAP
may be self-reported by airport operators through data collection accomplished by airport
inspectors who work for the State Aviation Agency, or operations data can be obtained
through other means.
17
       The 5010 airport data report supplies the operations data date, which includes data
for years prior to 2011 (Table 1).
                                18
Table 1:  Number of Facilities by Operations Data Year with Operations Counts for
Airports not in the TAP Database that Submit Operations Data to the FAA 5010 Data
Report
Year of
Operations
Data
None
1971 - 1979
1980-1989
1990-1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
Number of
Facilities
by
Operations
Data Year
107
61
223
179
16
12
10
8
13
39
34
35
130
381
554
509

5%
3%
10%
8%
1%
1%
<1%
<1%
1%
2%
1%
2%
6%
16%
24%
22%

















Sum of GA
Operations by
Operations
Data Year
t 350,487
198,475
519,898
499,226
50,427
9,342
14,000
24,805
14,975
86,583
29,303
87,458
533,392
2,008,553
2,329,070
2,965,160

4%
2%
5%
5%
1%
<1%
<1%
<1%
<1%
1%
<1%
1%
6%
21%
24%
31%
14 http://aspm.faa.gov/opsnet/sys/
15 http://aspm.faa.gov/opsnet/sys/Airport.asp
16 FAA's Terminal Area Forecast Summary (Fiscal Years 2011 - 2040), Appendix A (page 28)
http://www.faa.gov/about/office_org/headquarters_offices/apl/aviation_forecasts/taf_reports/media/TAF_s
ummary_report_FY20112040.pdf
17 In the absence of updated information from States, local authorities or Tribes, we are using the LTO data
provided in the FAA database.
18 The 12-month ending date on which annual operations data in the report is based.

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       Nationally, piston-engine operations have decreased in recent years,19 therefore
EPA did not use GA operations data from years prior to 2011 as reported; we scaled the
operations downward using a factor based on the decrease in national fuel production.
EPA multiplied the older GA piston-engine data (Section 6 describes the method EPA
used to calculate the number of piston-engine operations from total GA and AT activity
data) by scaling factors that were calculated by dividing the 2011 national amount of
avgas produced by the national amount of avgas produced in the year for which the
operations data were reported.20  A table with the scaling factors is provided in Appendix
A.  The annual data for the national volume of avgas produced comes from the DOE, EIA
website and is available for 1981 - 2011.21 For operations data older than 1981, EPA
divided the 2011 national amount of avgas produced by the average of the national
amount of avgas produced  from 1981 - 1989.

       As mentioned above, we have accounted for potential double-counting of piston-
engine aircraft LTOs, which is described here:  EPA obtains operations data from the T-
100 segment data from the Bureau of Transportation Statistics (BTS).  The aircraft in the
T-100 data are matched to  aircraft in the FAA's Emission and Dispersion Modeling
System (EDMS) using the  crosswalk table  developed for earlier versions of the NEI.
Generally the T-100 data covers commercial air carrier operations, but some AT
activities are included in the dataset that would double count with the TAP data at the
same airport.  To correct for possible double counting, first the AT LTOs included in the
T-100 data were compiled  using the aircraft type data included in the aircraft
make/models crosswalk.22  The resulting aggregated LTOs were compared with the
reported TAP LTOs for airports where there were overlaps. The T-100 AT LTOs were
then subtracted from the TAF  AT data to control for double counting.  Note that if the T-
100 AT value was larger than  the TAF value, the TAF value was set to zero to eliminate
the possibility of negative LTOs in the dataset.

       The 2011 NEI was  developed using the February 7, 2012 version of the 5010
airport data report.  In that  version of the report there were 19,782 airport facilities in the
U.S. that submitted data to the FAA. Among these 19,782 facilities, 69 facilities were
not relevant for the purposes of estimating lead emissions because they were either listed
as closed (56) or they were balloonports (13).23  Therefore, lead inventories were needed
19http://www.faa.gov/data_research/aviation_data_statistics/general_aviation/
20 The FAA General Aviation and Air Taxi (Part 135) Activity Surveys (source of national level piston-
engine operations data) are only available annually, starting in 1999. Because there are airports with
operations data older than 1999, EPA used avgas product supplied data as a surrogate for piston-engine
operations to estimate the change in piston-engine activity over the last four decades.
21 http://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=PET&s=mgaupusl&f=Ai  DOT recently changed
the way they estimate fuel consumption data, so while EPA used DOT data to determine the 2011 national
avgas lead inventory, for the purpose of calculating these scaling factors EPA used DOE's data in order to
have historical fuel data that is calculated in a consistent manner.
22 The T-100 data does not specify that the operations data is air taxi in nature; however, in discussions with
FAA, EPA determined that these flights are air taxi in nature and has assigned them in the 2011 NEI as
such.
23 Balloon craft do not use avgas

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                   r\t
for 19,714 facilities.   In the February 7, 2012 version of the 5010 airport data report, the
2011 TAP, and 2011 AT ADS data there were a total of 5,627 airport facilities for which
operations data were provided (many of which are facilities in FAA's TAP database).25
There were 14,087 facilities in the 5010 airport data report and the 2011 TAP data for
which there were no operations data.26 Section 4 of this document describes the method
EPA used to  estimate operations for the 8,430 airport facilities in the 2011 NEI that do
not have reported activity data. Section 5 describes the method EPA used to estimate
operations for the 5,557 heliport facilities in the 2011 NEI that do not have reported
activity data.27 Additionally,  as part of the review process for the 2011 NEI, EPA
received updated airport data from states.

       Section 6 describes how we estimate GA and AT piston-engine LTOs at airports
in the 2011 NEI, separate from GA and AT jet LTOs.
Section 4. Estimating LTOs at the 8,430 Airport Facilities with No LTO Data

       In order to estimate LTOs at airports that do not report these data, we investigated
the utility of data that could be used to provide reasonable estimates of LTO activity at
airports. Such estimating methods have been used previously by FAA and those analyses
were evaluated for possible use in the development of emission inventories.

       FAA has used regression models to estimate operations at facilities where
                               9R 9Q
operations data are not available.  '   In this work and other work, FAA identified
characteristics of small towered airports for which there were statistically significant
relationships with operations at these airports.30  Regression models based on the airport
characteristics were then used to estimate general aviation operations for a set of non-
towered airports. The airport characteristics identified by FAA and used to estimate
general aviation operations at small  airports include: the number of aircraft stationed at
an airport (termed 'based aircraft'), population in the vicinity of the airport, airport
regional prominence, per capita income, region, and the presence of certificated flight
schools. In the 2000 FAA report titled  'Model for Estimating General Aviation
Operations at Non-towered Airports,' a model of GA annual activity was developed
using information from small towered airports to explain GA activity at towered and non-
24 There was one facility in FAA's TAP database (72S) that was not in the 5010 Data Report, so the sum of
19,714 plus 69 is one larger than the 19,782 in the downloaded FAA 5010 Data Report.
25 Either GA Itinerant, GA Local, or Air Taxi operations data, as these operations can be performed by
piston-engine aircraft.
26 No GA Itinerant, GA Local, or Air Taxi operations data.
27 There are 100 facilities in the NPIAS report that have both 0 GA and 0 AT operations; however, EPA did
not estimate operations for these 100 facilities.
28 Federal Aviation Administration, Office of Aviation Policy and Plans, Statistics and Forecast Branch.
July 2001. Model for Estimating General Aviation Operations at Non-towered Airports Using Towered
and Non-towered Airport Data. Prepared by GRA, Inc.
29 Mark Hoekstra, "Model for Estimating General Aviation Operations at Non-Towered Airports" prepared
for FAA Office of Aviation Policy and Plans, April 2000.
30 GRA, Inc. "Review of TAP Methods," Final Report, prepared for FAA Office of Aviation Policy and
Plans under Work Order 45, Contract No. DTFA01-93-C-00066, February 25,  1998.

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towered airports.  The model explained GA activity at the towered airports well (R  of
0.75) but produced higher estimates than state-supplied estimates for non-towered
airports.31

       The relevant data available in the 5010 airport data report for the purposes of
estimating airport operations include: facility type (airport, balloonport, seaplane base,
gliderport, heliport, stolport,32 ultralight); number of GA aircraft based at each airport by
type (glider, helicopter, jet engine, military, multi-engine, single engine, ultralight);
operations data (AT, commercial, commuter, GA itinerant, GA local, military)33; and
operations date (12-month ending date on which annual operations data is based). We
merged the 2010 U.S. Census data with the 5010 airport data report to provide population
data for each airport's county.

       Using the FAA work referenced above, we explored relationships among the
airport data variables that best predicted aircraft activity (LTOs). We found that based
aircraft was a highly significant and positive regressor to LTOs. Table 2 shows that for
non-heliport facilities that did not have LTO data in the February 7, 2012 version of the
5010 airport data report, 6,314 had based aircraft data while 2,216 did not have based
aircraft data.34 Therefore, as described below, LTO estimates were derived using
different methods depending on data availability.
31 The mean absolute difference between the model operations estimate and the state operations estimate
was 16,940 operations.
32 Stolport is an airport designed with STOL (Short Takeoff and Landing) operations in mind, normally
having a short single runway.
33 As explained in footnote 14, an aircraft operation is defined as any landing or takeoff event, therefore, to
calculate LTOs, operations are divided by two. The 5010 airport data report from FAA reports aircraft
activity in numbers of operations which, for the purposes of calculating Pb emissions using the method
described in the TSD, are converted to LTO events.
34 These numbers include data for the following types of facilities: airports, balloonports, seaplane bases,
gliderports, stolports, and ultralights.

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Table 2:  Contingency table describing the numbers of non-heliport facilities that have or
do not have LTO data and/or based aircraft data for facilities in the February 7, 2012
version of the 5010 airport data report

                                                 HAVE LTO DATA
            HAVE
           BASED
         AIRCRAFT
            DATA

YES
NO

YES
4,807
728
5,535
NO
6,314
2,216
8,530

11,121
2,944
14,065
(a) Estimating LTO s at Facilities with Based Aircraft Data, but No LTO Data:

       There are 6,289 facilities in the 2011 NEI (not including heliports) for which the
5010 airport data report supplies the number of based aircraft35 but not activity data to
which the regression equation (based aircraft vs. LTOs) could be applied.36 Using the
4,807 airports for which both LTO and aircraft data is known, the initial relationship
found between based aircraft and LTOs was:
LTOs = 2956 + 166*aircraft
(R2 = 0.52)
(2)
       The FAA models found population to be another significant regressor. We used
the population of the county (from the 2010 U.S. Census) in which the airport is located
as the population variable.  Adding county population to the model gave the following
relationship:
35 Based aircraft for this purpose was limited to single- and multi-engine aircraft, helicopters, gliders, and
ultralights since these aircraft types can use leaded avgas.
36 There are 100 facilities in the NPIAS report that have both 0 GA and 0 AT operations; however, EPA did
not estimate operations for these 100 facilities. 25 of the 100 facilities have based aircraft data, hence the
difference between the 6,314 value in Table 1 and the 6,289 value stated in this sentence.
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LTOs = 2706 + 156*aircraft + 0.0025*county population                             (3)
(R2 = 0.53)
       EPA received numerous comments to the docket on its Advance Notice of
Proposed Rulemaking on Lead Emissions from Piston-Engine Aircraft Using Leaded
Aviation Gasoline37 indicating that aviation in Alaska is different than it is in the
continental U.S.  Commenters pointed out that in Alaska, 82% of communities are not
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accessible by road and rely on air transport for life sustaining goods and services.
Commenters also noted that Alaskans travel by air eight times more often per capita than
those in the continental U.S. For those reasons, we added a dummy variable in equation
4 to identify whether or not an airport is located in Alaska.  Because the relationship
between based aircraft and LTOs is likely different for Alaskan airports than it is for
airports that aren't in Alaska, we also added an interaction term to equation 4 (interaction
of an airport being in Alaska and its sum of based aircraft).

LTOs = 2472 + 167*aircraft + 0.0022*county population - 162*Alaska -              . ,
98*(AlaskaXaircraft)                                                                ( }
(R2 = 0.55)
       After analyzing the data and plot for the data underlying equation 4, we found
many airport facilities identified as commercial airports for which based aircraft was
extremely low (i.e., less than 10), yet LTOs were quite high (i.e., anywhere from 100,000
to more than 200,000 LTOs/year).39  These facilities were removed from the regression
analysis.  The resulting relationship was:

LTOs = 1974 + 168*aircraft + 0.0009*county population - 1181*Alaska -
125*(AlaskaXaircraft)                                                              (  '
(R2 = 0.63)
       When equation 5 was applied to the 6,289 airport facilities that report based
aircraft data but not LTO activity, the resulting sum of LTOs was almost 8 million.40
37 U.S. Environmental Protection Agency (2010) Advance Notice of Proposed Rulemaking on Lead
Emissions From Piston-Engine Aircraft Using Leaded Aviation Gasoline. 75 FR 22440 (April 28, 2010).
38 Comments to the docket on EPA's Advance Notice of Proposed Rulemaking on Lead Emissions from
Piston-Engine Aircraft Using Leaded Aviation Gasoline from the Alaska Air Carriers Association (dated 18
June 2010; comment number OAR-2007-0294-0323.1) and Alaska Governor Parnell (dated 25 August
2010; comment number OAR-2007-0294-0403.1).
39 From FAA's website, "Addresses for Commercial Service Airports", available at:
http://www.faa.gov/airports_airtraffic/airports/planning_capacity/passenger_allcargo_stats/addresses/media
/commercial_service_airports_addresses.xls
40 The accuracy of the based aircraft data on which equation 5 is modeled can be improved. F AA
recognizes the need to improve the integrity of the 5010 data report based-aircraft counts for all of the GA
airports and reliever airports in the NPI AS and is currently in the process of improving the data collection
and submission methods to accomplish this task. See: National Based Aircraft Inventory Program:
http://www.basedaircraft.com/public/FreauentlYAskedOuestions.aspx. accessed 2/17/2009
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EPA estimates that the number of LTOs at the airports that do not report activity data
should approximate the number of LTOs from the bottom of the distribution of the set of
airports that report activity data to the 5010 airport data report but that are not in the TAP
database.  The average number of GA LTOs per year from airports in the bottom 30% of
the set of airports that report activity data to the 5010 airport data report but that are not
in the TAP database is -82 LTOs/year.  Multiplying 82 by the number of airports that do
not report activity data equals 687,045 LTOs.41  Therefore, EPA used equation 5 to
generate the distribution of LTOs at the individual airports that report based aircraft data
but not activity data and then applied a scaling factor of 0.08 to those LTOs to obtain the
LTOs that are reported in the 2011 NEI.42  The sum of the LTOs from this set of airports
plus the sum of the LTOs at the airports that do not report either based aircraft or activity
data (described below in section (b)) sum to 687,045 LTOs. These LTOs are all assigned
to the GA, piston-engine category since they are assigned to smaller general aviation
airports that are assumed to have little to no air taxi or jet aircraft activity.

       Equation 5 and the scaling factor were used to estimate LTO activity for the
2011 NEI at the 6,289  airport facilities that report based aircraft data but not
activity data.
(b) Estimating LTOs at Facilities with Neither Based-Aircraft Data nor LTO Data:

       There are 2,141 facilities (not including heliports) for which the 5010 airport data
report supplies neither the number of based aircraft nor activity data.  EPA investigated
100 of these facilities using on-line searches and Google Earth satellite images to
ascertain whether these facilities exist and if so, whether aircraft activity appeared to be
occurring.  Because the majority of these facilities appeared to be active, we elected to
assign 1 LTO to each facility.
Section 5. Calculating LTOs at Heliports:

       There were 5,649 heliport facilities in the February 7, 2012 FAA 5010 data report
that were operational.  Of those, only 92 (or 2%) reported LTO data, and of those, only
29 reported both based aircraft and LTO data. Because of the limited information
regarding activity  at heliports, some municipalities have hired contractors to survey
activity in their local area.43' 44
41 This number is calculated by multiply ing 81.5 LTOs/year by 8,430, which is the number of airports that
don't report activity data (6,289 don't report activity data and 2,141 facilities don't report activity or based
aircraft data).
42 The scaling factor was calculated by dividing 684,904 LTOs by 8,608,829 LTOS; the 684,904 LTOs are
equal to 687,045 LTOs minus 2,141 LTOs (2,141 LTOs represent the sum of LTOs assigned to the 2,141
facilities that don't report either activity data or based aircraft data - the derivation of LTO estimates for
these facilities is described in Section 3 (b)). The 8,608,829 LTOs are the sum of LTOs that result from
applying equation 4 to the 6,289 facilities with based aircraft data but no activity data.
43 Executive Summary: Regional Helicopter System Plan, Metropolitan Washington Area, prepared by
Edwards and Kelcey for the Metropolitan Washington Council of Governments, 2005.


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       The summary statistics for LTO data provided at the 92 operational heliports is
presented in Table 3. These facilities report a wide range in activity from 1 LTO/year to
more than 18,000 LTOs/year.  Some facilities clearly have significant helicopter traffic
(i.e., thousands of LTOs/year) which is supported by the contractor summaries of heliport
activity in the Washington Metropolitan area.  The little data available to us suggests that
the median helicopter activity is less than 200 LTOs/year.  In the absence of more
information on which to base estimates of LTO activity, we assigned 51 LTOs (the
median of the reported heliport LTOs) to the GA category at all of the heliports which do
not report LTO data. The piston-engine fraction developed in Section 6 is applied to the
51 LTOs, resulting in 18 LTOs assigned to the GA, piston-engine category and 33
assigned to the GA, turbine-engine category.  This is an area of significant uncertainty in
the inventory and one for which EPA is seeking information from local agencies.
Table 3:  Heliport LTO Data for those Reporting LTO Data in the February 7, 2012
Version of the 5010 Airport Data Report
18,200
1
793
51
50
Maximum GA LTOs
Minimum GA LTOs
Average GA LTOs
Median GA LTOs
Mode GA LTOs
Section 6. Methodology for Estimating Airport-Specific Lead Emissions

       In 2008, EPA developed a method to calculate lead emissions at airports where
piston-engine aircraft operate.45 This method brings lead inventories into alignment with
the manner in which other criteria pollutants emitted by aircraft are calculated. This
method is described here and applied in developing airport lead inventories for the 2011
NEI.  In this section we first present the equation used to calculate lead emitted during
the LTO  cycle, then we describe each of the components of the input data:  piston-engine
LTOs, the emission factor for lead emitted during the LTO cycle, and the estimated
fraction of lead retained in the engine and oil.

       Typically aircraft emission inventories for gaseous and particulate matter (PM)
pollutants are calculated using FAA's EDMS.46 Currently, EDMS does not calculate
lead emissions and thus, it is not a readily available tool for determining airport lead
inventories related to aircraft operations.  To determine piston-engine aircraft lead
emissions, EPA relied upon the basic methodology employed in EDMS.  This requires as

44 Alaska Aviation Emission Inventory, prepared by Sierra Research, Inc. for Western Regional Air
Partnership, 2005.
45 U.S. EPA (2008) Lead Emissions from the Use of Leaded Aviation Gasoline in the United States,
Technical Support Document. EPA420-R-08-020. Available at: www.epa.gov/otaq/aviation.htm..
46 EDMS available from
http://www.faa.gov/about/office_org/headquarters_offices/apl/research/models/edms_model/
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input the activity of piston-engine aircraft at a facility, fuel consumption rates by these
aircraft during the various modes of the LTO cycle, time in each mode (taxi/idle-out,
takeoff, climb-out, approach, and taxi/idle-in), the concentration of lead in the fuel and
the retention of lead in the engine and oil. The equation used to calculate airport-specific
lead emissions during the LTO cycle is below, followed by a description of each of the
input parameters.
   T T-/-A T.U e*.    \    (piston-engine LTO) (avgas Pb g/LTO) (1-Pb retention)         ,,,
   LTO Pb (tons)  =                    907,180 g/ton                             (6)
(a) Calculating Piston-Engine L TO:

       Piston-engine LTOs are used to calculate emissions of lead that are assigned to
the airport facility where the aircraft operations occur. An aircraft operation is defined as
any landing or takeoff event, therefore, to calculate LTOs, operations are divided by two.
Most data sources from F AA report aircraft activity in numbers of operations which, for
the purposes of calculating lead emissions, need to be converted to LTO events. We
describe here the method used to estimate the fraction of GA and AT LTOs at an airport
that are conducted by piston-engine aircraft. These fractions are calculated separately
(one fraction for GA and one for AT). These fractions are multiplied by total LTOs
reported separately for GA and AT and then summed to arrive at the total LTOs
conducted by piston-engine aircraft at an airport.

       One use of the 2011 NEI is to identify airports that have inventories of 0.50 tons
per year or more since this is one of the criteria for identifying airports where lead
monitoring may need to be considered to evaluate compliance with the National Ambient
Air Quality Standard for Lead. To calculate the most airport-specific inventories for
airports that may potentially exceed 0.50 tons per year, we used a  more airport-specific
surrogate for piston-engine aircraft conducting GA activity at this subset of airports than
the remainder of the airports where we applied national default averages described below.
We used this approach because GA activity is dominated by piston-engine activity and
similar data are not available to allow airport-specific estimates of AT activity conducted
by piston-engine aircraft.  In some cases, airport master plans, airport layout plans,  noise
abatement studies and/or land use compatibility plans provide information regarding the
fraction of AT and GA activity conducted by piston-engine aircraft and in those cases, we
use these data sources.

       We used the fraction of based aircraft that are reported as single- or multi-engine
to calculate the number of GA LTOs that were conducted by piston-engine aircraft  at that
airport.47  The data regarding the population of based aircraft  at an airport is available for
47 These categories are reported separately from jet aircraft so they allow the closest estimate of piston-
engine powered aircraft. However, some turbojet and turbofan aircraft may be reported as single- or multi-


                                                                                 14

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a subset of airports in the FAA 5010 master records data report described in Section 3.
For example, if an airport reports 150 single-engine aircraft, 20 multi-engine aircraft and
a total of 180 aircraft based at that facility, then the fraction of based aircraft we would
use as a surrogate for piston-engine aircraft is 94% ((150+20)7180). We then multiply the
total GA LTOs for that facility by 0.94 to calculate piston-engine GA LTOs.

       We evaluated this surrogate by comparing the results obtained from using the
based aircraft data with piston-engine aircraft operations reported for airports that supply
this information in master plans, airport layout plans, noise abatement studies and/or land
use compatibility plans.  We could rarely find data from the same year for comparison
purposes; however, for the majority of airports, based aircraft and actual observed piston-
engine aircraft activity agreed within ten percent.48

       For the majority of airports in the 2011 NEI we used national average fractions of
GA and AT LTOs conducted by piston-engine aircraft that were derived using FAA's
General Aviation and Part 135* Activity Surveys - CY 2010 (GAATA).50  Table 2.4 in
the 2010 GAATA Survey reports that approximately sixty-six percent (66%) of all GA
and AT LTOs are from piston-engine aircraft which use avgas, and about thirty-four
percent (34%) are turboprop and turbojet powered which use jet fuel, such as Jet A.  The
LTO  data in Table 2.4 in the 2010 GAATA Survey does not distinguish LTOs as GA or
AT, and thus does not provide the information needed to separate jet from piston-engine
activity for GA and AT.

       In order to estimate the fraction of GA activity conducted by piston-engine
aircraft and the fraction of AT activity conducted by piston-engine aircraft, we used the
number of hours flown by piston-engine versus turboprop  or turbojet aircraft that are
reported in Table 1.4 in the 2010 GAATA Survey. We chose this approach since the
overall (i.e., for GA and AT combined) piston-engine percent of hours flown (65.8%) is
very close to the percent of LTOs that are conducted by piston-engine aircraft (65.7%).
The 2010 GAATA Survey reports that for GA activity, seventy-two percent (72%) of the
hours are flown by piston-engine aircraft while twenty-eight percent (28%) of the hours
engine aircraft in which case the use of these data would slightly overestimate actual piston-engine aircraft
activity (as noted later in this section).
48 Documents used to evaluate the use of based aircraft include the following:
Airport Master Plan Update Prescott Municipal Airport (Ernest A Love Field) (2009) Available at:
www.cityofprescottnet/_d/amp_tablecontents.pdf
Gillespie field Airport Layout Plan Update Narrative Report (2005) Available at: www.co.san-
diego.ca.us/dpw/airports/powerpoints/pdalp.pdf
Land Use Compatibility Plan for the Grand Forks International Airport (2006) Available at:
www.gfkairport.com/authoritv/pdf/land  use.pdf
McClellan-Palomar Land Use Compatibility Plan (Amended March 4, 2010) Available at:
www.ci.oceanside.ca.us/.../McClellan-Palomar_ALUCP_03-4-10_amendment.pdf
49 On-demand (air taxi) and commuter operations not covered by Part 121
50 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 2010 GAATA, see Appendix A at
http://www.faa.gov/data_research/aviation_data_statistics/general_aviation/CY2010/
                                                                                   15

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are flown by turboprop and turbojet powered aircraft.51  Twenty-two percent (22%) of all
AT hours flown are by piston-engine aircraft while seventy-eight percent (78%) of all AT
hours flown are by turboprop and turbojet powered aircraft.

       Approximately 5,000 of the total 20,000 airport facilities in the U.S. are heliports
at which only helicopters (rotorcraft) operate. Therefore, EPA also calculated the percent
of rotorcraft hours flown that are conducted by piston-engine aircraft. Thirty-six percent
(36%) of all GA rotorcraft hours  flown are by piston-engine rotorcraft while sixty-four
percent (64%) of all GA rotorcraft hours flown are by turboprop and turbojet powered
rotorcraft.  Two percent (2%) of all AT rotorcraft hours flown are by piston-engine
rotorcraft while ninety-eight percent (98%) of all AT rotorcraft hours flown are by
turboprop and turbojet powered rotorcraft.  Table 4 identifies the piston-engine and
turbine fractions that were used in the absence of airport-specific information to calculate
piston-engine aircraft operations  at airports and heliports in the 2011 NEI.
Table 4:  Piston-Engine and Turbine Activity Fractions used in the 2011 NEI


Piston-
Engine
Turbine
Powered
Airports
GA
72.1%
27.9%
AT
21.8%
78.2%
Heli]
GA
35.8%
64.2%
ports
AT
2%
98%
(b) Calculating the Piston-engine Aircraft Emission Factor: Grams of Lead Emitted per
LTO:

       The vast majority of piston-engine aircraft have either one or two engines. EDMS
version 5.0.2 contains information on the amount of avgas consumed per LTO for some
single and twin-engine aircraft.  For the single-engine aircraft, we averaged the amount of
fuel consumed per LTO using the six types of single piston-engine aircraft in EDMS that
best represent the in-use fleet.52  The EDMS scenario property used to calculate fuel
consumption per LTO was the ICAO/USEPA Default - Times in Mode (TIM), with a 16
minute taxi-in/taxi-out time according to EP A's Procedures for Emission Inventory
Preparation, Volume IV: Mobile Sources, 1992.53 The average fuel consumption for a
single-engine piston aircraft is 16.96 pounds of fuel per LTO (Ibs/LTO) or 2.83 gallons
per LTO (gal/LTO) (applying the average density of 100LL avgas of 6 pounds per
51 Numbers in the text may not add to 100% due to rounding; the percentages in Table 4 are the values we
used to calculate the 2011 NEI.
52 EPA understands that EDMS 5.0.2 has a limited list of piston-engines, but these are currently the best
data available.
53 U.S. EPA, Procedures for Emission Inventory Preparation, Volume IV: Mobile Sources, EPA-450/4-
81026d (Revised), 1992.
                                                                                16

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gallon). This same calculation was performed for the two twin-engine piston aircraft
within EDMS, producing an average LTO fuel consumption rate for twin-engine piston
aircraft of 9.12 gal/LTO. Since twin-engine aircraft have higher fuel consumption rates
than those with single engines, a weighted-average LTO fuel usage rate was calculated to
apply to the population of piston-engine aircraft as a whole.  To weight fuel consumption
by aircraft population prevalence in the fleet, the proportion of piston-engine LTOs
conducted by single- versus twin-engine aircraft was taken from the FAA's GAATA
Survey for 2008 (90% of LTOs are conducted by aircraft having one engine and 10% of
LTOs by aircraft having two engines).54'55

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

       To calculate the average lead emission  factor, the concentration of lead in fuel is
multiplied by the fuel consumption per LTO. The maximum lead concentration specified
by ASTM for 100LL is 0.56 grams of lead per liter or 2.12 grams of lead per gallon.
Multiplying this lead concentration in avgas by the weighted average fuel usage rate
produces an overall average emission factor of 7.34 grams of lead per LTO (g Pb/LTO)
for piston-engine aircraft: 3.46 gal/LTO x 2.12 g Pb/gal = 7.34 g Pb/LTO.
(c)  Retention of Lead in Engine and Oil:

       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.56 Thus,
the emitted fraction of lead is 0.95.
Applying these parameters to equation 6 above yields the following:
           , /+   ,   (piston-engine LTO) (7.34 g Pb/LTO) (0.95)                 ,_.
           Pb(tns)=               907,180 g/ton                               (7)
54 The LTOs from the categories of 1-engine fixed wing piston, piston rotorcraft, experimental total, and
light sport were summed to determine the total number of single-engine piston aircraft LTOs.
  Over time this fraction could be re-evaluated as the national aircraft fleet composition changes.
56 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.
                                                                                 17

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                                 which simplifies to:

                  Pb (tons) = (piston-engine LTO) (7.7 x 10'6)                      (8)
                                 \57
         Where piston-engine LTCT = (GA LTO x 0.721) + (AT LTO x 0.218)
(d) Estimating Lead Emissions from Piston-Engine Helicopters:

       The emission factor for helicopters (g Pb/LTO) was determined in the same
manner as described above for piston-engine fixed-wing aircraft. The concentration of
lead in avgas (2.12 g/gal) was multiplied by the weighted average fuel usage rate for four
types of Robinson helicopter engines.58  This produced an overall average emission
factor of 6.60 grams of lead per LTO (g Pb/LTO) for piston-engine powered helicopters.

       There are no national databases that provide heliport-specific LTO activity data
for piston-engine helicopters separately from turbine-engine helicopters. The 2010 FAA
GA and Part  135 Activity (GAATA) Survey reports that approximately 36% of all GA
helicopter hours flown are by piston-engine aircraft which use avgas and about 64% are
by turbine-engine powered which use jet fuel (which does not contain lead).59 The 2010
FAA GAATA Survey reports that approximately 2% of all AT helicopter hours flown are
by piston-engine aircraft which use avgas, and about 98% are by turbine-engine powered
rotorcraft.  We expect the fraction of helicopter activity conducted by piston-engine
rotorcraft to vary by heliport with some facilities having no piston-engine helicopter
activity and some hosting mainly or only piston-engine helicopters. However, in the
absence of heliport-specific data, the national default estimates of 36% for GA and 2%
for AT from the GAATA Survey were used. Therefore, to calculate piston-engine
aircraft LTO  as input for this equation, the helicopter GA LTOs were multiplied by 0.36
and helicopter AT LTOs were multiplied by 0.02.

       Lead  emitted at each heliport facility was calculated for the 2011 NEI with
equation 9, using either the LTO data provided in FAA databases or the estimate  LTO
activity (i.e.,  51  GALTOs):
     ,  u   ,    (piston-engine helicopter LTO) (6.60 g Pb/LTO) (0.95)             ,-.
     Pb(tns)=                     907,180 g/ton                                (9)
57 This equation for piston-engine LTOs only applies to non-heliport facilities.  See the text immediately
below for equations for calculating piston-engine LTOs and Pb emissions at heliports.
58 This was done using the following 4 engine types in EDMS 5.1: Robinson R22 IO-320-D IAD; Robinson
R22 IO-360-B; Robinson R22 O-320; Robinson R22 TSIO-360C. The fuel consumption rates were:
Robinson R22 IO-320-D1AD - 5.546 g Pb/LTO; Robinson R22 IO-360-B - 5.973 g Pb/LTO; Robinson
R22 O-320 - 6.276 g Pb/LTO; Robinson R22 TSIO-360C - 8.604 g Pb/LTO.
59 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/
                                                                                 18

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                                which simplifies to:

             Pb (tons) = (piston-engine helicopter LTO) (6.9 X 10~6)               (10)
  Where piston-engine helicopter LTO = (Helicopter GA LTO x 0.36) + (Helicopter AT
                                   LTO x 0.02)
Section 7. Improving Airport-specific Lead Emissions Estimates

       There are refinements to the methods described here that would improve airport-
specific inventories, most of which involve acquiring airport- and aircraft-specific input
data.  The following information describes data inputs that could be used to generate
airport lead inventories tailored to specific airports or otherwise improve the estimates
using currently available data.

       State and local agencies, in collaboration with airport sponsors, may be able to
collect airport-specific data that could be used to replace national average or default
values.  EPA requests and receives state and local authority review and data updates with
each NEI. The key data inputs that states and local authorities could provide that would
improve airport-specific lead  inventories are:

    1)   Airport-specific LTO activity for piston-engine aircraft,  including the fraction of
        piston-engine activity conducted by single- versus twin-engine aircraft. The
        activity data should be current and updated on a regular  schedule so that the data
        represents the inventory year as closely as possible.
    2)   The time spent in each mode of the LTO cycle.  EPA uses the EDMS scenario
        property of ICAO/USEPA Default -Times in Mode, with a 16 minute taxi--
        in/taxi-out time according to EPA's Procedures for Emission Inventory
        Preparation, Volume  IV: Mobile Sources,  1992. While some local authorities
        have confirmed that these are the relevant times in mode at their airports for
        piston-engine aircraft, the applicability of these times in mode will vary by
        airport.  EPA has learned that one of the important factors in piston-engine
        aircraft operation that is currently not included in NEI inventory estimates is the
        time and fuel consumption during the pre-flight run-up checks conducted by
        piston-engine aircraft prior to takeoff.
    3)   The concentration of lead in the avgas supplied at the airport (including
        variation in this concentration among the fixed-based operators  supplying fuel
        at the airfield and seasonal variation in concentration), the fraction of lead in
        fuel that is retained in the engine and oil, and aircraft-specific fuel consumption
        rates by the piston-engine aircraft in specific modes of operation for the airport.
                                                                                 19

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Section 8. Lead emitted in flight:

       Lead emissions, especially those at altitude, undergo dispersion and eventually
deposit to surfaces, and lead deposited to soil and water can remain available for uptake
by plants, animals and humans for long periods of time. Because lead is a persistent
pollutant, we are including all lead emissions - at airports and in-flight - in the NEI.60

       The mass  of lead emitted in-flight is calculated as the difference between the total
amount of lead emitted by piston-engine aircraft nationwide (obtained in equation 1) and
the sum of all the lead emitted at airports (as described in sections 3 through 6). In 2011,
the total amount of lead emitted in-flight was 238 tons.  For inventory purposes, lead
emitted in flight occurs during aircraft cruise mode and portions of the climb-out and
approach modes above the mixing height (typically 3,000 ft61).  This part of an aircraft
operation emits lead at various altitudes as well as close to and away from airports.
Because the precise area of lead emission and deposition is not known for these flights,
EPA assigns these emissions to states.

       In the 2011 NEI, EPA allocated in-flight lead emissions to states based on the
state-specific fraction of national GA and AT piston-engine LTO activity.  The state-
specific fractions  were calculated by multiplying the percent of GA and AT piston-engine
LTO activity in each state by 238 tons (the amount of lead we estimate was emitted in-
flight in 2011). Table 5 presents the total GA and AT piston-engine LTOs by state, the
state-specific faction of national GA and AT piston-engine LTO activity,  and the in-flight
lead emissions assigned to each state.
60 U.S. EPA, 2006. Air Quality: Criteria for Lead: 2006; EPA/600/R-5/144aF; U.S. Government Printing
Office, Washington, DC, October, 2006.
61 According to EPA's Procedures for Emission Inventory Preparation, Volume IV: Mobile Sources, 1992.
                                                                                 20

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Table 5: In Flight Lead Emissions by State
State
AK
AL
AR
AZ
CA
CO
a
DC
DE
FL
GA
HI
IA
ID
IL
IN
KS
KY
LA
MA
MD
ME
Ml
MN
MO
MS
MT
NC
ND
NE
NH
NJ
NM
NV
Total GA and
AT Piston-
Engine LTOs
629,006
734,038
697,003
1,174,215
3,429,597
742,024
199,414
330
79,825
2,519,221
676,310
141,849
341,285
486,059
909,758
537,510
588,003
289,393
643,217
588,864
414,238
224,202
724,730
701,245
411,676
439,636
279,156
769,909
304,287
297,604
152,060
419,007
228,784
312,672
Percent of
National GA
and AT Piston-
Engine LTOs (by
state)
2.0%
2.3%
2.2%
3.7%
10.8%
2.3%
0.6%
0.001%
0.3%
7.9%
2.1%
0.4%
1.1%
1.5%
2.9%
1.7%
1.8%
0.9%
2.0%
1.8%
1.3%
0.7%
2.3%
2.2%
1.3%
1.4%
0.9%
2.4%
1.0%
0.9%
0.5%
1.3%
0.7%
1.0%
Pb Emissions in
Flight (tons)
4.70
5.49
5.21
8.77
25.63
5.54
1.49
0.00
0.60
18.83
5.05
1.06
2.55
3.63
6.80
4.02
4.39
2.16
4.81
4.40
3.10
1.68
5.42
5.24
3.08
3.29
2.09
5.75
2.27
2.22
1.14
3.13
1.71
2.34
                                                                              21

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NY
OH
OK
OR
PA
PR
Rl
SC
SD
TN
TX
UT
VA
VI
VT
WA
Wl
WV
WY
949,455
1,237,154
435,141
551,685
847,858
80,788
49,965
464,252
218,646
524,272
2,256,065
293,692
573,055
23,743
72,202
1,168,777
775,600
133,037
107,779
3.0%
3.9%
1.4%
1.7%
2.7%
0.3%
0.2%
1.5%
0.7%
1.6%
7.1%
0.9%
1.8%
0.1%
0.2%
3.7%
2.4%
0.4%
0.3%
7.09
9.24
3.25
4.12
6.34
0.60
0.37
3.47
1.63
3.92
16.86
2.19
4.28
0.18
0.54
8.73
5.80
0.99
0.81
For additional information or if you have questions regarding the methods described in
this document, please contact Meredith Pedde (pedde.meredith@epa.gov) or Marion
Hoyer (hoyer.marion@epa.gov).
                                                                            22

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                                       APPENDIX A
Table A-1:  Scaling factors
Year
Before 198 163
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
U.S. Product Supplied of Aviation
Gasoline (Thousand Barrels)62

11,147
9,307
9,444
8,692
9,969
11,673
9,041
9,705
9,427
8,910
8,265
8,133
7,606
7,555
7,841
7,400
7,864
7,032
7,760
7,188
6,921
6,682
5,987
6,189
7,006
6,626
6,258
5,603
5,261
5,358
5,362
Ratio of 20 11
to Year X
0.55
0.48
0.58
0.57
0.62
0.54
0.46
0.59
0.55
0.57
0.60
0.65
0.66
0.70
0.71
0.68
0.72
0.68
0.76
0.69
0.75
0.77
0.80
0.90
0.87
0.77
0.81
0.86
0.96
1.02
1.00
1.00
62 Data from the Energy Information Administration's (EIA's) table, "U.S. Product Supplied of Aviation
Gasoline (Thousand Barrels)."  Available at:
http://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=PET&s=mgaupusl&f=A Accessed March 28, 2012.
63 EIA does not have data for volumes of avgas product supplied for years earlier than 1981. To calculate
the scaling factor to use for activity data from years before 1981, we used the ratio of 2011 avgas volume
product supplied to the average avgas volume supplied from 1981 to 1989.
                                                                                           23

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