Calculating Piston-Engine Aircraft 


Airport Inventories for Lead for the 


2008 National Emissions Inventory
 
Calculating Piston-Engine Aircraft 


Airport Inventories for Lead for the 


2008 National Emissions Inventory
 

Assessment and Standards Division 

Office of Transportation and Air Quality 

U.S. Environmental Protection Agency 

EPA-420-B-10-044 

December 2010 
 

 

 

 

 

 

 

 

 

 

 

Calculating Piston-Engine Aircraft Airport Inventories for Lead for the 2008 

National Emissions Inventory
 

December 2010 

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 2008 

National Emissions Inventory (NEI).1 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 reflect improvements to the methods used in 

developing the airport-specific piston-engine aircraft inventories in the 2002 NEI and the 

2005 NEI. 

Background information regarding the use of leaded aviation gasoline (avgas) in 

piston-engine powered aircraft is available in other documents.2,3 Briefly, most pistonengine 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.4 Lead emissions associated with GA and AT 

aircraft stem from the use of one hundred octane low lead (100LL) avgas. The lead is 

added to the fuel in the form of tetraethyl lead (TEL). This lead additive 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.5 Lead is not added to jet fuel that 

is used in commercial aircraft, most military aircraft, or other turbine-engine powered 

aircraft. Lead emissions from the use of leaded avgas comprised 45% of the national 

inventory for emissions of lead in 2002.6 

1 In this document ‘2008 NEI’ refers to 2008 NEI version 1 (January 2011), available at 

http://www.epa.gov/ttn/chief/net/2008inventory.html

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

http://www.chevronglobalaviation.com/docs/aviation_tech_review.pdf

6 U.S. Environmental Protection Agency (2008) EPA’s Report on the Environment EPA/600/R-07/045F. 

Available at: http://www.epa.gov/roe 

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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 inventories for lead. 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 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 that are in the 2008 NEI. 

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 take-off cycle at airports as well as emissions occurring at 

altitude.7 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 2008.8 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. EPA has 

historically 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 2008 NEI 

to calculate the national lead inventory in order to use a consistent data source. In this 

document, when we refer to avgas fuel volume data it is data supplied by DOT, except 

where noted. 

As demonstrated in the equation below, 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, minus the small amount of lead that is retained in the 

engine, engine oil and/or exhaust system. The volume of avgas used in the U.S. in 2008 

7 U.S. EPA, 2006. Air Quality: Criteria for Lead: 2006; EPA/600/R-5/144aF; U.S. Government Printing 

Office, Washington, DC, October, 2006.

8 U.S. Department of Transportation Federal Aviation Administration Aviation Policy and Plans. FAA 

Aerospace Forecast Fiscal Years 2010-2030. p.99. Available at: 

http://www.faa.gov/data_research/aviation/aerospace_forecasts/2010-

2030/media/2010%20Forecast%20Doc.pdf This document provides historical data for 2000-2008 as well 

as forecast data. 

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was 248,100,000 gallons.9 The concentration of lead in avgas ([Pb] in the equation 

below) 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 “100 Low Lead” or 100LL.10,11 The maximum lead 

concentration specified by ASTM for 100LL is 0.56 grams per liter or 2.12 grams per 

gallon.12 A fraction of lead is retained in the engine, engine oil and/or exhaust system 

which we currently estimate at 5%.13 

For the 2008 NEI, the national estimate of lead emissions from the consumption 

of avgas was 551 tons (see equation below). 

(248,100,000 gal)(2.12 g Pb/gal)(0.95) = 551 tons Pb 

907,180 g/ton 

As described above, DOE’s EIA also provides estimates of the annual volume of 

leaded avgas produced in a given year. For 2008, the volume of avgas produced in the 

U.S. was 5,603 thousand barrels or 235,326,000 gallons.14 Consumption of this volume 

of avgas equates to a national lead emissions estimate for this source of 522 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.15 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. Of these facilities, EPA’s 

NEI has in the past, reported emissions of lead (and other criteria pollutants and 

9 U.S. Department of Transportation Federal Aviation Administration Aviation Policy and Plans. FAA
 

Aerospace Forecast Fiscal Years 2010-2030. p.99. Available at: 

http://www.faa.gov/data_research/aviation/aerospace_forecasts/2010-

2030/media/2010%20Forecast%20Doc.pdf This document provides historical data for 2000-2008 as well
 

as forecast data.
 10 ChevronTexaco (2005) Aviation Fuels Technical Review. FTR-3.
 11 The 2008 General Aviation Statistical Databook & Industry Outlook report by General Aviation
 

Manufactures Association (GAMA) found that over 90% of avgas is 100LL.

12 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.

13 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. 14 DOE Energy Information Administration. Fuel production volume data obtained from
 

http://tonto.eia.doe.gov/dnav/pet/hist/mgaupus1A.htm accessed November 2006.
 15 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.
 

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hazardous air pollutants) at 3,410 airports.16 While the 3,410 airport facilities are among 

the most active in the U.S., they comprise only a small fraction of the total airport 

facilities where leaded avgas is used. 

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.17 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 (TAF) 

database that is prepared by FAA’s Office of Aviation Policy and Plans.18 The TAF 

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 TAF 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 

Network (OPSNET)19 which is publically available in the Air Traffic Activity System 

(ATADS) database.20 The operations data for the towered airports that is reported in 

OPSNET and ATADS is then reported to the TAF database. The operations data for the 

airports in the TAF database that do not have control towers represent estimates.21 The 

operations supplied in the 5010 airport data report for facilities not reported in the TAF 

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.22 

The 5010 airport data report supplies the date that the associated operations data 

represents.23 Because airports that are not in the TAF database submit data voluntarily to 

FAA for the 5010 data report, many of the airports have operations data that represent 

data for years earlier than 2008. Nationally, GA and AT piston-engine operations have 

decreased in recent years,24 therefore EPA did not use operations data from years prior to 

2008 as it is reported. Instead, EPA multiplied the older GA and AT piston-engine data 

(Section 6 describes the method EPA used to calculate the number of piston-engine 

16 These 3,410 facilities are the facilities for which the FAA’s Terminal Area Forecast (TAF) database 

provides information regarding aircraft activity. The TAF database is prepared by FAA’s Office of 

Aviation Policy and Plans and includes information for the airports in FAA’s National Plan of Integrated 

Airport Systems (NPIAS). One of the goals of the NPIAS is to identify airports that are significant to 

national air transportation. 

17 http://www.faa.gov/airports_airtraffic/airports/airport_safety/airportdata_5010/ 

18 http://aspm.faa.gov/main/taf.asp 

19 http://aspm.faa.gov/opsnet/sys/

20 http://aspm.faa.gov/opsnet/sys/Airport.asp 21 FAA’s Terminal Area Forecast Summary (Fiscal Years 2009 – 2030), Appendix A (page 28) 

http://www.faa.gov/data_research/aviation/taf_reports/media/TAF%20Summary%20Report%20FY%2020 

09%20-%202030.pdf 22 In the absence of updated information from States, local authorities or Tribes, we are using the LTO data 

provided in the FAA database.

23 The 12-month ending date on which annual operations data in the report is based. 24 http://www.faa.gov/data_research/aviation_data_statistics/general_aviation/ 

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operations from total GA and AT activity data) by scaling factors that were calculated by 

dividing the 2008 national amount of avgas produced by the national amount of avgas 

produced in the year the operations data represents.25 A table with the scaling factors is 

provided in Appendix A. The national volume of avgas produced data comes from the 

DOE, EIA website and is available for 1981 – 2009.26 For operations data older than 

1981, EPA divided the 2008 national amount of avgas produced by the average of the 

national amount of avgas produced from 1981 – 1989. Jet engines do not use avgas, 

therefore EPA did not apply scaling factors to the turbine operations for data from years 

prior to 2008. 

EPA also 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 data set that would 

double count with the TAF 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.27 The resulting aggregated 

LTOs were compared with the reported TAF LTOs for airports where there were 

overlaps. The T-100 AT LTOs were then subtracted from the TAF AT data to ensure 

that double counting was minimized. 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 2008 draft NEI was developed using the January 15, 2009 version of the 

5010 airport data report. In that version of the report there were 19,925 airport facilities 

in the U.S. that had submitted data to the FAA. Among these 19,925 facilities, 99 

facilities were not relevant for the purposes of estimating lead emissions because they 

were either listed as closed (85) or they were balloonports (14).28 Therefore, lead 

inventories were needed for 19,826 facilities. In the January 15, 2009 version of the 5010 

airport data report there were 5,654 airport facilities for which operations data were 

provided (many of which are facilities in FAA’s TAF database).29 There were 14,172 

facilities in the 5010 airport data report for which there were no operations data.30 As a 

25 The FAA General Aviation and Air Taxi (Part 135) Activity Surveys (source of national level pistonengine 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 three decades. 

26 http://tonto.eia.doe.gov/dnav/pet/hist/LeafHandler.ashx?n=PET&s=mgaupus1&f=A. DOT recently 

changed the way they estimate fuel consumption data, so while EPA used DOT data to determine the 2008 

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. 

27 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 2008 NEI as 

such. 

28 Balloon craft do not use avgas 

29 Either Commuter, GA Itinerant, GA Local, or Air Taxi operations data, as these operations can be 

performed by piston-engine aircraft.

30 No Commuter, GA Itinerant, GA Local, or Air Taxi operations data. 

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part of the review process for the draft 2008 NEI, EPA received updated airport data from 

states and also looked at more recent versions of the 5010 airport data report to update the 

status of airports, so the number of airports for which EPA estimated activity is slightly 

lower in the 2008 NEI than in the draft 2008 NEI. The following section of this 

document describes the method EPA used to estimate operations for the 14,132 airport 

facilities in the 2008 NEI that do not have reported activity data. 

As described in Section 1, most piston-engine aircraft fall into the categories of 

either GA or 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 LTO activity data for piston-engine aircraft separately from turbojet and 

turboprop aircraft. The databases described above report total GA and AT activity 

conducted by both piston-engine and jet-engine aircraft. Part (a) in Section 6 describes 

how we estimate piston-engine LTOs at airports in the 2008 NEI. 

Section 4. Estimating LTOs at the 14,132 Airport Facilities with No LTO Data 

FAA has used regression models to estimate operations at facilities where 

operations data are not available.31,32 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.33 Regression models based on the airport 

characteristics were then used to estimate general aviation operations for a set of nontowered airports. The airport characteristics identified by FAA and used to estimate 

general aviation operations at small airports include: the number of aircraft based at a 

facility (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 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-towered airports. 

The model explained GA activity at the towered airports well (R2 of 0.75) but produced 

higher estimates than state-supplied estimates for non-towered airports.34 

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,35 ultralight); number of GA aircraft based at each airport by 

31 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.
 32 Mark Hoekstra, “Model for Estimating General Aviation Operations at Non-Towered Airports” prepared 

for FAA Office of Aviation Policy and Plans, April 2000.

33 GRA, Inc. “Review of TAF 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.

34 The mean absolute difference between the model operations estimate and the state operations estimate 

was 16,940 operations.

35 Stolport is an airport designed with STOL (Short Take-Off and Landing) operations in mind, normally 

having a short single runway.
 

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type (glider, helicopter, jet engine, military, multi-engine, single engine, ultralight); 

operations data (air taxi, commercial, commuter, GA itinerant, GA local, military)36; and 

operations date (12-month ending date on which annual operations data is based). 

Census data was also merged with the 5010 airport data report to give 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 1 shows that for 

facilities that did not have LTO data in the January 15, 2009 version of the 5010 airport 

data report, 7,856 had based aircraft data while 6,316 did not have based aircraft data.37, 

38 Therefore, as described below, LTO estimates were derived using different methods 

depending on data availability. 

Table 1: Contingency table describing the numbers of airport facilities that have or do 

not have LTO data and/or based aircraft data for airport facilities in the January 15, 2009 

version of the 5010 airport data report 

HAVE LTO DATA 

HAVE
 

BASED
 

AIRCRAFT
 

DATA
 

YES NO 

YES 4,872 7,856 12,728 

NO 782 6,316 7,098 

5,654 14,172 19,826 

36 As explained in footnote 15, 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.

37 As described in Section 3, the number of facilities with no LTO data changed slightly from the draft 2008 

NEI to the 2008 NEI. In the 2008 NEI, of the facilities that did not have reported activity data, 7,837 

facilities reported based aircraft data and 6,295 did not report based aircraft data.

38 These numbers include data for the following types of facilities: airports, balloonports, seaplane bases, 

gliderports, heliports, stolports, and ultralights. 

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(a) Estimating LTOs at Facilities with Based Aircraft Data, but No LTO Data: 

There are 6,414 facilities in the 2008 NEI (not including heliports) for which the 

5010 airport data report supplies the number of based aircraft39 but not activity data to 

which the regression equation (based aircraft vs. LTOs) could be applied. Using the 

4,872 airports for which both LTO and aircraft data is known, the initial relationship 

found between based aircraft and LTOs was: 

Equation 1:
 

LTOs = 2494 + 208*aircraft R2 = 0.55
 

The FAA models found population to be another significant regressor. We used 

the population of the county in which the airport is located as the population variable. 

Adding county population to the model gave the following relationship: 

Equation 2:
 

LTOs = 2204 + 194*aircraft + 0.0038*county population R2 = 0.56
 

EPA received numerous comments to the docket on its Advance Notice of 

Proposed Rulemaking on Lead Emissions from Piston-Engine Aircraft Using Leaded 

Aviation Gasoline40 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 

accessible by road and rely on air transport for life sustaining goods and services.41 

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 

3 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 3 (interaction 

of an airport being in Alaska and its sum of based aircraft). 

Equation 3:
 

LTOs = 1937 + 205*aircraft + 0.0038*county population + 566*Alaska –
 

108*(AlaskaXaircraft)
 

R2 = 0.58 

After analyzing the data and plot for the data underlying equation 3, 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 

39 Based aircraft for this purpose was limited to single- and multi-engine aircraft, helicopters, and 

ultralights since these aircraft types can use leaded avgas.

40 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). 41 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). 

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to more than 200,000 LTOs/year).42 These facilities were removed from the regression 

analysis. Additionally, for reasons described below, heliports were also removed from
 

the regression. The resulting relationship was:
 

Equation 4:
 

LTOs = 1293 + 203*aircraft + 0.0019*county population - 473*Alaska –
 

144*(AlaskaXaircraft)
 

R2 = 0.65 

When equation 4 was applied to the 6,414 airport facilities that report based 

aircraft data but not LTO activity, the resulting sum of LTOs was almost 15 million. 

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 TAF 

database. The average number of 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 TAF database is ~63 LTOs/year. Multiplying 63 by the number of airports that do 

not report activity data equals 549,050 LTOs.43 Therefore, EPA used equation 4 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 0.0356 to those LTOs to obtain 

the LTOs that are reported in the 2008 NEI.44 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 549,050 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 4 and the scaling factor were used to estimate LTO activity for the 

2008 NEI at 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 2,260 facilities (not including heliports) for which the 5010 airport data 

report supplies neither the number of based aircraft nor activity data. In the absence of 

data to establish a relationship to airport activity, we assign a default value of LTOs to 

the GA, piston-engine category for each of these facilities. 

42 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

43 This rounded number is calculated by multiplying 63.298 LTOs/year by 8,674, which is the number of 

airports that don’t report activity data (6,414 don’t report activity data and 2,260 facilities don’t report 

activity or based aircraft data).

44 The scaling factor was calculated by dividing 528,710 LTOs by 14,862,767 LTOS; the 528,710 LTOs are 

equal to 549,050 LTOs minus 20,340 LTOs (20,340 LTOs represent the sum of LTOs assigned to the 2,260 

facilities that don’t report either activity data or based aircraft data - the derivation of LTO estimates for 

these facilities is described in Section 4 (b)). The 14,862,767 LTOs are the sum of LTOs that result from 

applying equation 4 to the 6,414 facilities with based aircraft data but no activity data. 

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The default value was determined by evaluating GA LTOs that are reported at the 

set of 2,471 facilities that report activity data to the 5010 airport data report but that are 

not in the TAF set of airports. The average number of LTOs reported to the bottom ten 

percent of these facilities (when sorted by total GA LTOs) was 9. These facilities are 

assumed to most closely approximate the set of 2,260 facilities that do not report any 

based aircraft or LTO data; therefore, we assigned 9 LTOs to the GA, piston-engine 

category for these airport facilities for purposes of developing inventory estimates. 

Section 5. Calculating LTOs at Heliports: 

There were 5,559 heliport facilities in the January 15, 2009 FAA 5010 data report 

that were operational. Of those, only 92 (or 2%) reported LTO data, and of those, only 

31 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.45, 46 

The summary statistics for LTO data provided at the 92 operational heliports is 

presented in Table 2. These facilities report a wide range in activity from 3 LTOs/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 141 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 

141 LTOs resulting in 51 LTOs assigned to the GA, piston-engine category and 90 

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 2: Heliport LTO Data for those Reporting LTO Data in the January 15, 2009 

Version of the 5010 Airport Data Report 

18,250 Maximum LTOs 

3 Minimum LTOs 

1,123 Average LTOs 

141 Median LTOs 

50 Mode LTOs 

45 Executive Summary: Regional Helicopter System Plan, Metropolitan Washington Area, prepared by
 

Edwards and Kelcey for the Metropolitan Washington Council of Governments, 2005.

46 Alaska Aviation Emission Inventory, prepared by Sierra Research, Inc. for Western Regional Air
 

Partnership, 2005.
 

10 
 

 

 

 

 

 

 

 

 

 

 

 

Section 6. Methodology for Estimating Airport-Specific Lead Emissions 

In 2008, EPA developed a method to calculate lead emissions at airports where 

piston-engine powered aircraft operate. 47 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 with changes that were made from previous 

methods (i.e., the method used to develop the 2002 inventory) and applied in developing 

airport lead inventories for the 2008 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: we describe how we calculate piston-engine LTOs from 

data available in FAA databases, we describe the derivation of the emission factor for the 

amount of lead emitted during the LTO cycle, and we describe the estimate of the amount 

of lead retained in the engine and oil that we do not include in the amount of lead 

released to the air. 

Historically, where aircraft specific activity data are available (such as T-100), 

aircraft gaseous and particulate matter (PM) emissions have been calculated through the 

FAA’s EDMS.48 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 has a limited number of pistonengine aircraft in its aircraft data and is currently not set up to calculate metal emissions 

and thus, it is not a readily available tool for determining airport lead inventories related 

to aircraft operations. In developing this approach to determine piston-engine aircraft 

lead emissions, EPA relied upon the basic methodology employed in EDMS. This 

requires as input the activity of piston-engine aircraft at a facility, fuel consumption rates 

by these aircraft during the various modes of the LTO cycle and 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. 

LTO Pb (tons) = (piston-engine LTO)(avgas Pb g/LTO)(1-Pb retention) 

907,180 g/ton 

(a) Calculating Piston-engine LTO: 

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 FAA report aircraft activity in numbers of operations which, for 

the purposes of calculating lead emissions, need to be converted to LTO events. We 

47 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. 48 EDMS available from 

http://www.faa.gov/about/office_org/headquarters_offices/aep/models/edms_model/ 

11 
 

 

 

 

 

 

 

 

 

 

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 2008 NEI is to identify sources of lead, including airports, that 

have inventories of 0.50 tons per year or more for the purposes of identifying locations 

where lead monitoring may be required 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 this inventory threshold, we used a 

more airport-specific surrogate for this subset of airports than the remainder of the 

airports where we applied national default averages described below. 

We used the fraction of based aircraft at an airport that are single- or multi-engine 

to calculate the number of GA LTOs at an airport that were conducted by piston-engine 

aircraft. The data regarding the population of based aircraft at an airport is available for 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)/180). We then multiply the 

total GA LTOs for that facility by 0.94 to calculate piston-engine LTOs. 

We evaluated this surrogate by comparing the results of using it with pistonengine 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.49 

For the majority of airports in the 2008 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 13550 Activity Surveys – CY 2008 (GAATA).51 Table 2.4 in 

the 2008 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 

49 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.cityofprescott.net/_d/amp_tablecontents.pdf
 

Gillespie field Airport Layout Plan Update Narrative Report (2005) Available at: www.co.sandiego.ca.us/dpw/airports/powerpoints/pdalp.pdf
 

Land Use Compatibility Plan for the Grand Forks International Airport (2006) Available at:
 

www.gfkairport.com/authority/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 

50 On-demand (air taxi) and commuter operations not covered by Part 121 

51 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 2008 GAATA, see Appendix A at 

http://www.faa.gov/data_research/aviation_data_statistics/general_aviation/CY2008/ 

12 
 

 

 

 

 

 

 

 

 

 

 

percent (34%) are turboprop and turbojet powered which use jet fuel, such as Jet A. The 

LTO data in Table 2.4 in the 2008 GAATA Survey does not distinguish LTOs as GA or 

AT, and thus does not allow us derive separate piston activity fractions for GA and AT. 

We are using the number of hours flown by piston versus turboprop or turbojet 

aircraft (reported in Table 1.4 in the 2008 GAATA Survey) to allow us to make separate 

estimates of the fraction of GA activity conducted by piston aircraft and the fraction of 

AT activity conducted by piston aircraft. We chose to use the fraction of hours flown by 

piston-engine aircraft as a surrogate to calculate the fraction of LTOs flown by piston 

aircraft since the overall (i.e., for GA and AT combined) piston percent of hours flown 

(66.4%) is very close to the percent of LTOs that are piston (65.7%). Table 1.4 of the 

2008 GAATA presents the total hours flown by aircraft type and separates GA from AT. 

Seventy-three percent (73%) of all GA hours flown are by piston-engine aircraft while 

twenty-eight percent (28%) of all GA hours flown are by turboprop and turbojet powered 

aircraft.52 Twenty-three percent (23%) of all AT hours flown are by piston-engine 

aircraft while seventy-seven percent (77%) 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 (rotocraft) operate. Therefore, EPA also 

calculated the percent of rotocraft hours flown that are conducted by piston-engine 

aircraft. Thirty-six percent (36%) of all GA rotocraft hours flown are by piston-engine 

rotocraft while sixty-four percent (64%) of all GA rotocraft hours flown are by turboprop 

and turbojet powered rotocraft. Two percent (2%) of all AT rotocraft hours flown are by 

piston-engine rotocraft while ninety-eight percent (98%) of all AT rotocraft hours flown 

are by turboprop and turbojet powered rotocraft. Table 3 identifies the piston and turbine 

fractions that were used in the absence of airport-specific information to calculate pistonengine operations at airports and heliports in the 2008 NEI. 

Table 3: Piston and Turbine Activity Fractions used in the 2008 NEI 

Airports Heliports 

GA AT GA AT 

Piston 

Powered 72.5% 23.1% 36.1% 2% 

Turbine 

Powered 27.5% 76.9% 63.9% 98% 

52 Numbers in the text may not add to 100% due to rounding; the percentages in Table 3 are the values we 

used to calculate the 2008 NEI. 

13 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

(b) Calculating the Piston-engine Aircraft Emission Factor: Grams of Lead Emitted per 

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 single and twinengine aircraft. The proportion of piston-engine LTOs conducted by single- versus twinengine 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).53 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. 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.54 This was calculated by averaging the singleengine 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, 1992.55 This gives a value of 16.96 pounds of fuel per LTO (lbs/LTO). The 

average single-engine fuel consumption rate was divided by the average density of 

100LL avgas, 6 pounds per gallon (lbs/gal), producing an average fuel usage rate for 

single-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 single- and twin-engine piston aircraft fuel consumption rates, a 

weighted average fuel usage rate per LTO was computed by multiplying the average fuel 

usage rate for single-engine aircraft (2.83 gal/LTO) by the fleet percentage of singleengine aircraft LTOs (90%). Next, the twin-engine piston aircraft average fuel usage 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 usage rates, the 

overall weighted-average fuel usage rate per LTO of 3.46 gal/LTO was obtained. 

To calculate the 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 per liter or 2.12 grams per gallon. This amount of lead is normally 

added to assure that the required lean and rich mixture knock values are achieved. 

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 pistonengines: 3.46 gal/LTO x 2.12 g Pb/gal = 7.34 g Pb/LTO. 

53 The LTOs from the categories of 1-engine fixed wing piston, piston rotocraft, experimental total, and
 

light sport were summed to determine the total number of single-engine piston aircraft LTOs.

54 EPA understands that EDMS 5.0.2 has a limited list of piston-engines, but these are currently the best
 

data available.
 55 U.S. EPA, Procedures for Emission Inventory Preparation, Volume IV: Mobile Sources, EPA-450/4-

81026d (Revised), 1992.
 

14 
 

 

 

 

 

 

 

 

 

 

 

 

(c) Retention of Lead in Engine and Oil (1-Pb Retention): 

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 is 0.95. This 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 parameters in the equation above yields the following equation: 

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

907,180 g/ton 

which simplifies to: 

Pb(tons) = (piston-engine LTO) (7.7 X 10-6) 

Where piston-engine LTO57 = (GA LTO x 0.725) + (AT LTO x 0.231) 

(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 powered helicopters separately from turbine-engine powered 

helicopters. The 2008 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 

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. 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-D1AD; 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. 

15 
 

 

 

 

 

 

 

 

not contain lead).59 The 2008 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 rotocraft. We expect the fraction of helicopter activity 

conducted by piston-engines to vary by heliport with some facilities having no pistonengine powered helicopter activity and some hosting mainly or only piston-engine 

powered 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 the heliport facility was calculated for the 2008 NEI using either 

the LTO data provided in FAA databases or the estimate LTO activity in the following 

equation (i.e., 141 LTOs): 

Pb(tons) = (piston-engine helicopter LTO) (6.60 g Pb/LTO) (0.95) 

907,180 g/ton 

which simplifies to: 

Pb(tons) = (piston-engine helicopter LTO) (6.9 X 10-6) 

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 airportspecific 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 authorities might have, or be able to

collect, better information for some of these key data inputs. 

State and local agencies might have access to airport-specific data that would 

improve the national estimates of lead emissions per LTO. These improvements largely 

involve replacing national average or default values with airport-specific data on the 

activity of piston-engine aircraft. Three key data inputs are: 

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/ 

16 
 

 

 

 

 

 

 

 

 

 

 

1)	 Airport-specific LTO activity for piston-powered aircraft, including the fraction 

of piston-engine activity conducted by single- versus twin-engine aircraft. Some 

airport facilities collect this information and states may use these data to 

calculate airport-specific lead inventories. 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 taxiin/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 aircraft, the applicability of these times in mode will vary by airport. EPA 

has learned that one of the important factors in piston aircraft operation that is 

currently not included in the time in mode or emissions estimates is the time and 

fuel consumption during the pre-flight run-up checks conducted by piston-engine 

aircraft prior to takeoff. 

3)	 Other data inputs for the airport-specific lead inventory calculation for which 

states or local authorities may provide airport-specific information include the 

concentration of lead in the avgas supplied at an airport, and 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. 

The accuracy of the based aircraft data on which equation 4 is modeled can be 

improved. FAA 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 NPIAS and is 

currently in the process of improving the data collection and submission methods to 

accomplish this task.60 

Section 8. Lead emitted in flight (i.e., outside the LTO cycle): 

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.61 

For inventory purposes, lead emitted outside the LTO cycle occurs during aircraft 

cruise mode and portions of the climb-out and approach modes above the mixing height 

(typically 3,000 ft62 ). 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 is using a simplistic approach to allocate 

60 National Based Aircraft Inventory Program: 

http://www.basedaircraft.com/public/FrequentlyAskedQuestions.aspx, accessed 2/17/2009
 61 U.S. EPA, 2006. Air Quality: Criteria for Lead: 2006; EPA/600/R-5/144aF; U.S. Government Printing
 

Office, Washington, DC, October, 2006.

62 According to EPA’s Procedurees for Emission Inventory Preparation, Volume IV: Mobile Sources, 1992.
 

17 
 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

these emissions for the purposes of the 2008 NEI. A brief explanation of the nature of 

GA flights is provided here for context regarding emissions of lead in-flight. 

FAA categorizes GA flights as either local area or itinerant operations and this 

distinction plays a role in the area over which lead is emitted. Local operations are those 

activities performed by aircraft operating in the local traffic pattern or within sight of the 

airport, aircraft executing simulated instrument approaches or low passes at the airport, 

and/or aircraft operating to or from the airport in a designated practice area located within 

a 20-mile radius of the airport. Local operations are common for GA aircraft. This 

includes applications such as recreational, proficiency and instructional flying as well as 

many common general aerial support tasks. Emissions during local flying are more likely 

to influence air and soil concentrations of lead in the vicinity of the airport because they 

occur near the airport, often at altitudes below the mixing height. 

Itinerant operations are all operations other than those described above as local 

operations. An itinerant aircraft operation usually is one in which the aircraft departs 

from one airport and lands at a different airport. Depending on air time and distance, an 

itinerant flight is much more likely to involve departing the local flying area of the 

originating airport and climbing to altitudes above the mixing height. It is reasonable 

then, to generally expect that lead emitted outside the LTO cycle during itinerant 

operations, in contrast with local operations, will be more widely dispersed and at greater 

distances from the airport. 

The portion of the national avgas lead emitted in flight (i.e., outside the LTO 

cycle) is calculated by subtracting the sum of airport facility lead inventories from the 

national avgas lead inventory. Even though FAA collects and reports information 

regarding the fraction of GA operations that are local and itinerant, there is no practical 

method to assign in-flight lead emissions to small geographic areas such as airports or 

census tracts. And similar data is not available for AT operations, a portion of which are 

conducted by piston-engine aircraft. Since the average duration of a piston-engine 

aircraft flight is approximately an hour, an itinerant flight can traverse county lines. 

Therefore, given the current data available, the best approach is to assign the out-of-LTO 

cycle lead to the state where the flight originated. 

In the 2008 NEI EPA allocated lead emissions that are calculated as being outside 

the LTO cycle to states based on the state-specific fraction of national GA and AT pistonengine LTO activity. The state-specific fractions were calculated by multiplying the 

percent of GA and AT piston-engine LTO activity in each state by 296 tons, which is the 

amount of lead we currently estimate is emitted outside of the LTO cycle nationwide. 

Table 4 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 out-of-LTO lead 

emissions assigned to each state. 

18 
Table 4: Out-of-LTO Lead Emissions by State 

STATE 

Total GA 

and AT 

Piston 

LTOs 

Percent of 

National GA 

and AT Piston 

LTOs (by state) 

Out of LTO 

Pb emissions 

(tons) 

AK 660,133 2.0% 5.86 

AL 671,026 2.0% 5.96 

AR 638,875 1.9% 5.68 

AZ 1,430,302 4.3% 12.71 

CA 3,881,357 11.6% 34.48 

CO 780,426 2.3% 6.93 

CT 226,807 0.7% 2.01 

DC 28,833 0.1% 0.26 

DE 84,617 0.3% 0.75 

FL 2,751,015 8.3% 24.44 

GA 750,876 2.3% 6.67 

HI 138,432 0.4% 1.23 

IA 281,961 0.8% 2.50 

ID 430,812 1.3% 3.83 

IL 920,908 2.8% 8.18 

IN 566,583 1.7% 5.03 

KS 459,720 1.4% 4.08 

KY 280,378 0.8% 2.49 

LA 622,011 1.9% 5.53 

MA 714,159 2.1% 6.34 

MD 436,861 1.3% 3.88 

ME 228,302 0.7% 2.03 

MI 880,818 2.6% 7.82 

MN 647,876 1.9% 5.76 

MO 389,551 1.2% 3.46 

MS 461,383 1.4% 4.10 

MT 270,311 0.8% 2.40 

NC 743,004 2.2% 6.60 

ND 214,139 0.6% 1.90 

NE 221,681 0.7% 1.97 

NH 173,355 0.5% 1.54 

NJ 466,961 1.4% 4.15 

NM 309,657 0.9% 2.75 

NV 298,712 0.9% 2.65 

NY 999,738 3.0% 8.88 

OH 1,180,583 3.5% 10.49 

OK 575,402 1.7% 5.11 

OR 596,730 1.8% 5.30 

PA 954,839 2.9% 8.48 

19 
 

PR 80,728 0.2% 0.72 

RI 45,348 0.1% 0.40 

SC 506,650 1.5% 4.50 

SD 228,198 0.7% 2.03 

TN 535,913 1.6% 4.76 

TX 2,422,722 7.3% 21.52 

UT 299,471 0.9% 2.66 

VA 502,559 1.5% 4.46 

VI 25,763 0.1% 0.23 

VT 88,318 0.3% 0.78 

WA 1,189,142 3.6% 10.56 

WI 778,320 2.3% 6.91 

WV 143,393 0.4% 1.27 

WY 106,190 0.3% 0.94 

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). 

20 
 

 

APPENDIX A 

Table A-1: Scaling factors 

Year 

U.S. Product Supplied 

of Aviation Gasoline 

(Thousand Barrels)63 

Ratio of 

2008 to 

Year X 

Before 

198164 0.57 

1981 11,147 0.50 

1982 9,307 0.60 

1983 9,444 0.59 

1984 8,692 0.64 

1985 9,969 0.56 

1986 11,673 0.48 

1987 9,041 0.62 

1988 9,705 0.58 

1989 9,427 0.59 

1990 8,910 0.63 

1991 8,265 0.68 

1992 8,133 0.69 

1993 7,606 0.74 

1994 7,555 0.74 

1995 7,841 0.71 

1996 7,400 0.76 

1997 7,864 0.71 

1998 7,032 0.80 

1999 7,760 0.72 

2000 7,188 0.78 

2001 6,921 0.81 

2002 6,682 0.84 

2003 5,987 0.94 

2004 6,189 0.91 

2005 7,006 0.80 

2006 6,626 0.85 

2007 6,258 0.90 

2008 5,603 1.00 

63 Data from the Energy Information Administration’s (EIA’s) table, “U.S. Product Supplied of Aviation
 

Gasoline (Thousand Barrels).” Available at:
 

http://tonto.eia.doe.gov/dnav/pet/hist/LeafHandler.ashx?n=PET&s=mgaupus1&f=A Accessed August 25,
 

2010.
 64 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 2008 avgas volume
 

product supplied to the average avgas volume supplied from 1981 to 1989.
 

21