Work Plan for Air Quality 

Modeling and Monitoring of Lead 

Emissions from Piston-Engine 

Powered Aircraft 

U.S. Environmental Protection Agency 

Office of Transportation and Air Quality 

Contractor: 

ICF Consulting

2009 
1

Project Background 

Tetraethyl lead is used as an additive in aviation fuel for most piston-engine powered 

aircraft. The 2002 National Emissions Inventory (NEI) estimates that annual lead (Pb) 

emissions from the use of these leaded aviation fuels (commonly referred to as “avgas”) 

are 623 tons, or approximately 45 percent of the air emission inventory for lead. 

Additional mobile sources of Pb include automobile brake wear, tire wear, and loss of Pb 

wheel weights to roadways. Lead is also present as a trace contaminant in gasoline and 

diesel fuel and is a component of lubricating oil. 

In October 2006, the Environmental Protection Agency (EPA) received a petition from 

Friends of the Earth (FOE) requesting that the Agency make a finding that lead emissions 

from general aviation aircraft may reasonably be anticipated to endanger public health 

and, following on that finding, take action to control Pb emissions from piston-engine 

aircraft.1

 EPA surveyed the available literature and found that there are few monitoring 

or modeling studies of Pb concentrations near airports servicing piston-engine aircraft 

that operate on leaded aviation gasoline. 

The primary purpose of this study is to develop and evaluate a modeling approach that 

can enhance inputs to EPA’s air quality model, which can then be used to model Pb 

emissions at general aviation facilities across the United States. The purpose of the 

monitoring analysis is to collect data that can be used to evaluate the performance of the 

modeling approach and to collect additional information to evaluate the gradient in Pb 

concentrations with distance from the emissions source. 

This document summarizes the air quality modeling and monitoring that is planned for 

2009 at the Santa Monica City Airport. This work plan is divided into three primary 

parts: overview of the location, description of the approach for the air quality modeling 

and description of the monitoring activities. 

Overview of Location 

The Santa Monica City Airport (SMO) was identified as a representative location for this 

study primarily due to the intensity of piston-engine aircraft activity and availability of 

data from a previous lead monitoring study. Established in 1919, the Santa Monica 

Airport is the oldest community airport operating in Los Angeles County. The airport is 

one of the busiest single runway airports in the nation. The airport occupies over 200 

acres (0.81 square kilometers) situated at the southeastern portion of the City of Santa 

Monica. The City’s southern boundary coincides with the airport’s southern property 

line. A triangular portion (approximately 34 acres) of the site’s eastern boundary lies 

within the City of Los Angeles. This land is owned in fee by the City of Santa Monica. 

Approximately 6,500 residents live within one kilometer of the airport. 

 

1

 See www.epa.gov/otaq/aviation.htm for more information. 
Copyrighted page/s removed. Copyrighted material is not available in 

Regulations.gov since it may not be reproduced without consent of 

the copyright holder. 

Contact the EPA Docket Center’s Public Reading Room to view 

or receive a copy of this document. 

Requests for copies may be made as follows: 

In person/writing: 

Environmental Protection Agency, Docket Center 

1301 Constitution Ave NW, 2822T, Room 3334 

Washington, DC. 20004 

Telephone: 

202-566-1744 

Fax: 

202-566- 9744 

Email: 

docket-customerservice@epa.gov 
3

Air Quality Modeling 

Emission Inventory Development 

The following section discusses the methodology for developing the aircraft lead 

emission inventory (the principal source of lead air emissions at the airport) along with 

the source of information for Pb emissions from other mobile and stationary sources. 

Piston-engine Aircraft Source: 

Emissions generated from aircraft operations at general aviation airports are based on the 

amount of fuel consumed during the landing and takeoff cycle (LTO) and the amount of 

time aircraft spend in each mode of operation. The five modes which define the LTO 

cycle are approach, taxi/idle-in, taxi/idle-out, takeoff and climb out.2

 Rotocraft 

(helicopter) display a slightly different sequence during the operating cycle; the modes 

which typify rotocraft operations are approach, idle and climb out. Each aircraft operates 

under a varied timeline depending on the type of aircraft and operational characteristics 

of the airport. Therefore, observational time-in-mode data will be collected for pistonengine aircraft at SMO. To quantify aircraft emissions, the Federal Aviation 

Administration (FAA) has incorporated into its aircraft emission model, Emissions and 

Dispersion Modeling System (EDMS) 5.1, fuel consumption information by LTO cycle 

for six single-engine piston aircraft and two twin-engine piston aircraft.3

 Information on 

fuel consumption in each mode will be used to determine lead emission rates for each 

LTO mode for each engine/aircraft type that visit SMO, using the Airport-Specific lead 

emission methodology discussed in EPA’s Technical Support Document on Lead 

Emissions from the Use of Leaded Aviation Gasoline in the Untied States (October, 

2008).4

The aircraft activity and associated emissions will be aggregated to develop an hourly 

emission profile5 to be used as input to AERMOD (a dispersion model used by EPA), 

with sets of profiles developed for each season and weekday/weekend. Leaded avgas 

fuel samples will be collected and analyzed for total Pb content so that site-specific fuel 

Pb concentrations are used in the development of the aircraft inventory. 

Other Mobile Sources: 

Emissions from on-road sources operating within and near the airport may contribute 

additional airborne lead emissions beyond those emitted from piston-engine aircraft. The 

South Coast Air Quality Management District (SCAQMD) recently completed their 

South Coast MATES-III air toxic modeling study which included the development of a 

 

2

 For the climb out and approach mode, we use the definition consistent with other airport related emission 

analysis, which is a default mixing height of 3,000 feet or almost one kilometer. 

3

 EDMS available from 

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

4

 U.S. EPA (2008) Technical Support document on Lead Emissions from the Use of Leaded Aviation 

Gasoline in the Untied States. EPA-420-R08-202. Available at: http://www.epa.gov/otaq/aviation.htm. 

5

 SMO is closed to all aircraft activity between 11 pm and 7 pm except for emergency police helicopters. 
4

lead emission inventory.6 The emissions inventory for MATES III consists of four 

components: (1) point sources; (2) area sources; (3) on-road mobile sources; and (4) offroad (or other) mobile sources. Point source emissions are from facilities having one or 

more pieces of equipment registered and permitted with the SCAQMD. Area sources 

represent numerous small sources of emissions that can collectively have significant 

emissions. On-road mobile sources include cars and trucks. All mobile sources not 

included in the on-road mobile source inventory are considered as off-road mobile 

sources, which include aircraft, ships, commercial boats, trains, recreational vehicles, and 

construction equipment. 

Point Source Characterization: 

To fully characterize other sources which may contribute to ambient levels of lead, 

nearby point sources should be included in the analysis. Point sources up to 20 km in 

radius from the airport will be incorporated into the analysis. Point sources will also be 

identified from comparison with the SCAQMD air permit database point source emission 

inventory for lead which has supporting information on stack parameters (exit velocity, 

stack height, stack diameter, stack temperature). 

Air Quality Analysis 

The EPA AERMOD model will be used for the air quality analysis. This latest version of 

EPA’s air quality model has undergone extensive model testing and evaluation in recent 

years and represents the current state-of-the-science and appropriate air quality model for 

assessing the potential emissions impacts on air quality from this facility. The model 

includes treatment for an urban nighttime boundary layer; applicability for all terrain 

types and a state-of-the-science approach for characterizing the fundamental boundary 

layer parameters and a treatment for plume meander as well as the inclusion of the stateof-the-science wet and dry deposition model. 

AERMOD will be run using one year of nearby representative on-site meteorological 

data from the SMO monitoring site. The Automated Surface Observation System 

(ASOS) monitoring site is located at the airport. The AERMET preprocessor model will 

be used to develop the meteorological dataset for use with AERMOD. 

Point sources will be modeled using standard point source information on location, stack 

height, stack diameter, exit velocity and temperature. As available, we will include 

information on the hourly variability in these emission rates. Area and mobile source 

emissions as obtained from the MATES-III study by category emission source (CES) 

code will be included as gridded area sources. All aircraft-related emission sources will 

be modeled as volume sources. 

 

6

 South Coast Air Quality Management District, Multiple Air Toxics Exposure Study-III (MATES III) July 

2008. Available at: http://www.aqmd.gov/prdas/matesIII/matesIII.html 
5

Receptor Sites 

Maximum Receptors:

The selection of receptors in AERMOD to find the maximum lead concentration will 

employ a nested Cartesian grid with receptors spaced as follows: 50-meter grid spacing 

extending 1 km around the facility boundary and 100-meter grid spacing extending out to 2 

km around the facility boundary. 

Receptors will be placed at 50 meter intervals around the airport boundary fence line. In 

addition, site-specific sensitive receptor locations will also be included within 2 

kilometers of the airport. Types of sensitive receptors include playgrounds, schools, and 

recreational areas. 

Sensitivity Analysis: 

A model sensitivity analysis will be conducted focusing on those parameters most 

uncertain in the analysis. This will provide information on the relative importance of 

these parameters to the overall lead concentration as well as providing information on the 

relative value in obtaining more detailed site-specific information. 

Sensitivity analysis will be conducted for the worst 3-month period identified from the 

one-year of modeling. At a minimum, the sensitivity tests will include the parameters: 

fuel consumption and time-in-mode. 

Monitoring Activities 

The monitoring activities will include: collection of air samples, soil samples and dust 

samples from areas in and around SMO. The primary purpose of the air monitoring is to 

provide data for comparison with AERMOD air quality data. Soil and dust samples will 

be collected to evaluate the potential for a gradient in Pb concentrations in soil with 

distance from the airport. Dust samples will be collected at various receptor sites to 

evaluate a potential impact of Pb from piston-engine aircraft emissions. 

Ambient Air Monitoring Plan 

Air samples will be located at a maximum of six locations on and around the airport 

property to attempt to both evaluate the concentration at the most highly impacted 

location and to evaluate the gradient in lead concentrations with distance from the airport. 

In the study conducted at SMO in 2005-2007 by SCAQMD, air monitoring was 

conducted at seven locations, the data from which was used to inform monitoring sites 

for this project.7

 

 

7

 South Coast Air Quality Management District, Philip M. Fine. Community-Scale Air Toxics Monitoring – 

Sun Valley Neighborhood and General Aviation Airports. Presented at the U.S. EPA Air Toxics Data 

Analysis Workshop - Chicago, IL October 2 - 4, 2007. 
6

Air sampling is planned for the summer of 2009. The sample period will run 

approximately seven days. The prevailing air flow throughout the annual cycle is 

onshore from the southwest. Air samples will be collected at a location that is in the 

prevailing upwind direction of the airport and in the prevailing downwind direction. In 

this study, we are planning to collect air samples in the community directly downwind of 

the runway and/or run-up areas. 

Soil and Dust Sampling Plan 

Soil Sampling:

Soil samples will be collected from a minimum of eight areas on or near airport property, 

including an elementary school and homes. Sampling areas are being selected based on a 

number of factors, including: proximity to take-off and landing areas, availability of 

relatively undisturbed and non-vegetated surficial earth materials, and accessibility. The 

sampling program is designed to gather data on the presence and distribution of total lead 

in bulk soil samples (i.e., present throughout the soil matrix) and in the fine-grained 

components of a bulk sample. It is the fine-grained components (clays and silts) of the 

soil that are potentially entrainable under certain wind and soil moisture conditions and 

thus subject to inhalation and ingestion by workers and residents in the surrounding area. 

Dust Sampling: 

Dust sampling is commonly used to assess the deposition of air-borne contaminants on 

surfaces. A minimum of ten dust samples will be collected from areas on and near 

airport property, including playground areas and homes. In addition, approximately five 

controlled dust samples will be collected in homes. A controlled dust sample will be 

collected from surfaces that have been pre-cleaned to remove any residual material. 

After a period of at least seven days, the dust accumulated on the surface will be 

collected. 

Timeline and Contact Information 

The study will be completed by October 2009. When available, the final report will be 

posted at www.epa.gov/otaq/aviation.htm. 

 

For additional information please contact: 

Meredith Pedde Marion Hoyer 

Environmental Protection Agency Environmental Protection Agency 

Office of Transportation & Air Quality Office of Transportation & Air Quality 

2000 Traverwood Dr. 2000 Traverwood Dr. 

Ann Arbor, MI 48105 Ann Arbor, MI 48105 

734-214-4748 734-214-4513 

pedde.meredith@epa.gov hoyer.marion@epa.gov