Aviation & Emissions

A Primer

Federal Aviation Administration

Office of Environment and Energy

January 2005
1 

Aviation & Emissions 

A Primer

Aviation plays a key role in the economic prosperity and lifestyle Americans enjoy. Our economy benefits 

greatly from the ability to move people and products all over the globe - quickly and safely. Aviation 

contributes to our quality of life - allowing us to visit friends and relatives, to travel, to experience new 

places, to shrink the borders of the world. The statistics are impressive. In 1903 the year of the Wright 

brothers’ first flight, earth’s population was 1.6 billion1

; today, over 1.6 billion people use the world’s 

airlines2

. The air transport industry provides 28 million direct, indirect, and induced jobs worldwide3. And 

aircraft carry about 40% of the value of all world trade4

, driving the “just in time” deliveries critical to 

productivity improvements. 

Air transport links our world and is a key tenet of continued economic development and security for the 

U.S. However, aviation also has environmental impacts – primarily noise and atmospheric emissions. 

While aircraft noise issues are better known, less focus has been placed on emissions. This paper provides 

a brief overview of important issues regarding aviation emissions. 

What emissions come from aviation?

Aircraft produce the same types of emissions as your automobile. Aircraft jet engines, like many other 

vehicle engines, produce carbon dioxide (CO2), water vapor (H2O), nitrogen oxides (NOx), carbon 

monoxide (CO), oxides of sulfur (SOx), unburned or partially combusted hydrocarbons (also known as 

volatile organic compounds (VOCs)), particulates, and other trace compounds. A small subset of the VOCs 

and particulates are considered hazardous air pollutants (HAPs). Aircraft engine emissions are roughly 

composed of about 70 percent CO2, a little less than 30 percent H2O, and less than 1 percent each of NOx, 

CO, SOx, VOC, particulates, and other trace components including HAPs. Aircraft emissions, depending on 

whether they occur near the ground or at altitude, are primarily considered local air quality pollutants or 

greenhouse gases, respectively. Water in the aircraft exhaust at altitude may have a greenhouse effect, and 
Aviation & Emissions – A Primer

2 

Emissions from Combustion Processes 

CO2 – Carbon dioxide is the product of complete 

combustion of hydrocarbon fuels like gasoline, jet 

fuel, and diesel. Carbon in fuel combines with oxygen 

in the air to produce CO2 . 

H2O – Water vapor is the other product of complete 

combustion as hydrogen in the fuel combines with 

oxygen in the air to produce H2O. 

NOx – Nitrogen oxides are produced when air passes 

through high temperature/high pressure combustion 

and nitrogen and oxygen present in the air combine 

to form NOx. 

HC – Hydrocarbons are emitted due to incomplete 

fuel combustion. They are also referred to as volatile 

organic compounds (VOCs). Many VOCs are also 

hazardous air pollutants. 

CO – Carbon monoxide is formed due to the 

incomplete combustion of the carbon in the fuel. 

SOx – Sulfur oxides are produced when small 

quantities of sulfur, present in essentially all 

hydrocarbon fuels, combine with oxygen from the air 

during combustion. 

Particulates – Small particles that form as a result of 

incomplete combustion, and are small enough to be 

inhaled, are referred to as particulates. Particulates 

can be solid or liquid. 

Ozone – O3 is not emitted directly into the air but is 

formed by the reaction of VOCs and NOx in the 

presence of heat and sunlight. Ozone forms readily in 

the atmosphere and is the primary constituent of 

smog. For this reason it is an important consideration 

in the environmental impact of aviation. 

occasionally this water produces contrails, which 

also may have a greenhouse effect. About 10 

percent of aircraft emissions of all types, except 

hydrocarbons and CO, are produced during 

airport ground level operations and during 

landing and takeoff. The bulk of aircraft 

emissions (90 percent) occur at higher altitudes. 

For hydrocarbons and CO, the split is closer to 

30 percent ground level emissions and 70 percent 

at higher altitudes. 

Aircraft are not the only source of aviation 

emissions. Airport access and ground support 

vehicles produce similar emissions. Such 

vehicles include traffic to and from the airport, 

ground equipment that services aircraft, and 

shuttle buses and vans serving passengers. Other 

emissions sources at the airport include auxiliary 

power units providing electricity and air 

conditioning to aircraft parked at airport terminal 

gates, stationary airport power sources, and 

construction equipment operating on the airport.

What determines aviation 

emissions? 

Aviation emissions reflect the level of overall 

aviation activity. The growth of air travel for the 

past several decades has been very rapid. 

Demand for travel services, both passenger travel 
Aviation & Emissions – A Primer 

3 

and freight transportation, is increasing 

substantially. According to the U.S. Bureau of 

Transportation Statistics5

 a 21.5 percent increase 

in population, 32 percent increase in the labor 

force, and 90 percent increase in GDP between 

1980 and 2000 have driven this demand. The 

chart6

 below shows the growth of aviation and 

the economy. Demand for air travel grows as the 

economy grows and prosperity increases. 

Over the long term, we expect that demand for 

air transportation will continue to grow rapidly 

to support our economic productivity, our quality 

of life, and our national security. More and more 

the worldwide transportation system is becoming 

an integrated transportation network. For most 

long-distance travel, however, aviation’s speed, 

convenience, and cost overcome consideration of 

other travel modes. It only faces competition on 

short trips or when moving low value or high 

volume products. Looking to the future, the 

forecast is for continued strong growth as shown 

in the following graph7

. This is consistent with 

the demand for transportation generally, which is 

increasing largely in response to very positive 

structural changes in both the domestic and 

global economies. 

As a result, growth of the aircraft fleet and 

expansion and further development of existing 

airports are expected. This also means that 

emissions from aviation activity are expected to 

grow and concerns about aviation emissions will 

also grow. 

What have been the trends 

in aviation emissions? 

Technological advancement has reduced aircraft 

fuel consumption and emissions significantly 

over the last 30 years and this is expected to 

continue in the future. 

For 20 years aviation growth in the U.S. outpaced the 

growth of the economy although all transportation has 

grown significantly. 

50.0

100.0

150.0

200.0

250.0

300.0

81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01

Growth Index 1981 = 100

Airline RMT

Roadway VMT

Gross Domestic

Product

Long range forecasts of aviation activity anticipate continued 

growth but at a somewhat slower rate than for the U.S. 

economy as a whole. 

0

50

100

150

200

250

2000 2005 2010 2015 2020 2025

Growth Index 2000 = 100

Gross Domestic Product

Commercial Aircraft Operations
Aviation & Emissions – A Primer 

4 

The industry’s historical transition from piston 

engines to modern high-bypass turbofans 

resulted in major advancements in energy 

efficiency and environmental performance. 

During this same era, the industry developed and 

deployed new, lightweight, high-strength 

materials, automated navigational, operational, 

and engine control systems, and employed vast 

new computational capabilities to improve 

aerodynamic efficiency and integrate highly 

complex operational strategies. 

Changes to fleet average fuel economy progress 

slowly as commercial passenger service aircraft 

typically remain in the fleet for 35-40 years. The 

next chart8

 shows the trend and projections in 

aircraft fuel economy over time. 

As they age, existing aircraft are retired and 

replaced with new aircraft. New aircraft also are 

added to the fleet for new capacity. By 2020, 

70% of the fleet will be aircraft added since 

2002, which will have advanced technology and 

capabilities. The chart below, replicated from an 

International Civil Aviation Organization 

(ICAO) report 9, illustrates this transition of the 

international commercial aircraft fleet. 

How do aviation emissions 

compare to general trends 

in local air pollutants? 

Compared to other sources, aviation emissions 

are a relatively small contributor to air quality 

concerns both with regard to local air quality and 

greenhouse gas emissions. While small, 

however, aviation emissions cannot be ignored. 

Over an 18-year period, many of today’s aircraft will be retired as 

they reach the end of their life. These aircraft will be replaced and 

other aircraft will be added to accommodate the growing demand for 

air travel. The new fleet will be much more energy efficient and have 

lower emissions. 

10,655

7,600

1,662

4,717

6,091

12,667

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

22,000

24,000

2002 2010 2020

12,317

Number of aircraft 24,984

18,408

Replacement

Growth

Retained in

service

17,384

40.0

50.0

60.0

70.0

80.0

90.0

100.0

110.0

19931995

19971999200120032005

200720092011

20132015

Fuel Efficiency Index 1993 = 100

actual forecast

Aircraft fuel efficiency has historically improved by about one 

percent per year. This trend is expected to continue for the 

foreseeable future.
Aviation & Emissions – A Primer 

5 

In the past three decades, aggregate emissions of 

the air pollutants EPA regulates (nitrogen 

dioxide, ozone, sulfur dioxide, particulate matter, 

carbon monoxide, and lead) have declined by 25 

percent nationally, according to their report 

National Air Quality 2001 Status and Trends10. 

As can be seen in the following chart, greater 

progress has been made with some individual 

pollutants than with others. 

Aircraft emissions have also declined over time 

when you consider the emissions from 

transporting one passenger one mile. The 

following chart11 shows that relative aircraft 

emissions have fallen consistently over time. 

Total aircraft emissions have increased, however, 

since aviation has grown considerably over the 

same period. As with emissions nationally, a 

great deal of progress has been made reducing 

emissions of HC and CO. 

NOx, a key constituent of ozone, has proven to 

be the most difficult pollutant to control both 

nationally and for aviation. NOx comes from a 

wide variety of sources in all sectors of the 

economy. Since esssentially all NOx comes from 

combustion processes, electric utilities, industry, 

and transportation are significant emitters and 

make up the largest share of the total inventory. 

Currently aviation contributes 0.4 percent of the 

inventory as can be seen in the illustration12 on 

the following page. 

 Aviation’s contribution to the national NOx

emissions inventory has recently declined further 

as air travel growth has been interrupted during 

the past two to three years due to the terrorist 

acts of 9/11, the war on terrorism in Iraq, the 

emergence of severe acute respiratory syndrome 

(SARS), and a generally difficult economic 

40

50

60

70

80

90

100

110

1980 1985 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001

Emissions Index 1980 = 100

NOx

SOx

PM10

HC

CO

Local air quality pollutants have declined steadily over the past 

several years. NOx has been the most challenging pollutant to 

constrain and progress has lagged that of other pollutants. 

Aircraft emissions of all species have declined over time, 

however, considerably more progress has been made with 

HC and CO than with NOx. 

NOx

CO2

H2O

CO

HC

1.0

0.5

0

1975 1980 1985 1990 1995

Relative Emissions/passenger-mile
Aviation & Emissions – A Primer 

6 

environment. These conditions have caused a 

more than ten- percent decline in air traffic and a 

similar drop in emissions. However, these factors 

are not likely to have a permanent effect on air 

transportation and growth of travel demand and 

emissions have recently resumed. 

Total national pollutant inventory numbers do 

not tell the full story with regard to aviation’s 

contribution in regions with air quality problems. 

The worst local air quality generally occurs in 

and around cities, which is also where aviation 

activity primarily occurs. The Clean Air Act 

requires EPA to identify air quality areas and to 

determine whether they comply with (i.e. attain) 

National Ambient Air Quality Standards13. 

Ozone is by far the principal air quality problem 

in U.S. cities today. According to EPA data14, 

there are currently 474 counties, out of 3,142 

counties nationally, that do not meet the new 8-

hour ozone standard and are considered 

nonattainment areas. Comparing this list to the 

location of primary U.S. airports, 37 of the 50 

largest airports are in ozone nonattainment areas. 

To calculate aviation’s contribution to regional 

NOx, we can examine local emission inventories. 

A multitude of sources comprises air quality area 

emission inventories. 

• Point sources – large stationary, industrial 

facilities that are regulated under Federal, 

state, or local regulations, 

• On-Road Mobile sources – cars, trucks, 

buses, and other vehicles licensed for 

highway travel, 

• Non-Road Mobile sources – aircraft, ground 

support equipment, construction equipment, 

farm equipment, boats, locomotives, and 

lawn and garden equipment, and 

• Area sources – small sources that 

individually have low emissions but that are 

significant when combined throughout the 

area like dry cleaning establishments, 

bakeries, painting, and vehicle fueling.

The table on the following page summarizes 

aviation’s contribution to NOx emission 

inventories in several metropolitan areas. All of 

these areas have at least one airport that is among 

the 50 largest airports in the country. To provide 

While all transportation makes up more than 55 

percent of the total national NOx inventory, aviation 

represents only about 0.4 percent. 

Transport

Each square represents 1% of total emissions inventory

Non-Road Vehicles

Misc. area/point sources

Electric Utilities On-Road Vehicles

Industry

Commercial/Institutional

Manufacturing

Aviation

Non- Transport Transport
Aviation & Emissions – A Primer 

7 

a context, Atlanta, Chicago O’Hare, and Los 

Angeles International are the three busiest U.S. 

airports. In 2002, Atlanta had nearly 900,000 

aircraft operations and enplaned over 37 million 

passengers; Chicago O’Hare had over 900,000 

aircraft operations and enplaned almost 32 

million passengers; and Los Angeles 

International had nearly 800,000 aircraft 

operations and enplaned almost 27 million 

passengers. 

 In the Southern California area, categorized as 

“severe” nonattainment, EPA’s most restrictive 

designation, aviation’s contribution was less than 

two percent even where the cumulative NOx

from multiple airports was included. While it is 

apparent from this data that aviation emissions 

make only a small contribution to regional 

emissions, even at the largest airports and even 

in areas with the worst air quality, it is still a 

contribution that needs to be dealt with 

effectively. 

Airport National Rank 

(enplanements)15

Ozone Attainment 

Area Status16

Airport Contribution 

to Area NOx Inventory 

Aircraft Contribution 

to Non-Road NOx

Inventory 

Hartsfield Atlanta 

International (ATL)17

1 Marginal 2.8% 14.1% 

Chicago Nonattainment 

Area (ORD, MDW)18

2 (ORD), 28 (MDW) Moderate 0.8-2.0% 10.5% 

South Coast California 

(BUR. LAX, LGB, ONT, 

SNA)19 

3 (LAX), 44 (SNA), 

51 (ONT), 61 (BUR ), 

93 (LGB) 

Severe 1.5% 5.7% 

Dallas/Fort Worth Air 

Quality Area (DFW, 

DAL, AFW)20

4 (DFW), 53 (DAL) Moderate 6.1% 19.9% 

Houston Bush 

Intercontinental (IAH)21

8 Moderate 0.7% 3.3% 

New York (JFK, LGA, 

EWR)22

12 (EWR), 13 (JFK), 

21 (LGA) 

Moderate 4.0% 13.8% 

Seattle-Tacoma 

International (SEA)23

15 Attainment 1.9% 6.7% 

St. Louis Lambert 

International (STL)24

17 Moderate 1.4% 8.5% 

Boston Logan 

International (BOS)25

20 Moderate 0.7% 2.3% 

Airports, including aircraft, ground support equipment, and all other vehicles operating around the 

airport, contribute only a small percentage of NOx emissions to regional inventories even in cities with the 

greatest concentration of aviation activity. All of the cities shown include at least one of the 20 largest 

airports in the country and, except for Seattle-Tacoma, are nonattainment for NOx under the new 8-hour 

ground-level ozone designation. 

(Inventories are computed from available data for 1996 Atlanta & Dallas/Ft. Worth, 1999 Houston, New York, Seattle & Boston, 2000 

Chicago & St. Louis, 2001 South Coast)
Aviation & Emissions – A Primer

8 

How do aviation local 

emissions compare to other 

transportation sources? 

Aviation has grown faster than other modes of 

transportation and is expected to outpace them in 

the future. Despite this growth, aviation’s 

contribution to local air quality inventories 

compared to other transportation sources has 

remained modest. 

 For example, as the chart below26 shows, the 

rate of growth in aviation NOx emissions has far 

outpaced on-road (i.e., cars and trucks) NOx

emissions growth. 

However, as the next chart shows27, the quantity 

of emissions of other transport modes far exceeds 

aviation’s NOx contribution. 

This is not surprising as most of an aircraft’s 

operations take place at altitude where emissions 

do not affect local air quality. This is in contrast 

to cars and trucks that primarily operate within a 

single air quality region and always at ground 

level28. 

In the future, NOx emissions from on-road 

vehicles should fall in response to the most 

recent environmental regulations. Aircraft, on the 

other hand, will be challenged to reduce their 

total NOx emissions. However, even if the other 

sources were able to reduce their emissions by 

half, a highly unlikely occurrence, aviation NOx

emissions would still be less than 3 percent of 

the transportation NOx inventory by 2020. 

Nonetheless, pressure on aviation sources will 

likely remain as many states and localities will 

face the twin challenges of meeting new ozone 

Total NOx emissions from on-road transportation dwarf 

emissions from all other transportation modes combined 

(1998 data). 

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

On-Road Railroad Marine Aviation

Tons of NOx (000)

Aviation and marine transportation grew substantially 

between 1970 and 1998 resulting in large percentage 

growth in NOx emissions. Percentage growth in on-road 

emissions is small due to the large baseline emissions. 

0

100

200

300

400

500

600

On-Road Railroad Marine Aviation

Cumulative Percentage Growth
Aviation & Emissions – A Primer

9 

and particulate matter standards at the same time 

non-aviation source reductions become more 

difficult and costly. 

Can a comparison be made 

between aviation emissions 

and non-transportation 

sources? 

There is an understandable interest in comparing 

aviation emissions to other sources in local air 

quality areas. For example, the total mass of 

emissions coming from an airport may be 

comparable to those of a power plant or 

petroleum refinery in the same region. 

Airports, however, are quite different from nontransportation sources. Like cities, they are 

comprised of a variety of different emission 

sources. Aircraft arrive at the airport, stay for a 

short period and depart, with a different aircraft 

taking off or landing every few minutes. 

Passenger cars, shuttle buses, and taxis calling 

on the airport do not operate there exclusively, 

also serving homes and retail, commercial, and 

governmental establishments. Power boilers and 

chillers at the airport are independently 

permitted, as is similar equipment at other 

locations. For these reasons it is difficult to 

compare the composite of sources that make up 

an airport to another emission source like an 

industrial facility or power plant even when their 

magnitude of emissions is similar. 

What role does aviation 

emissions play with regard 

to greenhouse gas issues? 

As noted earlier, the majority of aviation 

emissions occur at higher altitudes, thus 

generating greenhouse gases and potentially 

contributing to climate change. Also, under 

certain conditions, aircraft engine exhaust can 

produce contrails. Scientists in the U.S. and 

around the world are researching the potential 

impact of contrails to see whether they have a 

significant impact on the greenhouse effect.29 

Concern regarding greenhouse gas emissions has 

been building worldwide. The following graph30

shows the recent growth of total greenhouse gas 

emissions in the U.S. The drop in emissions in 

2001 reflects the slow economic growth and 

reduced industrial output that year in addition to 

the warm winter, which reduced fuel use for 

heating. Growth in greenhouse gas emissions is 

expected to resume as the economy recovers and 

continues to expand in the future. While there are 
Aviation & Emissions – A Primer 

10 

many different greenhouse gases, CO2 and NOx

are generally most relevant from an aviation 

perspective. 

The chart below31 breaks down national 

emissions of greenhouse gases. In the U.S., 

transportation makes up about 27 percent and 

aviation about 2.7 percent of the national 

greenhouse gas inventory. Global estimates32 are 

similar with emissions of the world’s aircraft 

fleet at about three percent of the total 

greenhouse emissions from fossil fuel, the 

majority of which come from commercial 

aviation. This compares with all transportation 

sources that contribute approximately 25 percent 

of total global fossil fuel combustion emissions. 

Greenhouse gas emissions from U.S. aviation 

have grown over the past 10 years and are 

projected to increase in the future33. The 

projection shown below conservatively assumes 

the relationship between aircraft operations and 

greenhouse emissions remains constant. As such, 

emissions track expected growth in aviation. 

According to the projection, aircraft greenhouse 

gas emissions in the U.S. will increase 60 

percent by 202534. 

Greenhouse gas emissions from aviation have declined recently due to 

the fall off in air travel following the terrorist acts of 9/11, the war on 

terrorism in Iraq, and the worldwide recession. As air travel recovers in 

the coming years, greenhouse gas emissions are expected to resume their 

climb. 

0

50

100

150

200

250

300

350

1990 1996 1997 1998 1999 2000 2001 2005 2010 2015 2020 2025

Tg CO2 Eq.

Note scale change

U.S. greenhouse gas emissions grew steadily throughout the 1990s as the 

economy expanded. The recent downturn is expected to be temporary due 

to economic recession. With recovery and expansion the upward trend is 

forecast to continue. 

6,200

6,300

6,400

6,500

6,600

6,700

6,800

6,900

7,000

7,100

1995 1996 1997 1998 1999 2000 2001

Tg CO2 Eq.

National greenhouse gas emissions in 2001 

came from all sectors of the economy with all 

transportation equal to 27% of the total 

Residential

Electric Utilities

Industry

Commercial

Agriculture

Transport Each square represents 1% of total emissions inventory

Aviation

Non- Transport Transport

Non-Road Vehicles

On-Road Vehicles
Aviation & Emissions – A Primer

11 

The energy intensity of aircraft and automobiles has 

improved substantially over the past several decades. 

Automobile energy intensity has fallen by almost one fifth 

while aircraft energy intensity has fallen by three fifths 

during the same period. 

0

2000

4000

6000

8000

10000

12000

1965 1970 1975 1980 1985 1990 1995 2000

Btu/passenger-mile

Aircraft

Automobiles

How do aviation’s 

greenhouse gas emissions 

compare to other 

transportation sources? 

Energy intensity, that is the amount of energy 

consumed to transport one passenger one mile, is 

a useful metric for comparing greenhouse gas 

emissions among different transportation modes. 

The different modes use similar fuels and 

greenhouse gas emissions are directly related to 

fuel use. 

As you can see in the following chart35, in the 

U.S., aircraft and automobiles have very similar 

energy intensities, with automobiles at 3,543 

Btu/passenger mile versus airlines at 3,666 

Btu/passenger mile. Rail has the lowest energy 

use, and hence emissions, per passenger mile 

among all transport modes. Personal trucks and 

transit buses have the highest energy intensities. 

Comparing the energy intensity of aircraft and 

cars shows how energy efficiency and 

consequently greenhouse gas emissions per 

passenger mile have changed over the past 35 

years. The chart below36 shows how significant 

this has been, especially for aircraft. 

The pie chart37 at the top of the following page 

shows the total energy consumption for each 

transportation mode. Since the fuels are similar, 

this is an indication of their total greenhouse gas 

emissions. Aviation is substantially less than 

automobiles and personal trucks though 

significantly more than rail and buses. However, 

given the greater potential to apply alternative 

Energy intensity in terms of energy used to carry one passenger one fuel technologies to land-based transport in the mile is lowest for rail, followed by aircraft and automobiles, with 

personal trucks and transit buses as the least energy efficient. 

0

1000

2000

3000

4000

5000

6000

Automobiles Personal

Trucks

Transit Buses Commercial

Airlines

Intercity Rail

(Amtrak)

Transit Rail Commuter

Rail

BTU/passenger-mile
Aviation & Emissions – A Primer 

12 

Energy consumption by the aviation industry is only a small portion 

of transportation energy use. Automobiles and personal trucks still 

account for the vast majority. 

Intercity Rail (Amtrack)

<1%

Transit Rail

<1%

Commercial Airlines

11%

Commuter Rail

<1%

Other (motorcycles,

recreational boats, general

aviation, intercity and

school buses)

4%

Automobiles

56%

Transit Buses

1%

Personal Trucks

28%

next two decades, aviation greenhouse gas 

emissions are likely to represent a greater share 

of transport sources over time. 

How are aviation emissions 

regulated? 

 There is some misperception that aviation in 

general and airlines in particular are the “only 

unregulated industry in the country,” or “are 

getting a free ride on air quality,” and “cars have 

reduced their emissions by over 98% while 

aircraft have done nothing.” In fact, there are 

many, varied regulations that constrain aviation 

emissions. For example, both cars and aircraft 

have improved their energy intensity over time 

using new technologies, advanced materials, and 

improved designs for energy conservation to 

reduce fuel consumption. 

Practically all aviation emission sources are 

independently regulated through equipmentspecific regulations, standards and recommended 

practices, and operational guidelines, which are 

established by a variety of organizations. For 

example, on-road vehicles, which take 

passengers to and from the airport, meet 

stringent Federal tailpipe standards set by EPA. 

Stationary sources on the airport, like power 

boilers and refrigeration chillers, must meet 

independent state regulations. And FAA 

certification is required for essentially all 

aviation equipment and processes. For example 

there are more than 60 standards38 that apply to 

aircraft engine design, materials of construction, 

durability, instrumentation and control, and 

safety, among others. These are in addition to the 

Fuel Venting and Exhaust Emission 

Requirements for Turbine Engine Powered 

Airplanes (FAR Part 34), which guide 

compliance with EPA’s aircraft exhaust emission 

standards. This comprehensive and complex 

regulatory framework has enabled our safe and 

efficient national air transport network. 

The International Civil Aviation Organization 

(ICAO) is a United Nations intergovernmental 

body responsible for worldwide planning, 

implementation, and coordination of civil 
Aviation & Emissions – A Primer

13 

aviation. ICAO sets emission standards for jet 

engines. These are the basis of FAA’s aircraft 

engine performance certification standards, 

established through EPA regulations. 

ICAO has long been the forum for evaluating the 

environmental performance of aircraft engines. 

ICAO has taken a “technology progressing” 

approach, raising standards within the 

capabilities of proven technologies and certified 

products (engines and aircraft) rather than a 

“technology forcing” approach, which sets 

standards based on technology that is not 

certified or may not even exist. The reason for 

ICAO’s approach is quite simple - the very high 

premium placed on the safety of aircraft 

operation restricts the use of unproven new 

technologies. 

Current NOx standards were established in 1996. 

New standards go into effect for engines entering 

service beginning in 2004, which reflect a 16 

percent NOx reduction over the 1996 standards 

and a 33 percent reduction over the original 

standards agreed to in 1981. Earlier this year, 

ICAO’s Committee on Aviation Environmental 

Protection recommended new certification 

standards that represent a further 12 percent NOx

reduction, with an effective date of 2008. 

Airport air emissions from all sources also are 

constrained by the General Conformity 

regulations of the Clean Air Act Amendments of 

1990. General Conformity requires Federal 

agencies to assure that actions that would 

increase emissions in nonattainment areas 

“conform” to the appropriate State 

Implementation Plan. These plans define the 

steps states are committed to taking to ensure 

their cities enjoy healthy air. Each year the 

environmental impacts of several hundred 

projects at airports throughout the country are 

analyzed in detail, including general conformity 

evaluations and analyses, using the best data and 

most advanced analytical models available. 

Emissions from the vast majority of these 

projects are well below the thresholds that trigger 

a “conformity determination.” The two or three 

projects a year that do require further analysis 

essentially are able to meet the needs of state air 

quality plans through minor project modification. 

EPA recently proposed new exhaust emission 

standards for non-road diesel engines. These 

standards, to be phased in between 2008 and 

2014, will require engine manufacturers to 

produce new engines with advanced emission 

control technologies. New ground support 

equipment with diesel engines, which are used 
Aviation & Emissions – A Primer 

14 

only on airport property, will be required to meet 

these standards. This new equipment will 

achieve emission performance comparable to 

today’s automobiles. 

While there are no national or international 

regulations for greenhouse gas emissions that 

apply to aircraft or other airport sources, the 

aviation industry has made significant strides 

here as well. Aircraft have a long history of 

continuously improved fuel economy, which 

reduces all greenhouse gas emissions. For 

example, according to Boeing, the B-777 is 300 

percent more efficient than its early jets.39 Fuel 

economy and energy conservation are also 

priorities at many airports. Dallas/Fort Worth 

International Airport for example looks at 

business practices at all of their facilities to 

minimize energy consumption. They realize that 

this benefits local air quality through reduced 

emissions as well as regional air quality as a 

result of reduced power purchases from electric 

utilities and an overall reduction in greenhouse 

gas emissions. 

Looking to the future, FAA is working through 

ICAO to evaluate policy options to limit or 

reduce greenhouse gas emissions from aviation. 

Various market-based options, such as voluntary 

agreements, open emissions trading, and 

emission related levies are being analyzed. 

Preliminary results from analyses of marketbased options show that emission related levies 

are not cost-beneficial, but voluntary 

arrangements and emissions trading may be cost 

effective in limiting or reducing greenhouse gas 

emissions. Additional analyses are underway at 

ICAO to evaluate further emissions trading and 

voluntary agreements as approaches to limit 

aviation emissions growth while allowing 

continued expansion of air travel40. 

Under this multidimensional regulatory and 

voluntary structure, aviation has made significant 

environmental progress. Given the complexity of 

the industry and the need for different strategies 

and technological approaches for different types 

of vehicles and equipment, a coordinated effort 

between the aviation industry and the many 

regulatory agencies that share environmental 

responsibility will continue. 

What is being done today to 

reduce aviation emissions? 

There are a number of initiatives underway that 

will achieve significant emissions reductions – 

both at airports and within the national aviation 
Aviation & Emissions – A Primer

15 

system – in the next few years. First, there are 

voluntary programs underway at airports to 

reduce emissions from ground support 

equipment and other airport vehicles. For 

example, FAA developed a pilot program, with 

EPA and DOE, to demonstrate air quality 

improvements with alternative fuel ground 

support equipment. The program is called the 

Inherently Low-Emissions Airport Vehicle 

(ILEAV) Pilot Program. 

To reduce emissions from these vehicle fleets, 

airlines have engaged in voluntary emission 

reduction programs. For example, California and 

Texas have agreements with the major airlines to 

reduce emissions from their ground support 

equipment. These new agreements will reduce 

emissions by converting gasoline and diesel 

equipment to electricity and alternative fuels. A 

national stakeholders group made up of 

representatives of FAA, EPA, major airlines, 

state and local environmental regulators, airports, 

and environmental interest groups is currently 

working to establish a national agreement to 

reduce ground support equipment emissions at 

other airports in air quality nonattainment areas. 

This has proved challenging, and it is still 

unclear whether it will be successful. 

In addition, many airports have independently 

taken action to reduce emissions from buses, 

trucks, taxicabs, and other on-road vehicles that 

operate in and around the airport. Hybrid-electric 

vehicles are being used for staff transportation 

and customer service vehicles. Airport police 

departments are using compressed natural gas 

automobiles and maintenance departments are 

using alternative fuel trucks. Airport shuttle 

buses in particular have been converted to 

compressed natural gas at a number of airports. 

Also, new clean diesel trucks are being used in 

heavy maintenance and construction. 

Based on their experience with the ILEAV 

Program, FAA and EPA have expanded the 

initiative to reduce ground emissions at 

commercial service airports in all air quality 

nonattainment areas. The new Voluntary Airport 

Low Emission (VALE) program expands 

eligibility for airport low emission projects under 

the Airport Improvement Program (AIP) and the 

Passenger Facility Charges (PFC) program. 

Through the use of funding and emission credit 

incentives, the voluntary program includes the 

conversion of airport vehicles and ground 

support equipment to low emission technologies, 

modification of airport infrastructure for 

alternative fuels, provision of terminal gate 
Aviation & Emissions – A Primer 

16 

electricity and air for parked aircraft, a pilot 

program to explore retrofit technology for airport 

ground support equipment, and other related 

emissions improvements. 

Second, it is also worth noting that many 

strategies for reducing the environmental impact 

of aviation are inherent to the intended design 

and operation of the air transport infrastructure. 

With airports for example, access roadways are 

often limited access, high-speed and free flowing 

and parking facilities are readily available. These 

features minimize motor vehicle emissions and 

keep them contained in areas away from the 

public. 

Third, looking at aviation more broadly, many 

recent changes have improved the system 

efficiency and reduced environmental impact. In 

the past few years, better meteorological 

information, available in the cockpit in real time, 

has allowed for optimized flight planning with 

shorter routing. Yield management tools have 

allowed airlines to increase load factors, which 

moves more people on every flight. The hub and 

spoke system, combined with the growth of low 

cost point-to-point carriers and a significant 

increase in the number and reach of regional 

airlines, has improved the efficiency of the entire 

aviation network. 

Fourth, operating procedures can have both 

direct and indirect effect on aircraft emissions. 

Airlines generally employ standard procedures 

for operating their aircraft to meet company 

goals for safety, adherence to flight schedules, 

fuel conservation, complying with labor 

agreements, and other factors. Standard 

procedures vary by aircraft type, airport-specific 

constraints, and weather. The use of alternative 

procedures or best practices offers some prospect 

for reducing emissions. 

Some procedures affect the engine-operating 

regime, which can directly influence the rate of 

pollutant emissions. NOx emissions are higher 

during high power operations like takeoff when 

combustor temperatures are high. On the other 

hand, HC and CO emissions are higher during 

low power operations like taxiing when 

combustor temperatures are low and the engine 

is less efficient. As a result, reducing engine 

power for a given operation like takeoff or climb 

out generally increases the rate of HC and CO 

emissions, reduces the rate of NOx emissions, 

and has little or no effect on CO2 emissions. 

Other operating procedures have a more general 
Aviation & Emissions – A Primer

17 

effect on engine use and can reduce all pollutants 

simultaneously. 

As another example of alternative operating 

practices at an airport, United Airlines launched 

a new initiative last year to reduce the average 

use of its auxiliary power units by using ground 

power whenever possible. Based on early tests of 

the program they expect to save approximately 

12 million gallons of fuel during the year, which 

will result in reduced emissions of all pollutants 

at the airport as well41. Many of the strategies 

discussed in this section are published in ICAO 

Circular 303 - Operational Opportunities to 

Minimize Fuel Use & Reduce Emissions42. 

New technologies to improve air traffic 

management will help reduce emissions in and 

around airports. Commonly referred to as 

CNS/ATM (communication, navigation, 

surveillance/air traffic management), many of 

these technologies will improve air traffic 

management efficiency in the terminal area air 

space, reduce congestion, and consequently 

reduce aircraft fuel use. They will ensure more 

accurate approach routes to precisely keep 

aircraft on track. They will increase the 

efficiency and capability of runways, reducing 

arrival spacing and making ground operations 

more efficient. These systems are expected to be 

in operation throughout the U.S. over the next 

10-15 years43. 

A near term example is RVSM – Reduced 

Vertical Separation Minimums. Reducing 

vertical separation between aircraft from 2000 

feet to 1000 feet separation at cruise altitude (i.e., 

above 29,000 feet) adds flight levels and 

increases airspace capacity by as much as 85%. 

These routes are among the most fuel efficient 

for long flights such as oceanic or cross-country 

traffic and increasing their availability allows for 

greater flexibility in flight scheduling and 

routing. RVSM has been in use for transatlantic 

flights since 1997 and will become standard in 

U.S. domestic airspace starting in January 2005. 

Fuel savings of more than 500 million gallons 

each year are expected in U.S. airspace alone 

with full implementation of RVSM44. 

What steps are being taken 

to reduce aviation 

emissions in the longerterm? 

The pace of technological change across the 

industry is increasing. New engine designs are 

improving fuel efficiency further, while 
Aviation & Emissions – A Primer 

18 

simultaneously reducing NOx emissions. New 

aircraft designs improve aerodynamics and 

reduce weight thereby improving fuel efficiency, 

reducing all pollutants at the same time. New air 

traffic control technologies, like new aircraft 

designs, reduce emissions by reducing fuel 

consumption (the effect on individual pollutants 

depends on the phase of flight most effected). 

And new management strategies like load 

management planning and code sharing are 

being used to optimize the entire system’s 

operation. 

With regard to engines, there are complex 

emission interrelationships that make it difficult 

to modify their design as a mitigation strategy 

since it forces a tradeoff among individual 

pollutants as well as between emissions and 

noise. For example, high-bypass turbofan 

engines were introduced to reduce noise and 

improve fuel efficiency. They require higher 

engine pressure ratios, which increase engine 

temperatures, and hence generate more NOx. It 

has only been in the past 25 years that the 

resulting NOx increase became a concern. FAA 

and other stakeholders have recently initiated an 

effort to better understand and quantify these 

interrelationships in an “environmental design 

space.” Eventually this will lead to guidelines for 

setting long term goals and standards that 

optimize overall environmental performance and 

avoid unintended consequences. 

Aircraft design improvements mostly fall into 

one of three areas: aerodynamics, weight 

reduction, and control systems. Continued 

improvement in all areas is expected in the 

future45. Some of the technologies in 

development for aerodynamic improvements 

include the design of winglets for wing tips, 

which reduce turbulence and vortex generation 

by the wings, laminar flow controls or systems 

for wing surfaces to reduce drag, and improved 

manufacturing techniques that will produce 

smoother surfaces. New and improved metal 

alloys and composite materials are being 

developed to reduce aircraft weight while 

simultaneously improving structural 

performance. Significant improvement of control 

systems has come about by replacing mechanical 

and hydraulic systems with electrical systems, 

which often reduce system weight while 

providing more precise control. Improvements of 

these systems and development of new systems 

for enhanced flight stability will contribute to 

improved overall fuel efficiency. 
Aviation & Emissions – A Primer

19 

Aircraft technology development and capital 

turnover follow relatively long cycles, which 

limits the pace of fundamental changes in design. 

It takes approximately 10 to 15 years for fleet 

average fuel efficiency to equal the efficiency of 

the newest aircraft46. However, the ongoing 

evolutionary change in technology has realized 

substantial benefits over time. According to the 

Intergovernmental Panel on Climate Change, in 

their report Aviation and the Global 

Atmosphere47, aircraft fuel efficiency has 

improved by 75 percent in the past 40 years 

through improvements in airframe design, engine 

technology, and rising load factors. 

While progress in the near- and mid-terms is 

expected, the most significant opportunities for 

emission reduction lie in the future when we can 

derive benefits from aggressive research goals. 

FAA, EPA, ICAO, and many other groups have 

been working to elucidate and characterize the 

environmental issues for some time while NASA 

is directing a research program aimed at 

significantly cutting emissions from aircraft 

engines48. 

A comprehensive research program starts with a 

clear and complete understanding of the effects 

of aviation on air quality. FAA has developed 

analytical tools to quantify emissions more 

accurately, which are used to understand 

aviation’s contribution to local air quality 

concerns and global emissions. These tools are 

developed on a foundation of research that FAA 

has conducted both independently an in 

conjunction with airports and other 

organizations. The Emissions and Dispersion 

Modeling System (EDMS) has been developed 

to quantify emissions from aircraft and other 

airport emission sources. It is used routinely to 

assess the impact of airport expansion projects 

and other operational changes. The System for 

assessing Aviation’s Global Emissions (SAGE) 

is being developed to assess the impact of 

aircraft engine emissions during the whole flight 

regime, especially climb out and cruise 

emissions. The model will be able to develop 

aviation emission inventories, both for baseline 

conditions and forecasted technology, and assess 

operational and market-based measures and 

improvements. New tools are also being 

developed to understand and assess the 

environmental design space, to evaluate 

interrelationships among all emissions and 

between emissions and noise due to changes in 

technology and operational procedures. 
Aviation & Emissions – A Primer 

20 

NASA is the U.S. federal agency responsible for 

pre-commercial aerospace research, 

development, and demonstration. One of the key 

themes of their research program is to “protect 

local environmental quality and the global 

climate by reducing aircraft noise and 

emissions." Their strategy is to research 

opportunities to reduce airframe weight and drag, 

optimize engine systems, and optimize 

operations at and around airports. Through this, 

NASA hopes their research program results in 

significant or total elimination of aircraft 

greenhouse gas emissions, minimized impact of 

emissions on local air quality, and elimination of 

unnecessary aviation emissions due to 

operational procedures. The goals of this 

program are to reduce NOx emissions of future 

aircraft by 70 percent by 2007, and by 80 percent 

beyond 2007 using 1996 ICAO standards as a 

baseline. They also intend to reduce CO2 

emissions of future aircraft by 25 percent and by 

50 percent for these same milestones using 2000 

state-of-the-art aircraft technology as a 

baseline49. 

The primary engine research project to achieve 

these objectives is the Ultra-Efficient Engine 

Technology (UEET) project, in NASA’s Vehicle 

Systems Program. According to NASA, the 

UEET project will develop and transfer to U.S. 

industry critical turbine engine technologies that 

will contribute to enabling a safe, secure, and 

environmentally friendly air transportation 

system. This project is currently underway. 

FAA, NASA, and Transport Canada have made 

a major commitment to researching aviation 

emissions as well as noise through the Center of 

Excellence for Aircraft Noise and Aviation 

Emissions Mitigation.50 The Center was 

established in September 2003 to foster 

breakthrough technical, operational, and 

workforce capabilities enabling quieter and 

cleaner aircraft. 

Achieving research goals will allow the aviation 

industry to significantly reduce its environmental 

impact and begin to reduce its total emissions of 

NOx and CO2. This takes time, however. As 

noted earlier it takes 10 to 15 years for fleet 

average performance to achieve current new 

technology performance. To go from NASA 

research to fleet average performance takes 20 to 

40 years51. Also, concerns have been raised 

about the likelihood of these goals being met due 

to budget restrictions. The National Research 

Council recently published a report, For Greener 

Skies: Reducing Environmental Impacts of 
Aviation & Emissions – A Primer

21 

Aviation52, that concluded, while “the goals of 

the federal research program are admirable and 

focused on the right issues, the schedule for 

achieving the goals is unrealistic in view of 

shrinking research budgets.” The report went on 

to call for further federal investment in engine 

research and technology development. 

Aviation emissions are 

being responsibly 

controlled. 

Aviation has progressively improved its 

environmental performance. Fuel economy, 

which is one strong indicator of environmental 

performance, has consistently improved. Aircraft 

engines have gotten more efficient and been 

designed with environmental performance in 

mind. Regulatory frameworks have developed to 

constrain emissions growth from many aviation 

sources. And improvements to the efficient 

operation of the complex aviation network have 

had a positive effect on the environment. 

Looking to the future, FAA has a roadmap for 

continuing to mitigate the environmental impacts 

of aviation. This includes continuing to improve 

its understanding of the role of aviation 

emissions on the environment. FAA is working 

with industry and other stakeholders to advance 

the performance of the national and international 

aviation system as well as to improve individual 

system components. And FAA is working in the 

international arena to evaluate alternative 

strategies for market-based opportunities for 

reducing emissions. 

FAA, together with EPA and NASA, is 

committed to ensuring aviation emissions do not 

pose health concerns for our citizens or restrain 

aviation’s mobility and economic benefits 

enjoyed by society. It will take consistent, 

coordinated effort and continuing success in 

technology research and development to achieve 

these goals.

 

1

 Population Timeline, http://www.pbs.org/kqed/population_bomb/danger/time.html. 2

 http://www.atag.org/files/FAST%20FACTS-120341A.pdf 

3 Ibid 

4

 http://www.iata.org 
Aviation & Emissions – A Primer 

22 

 

5

 U.S. Department of Transportation, Bureau of Transportation Statistics, Transportation Indicators

http://www.bts.gov/publications/transportation_indicators/december_2002/ , December 2002. 6

 U.S. Department of Transportation, Federal Aviation Administration, FAA Long-Range Aerospace 

Forecasts Fiscal Years 2015, 2020 and 2025, Office of Aviation Policy and Plans, FAA-APO-00-5, 

http://apo.faa.gov/lng00/lng00.pdf, June 2000. 7

 GDP - U.S. Department of Commerce, Bureau of Economic Analysis, National Accounts Data 

http://www.bea.gov/bea/dn1.htm; RTM - U.S. Department of Transportation, Bureau of Transportation 

Statistics, Historical Air Traffic Statistics, http://www.bts.gov/oai/indicators/airtraffic/annual/1981-

2001.html; VMT – U. S. Department of Transportation, Federal Highway Administration, Traffic Volume 

Trends, December 2002 http://www.fhwa.dot.gov/ohim/tvtw/02dectvt/tvtdec02.pdf. 8

 Ibid. Table 9-15. 

9

 Wickrama, Upali, International Civil Aviation Organization, Committee on Environmental Protection, 

Forecasting and Economic Analysis Support Group, Report of the FESG/CAEP/6 Traffic and Fleet 

Forecast, copy of Figure 8, 2003 op. cit. 10 U.S. Environmental Protection Agency, National Air Quality 2001 Status and Trends, 

http://www.epa.gov/airtrends/aqtrnd01/, September 2002. 

[http://www.epa.gov/air/airtrends/aqtrnd03/fr_table.html] 11 Waitz, I. A., Massachusetts Institute of Technology, private communication based on Boeing data, 

November 2003. 

12 U.S. Environmental Protection Agency, Average Annual Emissions, All Criteria Pollutants; Years 

Including 1980, 1985, 1989-2001, http://www.epa.gov/ttnchie1/trends/index.html, February 2003. 13 Clean Air Act Amendments of 1990, Title I – Provisions for Attainment and Maintenance of National 

Ambient Air Quality Standards, Section 101(d)(1), November 15, 1990. 

14 U.S. Environmental Protection Agency, 8-Hour Ground-level Ozone Designations, 

http://www.epa.gov/ozonedesignations/statedesig.htm, May 6, 2004. 15 U.S. Department of Transportation, Federal Aviation Administration, Enplanement Activity at Primary 

Airports, http://www.faa.gov/arp/planning/stats/2002/CY02CommSerBoard.pdf , November 6, 2003. 16 U.S. Environmental Protection Agency, Classifications of Ozone Nonattainment Areas, op.cit. 17 U.S. Department of Transportation, Federal Aviation Administration, Federal Highway Administration 

(cooperating agency), Final Environmental Impact Statement for 9,000-Foot Fifth Runway and Associated 

Projects: Hartsfield Atlanta International Airport, August 2001. 18Illinois Environmental Protection Agency, Illinois 1999 Periodic Emissions Inventory And Milestone 

Demonstration, December, 2001. The higher value for in the area inventory data in the table is for a typical 

summer day, which is the ozone season and probably represents a worst case since it is the most active 

period for aviation activity. The non-road data also is based on typical summer day. The lower value, which 

is more representative for an annual value is from U.S. Department of Transportation, Federal Aviation 

Administration, Final Environmental Assessment for the World Gateway Program and Other Capital 

Improvements: Chicago O’Hare International Airport, Chicago, Illinois, June 21, 2002. 19 South Coast Air Quality Management District, Emissions by Category, 2001 Estimated Annual Average 

Emissions, South Coast Air Basin.

http://www.arb.ca.gov/app/emsinv/emssumcat_query.php?F_DIV=0&F_YR=2001&F_AREA=AB&F_AB

=SC , 2001. 20 Texas Natural Resource Conservation Commission, Dallas/Fort Worth Ozone Nonattainment Area 

Emission Data, http://www.tnrcc.state.tx.us/air/aqp/ei/rsumdfw.htm, 1996 inventory data. Data includes all 

airports in the nonattainment area including, DFW International Airport, Dallas Love Field, and Alliance 

Airport. 

21 U.S. Department of Transportation, Federal Aviation Administration, Final Environmental Impact 

Statement Runway 8L-26R and Associated Near-Term Master Plan Projects; George Bush Intercontinental 

Airport/Houston, July 2000. 22 Compilation of data from the SIP inventories for New York and New Jersey provided by Mr. Raymond 

Forde, Region 2, U. S. Environmental Protection Agency, June 16, 2004. Additional data provided by Mr. 

Kevin McGarry, New York State Department of Conservation and Ms. Tonalee Key, New Jersey 

Department of Environmental Protection. 
Aviation & Emissions – A Primer

23 

 

23 Agyei, Kwame, Puget Sound Clean Air Agency, airport emissions calculated using EDMS 4.0; area nonroad and total emissions from 1999 Air Emission Inventory Summary spreadsheet, February 11, 2003. 

24 Nonattainment area non-road and total NOx emissions, 68 FR 25431, May 12, 2003; Airport emissions 

escalated from 1995 estimate by URS Greiner, Inc. (1997) based on 2000 data provided by Tony Petruska, U.S. 

EPA.

25 Massachusetts Department of Environmental Protection, Massachusetts Periodic Emissions Inventories 

1999, April 2003, for nonattainment area off-road emissions and total emissions, which are based on 

summer day emissions. U.S. Department of Transportation, Federal Aviation Administration, Final 

Environmental Impact Statement, Logan Airside Improvements Planning Projects: Boston Logan 

International Airport, June 2002 for Logan Airport emissions, which are typical for an annual value. 26 U.S. Environmental Protection Agency, National Air Pollutant Emission Trends, 1990-1998, 

http://www.epa.gov/ttn/chief/trends/trends98/index.html, March 2000. 27 Ibid. 

28 For NOx, aircraft represent anywhere from 60 to 80 percent of total airport emissions with the balance 

coming from the other sources like ground support equipment and ground access vehicles. This is based on 

a review of recent Environmental Impact Statements for eleven airports (ATL, BOS, CLE, DFW, IAD, 

IAH, LAX, ORD, PTI, SFO, and STL). 

29 For more information about the production of contrails by aircraft, see U.S. Environmental Protection 

Agency, Aircraft Contrails Factsheet, http://www.epa.gov/otaq/regs/nonroad/aviation/contrails.pdf, 

September 2000. 

30 U.S. Environmental Protection Agency, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-

2001, http://yosemite.epa.gov/oar/globalwarming.nsf/UniqueKeyLookup/LHOD5MJQ6G/$File/2003-

final-inventory.pdf, April 15, 2003. Estimates are presented in units of terragrams of carbon dioxide 

equivalents (Tg CO2 Eq.), which weight each gas (e.g., CO2 and NOx) by its Global Warming Potential, or 

GWP, value. 

31 U.S. Environmental Protection Agency, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-

2001, 2003 op.cit. 32 Intergovernmental Panel on Climate Change, Aviation and the Global Atmosphere, 1999. 33 Actual Emissions 1990-2001 – U.S. Environmental Protection Agency, Inventory of U.S. Greenhouse 

Gas Emissions and Sinks: 1990-2001, 2003 op.cit. 34 Forecast Emissions 2001-2025 calculated based on FAA long-range activity forecasts assuming a 

constant rate of emissions from aircraft. The forecast is deemed conservative since it does not account for 

improvements in aircraft energy efficiency over the next 20 years, which are deemed likely. Estimates are 

presented in units of terragrams of carbon dioxide equivalents (Tg CO2 Eq.), which weight each gas (e.g., 

CO2 and NOx) by its Global Warming Potential, or GWP, value. 35 U.S. Department of Energy, Oak Ridge National Laboratory, Transportation Energy Data Book: Edition 

22, http://www-cta.ornl.gov/data/tedb22/Full_Doc_TEDB22.pdf, September 2002. 36 US Department of Transportation, Bureau of Transportation Statistics, National Transportation Statistics 

2002 (BTS 02-08), Table 4-20: Energy Intensity of Passenger Modes (Btu per passenger-mile), page 281, 

http://www.bts.gov/publications/national_transportation_statistics/2002/pdf/entire.pdf. 37 Ibid. 

38 See FAR Part 33 – Airworthiness Standards: Aircraft Engines 

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgFAR.nsf/CurrentFARPart?OpenView&St

art=1&Count=200&Expand=10. 39 Colpin, J. and Altman, R., Dependable Power Reinvented, AIAA 2003-2882, AIAA-ICAS International 

Air and Space Symposium and Exhibit: The Next 100 Years, July 14-17, 2003, Dayton, OH. 40 The use of market-based options for limiting or reducing greenhouse gas emissions from aviation may 

also prove potentially useful applied to local air quality emissions. 

41 Air Transport World, United says cutting APU runtime to save $12 million, ATW Online.com, February 

10, 2003. 

42 International Civil Aviation Organization, Circular 303 - Operational Opportunities to Minimize Fuel 

Use & Reduce Emissions, February 2004. 
Aviation & Emissions – A Primer 

24 

 

43 U.S. Department of Transportation, Federal Aviation Administration, National Airspace System 

Operational Evolution Plan, December 2002 44 U.S. Department of Transportation, Federal Aviation Administration, Final Regulatory Impact Analysis, 

Final Regulatory Flexibility Determination, Unfunded Mandates and Trade Impact Assessment, Reduced 

Vertical Separation Minimum Operations in United States Domestic Airspace, March 10, 2003 45 Drew, P., et al., Technology Drivers for 21st Century Transportation Systems,” AIAA 2003-2909, AIAAICAS International Air and Space Symposium and Exhibit: The Next 100 Years,” 14-17 July 2003, 

Dayton, OH 

46 Waitz, I. A., Massachusetts Institute of Technology, Aircraft, Gas Turbine Engines and Emissions 

Primer, August 3, 2001. 47 Intergovernmental Panel on Climate Change, 1999 op.cit. 

48 ICAO has established a Long-Term Technology Goals (LTTG) task group within Working Group 3 to 

monitor and track future aircraft technologies that may demonstrate better environmental performance. The 

LTTG will evaluate the prospects for setting emissions goals as targets for future technology performance. 49 National Aeronautics and Space Administration, NASA Aerospace Technology Enterprise Strategy – 

2003, http://www.aerospace.nasa.gov/strat_plan2003_low.pdf. 50 More information on the FAA-NASA Center of Excellence for Aircraft Noise and Aviation Emissions 

Mitigation can be found at http://web.mit.edu/aeroastro/www/partner/. 51 Waitz, I. A., Massachusetts Institute of Technology, 2001 op. cit., estimates “22 to 37 years total time 

from basic technology (e.g. NASA research) to significant fleet impact.” 52 National Research Council, Division on Engineering and Physical Sciences, Aeronautics and Space 

Engineering Board, Committee on Aeronautics Research and Technology for Environmental Compatibility, 

For Greener Skies: Reducing Environmental Impacts of Aviation, available at 

http://bob.nap.edu/html/greener_skies/notice.html, 2002.