Report No. 1 1 3!*-1
NATURE AND CONTROL OF AIRCRAFT
ENGINE EXHAUST EMISSIONS
Northern Research and Engineering Corporation
Cambridge, Massachusetts London, England
-------
Report No. 1134-1
NATURE AND CONTROL OF AIRCRAFT
ENGINE EXHAUST EMISSIONS
Prepared for the
National Air Pollution Control Administration
Department of Health, Education, and Welfare
(Contract No. PH22-68-27)
NORTHERN RESEARCH AND ENGINEERING CORPORATION
219 Vassar Street
Cambridge, Massachusetts 02139
November, 1968
Copy No. 53
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This work was carried out under the direction of Dr. D. M. Dix
with Dr. E. K. Bastress as.sum-ing the project responsibility.
The other
principal participants in this program were Dr. P. L. Duffield, Dr. R. S.
Fletcher, and J. E. Smith.
Contributions to portions of this study deal ing with pollutant
characteristics, impact, control, and measurement were made by the Singco
Department of Bolt Beranek and Newman, Inc., under the direction of C. Y.
Sing.
Professor A. H. Lefebvre, Professor J. R. Mahoney, Professor
R. F. Sawyer, and Dr. Amos Turk contributed to this effort in a consulting
capacity.
The Project Officer for this program was G. D. Kittredge, Chief,
~
Research Branch, Division of Motor Vehicle Research and Development,
National Air Pollution Control Administration.
During the program, many
helpful suggestions were received from Mr. Kittredge and from Mr. J. C.
Romanovsky, Office of the Director, Bureau of Standards and Criteria, NAPCA.
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ACKNOWLEDGEMENTS
Information useful in the conduct of this study was provided
by the following organizations:
Aero Commander Division
North American Rockwell Corporation
Aerospace Industries Association of America, Inc.
AiResearch Manufacturing Company
Garrett Corporation
Air Transport Association of America
All ison Division, General
Motors Corporation
Avco Lycoming Division
Avco Corporation
Beagle Aircraft Limited
The Boeing Company
British Aircraft Corporation (Operating) Limited
Britten-Norman Limited
Cessna Aircraft Company
Continental Motors Corporation
Dornier GMBH (Munchen)
Douglas Aircraft Division
McDonnell Douglas Corporation
Federal Aviation Administration
u. S. Department of Transportation
General Electric Company
Lear Jet Corporation
Lockheed-California Company
Lockheed Aircraft Corporation
Los Angeles County Air Pollution Control District
- v -
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National Business Aircraft Association, Inc.
Northeast Airl ines
Piper Aircraft Corporation
Port of New York Authority
Pratt & Whitney Aircraft Division
United Aircraft Corporation
Rolls-Royce Limited
Short Brothers and Harland Limited
Turbomeca Soci~t~
U. S. Civil Aeronautics Board
U. S. Department of Defense
- vi -
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TABLE OF CONTENTS
SUMMARY.
. . . .
. CI . . . . . . .
. . . . . . . . .
. . . . . .
Nature and Extent of Aircraft Engine
Exhaust Emissions. . . . . . . . . .
. . . . . .
Reduction of Aircraft Engine Exhaust Emissions
. . . .
Impact of Aircraft Engine Exhaust Emissions. . .
Control of Aircraft Engine Exhaust Emissions
. . 0 . .
CONCLUSIONS. . .
. . . .
. . . . . .
. . . .
. . . .
RECOMMENDATIONS. . . . . .
. . . . .
. . . . .
INTRODUCTION
. . . . .
. . . . .
o . . . . .
. . . 0
Background
. . . . .
. . . . .
Methodology.
. . . .
. . . . . . . . . . .
. . . . . .
NATURE OF AIRCRAFT, ENGINES AND FUEL SYSTEMS
. . f# .
. . . . . .
Aircraft
. . . .
. . . .
. . . .
. . . . . . . .
Aircraft Engines
. . . .
. . . .
. . . . . .
. . . . .
Fuel Systems
. . . . .
. . . . .
. . . . .
Summary. . .
. . . . . .
. . . .
. . 0 . . .
. . . . .
AIRCRAFT AND AIRCRAFT ENGINE POPULATION, PRODUCTION,
AND ACT I V I TY . . . . . . . . . . . . . . . . . . . . . . .
Aircraft and Aircraft Engine Population. .
. . . . . 0
Aircraft and Aircraft En~ine Production
. . . .
. . . .
Aircraft Activity
. . . . .
. .. . . .
Summary
. . . 0 .
. . . 0
. . . .
........
A I RCRAFT FUELS
. . . . .
. . II . .
. . . . . . 0
. . . . .
Fuel Characteristics
. . . . . .
. 0 . .
. . . .
Fuel Consumption
. 0 . 0
. . . .
. . . . 0
Summary. . . . . . . . .
. . . .
. . . .
. . . . . . .
- vi i -
4
5
9
13
19
23
23
26
28
28
37
58
61
62
62
68
70
75
77
77
87
89
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AIRCRAFT ENGINE EMISSIONS
. . . . . .
. . . .
. . . . . . . . . .
90
Characteristics of Aircraft Engine
Exhaus t Gases. . . . . . . . . . .
. . . .
91
Formation of Pollutants in Aircraft Engines
. . . 101
Rates of Pollutant Emission by Aircraft
Engines. . . . . . . . . . 0 . . " . . . . . . . . . . 105
Quantities of Pollutants Emitted by
Aircraft Engines. . . . . . . . .
. . . .
. . . 113
. . . . . . 118
Future Trends in Aircraft Engine Emissions
Summary. . . .
. 0 . . . .
. . . . . . . .
. . . 121
IMPACT OF AIRCRAFT ENGINE EMISSIONS. .
. . . . 0 .
. . . .
. . . 123
. . 124
Factors Influencing Impact
. D . . . . . . .
Local Impact of Aircraft Emissions
. . . .
. . . 142
Relative Importance of Aircraft Emissions in
Total Community Air Pollution. . . . .
. . . . . 152
Interactions Between Aircraft Safety, Noise,
and Pollutant Emission. . . . . . . . . .
Summa ry . .
. . . . . .
. . . 159
. . 162
. . . . . . .
. . . .
Modifications to Engines
. . . . . .
. . 167
. . . 167
REDUCTION OF AIRCRAFT ENGINE EMISSIONS
. . . . .
Modifications of Aircraft. . .
. . . .
. . . . . . . . 190
Fuel Modifications
. . . . .
. . . . .
. . . .
. . . . 191
Modifications of Ground Operations
. . . . .
. . 193
. . 195
Modifications of Flight Patterns
. . . . . .
Emission Reduction Attainable. .
. . . .
. . . . 197
. 198
Reduction of Odors
o . . . . .
. . . .
. . . . . . .
Reduction of Pollutant Impact.
. . . . .
. . . .
. . . 201
Summary.
. . . . . .
. . . .
. . . . . .
. . . . .
. . 202
- vi i i -
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Control Requirements.
. .. . . .
. . . .
. . . . .
. . 204
. . 204
CONTROL OF AIRCRAFT ENGINE EXHAUST EMISSIONS.
. . . . . . .
Approaches to Emission Control.
. . . . .
. . . .
. . 209
RESEARCH NEEDS. . .
. . . . . .
. . . .
. . . .
. . . . . .
. . 217
Aircraft Emissions and Emission Reduction. . . . . . . 217
Impact of Aircraft Emissions
. . . .
. . . . . . .
. . 219
Related Areas
. . . .
. . . .
. . . .
. . . .
. . . . 220
REFERENCES. . .
. . . . . . .
. . . .
. . . . . . . . .
. . . . 221
TABLES. . .
. . . .
. . . .
. . . . . .
. . . .
. . . . . . . . 231
. . . . 307
FIGURES
. . . .
. . . . . .
. . . . . .
. . . . . . . .
APPENDICES. . . .
. . . . .
. . . . . .
. . . .
. . . . . . . . 329
I:
SAMPLING AND MEASUREMENT METHODS.
. . . . .
. . . 331
I I :
THE ORIGIN AND MEASUREMENT OF ODOR IN
AIRCRAFT ENGINE EXHAUST EMISSIONS. . . . .
. . . 357
III:
ANALYSIS OF COMPLAINTS CONCERNING POLLUTANT
EMISSION BY AIRCRAFT. . . . . . . . . . . .
. . . 383
- ix -
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Table
Table
LI ST OF TABLES
1 :
Aircraft Classification System for Assessing
Exhaust Emissions. . . . . . . . . . . . .
. . . . . . 233
2:
Aircraft Performance Characteristics During
Landing and Take-Off Operations
. . . . . . 234
Table 3: Aircraft Registered wi th FAA by Type:
January I, 1967 . . . . . . . . . . . . . .236
Table 4: U. S. Population of Active, C ivi I Aircraft,
Past and Future . . . . . . . . . . . . . . . .237
Table 5: Active, Civi I Aircraft by Year of Manufacture
as of January I, 1967 . . . . . . . . . . . . . . . . . 238
Table
Table
Table
Table
Table 10:
Tab1 e 11:
Table 12:
Table 13:
Table 14:
Table 15:
Table 16:
Table 17:
Table 18:
6:
Composition of the U. S. Air Carrier Fleet,
Past and Future . . . . . . . . . . . . . .209
7:
Aircraft of the U. S. Air Carrier Fleet
(January 1968) ............
. . . . . . . . 240
8:
U. S. Air Carrier Aircraft by Country of Manufacture
January 1968 . . . . . . . . . . . . . . . . . . . . .243
9:
Composition of the U. S. General Aviation
Fleet, Past and Future. . . . . . . . . .
. . . .
. .244
Active, General Aviation Aircraft by Type. .
. .245
U. S. Department of Defense Inventory of Active
Aircraft. . . . . . . . . . . . . . . .
. . . . 246
Turbine Engines in the U. S. Air Carrier Fleet
(January 1968) . . . . . . . . . .
. . . .247
Piston Engines in the U. S. Air Carrier
Fleet, January 1968 . . . . . . . . . . .
Aircraft Production in the United States
. . .246
. . . .2£+9
. . . .
Major United States Manufacturers of Civil
Aircraft. . . . . . . . . . . . . . . . .
. . . . . . 250
Foreign-Made Aircraft Del ivered to U. S.
Customers. . . . . . . . . . . . . .
. . .25:1
Aircraft Engine Production in the United States. .. .252
Major United States Aircraft Engine Manufacturers. . .253
- xi -
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Table 19:
Table 20:
Table 21:
Table 22:
Table 23:
Table 24:
Table 25:
Table 26:
Table 27:
Table 28:
Table 29:
Table 30:
Tab 1 e 31:
Table 32:
Table 33:
Foreign Manufacturers of Aircraft Engines
Sold to U. S. Civil Aircraft Manufacturers. . . . . . 254
Annual U. S. Air Terminal Traffic Activity
(Landing-Take-Off Cycles - Millions) . . .
. . . 255
1967 Air Traffic Activity at Major Air Terminals
in the New York City Metropol itan Area (Landing-
Take-Off Cycles - Thousands) . . . . . . .
. . . 256
1967 Air Traffic Activity at Major Air Terminals
in the Washington, D. C., Metropolitan Area
(Landing-Take-Off Cycles - Thousands) ......
. . 257
1967 Air Traffic Activity at Air Terminals in the
Los Angeles Metropol itan Area (Landing-Take-Off
Cycles - Thousands). . . . . . . . . . . . .
. . 258
Aircraft Activity Levels by Aircraft Class
at Various Terminals and Metropol itan Areas
. . . . . 259
1967 Air Traffic Activity Rates at Major Air
Terminals in the New York City Metropol itan
A rea. . . . . . . . . . . . . . . . . . . .
. . . . . 260
1967 Air Traffic Activity Rates at Major
Air Terminals in the Washington, D. C.,
Metropol itan Area. . . . . . . . . . . . . . . . . . 261
1967 Air Traffic Activity Rates at Air
Terminals in Los Angeles County
. . . . . 262
Scheduled Air Carrier and Air Taxi Arrivals
at J. F. Kennedy International Terminal,
May I, 1968 . . . . . . . . . . . . . . . . .
. . . . 263
Scheduled Air Carrier and Air Taxi Arrivals by
Aircraft Type, May 1, 1968~Washington National
Terminal. . . . . . . . . . . . . . . . . . .
. . . . 264
Scheduled Air Carrier and Air Taxi Arrivals
byAi rcraft Type, May 1, 1968; .Los Angeles
International Terminal. . . . . . . . . . .
. . . . . 265
Specifications for Aviation Gasol ines (Taken
from Reference 41) . . . . . . . . . . . . .
. . 266
. 268
Properties of Aviation Turbine Fuels.
. . . . . . .
Specifications for Aviation Turbine Fuels
. . 269
. . . .
-xi i .-
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Table
Table
Table
Table
Table
Table
Table
Table 41a:
Table 41b:
Table 41c:
Table
40:
34:
United States Consumption of Aircraft Fuels,
Past and Future. . . . . . . . . . . . . . .
. . . . . 271
35 :
Fuel Consumption Rates for Representative
Eng i nes. . . . . . . . . . . . . . . . . .
. . . . . . 272
36 :
Fuel Consumption During Landing and Take-Off
Operations for Representative Engines. . . . . . . . . 273
37:
Aircraft Fue1 Consumption During Air Termina1
Ope rat ions. . . . . . . . . . . . . . . . . .
. . . . 274
38:
Composition of Exhaust Products from Typical
Aircraft Engines. . . . . . . . . . .
. . . . . 275
39:
Detailed Analysis of Organic Emissions from
a Turbojet Engine. . . . . . . . . . . .
. 276
Emission Indices for Aircraft Engines.
. . . 277
.. " . 0 0
Turbine Engine Emission Data - Idle Condition.
. 279
Turbine Engine Emission Data - Approach Mode
. . 280
Turbine Engine Emission Data - Take-Off Mode
. 281
o . . .
42:
Engine Emission Levels During a Landing and
Take-Off Cycle. . . . . . . . . . . . . . . .
. . . . 282
Table 43: Relative Em i s s ion Loads by Engine and Aircraft
Type . . . . . . . . . . . . . . . . . . . 283
Table 44: Aircraft Exhaust Emiss ions at New York Area
Terminals - 1967 . . . . . . . . . . . 284
Tab1e 45: Aircraft Exhaust Emi ss ions at Washington Area
Terminals - 1967 . . . . . . . . . . . . 285
Table 46: Aircraft Exhaust Emi ss ions at Los Angeles Area
Terminals - 1967 . . . . . . . . . . . . . . . 286
Table
Table
Table
47:
Aircraft Exhaust Emissions at all FAA - Controlled
Term i na Is - 1967 . . . . . . . . . . . . . . . . .
. . 287
48:
Pollutant Emission by Aircraft During Air Terminal
Operations - 1967. . . . . . . . . . . . . . . . . .
. 288
49:
o . . .
. . 289
Aircraft Exhaust Emissions During Cruise.
- xi i i -
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Table 50:
Table 51:
Table 52:
Table 53:
Table 54:
Table 55:
Table 56:
Table 57:
Table 58:
Table 59:
Table 60:
Table 61:
Table 62:
Table 63:
I, ~
Total Emissions in the United States from
Aircraft (1967) . . . . . . . . . . . . . . . . . . . . 290
Elements Used and Assumptions Made in Calcu-
lation of Emission Loads. . . . . . . . . . .
. . . . . 291
Error Factors for Aircraft Emission Loads.
. 293
. . . . .
Aircraft Activity During Busy and Peak
Hours. . . . . . . . . . . . . . . .
. . . . . . . . . 294
Maximum Possible Emission Loads at J. F.
Kennedy Airport During 1967 . . . . . . . . . . . 295
Emissions by Civi 1 Aircraft at all FAA -
Controlled Terminals - 1967 & 1979. . . . . . . . . . . 296
Land Use Near J. F. Kennedy, Washington
National and Los Angeles International
Airports. . . . . . . . . . . . .
. . ... .
. . . 298
Source Data Used With the Airport Area -
Source Model. . . . . . . . . . . . . . .
. . . . 299
Comparison of Concentrations of Aircraft Emis-
sions at Air Terminals With Community Concen~
t rat ions. . . . . . . . . . . . .
. . . .
. 300
. 301
Emissions per Unit of Path Length
. . . . . . .
Density of Aircraft Exhaust Emissions at Air
Terminals Compared With Emissions in surround-
ing Regions. . . . . . . . . . . .
. . . . 302
Variations of Emission Densities in Urban
Areas. . . . . . . . . . . . . . . . . . . . . . . . . 303
Aircraft Engine Emissions Compared With Emis-
sions From Other Sources (1967 Average Dai ly
Em i ss ions). . . . . . . . . . . . . . . . . . .
. . . . 304
Estimated Reductions in Aircraft Exhaust Emis-
sions Attainable by Various Methods. . . . . .
. . . . 305
- x i v -
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Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figure
Figl,Jre
Figure
Figure
Figure 12:
Figure 13:
Figure 14:
LIST OF FIGURES
1 ;
Typical Fuel Systems for Light, Piston-Engine
Aircraf~ Courtesy of Cessna Aircraft Company
(Refs 10 and 11) . . . . . . . . . . . . . . . . . . 309
2:
Typical Fuel Systems for Non-Afterburning
Turbine Engine. . . . . . . . . . .
. . 310
3:
4:
Turbine-Engine Fuel Injectors
. . 311
. . . .
. 0 . . .
Composition of the United States Air
Carrier Fleet. . . . . . . . . . . . .
. . . . . . 312
5:
Composition of the United States General
Aviation Fleet. . . . . . . . . . . . . . . . . . . 313
6:
Annual Air Traffic Activity at United
States Air Terminals. . . . . . . . .
. . . .
. . . 314
7:
Hourly Variation of Aircraft Activity in Five
Metropolitan Areas - May 1967 (Scheduled Air
Carrier and Air Taxi Activity Only) .....
. . . 315
8:
Products from a Typical Crude Oil Refining
Operation. . . . . . . . . . . . . . . . . . . . . 316
9:
Luminometer Rating of Aviation Kerosines
as a Function of Crude Oil Source (Taken
from Reference 40) . . . . . . . . . . . . . . 317
10:
National Consumption Rates of Aviation
Fuels, Years 1960-1979 . . . . . . . . . . . . .
. . 318
11 :
Carbon Monoxide Emission by Piston Engines. . . .
. 319
Emission of Orga~cs by Piston Engines
. 320
Emission of Nitrogen Oxides by Piston Engines
. . . 321
Air-Fuel Ratio Curves for Typical Aircraft
Pi s ton Eng i nes . . . . . . . . . . .
. . 322
Figure l5a: Turbine Engine Emission Data, Carbon Monoxide . . . 323
Figure 15b: Turbine Engine Em is s ion Data, Organics as CH4 . . . 324
Figure 15c: Turbine Engine Emission Data, Nitrogen Oxides
as NO . . . . . . . . . . . . . . . . . . . . 325
- xv -
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Figure 15d:
Figure
Figure
Turbine Engine Emission Data, Particulates.
16:
Monthly Mean Ventilation Rates for New York,
Washington, and Los Angeles. . . . .
17:
Carbon Monoxide Concentration in the Wake
of Taxiing Aircraft. . . . . . . . . . .
.,. xvi-
. . . . 326
. . . . 327
. . . . . 328
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SUMMARY
This report is the result of a study of the emission of air
pollutants by aircraft engines in the United States.
The objectives of
the study were to:
1.
Determine the nature and extent of aircraft engine exhaust
emissions.
2.
Determine the effects or impact of aircraft engine exhaust
emissions.
3.
Evaluate approaches to reducing the emission of air pollutants
by aircraft engines.
4.
Evaluate approaches to governmental control of aircraft
engine exhaust emissions.
In achieving each of these objectives, an attempt was made to compile and
analyze, as far as possible, all available relevant information.
As a
result, this report repres~nts our current level of understanding of the
nature,
impact, and control of aircraft exhaust emissions.
Nature and fxtent of Aircraft
Enqine Exhaust E~issions
Engines used for aircraft propulsion are of two basic classes--
piston engines and turbine engines.
There ace twq types of piston engines
in common use--opposed engines which are instal led generally in 1 ight air-
craft used for pleasure, business or util ity purposes, and radial engines
which are in use mainly in older models of transport aircraft.
There
are three common types of aircraft turbine engines--turbojet, turboprop,
and turbofan engines.
All are used primarily for propulsion of trans-
port aircraft and medium-size business aircraft.
Both piston and
This report is the appendix to the Report of the Secretary of
and Welfare to the U. S. Congress, pursuant to Section 211 (b)
90-148, The Air Qual ity Act of 1967.
Health, Education
of Publ ic Law
-------
2
turbine engines are used for hel icopter propulsion.
The exhaust gases from aircraft piston and turbine engines are
distinctly different.
A turbine engine operates at air-fuel ratios five
to twenty times greater than piston engine air-fuel ratios.
Consequently,
exhaust concentrations of all combustion products are correspondingly less,
Also, because of differences in fuels and combustion chamber operation,
total quantities of pollutants emitted are different.
Pollutants of concern from aircraft piston engines are the same
as those from automobiles:
carbon monoxide, organics, oxides of nitrogen,
and particulates.
As with automobiles, particulates consist primarily of
lead compounds.
However, the specific physical and chemical characteristics
of aircraft lead emissions may differ from those emitted by automobiles.
During operations at air terminals, aircraft piston engines are operated
at comparatively rich air-fuel ratios.
This is particularly true during
take-off where rich mixtures are required to obtain maximum power and to
avoid engine knock and overheating.
As a result, exhaust gases from air-
craft piston engines contain comparatively high concentrations of CO and
organics, and low concentrations of nitrogen oxides.
Turbine-engine exhaust gases contain the same pollutant types
as piston engines--CO, organics, NO , and particulates.
x
However, particulates
from turbine engines consist mainly of carbon (soot).
The detailed com-
position of organics from turbine engines is not known, but available
evidence indicates that they are different in character, and presumably
in photochemical reactivity, from organics in piston-engine exhaust gases.
During all fl ight operations, concentrations of CO and organics in turbine-
engine exhausts are very low, but during certain ground operations (idle
-------
3
and taxi), these concentrations are higher by factors of 50 to 100.
Con-
centrations of NO and particulates, on the other hand, are greater during
. . x
flight operations, though the variation with power level is not nearly so
great as with CO and organic emissions.
Both aviation gasol ine and kerosine contain small quantities of
sulfur compounds as impurities, and these are emitted in engine exhaust
gases as sulfur dioxide.
The sulfur content of these fuels, however, is
much lower than that of fuels used for space heating and power generation.
C,~,nsequently, emission of S02 by aircraft is only of secondary concern.
. Data on aircraft activity, engine fuel consumption and exhaust
composition have been assembled and util ized to determine rates of pollutant
emission at certain air terminals.
Emissions at terminals in the New York City
area and aLall F/I,A-controlled terminals in the United States are as shown below:
Pollutant Emission by Aircraft
During Air Terminal Operations
Ai rcraft Estimated Average Daily Emission in 1967,
Engine 1000 1 bs
Air Terminals ~ CO Organics NOx Particulates ~
John F. Kennedy Piston 14 2 0.02 0.03 a
I nternat i ona 1 Turbine 53 24 4.8 1.5 1.5
All types 67 26 4.8 1.5 1.5
Teterboro Piston 7 1 0.02 0.02 a
(General Aviation) Turbine 0 0 0 a 0
All types 7 I 0.02 0.02 0
All FAA-controlled Piston 92 11 0.2 0.2 0.02
and mi 1 i tary terminals Turbine 74 32 7.6 2.7 2.4
in New York City area All types 166 43 7.8 2.9 2.4
All FAA-controlled Piston 4,322 547 7.3 9.0 0.9
terminals in United Turbine 807 282 78.2 25.5 28.4
States All types 5,129 829 85.5 3I-f. 5 29.3
-------
4
Emissions from turbine and piston engines are shown separately and reflect
the differences in aircraft types utilizing different air terminals.
Estimates have been prepared of pol 1utant emission in the U. S.
by all aircraft including both civil and mil itary aircraft and all operating
modes--cruise and air terminal operations.
These estimates are shown below
along with similar estimates for all motor vehicles:
Annual Pollutant Emission in the U. S.
(Mi 11 ions of tons pe r yea r)
CO Organics NO Particulates Lead S02
-x
Aircraft 2.4 0.3 0.3 0.03 0.01 0.03
Motor
Veh iC les 66 12 6 1 0.19
Changes in the nature and extent of aircraft exhaust emissions in
future years will occur as a result of changes in aircraft activity levels
and changes in equipment.
Substantial
increases in the rates of emission
of all pollutants from aircraft engines are expected unless positive steps
are taken to reduce these emissions.
Reduction of Aircraft Enqine Exhaust Emissions
Methods of reducing pollutant emissions can be categorized as
fo 11 ows :
1.
Engine modifications
2.
Ai rcraft modifications
Fuel modifications
3.
4.
Fl ight pattern modifications
5.
Ground operation modifications
-------
5
A brief analysis of aircraft and fl ight pattern characteristics and their
relationships with pollutant emission has revealed that categories 2 and 4
do not offer practical approaches to emission reduction.
Practical approaches
fall in the categories of modifications to engines, fuels, or ground operations.
Certain of these approaches, if util ized, would be effective in
reducing certain aircraft emissions from their present levels.
Estimates
of the potential reductions attainable indicate that CO and organic emissions
at air terminals can be reduced substantially by using approaches which are
currently feasible.
Similarly, a reduction in particulate emission could be
expected, though the indicated reduction would be partially offset by
increases in aircraft activity.
The net effect on particulates would be a
reduction of visible smoke, but I ittle change in total emission.
The major
pollutants for which no effective reduction techniques exist are oxides of
nitrogen.
The combined effects of equipment changes, reduction of other
pollutants, and increased aircraft activity would lead to a rise in NOx
emi ss ion.
Similar trends exist in NO emission from other sources, including
x
automobiles.
Impact of Aircraft Enqine Exhaust Emissions
At the present time, two aspects or categories of impact of air
pollutants are recognized.
The first of these is the exposure of persons
or property' to concentrations of pollutants which could cause injury or
discomfort.
The second aspect is the degradation of the atmospheric environ-
ment.
Whereas the first aspect is concerned with the health of persons and
the maintenance of their property, the second is concerned with esthetic
values associated with life in an urban community.
Aircraft emissions, like
pollutants from other sources, are of concern from both standpoints.
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6
Aircraft emissions having the greatest impact are those released
during air terminal operations because of the concentrations of aircraft
activity and the fact that this activity occurs largely at ground level.
Because of this concentration of activity at air terminals, emissions from
aircraft are expected to have local effects which differ from their effects
on the over-all community.
Pollutant concentrations at air terminals, as indicated by field
measurements, are similar to those in surrounding communities.
Thus, the
impact of aircraft emissions cannot be determined directly because they
cannot be distinguished from pollutants from other sources.
The local
impact of aircraft emissions can be assessed, however, by comparing the
density of emissions at air terminals with emission densities in surrounding
communities.
Such a comparison, shown below, indicates that the densities
of emissions of certain pollutants at major air terminals from aircraft alone
are comparable to densities of emissions from other sources in adjacent
communities.
Density of Aircraft Exhaust Emissions at
J. F. Kennedy International Terminal Compared
With Emissions in Surrounding Regions
Average Emission Density in 1967
1 ,000 lb/day per sq mi
Land Area
Region sq mi- CO Orqanics NOx Particulates
J. F. Kennedy Inter-
na t i ona 1 Terminal 4.5 12.2 4.4 0.44 O. 11
Queens County 113 30.2 8.4 5.72 1.10
Kings County 76 25.4 7.2 6.00 2.48
Another basis for comparing the impact of aircraft emissions with
those from other sources is provided by calculating pollutant concentrations
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7
at air terminals resulting from aircraft operations.
Pollutant concentrations
from aircraft at air terminals are found to be of the same magnitude as
average concentrations from other sources in metropolitan areas.
In future years, quantities of pollutants emitted by aircraft
are expected to increase if no emission controls are adopted.
Concentrations
of these pollutants in air terminal vicinities will increase proportionately.
During the next ten years, concentrations of CO, organics, and particulates
are expected to increase by 50 to 100 per cent, and NO concentrations wi 11
x
increase by a greater amount.
Consequently, the impact of these emissions
on persons in air terminal vicinities, though perhaps small today, wi. 11
become more serious in the future.
With regard to the impact of aircraft emissions on community-wide
air pollution, the relative contribution by aircraft can be determined by
comparing estimates of emission rates from aircraft with rates from other
sources.
Such a comparison is shown below for the New York City area.
Aircraft Enqine Emissions in the New York City
Area Compared with Emissions from
Other Sources
CO Orqanics
Source 1 ,000 1 b/day % of Total 1,000 lb/day % of Total
Aircraft operations 166 0.6 43 0.6
Ground-All term- 103 30
inals
F1 i ght 63 13
Surface transportation 27,800 95.0 NA NA
Stationary sources 1,290 4.4 NA NA
All sources 29,300 100.0 7,780 100.0
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8
NO
-x
Particulates
Source
1 ,000 1 b/~ay
% of Total
1 ,000 1 b/day
% of Tot~l
Aircraft operations
Ground - All term-
inals
Flight
Surface transportation
Stationary sources
All sources
7.8
0.2
2.9
0.2
3.2
4.6
NA
NA
4,210
NA
NA
100.0
0.9
2.0
189
1,070
1.260
15.0
84.8
100.0
As indicated, pollutants from aircraft constitute less than 1 per cent of the
total quantities of pollutants emitted by all sources in the New York City
a rea.
In the future, however, increases in aircraft activity and other
factors will bring about substantial increases in aircraft emissions.
At
the same time, emissions from other sources are expected to be reduced as a
result of control measures.
It is estimated that contributions of CO and
organics by aircraft, if uncontrolled, will increase from current levels of
less than 1 per cent to 3 to 5 per cent over a ten year period in certain
urban areas.
Certain emissions from aircraft engines are not regarded as
hazardous to health, but do produce adverse sensory effects.
Such emissions
can be regarded as having an esthetic impact.
Aircraft emissions in this
category are smoke and odor.
Emission of smoke by turbine-engine aircraft has an impact upon
the populace beyond its contribution to local and community particulate con-
centrations.
The quantity of solid material in an aircraft exhaust trail
is small, but, due to the. physical characteristics of this material,'it is
highly visible even at low densities.
The impact of smoke trails, therefore,
must be regarded as sensory or esthetic.
Nevertheless, smoke must be taken
seriously sl.nce it is a source of criticism from the publ ic.
The fact that
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9
its impact has been registered with the aircraft industry is evident from
efforts by engine manufacturers to el iminate smoke trails.
Results of
these efforts will be evident as new civil aircraft engines are put in
service.
Odors resulting from the operation of aircraft turbine engines
frequently are noticeable in air terminals.
These odors are generally
objectionable and their presence is regarded as an adverse sensory effect.
At present, substances which are responsible for odors from aircraft have
not been identified precisely, nor are the mechanisms of odor production well
understood.
In addition, there are no straightforward methods of measuring
odor intensity.
The response of human subjects is the only method currently
used for measuring odors.
Even though odors at air terminals are associated
with aircraft activity, it does not necessarily follow that odor intensity is
proportional to activity levels.
Thus, it is clear that odor represents an
effect which should be el iminated, but effective approaches to odor reduction
do not exist at the present time.
Control of Aircraft Enqine Exhaust Emissions
Two basic approaches to the control of aircraft emissions have been
considered.
In the first, aircraft would be treated as motor vehicles and
subjected individually to emission controls.
In the second, an air terminal
would be treated as a stationary source and controls would be applied to total
emissions from aircraft operations within the terminal area.
These approaches
are not mutually exclusive.
They could be employed jointly to achieve sub-
stantial reductions in aircraft emissions.
The approaches differ, however,
in their suitabil ity for use by different government agencies.
The first
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10
approach, that of treating an aircraft as a motor vehicle, is best appl ied
by the Federal government.
The second approach, that of treating air
terminals as stationary sources, is more amenable to use by state, regional,
or local governmental agencies.
Approaches which can be taken by the Federal government to reduce
the emission or the impact of pollutants from aircraft engines fall into
six categories.
a.
Specification of exhaust emission standards
b.
Regulation of aircraft appl ications
c.
Regulation of aircraft operations
d.
Taxation
e.
Government procurement
f.
Research and development funding
Specification of standards is the most direct approach to exhaust
emission reduction.
It is being used by the Federal government for the con-
trol of emissions from many types of pollutant sources, including automobiles.
In the case of aircraft emissions, various pollutant types could be con-
trolled by the application of standards to either engines or fuels.
Standards
on emission of CO, organics, and particulates could be imposed on new air-
craft engines, provided that engine manufacturers were given sufficient lead
time to incorporate the necessary modifications in engines currently in pro-
duction.
There is, however, no basis at present for setting a standard on
emission of oxides of nitrogen from aircraft engines.
Standards could be
imposed on aircraft fuels to control emission of S02 and lead.
Because of
the basic similarity of aviation and automobile gasol ines, they are amenable
to similar standards.
Aircraft turbine fuels do not contain lead, and their
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II
sulfur content is limited to relatively low values to prevent corrosion of
engine elements.
The costs associated with further reductions of sulfur
content could not be justified.
Regulation of aircraft applications is an approach available to
the Federal government through its aircraft certification and registration
procedures.
These procedures might be useful in the enforcement of emission
standards or in providing a basis for pollutant emission taxation, but they
offer no unique advantages as primary control measures.
Regulation of aircraft fl ight operations is an approach which
could be used, at least in principle, to reduce emissions at FAA-controlled
air terminals.
However, emission reductions attainable by this approach
are small.
Therefore, operational regulation does not offer the Federal
government a means to effective pollutant control.
On the other hand,
control of ground operations could be an effective approach by local govern-
ment agencies.
Taxation might be uti] ized to induce the same reductions in emissions
which might otherwise be achieved by the establishment of emission or fuel
standards.
There are two considerations dictating against taxation, however.
The first and foremost is that taxation does not assure emission reduction
unless tax rates are prohibitively high.
The second consideration is that
taxation has not been used to date in the United States as an air pollution
control method and it would be inappropriate to establish a precedent for
taxation by applying it to a minor source of pollutants such as aircraft.
Government procurement has been used by the Federal government as
a means for inducing automobile manufacturers to incorporate certain safety
features in automobiles.
By specifying emission standards for government-
purchased aircraft engines, the emission loads from military aircraft could
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12
be reduced, and the technology would exist for reducing emissions from
civilian versions of the same engines.
The Federal government does not
purchase significant numbers of aircraft piston engines, and thus, cannot
exercise the same leverage in bringing about a reductioQ in piston-engine
emissions.
However, the Federal government is a substantial consumer of
aircraft fuels, and by this approach could reduce emissions which are
associated with fuel composition.
Research and development funding will be necessary to provide
the techniques for reducing pollutant emission rates below levels current\y
attainable.
Rand D will be required on piston-engine emissions, turbine-
engine emissions, and fuel modifications.
The Federal government should
participate in the funding of such activity.
Classification of an air termina\ as a stationary source of air
pollutants provides a basis for control of aircraft emissions by local
authorities.
Contro\ measures would consist of restrictions on aircraft
operations, or engine operating time.
Criteria for such control measures
should be establ ished by the Federa\ government and based upon differen~es
in engine pollutant emission as determined by standardized measurement
techniques.
A distinct advantage of this approach is that the degree of
control can be varied with time and with terminal location in response to
local air quality conditions.
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13
CONCLUSIONS
The principal conclusion drawn from this study is that the nature
and extent of air pollutant emission by aircraft in the United States can be
assessed from existing knowledge with sufficient accuracy to allow a com-
parison between aircraft and other emission sources.
On this basis, air-
craft are a smal] contributor of pollutants in metropol itan areas.
In the
vicinities of air terminals, however, the density of pollutant emission by
aircraft and the resulting pollutant concentrations are comparable to
emission densities and concentrations in adjacent communities of the same
pollutants from other sources.
Thus, the principal impact of aircraft
emissions is local in nature and is expected to become more severe in
future years.
It is also I ikely that aircraft emissions will constitute
a more significant portion of community-wide pollutant loadings as new
aircraft are introduced and as emissions from other sources are reduced.
It is further concluded that, whenever a reduction of aircraft emissions
becomes desirable, a variety of practicable approaches exist to reducing
both the quantities of pollutants emitted and their impact upon the com-
munity.
Specific conclusions resulting from this study of aircraft
exhaust emissions are as follows:
1.
Pollutant Emission
a.
Aircraft exhaust emissions of primary concern include
three pollutants emitted as gases or vapors--CO, organics,
and nitrogen oxides--and particulate matter consisting
mainly of lead compounds or carbon.
Sulfur dioxide is
emitted by aircraft but is of secondary concern because
total quantities emitted are small.
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14
b.
Both piston and turbine aircraft engines contribute
to significant emission loads of carbon monoxide and
organics at air terminals.
Turbine engine emissions
are most serious during idle and taxi conditions,
whereas piston engine emissions of CO and organics are
high during all operating modes except cruise.
It is
possible that afterburning of piston engine exhausts
may occur during some operating modes, thereby reducing
the effective rates of emission.
However, the extent
to which afterburning occurs is unknown at present.
c.
Emission of oxides of nitrogen by aircraft piston
engines is less than that from automobile engines of
comparable size or fuel consumption due to differences
in operating conditions.
NO emissions by turbine
x
engines are greater than those from aircraft piston
engines, but the aggregate emission load in any urban
area is very small compared to that from other sources.
Increased NO emission is expected from engines currently
x
under development, but the extent of this increase is
not known.
d.
Particulate emission from aircraft piston engines has
not been investigated, but probably consists mainly
of lead compounds.
The lead content of aviation gasol ine
is sl ightly greater than that of automotive gasoline, but
the physical state of lead emissjons from the two sources
may be substantially different.
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2.
15
Particulate emission from turbine engines consists
mainly of carbon.
Quantities of carbon emitted by
turbine-engine aircraft are small compared to those
from oi I-fired combustion systems, both in terms of
pounds-per-pound of fuel and total quantities emitted.
e.
Emissions by aircraft in urban areas, if uncontrolled,
can be expected to increase with time due to increases
in air traffic activity and design changes in aircraft
engines.
Aircraft activity, in terms of fuel consumption
or air terminal operations is expected to increase by
nearly 200 per cent during the next ten years, and pol-
lutant emission can be expected to increase proportionately.
Engine changes which will affect emissions include the
increased use of turbochargers on aircraft piston engines,
higher compression ratios and combustion chamber modi fica-
tions in turbine engines, and replacement of piston
engines with turbine engines.
Pollutant Impact
a.
The density of aircraft emissions at air terminals and
the resulting concentrations of pollutants are comparable
in -magnitude to emission densities and pollutant con-
centrations in neighboring communities.
On this basis,
the impact of aircraft emissions on persons in the
vicinity of an air terminal is considered to be com-
parable to the impact on persons in urban areas of
emission from other sources.
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16
b.
Emissions of all pollutants by aircraft are expected
to increase with increases in activity and changes in
equ i pment.
The impact of these pollutants in the
vicinities of major air terminals also will increase.
Whe reas the
impact of aircraft emissions may be re-
garded as marginal at the present time, it is expected
to become more serious in the near future unless emis-
sion controls are adopted.
c.
From the standpoint of community pollution, aircraf~
contribute a small fraction of all pollutants emitted
in an urban area.
This fraction will become more
significant as aircraft activity increases and emis-
sions from other sources are reduced.
However, the
principal impact of aircraft emissions will continue
to be I imited to the air terminal vicinity.
d.
Pollutant emissions during aircraft fl ight operations
have I ittle impact on the community becaus~ the total
quantities emitted and the resulting emission densities
are small.
However, visible trails of particulate
matter left by turbine-engine aircraft do have an
esthetic impact.
e.
Odors resulting from aircraft operations also produce
an adverse sensory effect in the vicinities of air
terminals.
However, practical approaches to the re-
duction of odors do not exist.
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3.
17
Emission Reduction
a.
Reduction of particulate emission by aircraft turbine
engines can be accompl ished through modifications of
engine combustion chambers.
Modification techniques
have been developed sufficiently to el iminate visible
smoke trails.
b.
Reduction of CO and organic emission by aircraft piston
engines can be accomplished by replacing these engines
with turbine engines, or by incorporating emission
control features.
Emission control systems most
applicable to aircraft piston engines are exhaust
treatment systems which have been developed for use
with automobile engines.
c.
Reduction of CO and organic emission by aircraft turbine
engines can be accomplished through modification of
combustion chambers.
However, emission reduction
methods are not well developed.
d.
No practical methods have been developed for reducing
NO emission by aircraft piston or turbine engines.
x
e.
Reduction of CO and organic emission at air terminals
can be accomplished by curtail ing ground operations of
transport aircraft.
The most effective technique would
involve the use of auxil iary vehicles to tow aircraft
or transport passengers.
f.
Fuel modifications do not offer practical approaches
to emission reduction except for reduction of lead com-
pounds by piston engines.
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18
4.
g.
If all approaches to emission reduction which are presently
feasible and practical were put into effect, substantial
reductions would result in emissions of CO, organics,
and particulates by aircraft.
Emission of NO , on the
x .
other hand, would
increase.
Emission Control
a.
Effective control of emissions of CO, organics, and
particulates by aircraft engines could be accompl ished
by the establ ishment of emission standards based upon
current technology.
Measurement techniques are suf-
ficiently well-developed at this time to support ~he
development of standards.
b.
Alternate approaches to the control of CO, organic, and
particulate emission by ~ircr~ft inv61ve the use of
taxation and government procurement practices.
However,
the effectiveness of these approaches is less certain
than the use of emission standards.
c.
Control of aircraft emissions at air terminals can be
accompl ished by local authorities by treating air
terminals as stationary sources.
By this approach,
controls on total emissions at air terminals can be
established in accordance with local abatement require-
ments.
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19
RECOMMENDATIONS
The aviation industry is one of the most dynamic areas of
commercial activity in this country and in other industrialized nations.
The industry is characterized by frequent changes in equipment and services
offered, and
rapid growth in all categories of flight activity.
It also
can be characterized as involving relatively large financial investments
when decisions are made to proceed with the development of new equipment.
Because of these factors, the aircraft industry is particularly sensitive
to changes in standards and regulations which affect its operations and
utilization of equipment.
At the present time, there are under development several new
types of aircraft and many engines which will power these aircraft.
In
some cases, these aircraft and engines depart considerably in size and
performance from equipment in current use.
Needless to say, the financial
investment in this new equipment is large.
Government control of aviation activity must be considered for
several purposes, including safety, noise abatement, and air pollution.
At the present time, pollutant emission by aircraft is of less concern
than other problem areas.
However, it is inevitable that control of
aircraft emissions will be instituted at some future time.
In order
that the imposition of emission controls have the minimum impact on
the industry, it is imperative that the Federal Government establish
a control philosophy for aircraft emissions as soon as practicable.
The early development of an emission control philosophy for aircraft is
the first and principal recommendation of this report.
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20
The second recommendation is that the NAPCA encourage and
support research and exploratory development in technological areas
relevant to aircraft pollutant emission.
Continued investigation of
the nature) impact) and control of aircraft emissions is warranted in
order to provide a sound basis for the establ ishment of an emission
control program.
Specifically) it is recommended that the NAPCA undertake
the following program of activity with regard to aircraft emissions:
1.
Initiate a program of action to insure that aircraft
emissions do not become a serious problem, to include
the following elements:
a.
Official recognition of specific aircraft emissions--
carbon monoxide, organics) oxides of nitrogen,
lead compounds) and other particulates--as potential
pollutant problem areas.
b.
Provision of technical guidance and engineering
criteria for use by the FAA and/or other regulatory
groups at air terminals.
c.
Continued study of approaches to the control of
aircraft exhaust emissions) including their effectiye-
ness and impact on the aviation industry.
d.
Monitoring of civil aviation activities, including
equipment development, so that significant changes
in aircraft emissions can be anticipated.
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21
e.
Extension of surveillance by the NAPCA of Federal
activities to include aircraft operations.
2.
!nitiate a program of study of aircraft emissions and their
impact to provide the technological basis for future
monitoring and control activities.
The program should
include the following elements:
a.
A study of pollutant emission by aircraft piston
engines for the purpose of establishing the actual
rates of pollutant emission and the effects of natural
afterburning on emissions.
This study also should'
include an evaluation of the effectiveness of exhaust
gas treatment systems as applied to aircraft piston
engines.
b.
A study of pollutant emission by aircraft turbine
engines with particular emphasis on future engine types.
The objective of this study would be to determine
relationships between engine emission rates and design
variables, and to predict the effect of future engine
developments on aircraft emission loads.
c.
A study of sampling and analysis techniques for
characterizing organic emissions from aircraft turbine
engines.
The objective of this study would be to
develop techniques appl icable to exhaust gases con-
taining organic compounds of high molecular weight and
low volatility.
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22
d.
A study of pollutant emission by aircraft during ground
operations at major air terminals.
The objective of
this study would be to determine quantit)es of pol-
lutants emitted by all sources during ground operations
and to determine the impact of these emissions on person~
within and near air terminals.
This study ,also sho~ld
include an evaluation of techniques for reducing ~ir-
craft emissions through modifications of ground
operations.
3.
Continue studies of pollutant emission problems which are
not unique to aircraft engines.
Such problems include:
a.
Emission of lead compounds
b.
Emission of odors
c.
Dispersion of emissions from mobile sources s~ch a~
aircraft
The need for study of these problems has arisen as a
result of pollutant emission from automotive vehicles
as well as aircraft.
Solutions to these problems, when
they are developed, will be appl icabl~ to both types of
sources.
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23
INTRODUCTION
This report is the result of a study of the emission of air
pollutants by aircraft engines in the United States.
The study included
four aspects of aircraft engine emissions:
1 .
Nature of aircraft engine emissions and quantities
emitted.
2.
Effects or impact of aircraft engine emissions on the
populace.
3.
4.
Reduction of aircraft engine emissions.
Governmental control of aircraft engine emissions.
Each of these aspects was investigated and is discussed in this report.
In addition, the subject of emission control requirements was considered
and a set of guidel ines was developed which can be used in determining
the degree of control needed.
However, specification of control needs,
and establishment of a time schedule for control measures were considered
to be beyond the scope of this study.
Backqround
Recognition of motor vehicle engines as major sources of air
pollutants evolved generally during the late 1940's and early 1950's and
led to widespread investigations of automobile emissions and means for
their control. ,In the late 1950's, automobile engine manufacturers began
to incorporate emi,ssion reduction features in their products, and, as is
well-known, effort to reduce automobile emissions has increased steadily
during this decade.
During the 1940ls and early 1950's, 1 ittle attention was given
to aircraft as sources of air pollution.
A general feel ing probably
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24
existed that aircraft represented a comparatively small source of pol-
lutants because of their small population, and that control of aircraft
emissions was not warranted.
This feeling changed abruptly, however,
in the late 1950ls with the introduction of turbojet aircraft into
air carrier,service.
These aircraft emitted highly visible exhaust
plumes during take-off and landing operations, with the densest plumes
resulting from the use of water injection during take-off.
Exhaust smoke
from turbojet engines, coupled with their characteristic fuel odor,
brought about a demand for reduction of emissions by jet aircraft.
As a result, at least two studies were initiated, one by the Los Angeles
County Air Pollution Control District (Ref 1), and another by the
CO,ord i nat i ng Research Counc iI, I nc. (Ref 2).
In the report of the
first study, issued in April, 1960, the authors concluded that "tptal
contaminant emissions from jet aircraft operations are at this time
insufficient to produce any generalized deterioration of air quality",
and that "visible smoke emissions from commercial jet aircraft...do npt
constitute violations of opacity standards".
The authors also reported
a lack of evidence of property damage from aircraft emissions.
The
report from the second study, also issued in 1960, concluded with the
statement that "the relative magnitudes of the emissions from aircraft
and from ground vehicles are such that we do not feel that further
study is warranted by (this) group".
Thus, aircraft emissions were
relegated 'to a status of secondary importance and were not subjected
to further investigation during the first half of this decade.
In 1965, the Los Angeles County Air Pollution Control Distric~
undertook a second study of aircraft emissions which resulted in a
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25
comprehensive report of pollutant emission by all types of civil
air-
craft in the district (Ref 3).
The current (1965) rates of pollutant
emission by commercial jet aircraft were found to agree well with pro-
jections for 1965 which had been made in 1960 (Ref 1).
However, total
emissions from aircraft were found to exceed substantial1y any estimates
which had been made previously.
This disparity was a result of the
inclusion of piston-engine aircraft in this study which, according to
the report, were responsible for organic and carbon monoxide emissions
far greater than those from turbine-engine aircraft.
The report con-
eluded with a comparison of aircraft emissions to those of other sources
indicating that aircraft contribute between 1 and 2 per cent of all
organic gases, carbon monoxide, and oxides of nitrogen, and approximately
10 per cent of all aerosols (particulates) emitted in Los Angeles County.
The 1965 LAC-APCD report was brought to the attention of the
United States Congress in February, 1967 by Mr. Louis J. Fuller, Los
Angeles County Air Pollution Control Officer, during hearings before
the Senate Publ ic Works Subcommittee on Air and Water Pollution.
The
subject of these hearings was "Problems and Progress Associated with
Control of Automobile Exhaust Emissions", and the LAC-APCD report was
included in the record of the hearings.
Subsequently, in preparing the
text of the Air Quality Act of 1967, the Subcommittee specifically
identified aircraft emissions as a subject of concern,and ordered an
investigation of this subject by the Department of Health, Education
and Welfare.
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26
Methodoloqy
As mentioned previously, the principal aspects of aircraft
exhaust emissions of concern in this study are (1) quantities Qf
po 11 utants em i tted, (2) impact of these poll utants, (3) reduct i on of
pollutant emission, and (4) governmental control of pollutQnt emission.
Each of these aspects was investigated in depth and is the subject of
a separate section of this report.
To provide a basis for these investigations, background
material was gathered which is relevant to aircraft engine emissions
and their control.
This information includes descriptive material on
aircraft and engines, and statistical data on aircraft population, pro~
duction, activity, and fuel consumption.
This information was required
for determining the nature and extent of aircraft emissions and for
evaluating emission reduction and control, and is summarized in the
following three sections of this report.
The information in these
sections is not necessary for an understanding of the results and con~
clusions contained in. later secti9ns.
However, this material has been
included to provide the reader with the background data upon which the
various investigations were based.
This material also provides an
introduction to certain aspects of the aviation industry which influence
air pollution, and thus, is useful for the reader who is not familiar
with this industry.
In the investigation of aircraft emissions and their impac~,
reduction, and control, effort has been directed primarily toward the
emissions resulting from aircraft operations at air terminals.
These
operations are of concern because the concentration of aircraft activity
-------
at air terminals results in local ized sources of pollutants within urban
areas.
These pollutants, in contrast to pollutants emitted during
cruising flight, are emitted within a relatively smal I volume and at
low altitude, and as a result, have a greater impact upon persons at
ground level.
Pollutants emitted by aircraft at high altitude do not
affect the populace directly, though there is some concern over possible
indirect effects of high altitude emissions.
27
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28
NATURE OF AIRCRAFT, ENGINES AND
FUEL SYSTEMS
It is the purpose of this chapter to introduce certain
features of aircraft and their engines and fuel systems which are
relevant to pollutant emission.
The features of primary concern are
those which affect the quantities of pollutants emitted by an indi-
vidual aircraft during its operations at air terminals.
Aircraft
Classification of Aircraft
For purposes of this investigation, civil aircraft in current
use have been classified according to their air pollutant emission poten-
tial.
The quantities of pollutants emitted by an aircraft during landing
and take-off operations are determined by the duration of these operations
and the rates of emission of pollutants.
The emission rates, in turn,
are dependent upon the type of engine (primari ly piston or turbine) and
its size or power rating.
Based on these factors, an aircraft classifi-
cation system has been formulated consisting of seven classes as de~cribed
in Table I.
All aircraft within a given class are assumed to emit equal
quantities of pollutants (per engine) during air terminal operations.
The representative engine for each aircraft class listed in the table Is,
in most cases, the engine in greatest use in U. S. aircraft of that class.
The classification system described in Table I is applicable
to most civil aircraft in use in the United States at the present time.
Certain military aircraft, such as fighter and attack aircraft, do not
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29
fit well into this system.
However, activity levels by mi litary aircraft
in urban areas are not sufficient to warrant a separate category.
Conse-
quently, this system was used for both civi I and military aircraft with
adjustments made where necessary to account for differences in pollutant
emission rates.
Classification of Aircraft Operations
As mentioned previously, aircraft activity of primary interest
to this study is that occurring at air terminals.
To faci litate an analy-
sis of pollutant emission resulting from terminal operations, an aircraft
operational cycle has been defined and termed 'Ilanding-take-off cycle" or
LTO-cycle.
An LTO-cycle includes all normal operational modes performed
by an aircraft between the time it descends through an altitude of 3000
feet above the runway on its approach path to the time it subsequently
reaches the 3000 foot altitude after take-off.
The term "operation'l has
been avoided because of its use by the FAA to describe either a landing
or a take-off.
Two operations are involved in one LTO-cycle.
An altitude
limit was selected in this study, as in previous studies (Refs I and 3),
which is a reasonable approximation to the meteorological mixing depth
over major U.. S.. metropolitan areas.
The implication is that emissions
released above 3000 feet do not reach ground level, and that all emissions
below 3000 feet have equal impact upon the populace.
Actually, the
impact of aircraft emissions decreases steadily with altitude, but the
3000 foot limitation'is a useful approximation for analysis purposes.
The aircraft LTO-cycle has been divided into six segments or
operat i ona I "modes'l, and these have been categor i zed as ground or f light
operations, as follows:
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30
Aircraft Operational Modes
Ground Operations
Taxi
Idle
Landing Run
Take-off Run
Flight Operations
Landing Approach (Descent from 3000 feet to touch-down)
Climb-Out (Ascent frbm lift-off to 3000 feet)
During each operational mode, engine operating conditions and pollutant
emission rates are assumed to remain constant.
The modes are grouped
according to ground and flight operations to allow for separate study of
emissions occuring at ground level and those occurring above ground leyel.
Performance characteristics of aircraft of the various classes during
these operational modes are listed in Table 2.
Characteristics of inter-
est are mode duration, aircraft velocity, and distance traveled.
Thl'!
methods used to evaluate these characteristics are described in the next
section.
Performance Characteristics of Aircraft
The purposes of this section are to describe the characteris~
tics of LTO-cycles for typical aircraft in each of the classes defined
previously, and to present the functional dependence of LTO-cycle
characteristics upon aircraft characteristics.
Typical LTO-cycles ary
used later in this report to compute pollutant emission loads at air
terminals.
The relationships between the characteristics of aircraft
and the duration of LTO-cycles are used to evaluate means of reducing
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31
emissions by changing aircraft design parameters and operating conditions.
It is useful to isolate those characteristics of aircraft that
significantly influence the emission of pollutants and their impact at
ground level.
Rates of pollutant emission by an aircraft engine are only
indirectly affected by the aircraft itself.
Aircraft performance charac-
teristics affect the duration of the LTO-cycle and the position and
velocity of the emission sources (engines) as a function of time.
The
time spent in the LTO-cycle wi 11 influence the total quantity of pollutants
emitted, the position of the emission sources will influence the impact
of the pollutants emitted, and the velocity of the emission source will
influence the quantities of pollutants emitted per unit distance along
the flight path.
The times spent by an aircraft in taxi and idle modes are
independent of the characteristics of the aircraft itself.
During other
operational modes, aerodynamic, gravitational, and inertial forces are
acting upon the aircraft and affect its velocity and acceleration.
During
the landing run, an aircraft will also experience decelerating forces
from wheel or air brakes and thrust reversal.
Only those aircraft char-
acteristics contributing to these forces are considered in this section.
Take-Off Run
During a take-off run, the net accelerating force acting upon
an aircraft is the difference between the thrust from the engines and the
sum of the aerodynamic and wheel drag forces.
The net accelerating force
is equal to the product of the aircraft mass and its acceleration.
The
aircraft will accelerate unti 1 a velocity is reached at which the aero-
dynamic lift is equal to the aircraft weight.
At this point the aircraft
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32
wi II I if t off.
The take-off distance S .may b~ expressed as
S = W2/k d T A CLLO
( I )
where W = aircraft weight
d = air density
T = take-off thrust
A
= effective wing area
= lift coefficient at take-off = LLO./ t d VL~ A
CLLO
LLO
V LO
= aerodynamic lift at take-off
= air speed at lift-off
k
is a constant defined by Domasch, et aI, (Ref 4) as
k = Q - ( FLO / FSO /In (FLO I FS)~0.4 + 0.6 (FLO I FS)
(2)
where FLO = accelerating force at lift-off
FS = static accelerating force
If it is assumed that the acceleration is constant, the time to lift-off
can be expressed as follows:
1
. tLO = 2S/VLO = (W/kT) (2W/CLLO d A)~
0)
Perkins and Hage (Ref 5) show that the distance to clear an obstacle 50 f~
high increases the distance given by Equation I by 10 per cent fo~ jets
and 25 per cent for propeller aircraft.
Similar expressions for tLO can be
rewritten for propeller aircraft, using equivalent shaft horse power Instead
of thrust.
It should be noted that tLO is shown to be a weak function of
wing loading and air density, but I inearly dependent upon WIT.
Typical
values for fully loaded aircraft are given below.
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33
Aircraft Class
Take-Off Time
(Minutes)
1.0
2
0.8
3
4
0.4
0.6
5
6
0.6
0.4
Assumptions used include zero wind, zero runway slope, and standard day
at sea level.
Effects of wind speed on the take-off period are small.
A
20 knot headwind will decrease tLO by about 5 per cent.
Landing Run
The equations of motion during an aircraft landing run are very
similar to those for the take-off run.
The major differences are that all
external forces acting on the aircraft tend to decelerate it, and the drag
components include the effects of braking and thrust reversal.
The times
spent in the landing mode are, in general, smaller than those in the take-
off mode, except for small business jets (class 3) and large piston air-
craft (c I ass 5).
Comparisons of landing and take-off times are shown in
the following table which was prepared from data from manufacturers speci-
fications and Reference 6.
Aircraft C I ass
Landing Time
(Minutes)
Landing Time/Take-Off Time
0.4
0.4
2
0.3
0.4
0.4
3
4
O. I
5
6
0.3
0.6
0.5
1.0
0.3
0.75
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34
The relatively long landing time for the Class 3 aircraft
may be attributed to an absence of thrust reversal.
The corresponding
explanation for the Class 5 is not as clear, but could be attributed to
a less efficient braking system or to less reverse thrust when the pro-
pellers are reversed.
C 1 i mb-Out
During the cl imb-out mode, aerodynamic lift is approximately
equal to the aircraft weight, and the net accelerating force (T-D) is
equal to the component of aircraft gravitational force which acts along
the flight path.
These two relationships enable the following expression,
to be derived for the rate of cl imb:
Rate of Climb = V c @w - II (LID)] (4)
where V = air speed
c
LID = lift-drag ratio
It may be readily seen that the rate of climb increases with increasing
thrust to weight ratio and lift-drag ratio.
In many instances, the climb-out mode is regulated by require.
ments of the FAA and local authorities.
Below 10,000 ft in altitude,
flight speeds may not exceed 250 knots.
Cl imb-out speed is usually constant
at approximately 200 knots for jet aircraft, and noise abatement reqyire-
ments may restrict engine thrust levels and aircraft speeds further when
operating at altitudes between 1000 ft and 1500 ft (Ref 7).
However, the
time spent in this low-noise mode is a small portion of the total cl imb-
out time to 3000 ft (approximately 1/6).
Typical rate-of-climb data are given for fully loaded aircraft
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35
in the following table.
These are average values over the first 3000 ft
of altitude based upon performance data from aircraft manufacturers, and
they do not include noise abatement constraints.
2
Rate of Climb (ft per min) Time to 3000 ft (m in)
1365 2.2
1580 1.9
6000 0.5
850 3.6
600 5.0
1200 2.5
Aircraft C I ass
3
4
5
6
Approach
In practice, the approach path slope is fixed for most aircraft
at 3 degrees.
The flaps and throttle are set to maintain sufficient velo-
city and lift to comply with this approach angle requirement.
Under these
circumstances, the approach velocity and approach time from 3000 ft are
given by:
V A = G l~ d A C L~l
(5)
and
tA = h/VA
sin a
(6)
where h
= altitude at start of approach (in this study, 3000 ft)
a
= approach path slope
and the subscript A
refers to approach conditions.
Typical values of
approach time, based upon manufacturers performance data, are as follows:
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36
Aircraft Class
Time (min) from 3000 ft
3.6
2
3.0
1.6
3
4
5
6
4.5
4.6
3.8
Equations 5 and 6 illustrate that the period spent on approach is a weak
function of wing loading ( W / A
) and approach lift coefficient ( CLA ).
He 1 i copters
Helicopters must be considered in a different manner from
conventional aircraft because of differences in operational procedures.
Helicopters operating in and around urban areas generally fly at altitudes
be low 3000 f to
Therefore, pollutant emissions from this class of aircraft
are of interest, within the context of this study, throughout its complete
flight profile.
A typical trip of 13 minutes duration has been chosen to
represent class 7 aircraft, and this period has been divided equally and
assigned to the climb-out and approach operational modes.
Helicopters are
assumed to spend no time in operations corresponding to the take-off and
landing runs of fixed-wing aircraft.
Idle and Taxi
Idle and taxi modes of operation are not directly dependent
upon aircraft characteristics.
The times spent in these modes depend in-
stead upon airport layout and traffic density.
For the purposes of this
study, the durations of taxi and idle modes are assumed to be the same for
all aircraft, excluding helicopters.
Times assigned to these modes are
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37
12 minutes taxiing (6 minutes for helicopters) and I minute at idle.
These
periods are based upon personal observations and correspond to moderate
traffic density conditions.
Summary
In this section, it has been shown that the durations of certain
operational modes depend upon thrust-to-weight ratio, wing loading, aero-
dynamic lift coefficient, decelerating power (braking and reverse thrust),
and lift-to-drag ratio.
The following relationships have been used to
evaluate operational mode durations and will be used later to evaluate
approaches to emission reduction:
( ) I 1 1
tLO time to lift-off ~(T/wf , (w/Af2, (CLLO)-2
tco (climb-out time) r...J(T/W - l/(L/D))-l
(h' ) -~ 1
tA approac time rv(W/A) 2, CLA2
tL
(landing time)
"-It LO
The take-off and landing pe~iods also vary with air density, windspeed,
and runway slope.
The approach period varies inversely with the approach
angle.
Operational mode characteristics determined by these relationships
are summarized in Table 2.
Aircraft Engines
it is the purpose of this section to present a brief description
of the two basic classes of aircraft engines~-p~~t6n and 't8rbi~e--and
the design variations within each class which are in current use.
Parti-
cular emphasis has been directed toward descriptions of combustion cham-
bers since processes occurring in this part of the engine have the greatest
influence on the exhaust composition.
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38
Piston Enqines
Classification
Aircraft piston engines are very simi lar to automobile engines
in their manner of operation.
The basic engine element is the combustion
chamber or "cy Ii nder" where in fue I
and air mixtures are burned and from
which energy is extracted through a piston and crank mechanism.
Nearly
all aircraft piston engines have two or more cylinders, and such engines
are generally classified according to their cylinder arrangements (Ref 8).
Throughout the history of piston engine development, several cylinder
arrangements have been used.
However, only two basic arrangements are in
general use, these being the opposed and radial configurations.
Opposed (a-type) engines have an even number of cylinders ar-
ranged in two opposing rows.
The cylinder rows may be arranged vertically,
such an engine being termed vertically opposed (va-type), or the rows may
be horizontal as in the more common horizontally-opposed (HO-type) engine.
Four and six-cylinder engines are most common, but two and eight-cylinder
engines are avai lable.
Engine power levels range approximately from 60
to 400 horsepower.
An important performance characteristic of an aircraft
piston engine is its power-to-weight ratio.
The value of this parameter
for a-type engines currently in production varies between 0.55 and 0.73
take-off horsepower per pound as compared to values of 0.4 or less for
most automobile engines. Opposed piston engines are produced in large
numbers and are installed in most light aircraft.
Radial (R-type) engines are constructed with cylinders arranged
in circular arrays or "banks".
Each bank contains an odd number of cylinders,
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39
usually 7 or 9, and the pistons in one bank of cylinders are joined to a
common connecting rod assembly.
Most radial engines consist of I or 2
cylinder-banks.
However, one four-bank, 28-cylinder engine - the Pratt &
Whitney R-4360 - is in service in certain military transport aircraft.
Power levels of radial engines range from 250 to 3800 horsepower, and their
power-to-weight ratios vary from 0.5 to 1.05 take-off horsepower per pound.
Radial piston eng!nes have been used extensively in transport aircraft,
but are being replaced rapidly by turbine engines.
Operating Characteristics
Processes occu~ring in an aircraft piston engine combustion
chamber are similar to those of an automobile engine.
The operating cycle
consists of 4 strokes - intakep compression, power, and exhaust - with a
complete cycle occurrIng dur~ng two revolutfons of the crankshaft.
A mix-
ture of fuel-vapor and air 1s drawn into the chamber during the intake
stroke and is compressed during the compression stroke.
The mixture is
ignited by a spark at the beginning of the power stroke and, as a result
of the pressure increase from combustion, power is transmitted through the
piston to the crankshaft.
During the exhaust stroke, the combustion pro-
ducts are expel led to the exhaust system.
Even though the aircraft piston engine is similar in operation
to the gasoline-fueled automobile engine, certain differences between the
two are worthy of ment!on as they may.result in differences in exhaust
gas composition.
1.
Air induction system.
Many medium and large piston engines
use a supercharger, or "blower", to increase the engine
operating pressure and thereby increase the power output.
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40
Super-chargers are driven mechanically by the engine or by
a turbine (turbocharger) driven by the engine exhaust gases.
With a turbocharger, the engine is operated highly fuel-rich
during certain modes in order to maintain the exhaust gas
temperatures below a level which would cause damage to the
turbine.
Fuel-rich operation occurs mainly during take-off
and climb-out when high engine power is required.
2.
Fuel meterinq system.
air-
As with automobiles, most small
craft engines uti lize a float-type carburetor which meters
fuel into the intake air upstream from the distribution mani-
fold.
However, most large engines and a significant number
of smaller engines use a fuel-injection system which meters
the fuel individually to each cylinder.
Fue I i nj ect ion pro-
vides greater uniformity in fuel-air ratio from cylinder to
cylinder.
3.
Iqnition system.
Nearly all aircraft engines have dual ig-
nition systems, including two spark plugs per cylinder.
The
dual system provides more reliable ignition and, thereby, a
lower rate of ignition failure.
The ignition failure rate
in automobile engines is high, particularly at high speeds.
4.
Exhaust system.
Aircraft engine exhaust systems differ from
those of automobile engines mainly in the exhaust stack
length.
The short stack length results in a higher exhaust
gas temperature which increases the possibi lity of after-
burning, that is, spontaneous combustion of fuel-rich exhaust
products with air after emission from the stack.
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41
5.
Coolinq system.
Nearly all aircraft piston engines are air-
cooled in contrast to automobile engines of which the major-
ity are water-cooled.
Air-cooling results in higher cylinder
wall temperatures which may affect combustion product compo-
sition.
However, to the knowledge of the authors, no rela-
tionship between these factors has been observed to date.
The crankshaft of a small, aircraft piston engine usually is con-
nected directly to the propeller shaft.
Medium and large piston engines,
on the other hand, generally transmit power to the propeller through a sys-
tem of gears such that the propeller speed is less than that of the engine.
The requirement for gearing stems from the desirability of maintaining
propeller tip-speeds at subsonic levels.
Turbine Enqines*
Classification
There are four basic types of gas turbine engines used for air-
craft propulsion:
turbojet, turboprop, turboshaft, and turbofan engines.
The basic element of all turbine engines is the gas turbine, consisting of
a compressor, a combustion chamber, and a turbine.
Air enters the forward
end of the engine, is compressed by the compressor, is heated by combustion
of fuel in the combustion chamber, and expends part of its energy in driv-
ing the turbine which, in turn, drives the compressor.
The remaining
energy in the air stream is used for aircraft propulsion.
* This section reproduced from Reference 9 with permission of the Hayden
Book Co.
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42
Turboj ets
When used as an aircraft power plant, a gas turbine is provided
with a tailpipe and jet nozzle, which makes it a turbojet.
Turboprops,
turbofans, and gas-turbine engines that turn a shaft for helicopter
use are more sophisticated versions of the basic gas turbine.
These
engine types will be discussed later.
For the moment, let us consider
only the uncomplicated turbojet.
Engine
Air Inlet
~
Engine Case
Combustion Chamber
or Combustor
Externally, a turbojet engine somewhat resembles a large,
Irregularly-shaped piece of stovepipe open at both ends.
Huge quantities
of air enter the engine at the front and exhaust, greatly heated and
accelerated, through a big hole at the rear.
The forward part of the
engine shell, or case, houses a compressor that squeezes and compresses
the incoming air before passing it on to a burner section, or combustion
chamber.
The fuel Is sprayed through nozzles into the front of the com-
bust ion chamber.
The resulting mixture of fuel and air is burned to pro-
duce hot, expanding gases that rush to the rear of the engine where they
are exhausted to the outside through a short duct called the engine tail-
pipe.
The opening at the rear of this pipe, or exhaust duct, Is called a
jet nozzle.
I
,
I
I
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43
Before the gases enter the engine tai1pipe, they pass through
a turbine mounted direct1y behind the combustion chamber.
Their high
ve10city causes the turbine to rotate.
The power the turbine extracts
from the gases is used to drive the compressor.
The turbine and the
compressor are both mounted on the same shaft and rotate as a slng1e unit,
so it might be said that a slng1e-compressor turbojet engine has on1y
one major moving part.
Turbojets are c1asslfled according to the kind of compressor
they use.
For years, they had on1y centrlfuga1 compressors because this
was the type that designers knew best how to bul1d.
Centrifuga1 compres-
sors operate by taking in air near a hub at the center and rotating It
with an Impe11er.
As the Impe11er whir1s the air at high speed, centrlfuga1 force
carries the air to the perimeter of the impe11er at a considerab1e ve10-
city.
Here the air Is c011ected In a diffuser to Increase the pressure,
then 1ed to a manifold which, In turns, feeds It to the engine's burners.
The ear1y centrifugal compressor turbojets were (and stilI are)
both reliable and simp1e.
But the amount of thrust they can produce Is
relatively low because their compression ratio Is not very high.
Neverthe-
1ess, there are severa1 turboprop and turboshaft engines now in current
production that employ a compressor arrangement using one or more
centrlfuga1-type compressors.
The improved design of these engines makes
them far superior to the centrifugal-compressor power plants of several
years ago.
The majority of today's turbojets use an axla1 compressor 11ke
those which are 111ustrated.
Axla1 compressors are used, especla11y In
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44
the larger engines, because they are capable of producing high compression
ratios, sometimes as high as 13:1, or more.
An axial compressor, as the
name implies, compresses air as it flows in an axial direction, through
an engine.
A series of rotating blades and stationary vanes work on the
air as it passes through a series of stages Inside the compressor.
Each
stage adds to the compression process.
There are two types of axial-compressor engines, those with so-
called single compressors and those with dual compressors.
In dual-
compressor engines (sometimes called twin-spool engines), there are two
compressors that are mechanically independent of one another, although they
are related as to airflow.
Each compressor has its own turbine.
The tur-
bine for the forward, or low-pressure compressor, is the rear turbine.
It
is connected to the low-pressure compressor by a drive shaft that passes
through the hollow drive shaft for the high-pressure -compressor and turbine
unit.
Low-Pressure Compressor & Turbine
High-Pressure
Compressor & Turbine
DUII-Axll' Compressor TurboJlt
Turboprops
If a gas turbine turns an aircraft propeller through a system
of gears, it becomes a turboprop.
The British and many commercial airlines
1-
-------
,~-
45
call such an engine a propjet.
The propeller-drive reduction gearing may
be driven by the shaft from the same turbine that rotates the compressor,
or the gearing may be driven by a shaft from a so-called free turbine that
rotates independently in the exhaust gas stream of the basic gas turbine.
In either case, the gas turbine for a turboprop might be either a single
or a dual-compressor type, although, as this is written, there are no dual-
axial compressor turboprops in production.
There are, however, a number
of turboprops whose compressors have novel arrangements.
One of these is
the Rolls Royce Dart, which employs two centrifugal compressors in tandem.
pther successful turboprops have axial compressors with a centrifuga1
compressor Immediately following.
These engines are also produced in
turboshaft configurations.
Slnl(le-AxIII Compressor,
Direct-Drive Turboprop
Slnl(le-Axfll Compressor,
Fre. Turblne-DrIvt Turboprop
Although a turboprop is more complicated and heavier than a
turbojet engine of equivalent size and power, it will deliver more thrust
up to medium-high subsonic airspeeds.
However, the advantage decreases
as flight speed increases.
In normal cruising-speed ranges, the propulsive
efficiency (output divided by input) of a turboprop remains more or less
-------
~-~........--
46
constant, whereas the propulsive efficiency of a turbojet increases
rapidly as airspeed increases.
The spectacular performance of a turbo-
prop during take-off and climb is the result of the ability of the propeller
to accelerate a large mass of air whi Ie the aircraft is moving at relatively
low ground and flight speed.
----------------
Fan.
Discharge
Compressor P
Inlet ~
Main
Engine
Exhaust
Fan
Discharge
----------------
SlnKfe-Compnlssor. Aft-Fan EnJlne
Turbofans
Fanjets, as they are called by some of the commercial airlines,
and turbofans are one and the same thing.
In principle, the turbofan (or
"fanjet) is the same as the turboprop except that the ratio of the secondary
airflow (i.e., the airflow through the fan or propeller) to the primary air-
flow through the basic engine is less.
Also, in the turbofan, the gear-
driven propeller is replaced by a duct-enclosed, axial-flow fan whose rotat-
ing blades and stationary vanes are considerably larger but otherwise
simi lar to the blades and vanes of an axial compressor.
There are two principal configurations for a turbofan, each of
which has several variations.
In one configuration, the fan Is placed at
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47
the front of the engine where it is an integral part of the compressor.
When the engine is a dual-compressor type. it is a part of the forward.
low-pressure compressor.
In the other co~figuration, the fan is mounted
at the rear of the ergine where it forms the rim. or outer perimeter. of
a free turbine that rotates by itself in the exhaust gases discharged from
the engine.
These two turbofan designs are called forward fan and aft fan
engines. respectively.
In both turbofan configurations, the fan makes a substantial
contribution to the total thrust.
Over and above the thrust produced by
the basic engine. the fan acceierates the air passing through it to generate
thrust of its own in the manner of the propeller of a turboprop.
The fan
air is exhausted without passing through the engine; it is not burned with
fuel or used for internal engine cooling.
Two different duct designs are used with forward-fan engines.
Either the air exhaused by the fan may be ducted overboard directly after
it leaves the fan, or it may be ducted along the outer case of the basic
engine to mix, or not mix (depending upon the design). with the turbine
exhaust gases before the gases pass through the jet nozzle.
. Forward Turbofan With
Mixed Exhaust
~
Nonmlxed Exhaust
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48
One fundamental difference between a turbofan and a turboprop
is that the airflow through the fan is controlled by the design of the
engine in such a manner that the air velocity through the fan blades is
not affected very much by the speed of the aircraft.
This means that the
loss of operational efficiency at high air speeds that limits the airspeed
capability of turboprop aircraft is eliminated in turbofan aircraft.
In-
deed, supersonic aircraft not only can, but are being powered by turbofans.
The military F-III, an all-purpose, fighter-type airplane that attains
speeds in excess of Mach 2.0, is a typical example.
Turbofans are rapidly becoming the most widely used of all the
types of jet engines, particularly in large multi-engine aircraft.
The
turbofan is, in effect, a compromise between the good operating efficiency
and high-thrust capability of a turboprop and the high speed, high-altitude
capability of a turbojet.
At cruising altitude, the engine-propeller
combination of a turboprop loses efficiency rapidly at airspeeds above
400 knots.
Not only does the turbofan have no such limitation but it is
much simpler than a turboprop.
The complexity and weight of the propeller
reduction gearing and the intricate propeller-governing feature of a
turboprop are completely eliminated in a turbofan.
The turbofan is there-
yore not only lighter than a turboprop but can never be plagued by any of
the malfunctions to which a propeller and its associated systems are
susceptible.
-The fact that the fan air does not pass through the basic engine
enables a turbofan to achieve a relatively low specific fuel consumption.
In addition, because it accelerates a large mass of air to relatively low
velocity, even at very low aircraft speeds, a turbofan, like a turboprop,
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49
produces much more thrust than a turbojet during take-off and the initial
climb.
Another advantage of the turbofan is a lower noise level, which
is an important feature at al I commercial airports.
The lower Jevel of
noise occurs because a turbofan engine has at least one additional turbine
stage to drive the fan.
Extraction of more power from the engine exhaust
gases as they pass through the additional turbine (or turbines) serves to
reduce the velocity of the engine exhaust.
nozzle results in less noise.
Less velocity through the jet
Note:
In the curves shown, all performance data has been reduced
to a common denominator, thrust in pounds. 'The engines used to make this
comparison are actual engines that use the same basic gas turbine, and
the curves have been plotted from actual performance data.
G
"-
en
!=.
z
a
~
"-
..:
::I
'"
Z
;r
<..>
ii:
U
...
"-
en
....
'"
:;)
0::
~
o
200 400 600
mUE AIRSPEED - KNOTS
SEA LEVEL
Comparison 01 TUrbo/.t,
Turboprop,and Turbolan
Performance
Take-off Thrust
(Turboprop)
800
'"
m
-'
I
o
200 400 600
mUE AIRSPEED - KNOTS
SEA LEVEL
-------
I
50
Afterburning Turbojets and Turbofans
Frequently, an engine is provided with an afterburner for
increased thrust.
The British say that afterburning is "reheating" and
they call an afterburner a "reheater."
The increased thrust that comes
with afterburning can be accomplished regardless of the type of compressor
and regardless of whether the engine is a turbojet or a turbofan.
Only about 25 per cent of the air entering an engine at the
compressor inlet is used to support combustion; the rest is used for
internal cooling in the main part of the engine, before it passes out the
tailpipe.
Essentially, an afterburner is an enormous piece of stovepipe
attached at the rear of the engine in lieu of a tailpipe and jet nozzle.
Fuel is injected through fuel nozzles and ignited in the forward section
of the afterburner.
Combustion is possible because 75 per cent of the
air entering the afterburner, no longer needed for cooling, Is still un-
used for combustion.
As the excess air and the added fuel burn together in the
Turbine Exhaust
Case
Afterburner
Combustion
hamber
Afterburner
Diffuser Case
Exhaust
Nozzle
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51
afterburner, the exhaust gases are again expanded and acce1erated which,
in turn, means more thrust.
The afterburner is provided with f1ame h01ders
to prevent the flame from being blown out of the exhaust and with a two-
position, variable-area exhaust nozz1e that is fu11y c10sed when the after-
burner is not in use.
The nozz1e opens automatically when the afterburner
is turned on.
An afterburner is capable of increasing the tota1 engine thrust
by 50 percent, or more.
Although the total fuel consumption more than
doubles, the net result is profitable for bursts of aircraft speed such as
a much faster climb or an acceleration to supersonic flight.
By c limb i ng
rapid1y with the afterburner on, a jet-powered airplane wi11 use less fue1
in reaching a given altitude than it will by climbing more slowly without
the afterburner.
But the weight and noise of an afterburner which, on
long flights, might be used only occasionally, precludes the device being
employed in present-day, transport-type airplanes and commercial aircraft.
Afterbur.ners are presently used only on military fighters and supersonic
bombers.
Miscellaneous Jet Engine Types
Turboshaft Enqines:
Turboshaft engines are c10sety related to
turboprops.
If a gas turbine engine delivers power through a shaft that
operates something other than an aircraft propeller, the power plant is
called a turboshaft engine.
Like the propeller drive shaft of a turboprop,
the shaft may be coupled to the engine's turbine directly, through a system
of reduction gears, or the shaft may be driven (also through reduction
gears) by a free turbine of its own in the exhaust-gas stream.
Engines of
this type are used in helicopters.
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I
I
I
52
Bypass Enqines:
In Great Britain, forward-fan turbofans of the
mixed and non-mixed exhaust types are called bypass engines, the Rolls
Royce Conway being a typical example.
In this country, a bypass engine
is general1y considered to be an engine in which the secondary airstream
is subject to ram pressure only.
In effect, this means a ramjet engine
built around the outer case of a turbojet.
This is a confIguration not
In current use.
Afterburner.Type
Fuel Spray Nonles
Byplss Enllne
IAmerlcln version)
Tulbe'ln WItI1 Duct Hemr
Enqines with Duct Heaters:
If an afterburner-type fuel nozzle
and flameholder arrangement were to be placed in the open duct of a turbo-
fan engine with a non-mixed exhaust, the device would be called a duct
heater and it would operate like an afterburner.
The air in the duct would
be burned with fuel to Increase the momentum of the air and gases passing
through, thus producing more thrust.
Engines with duct heaters are not in
production now, but the desIgn has been Investigated and may be used
someday.
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53
Combustion Chamber Operation
The burner section of a turbine engine, which contains the
combustion chamber, is designed to burn a mixture of fuel and air, and to
deliver the resulting gases to the turbine inlet at a temperature that will
not exceed the maximum permissible.
The burner section, within a very
limited space, must sufficiently heat and expand the gases passing through
the engine to produce the desired thrust for the engine and power for the
turbine.
In a jet engine, the fuel nozzles, the air and fuel mixing vanes,
and the combustion chamber are so skillfully designed that the heat re-
leased per cubic foot of combustion ~pace is about one thousand times as
great as the heat released in an equivalent burner space in an ordinary
home-heating furnace.
The burner has a big job to do.
With only a minimum drop in
pressure, it must provide the correct amount of air at the proper point
in combustion chamber to support combustion under all operating conditions;
it must provide the combustion air with the proper flow patterns to assist
the burning process; and it must provide unb~rned air at the proper places
and in the proper quantity to establish a cooling layer of air on the
inside of the combustion-chamber liner.
The burner must also supply air
to mix with the burned gases and thereby reduce the temperature at the
turbine inlet.
Fortunately, a burner which can satisfy all of these condl-
tions will also have satisfactory engine starting characteristics.
Combustion chambers may be either of the can, the annular, or
the so-called can-annular type.
For all of these, the design is such that
only about 25 per cent of the total volume of air entering the chamber is
permitted to mix and burn with the fuel.
The remaining 75 per cent bypasses
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54
75% 01 Air
1
-
Air Irom
Compressor
the fuel nozzles and is used to cool the combustion-chamber liner and to
mix with and cool the burner gases before they enter the turhine.
Multiple Can-Type Combustion Chamber:
An arrangement of can-
type combustion chambers is usually found on the older type centrifugal-
compressor turbojets.
In a burner section of this kind, the air from the
compressor is divided as it leaves the diffuser and ducted to the indivi-
dual combustion cans, or chambers, which are arranged around the circum-
ference of the burner section of the engine.
Each can contains its own
fuel nozzle and combustion-chamber liner.
Primary air (air for burning)
is introduced at the nozzles where it serves to support the initial phase
of the burning process.
Cooling, or secondary, air passes between the
liner and the combustion-chamber case.
The liner is provided with several
series of holes or axial slots through which some of the secondary air
enters the burning chamber to help support the combustion process.
The
holes or slots also furnish a layer of cooling air which flows down the
inside of the liner to cool the inside surface.
After combustion is
completed, the burned gases and the surplus heated air that was used
for cooling merge, Just upstream from the entrance to the turbine.
This
reduces the temperature of the burned gases to a level that the turbine
can tolerate.
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55
Turbine
-
Exhaust
Compressor
Discharge
Individual
Combustion
Chamber
Complete
Assembly
Multiple Cln-Type Combustion Chlmber
Annutar Combustion Chamber:
Some axiat-compressor engines, the
smatter modets in particutar, have an annutar combustion chamber.
The
liner of this type of chamber consists of continuous, circular, inner and
outer shrouds around the outside of the compressor-drive housing.
The
liner is sometimes referred to as a burner basket because it is perforated
with holes which give it a basket appearance.
The hotes or slots in the
shrouds attow secondary cooting air to enter the combustion area, thereby
keeping the flame away from the shrouds.
Fuel is introduced through a
series of nozztes at the upstream end of the tiner.
Annutar combustion chambers are able to use the timited space
available within the burner section to better advantage than any other
kind of chamber.
An optimum ratio of the inner surface area of the liner
,to the volume of the chamber Is provided, ensuring maximum coo11ng of
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56
~=--
t' ---
~~
~~
Turbine
Compre$SOl'o
UrfY8HousInl
TJpIClI Annul., Combvltlon Chlmblr
the gases and the liner surfaces as combustion takes place.
The design
is strong enough to prevent the heat within the chamber from warping the
liner, a problem in other types of chambers.
But this is offset by the
fact that the liner cannot be replaced or repaired without removing and
disassembling the engine.
'Can-Annular Combustion Chamber: A can-annular, combustion-
chamber design is used on many of the larger Jet engines.
Individual
burner cans are placed side by side in an annular chamber.
The cans are
essentially individual combustion cylinders with concentric rings of
perforated holes to admit air for cooling.
On some models, each can is
provided with a round, perforated tube which runs down the middle of the
can.
The tube carries additional air which enters the can through the
perforations to provide more air for burning and cooling.
The effect Is
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r-
Fuel Nozzles
Individual Combustion Can
Airflow Schematic
57
tomplete
Assembly
Can-Annular Combustion Chamber
to permit more burning per Inch of can length than could be accomplished
otherwise.
Several fuel nozzles are placed around the perimeter of the
forward end of the can.
The burner cans are relatively small in diameter,
which gives them an Inherent resistance to the buckling caused by heat.
Each can has two holes which are opposite each other near the forward end
of the can.
One hole has a collar called a flame tube.
When the cans
are assembled In the annular chamber, these holes and their collars form
open tubes from can to can so a flame In one will pass to the others dur-
Ing engine starting.
The can-annular combustion chamber combines the advantages of
both the can and the annular combustion-chamber designs.
I t a Iso ell m I -
nates many of their disadvantages.
A removable or telescoping shroud
i
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i
58
covers the entire burner assembly.
This permits easy access to the
individual cans, which may be removed for inspection and replaced with-
out removing the engine.
Fuel Systems
Aircraft fuel systems are of interest to this study primarily
because they control the rate of flow of fuel to the aircraft engine and
the physical state of the fuel as it enters the combustion chamber.
These
factors, in turn, affect the rate of production of pollutant species in
the engine.
The fuel system also is of interest as a source of pollu-
tants - primarily unburned fuel.
However, sources other than engine
exhausts have not been included in this study.
The main function of a fuel system is to transport fuel in
sufficient quantity and with sufficient quality and pressure to satisfy
engine requirements under all operating conditions.
A secondary function
that will become of increasing importance in supersonic aircraft is the
use of fuel as a coolant for other aircraft systems.
The complexity of a
fuel system depends, therefore, upon both the aircraft performance and
the type of engine installed.
The principal components of fuel systems for piston-engine and
turbine-engine aircraft are shown in Figures I and 2.
These systems have
certain common components:
fuel tank, fuel strainer, fuel pump (except
for gravity-fed systems), and a fuel control unit.
The function of each
of these components is the same in each fuel system.
The fuel control unit is of interest from the standpoint of air
pollutant emission.
This unit controls the fuel flow rate and the fuel-
air ratio to the engine.
In a turbine-engine fuel system, the fuel
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59
control unit is a complex, mechanical, computer-type device.
It is
programmed to supply the correct fuel rate in response to engine operat-
ing conditions and throttle setting.
The fuel control unit for a piston
engine is less complex and consists of either a carburetor or a fuel-
injection control device simi lar to units used in automotive fuel systems.
These devices also respond to engine operating conditions and throttle
setting.
There is, however, an additional manual adjustment incorporated
in piston-engine fuel systems known as the mixture control.
The mixture
control allows the fuel rate and fuel-air ratio to be changed manually
by the pilot.
In practice, this control is set at IIfull rich" during air
terminal operations to provide maximum engine power and to prevent over-
heating. . During cruising fl ight, the mixture control usually is adjusted
to provide leaner, more economical, fuel-air mixtures.
Because of this
practice, aircraft piston engines operate at comparatively rich fuel-air
ratios during all air terminal operations, and, as a result, their ex-
haust gases contain higher concentrations of carbon monoxide and unburned
fuel than automobile exhausts.
This fact is significant from the stand-
point of air pollution.
The fact that the engine fuel-air ratio is
manually controlled by the pilot also is significant.
The pi lot of a
turbine-engine aircraft has no corresponding control which affects the
rate of pollutant emission from his engines.
The significance of the
manual mixture control in piston engines and their rich fuel-air mixtures
will be discussed in later sections dealing with pollutant emission and
emission reduction.
The methods used to inject fuel into engine combustion chambers
are different in piston and turbine engines.
In piston engines, fuel is
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60
injected into the air intake manifold where it is vaporized before entering
the cyl inders.
The fuel-air mixture is nearly homogeneous prior to igni-
tion.
The injection system, therefore, has little direct effect on the
combustion process or the nature of the exhaust products, except that non-
uniform injection can cause variations in fuel-air ratio and pollutant
emission rate among cylinders.
In turbine engines it is currently the practice to spray the
fuel in atomized form into the combustor and to allow vaporization and
combustion to proceed simultaneously.
This practice creates many practical
difficulties and the design of spray nozzles has changed many times over
the years.
The characteristics of the fuel spray affect combustor effi-
ciency, ease of ignition, combustor wall heating, and various other prob-
lems associated with engine performance.
In addition, the nature of the
fuel spray affects the formation of pollutant species within the combustor -
particularly smoke.
It is difficult to develop a fuel nozzle with spray characteris-
tics which are satisfactory over the wide range of fuel flow rates en-
countered in a turbine engine.
Most engines use a dual-orifice, pressure
nozzle similar to that shown in Figure 3 which operates from two indepen-
dent fuel manifolds.
Much attention is currently focussed upon the 'method
of fuel injection, however, and attempts are being made to uti lize inject-
ors which provide some fuel vaporization before combustion.
An example
of such an injector is the airspray fuel atomizer also shown in Figure 3.
It is believed that a significant reduction in smoke emission can be
achieved through the use of such injectors, and they are being incorporated
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61
in engines currently in development (Refs 12 and 13).
Summary
In this section, certain aircraft systems have been described
which affect the emission of air pollutants in engine exhaust gases during
aircraft operations at air terminals.
These systems are the aircraft
structure or airframe, its engines, and its fuel system.
These systems
affect both the duration of landing and take-off operations and the rates
of pollutant emission during these operations.
The mechanisms of pollu-
tant formation, rates of emission,and emission reduction methods will be
discussed in later sections of this report.
There are other sources of air pollutants associated with aircraft
operations which have not been included in this investigation.
These
sources add to the total quantities of pollutants emitted during air termi-
nal operations and include:
( I )
(2)
(3)
(4)
(5)
Exhaust gases from aircraft auxi liary power units.
Exhaust gases from service vehicles.
Evaporative losses from aircraft fuel systems.
Evaporative losses from fuel storage and transfer equipment.
Organic emissions from various servicing materials includ-
ing paint, solvents, lubricants, and deicing agents.
Sources such as these should be included in future studies of pollutant
emission at air terminals.
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62
AIRCRAFT AND AIRCRAFT ENGINE POPULATION,
PRODUCTION, AND ACTIVITY
It is the purpose of this chapter to present certain statistical
data on aviation in the United States which are relevant to air pollution.
Data on aircraft population, production, and activity are important in
assessing the nature and quantities of aircraft exhaust emissions, and in
evaluating approaches to the reduction of exhaust emissions and their im-
pact.
Information contained in this chapter has been taken mainly from
publications of the United States Federal Aviation Administration, the
United States Civil Aeronautics Board, and the Aerospace Industries Associ-
ation of America, Inc.
Aircraft and Aircraft Enqine Population
Civil Aircraft Population
Civi I aircraft of interest to thi~ study are those which are
approved for use in regular service in the United States.
Such an air-
craft must be registered with the FAA and have a current FAA air-worthiness
certificate.
The latter is obtained through annual or continuing inspec-
tion.
A registered, certificated aircraft is designated by the FAA as
"eligible", whereas a registered, but uncertificated, aircraft is desig-
nated "inel igible".
The numbers of registered aircraft of various types are shown
in Table 3 for 1967.
The total number of eligible aircraft in 1967
(107,085) increased by 9344, or approximately 10 per cent, from the
previous year.
The total number of eligible turbine-powered aircraft,
however,
increased from 1624 to 2286 during 1966, representing an increase
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63
of approximately 40 per cent.
It is apparent that turbine-powered aircraft,
even though constituting only 2 per cent of the current population of civi 1
aircraft, will occupy a larger fraction of the total in ensuing years.
Future projections of civil aircraft population, as published by
the FAA, are listed in Table 4.
The projections indicate an average in-
crease of 8000 active aircraft per year.
This projected yearly increase
wi 1 1 be composed of 6000 single-engine, piston-powered aircraft, 1200 multi-
engine, piston-powered aircraft, and 800 turbine-powered aircraft - the
latter category including both fixed and rotary-wing (helicopter) aircraft.
The distribution of active civil aircraft by year of manufacture
is presented in Table 5 for aircraft manufactured during 1966 and earlier.
From this Table, it is observed that the median age of these aircraft is
approximately 8 years.
That is, approximately 50 per cent of the active
civil aircraft in the United States are over 8 years old.
The distribution of all registered civil aircraft by type of
registrant, as of March 31, 1968, was as follows:
Individual 93,008
Corporation 54,848
Coowner 9,801
Partnership 7,912
Government 2,790
This list was determined by the FAA from an analysis of aircraft registra-
tion data (Ref 15).
Civi 1 aircraft operations are generally classified into two
broad categories:
air carriers and general aviation.
The distributions
of aircraft types in these categories are described in the following sections.
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64
Air Carrier Aircraft.
Air carrier aircraft. are a category of civil.aircraft which are
used for the transportation of persons.or,property for hire.
These air:craft
are operated by certificated. route air carr)ers, supplemental air carriers,
and commercial operators.
Approximately 90 per cent of thea~~cra~t in.
this category are operated by the certificated r~ute air carriers, or
"scheduled airl ines!'.
Supplemental air carriers are .authorized to perform
passenger and cargo charter service and s~heduled operations on a limited
or temporary basis.
Commercial operators are authorized to transport
passengers or cargo on a private for-hire basis.
Air taxi operators are
not included in the air carrier category, but are included under General
Aviation.
The composition of the United. States Air Carrier fleet..i~.~es-
cribed in Table 6 as reported by the FAA for recent years and projected
for future years.
A more detai led de~cription of the air carrier fleet,
as of January, 1968, is presented in Table 7.
The total number of aircraft
in
the fleet (approximately 2500) is a small fraction of the total United
States aircraft popu I at ion .(2 per cent).
However" air carrier aircraft
are responsible for a highly disproportionate share of total aircraft
activity.
Since air pollutant emission is more directly related to acti-
vity than population, air carriers constitute a category of aircraft of
particular importance to this study..
The changing size and composition of the air carrier fleet is
shown in Figure 4.
The projected rate of growth of the fleet, 50 per cent
increase over the next 10 years, is ~omewhat less than the corresponding
projection for all civi 1 aircraft (70 per cent).
However, a more striking
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65
change is the rapid conversion of the fleet to turbine-powered aircraft.
Piston-powered aircraft constituted nearly 90 per cent of the total in
1960, but make up only 15 per cent today, and this percentage will continue
to diminish.
Within the turbine-powered category, aircraft fitted with
turbofan engines will be responsible for the over-all growth of the air
carrier fleet.
Turbojet and turboprop aircraft are expected to remain
essentially constant in number in the near future.
Aircraft built by foreign manufacturers are of interest from
the standpoint of emission control in that control methods cannot always
be applied to these as readily as with aircraft built in the United States.
Aircraft operated by air carriers which were built in foreign countries
are 1 isted by type in Table 8.
Foreign-made aircraft constitute approxi-
mately 7 per cent of the total fleet, and this fraction consists almost
entirely of turbine-powered, fixed-wing aircraft.
As stated above,
future growth of the air carrier fleet will consist largely of turbofan-
powered aircraft.
At the present time, foreign-made aircraft constitute
approximately 10 per cent of this category, and these aircraft were built
by two manufacturers, the British Aircraft Corporation (BAC 111) and
Avions Marcel Dassault (Fan Jet Falcon).
However, of 940 fanjets on
order by the air carriers on May 15, 1968 (Ref 21), only 7 will be pur-
chased from a foreign manufacturer (BAC).
Consequently, the foreign-
built segment of the air carrier fleet is expected to decrease, both
numerically and in percentage, during the next five years.
This trend
may change sl ightly with the introduction of the supersonic Concorde,
but the future of this aircraft is uncertain at present.
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66
General Aviation Aircraft
General aviation is, a broad category including all civil aircraft
except those of the air carriers.
This category in~ludes aircraft used
in the following types of flying, ~s defined by th~ FAA:
1.
Business
(a)
(b)
Executive transportation (professional pilot)
Business trpnsportation (owner-piloted)
2.
Personal
Instructional
3.
4.
Commer i ca I
(a)
(b)
Air taxi
Aerial application (agricultural spraying, etc.)
Industrial/special (photography, advertising, etc.) I
(c)
5.
Other
The "other" category includes aircraft Qperated by federal, state, and local
government agencies.
Numbers of various typeS of active general aviation aircraft are
listed in Table 9 for recent years, and as projected by FAA for future years.
A more detai led description of general aviation aircraft, as of January,
1967, is presented in Table 10.
Population growth rates are indicated in
Figure 5.
The growth rate of the GA aircraft population increased abrupt-
ly in 1965 and currently is about 8000 aircraft per year.
This rate is
expected to continue into the foreseeable future.
The air taxi fleet is an element of the general aviation fleet
which is growing rapidly and is responsibl~ for a significant fraction of
GA activity, particularly at air commerce airports.
As of October 1967,
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67
the fleet of the scheduled air taxi operators consisted of the following
aircraft (Ref 22):
Fixed-Wing
Single-engine piston
200
Multiengine piston
452
24
Turbine
Helicopter
9
685
Total Aircraft
Most air taxi operators are located around traffic hubs and serve as
feeders and extensions to the air carriers.
In contrast to the air carrier fleet, general aviation aircraft
are powered mainly by piston engines.
Turbine-powered GA aircraft consti-
tute about I per cent of the total population today, and this fraction is
expected to increase to 3 per cent in 1979.
Single-engine, piston-powered
aircraft, which are popular for personal, instructional, and small-business
flying, dominate the population figures.
The fraction of United States general aviation aircraft bui It
by foreign manufacturers is very small, probably less than 1 per cent of
the total number of active aircraft.
In certain categories, however, the
fraction is higher.
From 5 to 10 per cent of aircraft used for air taxi
service and turbine-powered, business aircraft are bui It by foreign manu-
facturers.
Mi litary Aircraft Population
The aircraft inventory of the United States Department of Defense,
as of December 31, 1967, consisted of 33,749 aircraft.
Their distribution
among the services is shown in Table II.
Information on the distribution
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68
of aircraft types is not avai lable.
However, engine production figures
indicate that the military inventory is powered mainly by turbine engines.
Aircraft Enqine Population
Aircraft engines of principal interest in this report are those
installed in aircraft active in the United States.
Other engines of lesser
interest are those instal led in inactive aircraft and engines held in
inventory for new or replacement installation.
The latter category does
not include a significant number of engines as most aircraft engines are
bui It on order for installation in aircraft under production.
Also,
engine replacement in civil aircraft is required only infrequently.
En-
gines are subject to regular overhaul and parts replacement, but most
engines retain their original identity and last the life of the aircraft
in which they are installed.
Turbine engines in use in the United States
air carrier fleet are listed in Table 12, and piston engines are listed in
Table 13.
Corresponding population data on general aviation aircraft
engines could be obtained by analysis of FAA aircraft registration data.
Aircraft and Aircraft Enqine Production
Aircraft Production
Numbers of aircraft produced in the United States during recent
years and projections for future years are listed in Table 14.
The frac-
tion of civil aircraft which are exported is between 15 and 20 per cent
currently.
The major manufacturers of civil aircraft in the United States
are listed in Table 15.
These figures include all domestic production of
transport aircraft, commercial helicopters, and nearly all general aviation
aircraft.
Not included are small manufacturers and individuals who account
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69
for a small fraction of the production of general aviation aircraft.
Foreign manufacturers of aircraft sold to United States parties are
1 isted in Table 16.
Aircraft Enqine Production
Numbers of aircraft engines produced in the United States
during recent years and projections for future years are listed in Table
17.
As in the case of aircraft, 15 to 20 per cent of United States-
produced, civi 1 aircraft engines are exported.
United States manufacturers of civil aircraft engines are
listed in Table 18.
Compared to aircraft manufacturers, the number of
engine manufacturers is small.
Two manufacturers supply nearly all
air-
craft piston engines, and two others supply most aircraft turbine engines.
However, other turbine engine manufacturers, notably Allison and Garrett,
are increasing their sales of engines for civil aircraft.
Aircraft engines produced by foreign manufacturers are imported
either installed in foreign-made aircraft, or separately for installation
in United States-made aircraft.
Installed engines are listed in Table 16,
and separate engines are listed in Table 19.
At the present time, most
engines imported into the United States, either installed or separate,
are turbine engines and all are produced by three manufacturers:
Ro lls-
Royce, limited, of the United Kingdom, Societe Turbomeca of France, and
United Aircraft of Canada, limited.
In contrast with the automobile industry, nearly all manufac-
turers of aircraft engines are independent from aircraft manufacturers.
Also, the number of engine manufacturers is small compared to the number
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70
of aircraft manufacturers.
Because of these factors, governmental control
of pollutant emission by aircraft, if required, could be applied more con-
veniently to aircraft engines than to aircraft.
Aircraft Activity
A variety of measures can be used to describe aircraft activity,
e.g.,
landings, take-offs, hours flown, passengers carried, etc.
From the
standpoint of engine emissions and their local and community effects, the
most significant activity is that which occurs in the air terminal vicinity.
In this report, the "landing-take-off (LTO) cycle", as defined earlier, has
been adopted to characterize the operation of an aircraft between the tim~
it begins its approach to a terminal for landing and the time it subse-
quently leaves the terminal area after take-off.
In this section, LTO-
cycle frequency is used as a measure of aircraft activity.
In later chap-
ters, the LTO-cycle concept is uti lized to assess aircraft emissions and
their impact.
Data presented on aircraft activity in this section have been
take~ from various FAA publications which describe activity at air termi-
nals with FAA-operated air traffic control towers and at mi litary installa-
tions.
Activity at non-FAA-controlled, civi I air terminals is not
included except for Los Angeles County.
However, most terminals within
other major metropolitan areas are controlled either by the FAA or by pne
of the mi litary services.
Thus, most of the activity affecting community
air pollution is included.
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71
Aircraft Activity at All Major U. S.
Air Terminals
The numbers of LTO cycles occurring annually within the United
States, as reported by the FAA, are listed in Table 20 for recent years.
Projections of civi 1 aircraft activity for future years also are listed.
These numbers are shown graphically in Figure 6.
These activity figures
are for FAA-control led air terminals of which there were 913 in 1967 com-
pared to a total of 9673 civi 1 airports in the United States.
Consequently,
a substantial amount of general aviation activity is not included in these
figures.
However, most of this activity occurs outside of urban areas and,
consequently, has little impact on urban air pollution.
The two primary observations which can be made from these num-
bers is that nationwide aircraft activity is increasing at a rapid rate
(approximately 10 per cent per year), and that general aviation aircraft
account for the bulk of this activity.
However, the distribution of
activity by aircraft category as shown is not typical of individual air
terminals or communities.
Most mi litary activity occurs at installations
removed from major metropolitan areas, and civi I air terminals vary widely
as to the ratio of air carrier to general aviation activity.
Aircraft owned by foreign organizations or individuals and
operated in the United States are a special activity category.
These
aircraft probably would not be subject to emission controls established
by pollution control agencies in the United States.
Consequently, the
fraction of U.. S. aircraft activity represented by foreign-owned aircraft
is of interest to this study.
Air carriers are the only aircraft category
with a significant amount of activity by foreign-owned aircraft.
According
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72
to an analysis of fl ight schedules (Ref 31), the fraction of air carrier
activity (LTO-cycles) conducted' by foreign aircraft rose from 2 per cent
in 1965 to approximately 6 per cent in 1967 (excluding special flights by
Air Canada serving Expo 67).
During this same period, the number of foreign
'. . :
air carriers operating at United States ~ir terminals increased from 24 to
49.
For comparison, there are 17 United States carriers engaged in inter-
"
national operations and these account for 2 to 3 per cent of total acti-
vity at United States terminals.
Thus, it is observed that, on a national
basis, foreign-owned aircraft account for a small, but growing fraction
of air carrier activity.
This fraction will be greatest at the international
air terminals, such as John F. Kennedy.
Average Aircraft Activity at Selected Major
Air Terminals
The number of aircraft LTO-cycles performed during 1967 at
major air terminals in the New York City, Washington, D. C., and Los
Angeles metropolitan areas are 1 isted in Tables 21, 22, and 23.
It is
observed from these tables that the distribution of aircraft activities
among the major categories in these areas differs from the national dis-
tribution, the principal difference being in the air carrier category.
The statistics for the New York City area depart the most from the national
average in that 40 per cent of all LTO-cycles were performed by air carriers.
In examining activities at individual air termina1s, it is ob-
served that nearly all terminals can be characterized by a single aircraft
category, that is, terminal activities are predominately air carrier,
general aviation, or mil itary.
The only exception in the areas examined
. . .. .
is Dulles International which, in 1967, had a rather even distribution of
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73
activity in the three categories.
Of particular interest to this study is the distribution of
aircraft activity by aircraft type.
Records of certificated route air
carrier activity by type of aircraft are published jointly by the CAB
and FAA (Ref 32).
These records were used to determine the distribution
of air carrier activity during calendar year 1967 by aircraft class.
Commercial operator, supplemental, and foreign air carrier activity, not
included in these records, was assumed to consist of one-third class 1
aircraft and two-thirds class 2 aircraft.
No records are kept of general aviation activity by aircraft
type.
For this study, all GA activity has been assumed to consist of
class 6 aircraft.
Simi larly, no information has been obtained on military activity
by aircraft type.
An estimate of the distribution of mi litary aircraft
types was made based upon various compi lations of aircraft currently in
service (Refs 19 and 33).
is as follows:
Class 3 aircraft
Class 4 aircraft
Class 5 aircraft
Class 6 aircraft
Class 7 aircraft
The estimated distribution of military activity
50 per cent
15 per cent
10 per cent
20 per cent
5 per cent
In preparing this distribution, it was assumed that strategic bomber air-
. craft, which might be considered to fall into class 1, do not operate from
terminals within the metropolitan areas included in this study.
Attack
and fighter aircraft are typified by the class 3 category, at least in terms
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74
of performance.
The fuel consumption rates of these aircraft are
considerably greater than those of civil, class 3 aircraft.
This
difference has been taken into account in calculating fuel consumption
and pollutant emission at air terminals.
Using the approaches outlined in the preceding paragraphs,
estimates of dai Iy activity by aircraft class have been made for five
air terminals, three metropolitan areas, and for all FAA-control led
terminals combined.
These activity levels are listed in Table 24.
Timewise Variations of Aircraft Activity
Variations in activity levels from average levels at civi I
airports are published occasionally by the FAA, the most recent data
being for fiscal year 1965 (Ref 34).
Using these data and assuming that
the same peak-to-average ratios existed in 1967, peak daily and hourly
activity rates were calculated for each of the civi I air terminals listed
in Tables 21, 22 and 23, and these rates are listed in Tables 25, 26 and
27.
The times at which these peak rates occur are not reported.
However,
timewise variation in activity rates for air carrier operations have been
reported (Ref 31). The daily rate (nationwide) of air carrier activity
reaches a peak on Friday. Activity levels are less by about I per cent
on Monday through Thursday and by 17 and 15 per cent on Saturday and
Sunday, respectively.
Hourly levels of scheduled air carrier and air
taxi activity for five municipal areas are shown in Figure 7~
In general,
the activity rates are high from 10 am to 10 pm and lower during the other
half of the day.
Activity peaks occur in the morning and the early evening,
and the lowest activity level occurs around 4 am.
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75
Current activity levels at John F. Kennedy, Washington National,
and Los Angeles air terminals are listed in Tables 28, 29 and 30 by hour
of arrival and type of aircraft.
These figures are for scheduled activity
and were taken from References 35 and 36.
Passenger and cargo air carrier
activities and air taxi activities are included.
Some intrastate opera-
tions are not included, but these represent a small fraction of the total.
The number of scheduled flights actually flown is typically about 95 per
cent of those scheduled.
The timewise variations of activity levels at
general aviation
and mi litary air terminals are not published.
However, it is reasonable
to assume that most operations occur during daylight hours.
Summary
This section is a compi lation of statistical data on aircraft
population, production, and activity which have been used in this study
in determining rates of pollutant emission and evaluating emission control
methods.
In compi ling this information, the following general observations
have been made:
1.
The Federal Aviation Administration classifies civil aircraft
into two broad categories:
air carriers and general avia-
t ion.
Air carrier aircraft consist mainly of turbine-engine
transport aircraft.
General aviation aircraft consist
mainly of medium and small-size, piston-engine aircraft.
2.
The population of active, civil aircraft is approximately
100,000 and is increasing at the rate of about 8000 aircraft
per year.
Air carrier aircraft constitute about 2 per cent
of the total population.
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76
3.
The number of aircraft engine manufacturers in the United
States is small, (approximately 8)compare~ to the, n~~ber qf
. t. '". I .~ . .. ~ . .
aircraft manufacturers. . Also, engine ,manufacturers are
largely independent from aircraft manufacturers.
, , '
...,1', "
4.
Activity at most air terminals is dominated byo~e of three
classes of aircraft:
air carrier" general aviatio,n, o~.'
military.
Activity at major metropolitan terminals consists
mostly of air carrier and air taxi activity.,
5.
Civil aircraf~ activity levels, as measured by.frequency of
landing and take-off operations, are, increasing a.t.a rate of
approximately 10 per cent per year.
~~eneral aviation acti-
vity levels are increasing at the greatest rate.
These observations are pertinent to the problems of pollutant
emission by aircraft and its control.
Their implications are brought out
in later sections of this report.
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77
AIRCRAFT FUELS
The rates of emission of pollutants by most internal combustion
systems, including aircraft engines, are determined partly by the nature
of their fuels and their rates of fuel consumption.
Thus, a knowledge of
fuel characteristics and consumption rates can be used to estimate the
rate of pollutant emission by a particular source.
This approach is
particularly useful in the case of aircraft engines since fuel consumption
data for these engines are readi ly avai lable.
In this section, characteristics of aircraft fuels are described,
and data on fuel consumption are presented for individual aircraft engines.
These data have been used with aircraft activity data from the previous
section to determine over-all rates of consumption of aircraft fuels at
air terminals and in metropolitan areas.
In the following section, these
consumption data are used, along with data on engine exhaust characteris-
tics, to determine rates of pollutant emission.
Fuel Characteristics
Fuels currently used in aircraft engines consist of mixtures of
hydrocarbons produced by the disti llation and post-processing of crude
oi 1.
The products of a typical refining operation and the relative quanti-
ties produced by atmospheric disti llation are shown in Figure 8.
Aviation
fuels are taken from the gasoline and kerosine fractions, and consist of
many organic compounds with boi ling points within the range of 140 to
550 deg F.
A typical gasoline contains as many as 240 chemical compounds
(Ref 37) and JP-4, a mi litary jet fuel, may contain as many as 5000 to
10,000 different compounds.
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78
Specifications on properties of aircraft fuels ~re based upon
several factors, including engine requirements, storage stabi lity, air-
frame requirements (minimization of fuel tank size, limitation of evapora-
tive losses, and prevention of autoignition in high speed aircraft), an~,
one that is becoming of increasing importance, avai'lability.
The kerosine
fraction from crude oi 1 has to meet requirements 'of other users besides'
aircraft and it is clear from Figure 8 that the fraction avai lable is
only about 10 per cent of each unit of crude oil processed.- With the de-
~and for turbine-engine fuels increasing rapidly, a shortage of kerosine
could develop.
Such a shortage could be overcome by various means, includ-
ing chemical conversion of other less useful fractions of crude oil (at
an increase in cost of the fuel), modification of fuel specifications,
or importation of kerosine from other countries.
The last two solutions
are currently employed.
Specifications for military fuels allow a greater
fraction to be used, equal to approximately 40 per cent of the crude oi 1,
thus avoiding any shortage for military use in time of em~rgency.
A ls6,
jet fuel is imported in significant quantities.
For example, 16 per cent
of the total U. S. consumption of jet fuel in 1966 was imported (Ref 38).
The present trend in refining, however, is toward chemical processing
(hydrocracking) in order to produce additional kerosine and gasoline type
fuels from the heavier gas oi Is (Ref 39).
Fuel specifications are usually defined in terms of limits on
certain physical properties, and fuels of significantly different chemical
composition can satisfy the same physical property requirements.
It is
also necessary to specify composition limits of certain undesirable
chemical groups.
For example, aromatic compounds such as naphthalenes are
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79
undesirable as they have a strong tendency to produce smoke during
combustion.
The basic chemical nature of a fuel depends mainly upon the
source of the crude oi I from which it is derived since important differ-
ences exist in crude oi Is.
Figure 9 shows the variation in one physical
property, namely, the tendency to smoke, of the kerosine fractions pro-
duced from different' oi I sources.
The effect of removing all aromatics
from the kerosine is also indicated.
South American crude oi Is are shown
to be the least desirable from this particular aspect as, even after the
expensive"step of aromatic removal, they produce kerosine fractions which
are as prone to smoking as the untreated kerosine derived from African
and Middle East crude oils.
Crude source, therefore, is also an indirect
factor influencing fuel specifications which are usually written primari Iy
to ensure delivery of a satisfactory fuel at as Iowa cost as possible.
Piston-Enqine Fuels
Fuels used in aircraft piston engines are simi lar to autGmobile
fuels and are referred to as aviation gasolines, often abbreviated as AVGAS,.
They are classified according to a combustion characteristic termed anti-
knock quality.
The fuel-air mixture in the cylinder of a piston engine
wi II detonate under certain conditions instead of burning normally.
Deton-
ation or knock is usually inaudible in an aircraft engine, but if permitted
to continue, can result in serious loss of power and damage to the engine.
The antiknock value, or octane rating, of a fuel indicates its abi lity to
I
prevent such an occurrence, higher octane values being more desirable.
Specifications for aviation gasol ines define five grades with different
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80
octane ratings but only two are commonly avai lable with,ratings of
100/135 and 115/145.
The two values in each rating are lean and rich
ratings corresponding to full-lean and full-rich mixture control set-
tings.
(See Aircraft Fuel ,Systems.)
Aviation gasolines are mainly complex mixtures of relatively
volati Ie hydrocarbons.
They contain some impurities, such as sulfur
, , '
compounds, which originate in the crude oi 1.
In addition, certain
materials are added to improve quality of performance.
The most impor-
tant additive is tetraethyllead which is added to increase the octane
rating of the fuel.
It is added as a fluid together with an organic
halide scavenging agent which is necessary to keep the tetraethyllead
combustion products volati Ie so that they will be discharged from the
cylinder.
Antioxidants are also added in small quantities to inhibit
the formation of insoluble gums during storage of the fuel.
Aviation fuels cannot be defined precisely due to their complex
chemical composition.
Fuel specifications, therefore, are stated in
terms of limits on physical and sometimes chemical properties of the de-
sired fue 1.
The limits are prepared from a consideration of those fa~tors
that significantly affect aircraft operation together with others such
as cost and avai labi lity of the fuel.
The most significant factors are
listed below together with the standard test methods which are used to
assign quantitative values to these properties of interest (Ref 41)~
Detai led specifications for all five grades of aviation gasoline are given
in Table 31.
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81
IMPORTANT CHARACTERISTICS OF AVIATION GASOLINE
Factors of Siqnificance
Test Methods
Antiknock quality
Knock test Tetraethyllead
analysis
Fuel metering and aircraft range:
Net heat of combustion
Carburetion and fuel vaporization:
Vapor pressure
Distillation
Corrosion of fuel system and engine
parts:
Acidity of distillation residue
Copper strip test
Sulfur analysis
Fluidity at low temperatures:
Freezing point
Fuel cleanliness, handling and
storage stabi lity:
Water tolerance
Potential gum
Visible lead precipitate
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82
Turbine-Enqine Fuels
Turbine-engine fuels,~re notcJassified in terms of engine
performance factors.
The engine itself is not as sensitive to fuel
properties as the piston engine, but other fact6r~ 'are ~ore significant.
For example, airframe requirements are more demanding due to the higher
altitudes and speeds at which turbine-powered aircraft operate.
,Also,
the relative availabi lity of the kerosine fraction favored for these
engines is far more limited than the availability of gasoline.
On the
basis of these factors, turbine-engine fuels can be separated into four
main types:
fuels for civil aircraft, for the Air Force, ,for the Navy,
and for experimental aircraft.
The two fuels most commonly used in civi I aircraft are taken
directly from the kerosine fraction and are referred to as Jet A or
Avtur 40 and Jet AI or Avtur 50.
The Avtur number indicates the freez-
ing point of the fuel in degrees centigrade (below zero).
Jet AI or
Avtur 50 for example has a freezing point lower than -50 deg C.
This
was the fuel first used in jet engines, but due to its limited supply,
the alternative fuel, Jet A,
is now in more common use.
Its 10 degree
higher freezing point allows refinery blending of Jet AI with heavier
fuels which are in less demand, and hence more turbine fuel is obtained
per unit of crude oi I.
To satisfy avai lability requirements in time of emergency, the
Air Force operates on a different fuel known as JP-4.
(Jet B, wide-cut,
and Avtag also are used to describe this fuel).
The specifications for
Jp-4 allow nearly 40 per cent of the crude oi I to be converted into
usable fuel.
Jp-4 contains a higher concentration of light hydrocarbons
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83
than other turbine engine fuels, and, as a result, is appreciably more
volati Ie and ignites more readily than the Jet A and Al fuels.
It is
claimed by some to be unsafe for commercial use because of its volatility
(Ref 42).
The fuel used by the Navy was developed for aircraft carrier use
and is called JP-5.
It is less volati Ie than even Jet A and ignites less
read i I y.
The fourth fuel category includes fuels used in experimental
aircraft.
Military specifications have been prepared or proposed for sev-
eral such fuels including JP-6 and JP-150.
They are intended for use in
high-speed, supersonic aircraft, and this application calls for fuels with
low volatility and high thermal stability.
Most turbine-engine fuels--Jet A, Jet AI, JP-4, JP-5 and JP-6--
are specified mainly by their physical properties, but their chemical
compositions vary with crude oil and refinery sources.
JP-150 fuel, how-
ever, is specially refined to consist mainly of paraffins.
Some indica-
tions of the approximate composition by chemical groups of all turbine
engine fuels are given in Table 32.
Appreciable variations in composition
do exist for fuels satisfying the same specifications (Ref 45).
As with aviation gasolines, turbine-engine fuels contain
impurities derived from the crude source and other substances which are
added to improve fuel performance.
Sulfur is present as an impurity with
a concentration level of approximately 0.05 mass per cent.
The main com-
pound added to these fuels is an antioxidant which prevents the formation
of insoluble gums during storage.
The quantity added is approximately
0.002 mass per cent.
Experimental attempts have been made in recent years
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84
to reduce jet engine exhaust smoke with fuel additives and successful
results have been obtained using metal-organic compounds of barium,
manganese, and iron (Ref 96).
Concentration levels of 0.1 per cent were
observed to be effective when used with JP-S fuels.
However, detai led
study of the effects of additives has shown that engine performance deter-
iorates rapidly when such additives are used as a result of deposition
of particulate matter upon the combustor and turbine parts.
This effect,
coupled with possible toxicity problems, makes it very unlikely that the
use of additives for smoke reduction wi 11 ever be widely accepted.
Desirable characteristics of turbine-engine fuels are listed
below with the physical or chemical property normally measured to compare
the effectiveness of different fuels (Ref 49).
Factors of Siqnificance
Requirements
Combustion Characteristics:
Fuel Vaporization
Flame Cleanliness
Volatile Disti llation Properties
High Luminometer Number
Fuel Metering and Aircraft Range:
Value of Net Heat of Combustion
Airframe Considerations:
Fuel Fluidity at Low Temperatures
Fuel Tank Size
Fuel Cooling Capability
Evaporative Losses
Autoignition
Low Freezing Point
High Specific Gravity
High Specific Heat
Low Vapor Pressure
High Flash Point
Corrosion of Fuel System:
Low Acidity
Low Sulfur Content
Fuel Cleanliness, Handling, and
Storage Capabilityi
High Water Tolerance
Low Existent Gum
Low Potential Gum
Good Fuel Lubricity
Low Viscosity
High Thermal Stability
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85
Characteristics of kerosine which were of little interest before
the advent of the turbine engine include flash point, thermal stability,
specific heat, fuel lubricity and the luminometer number of the fuel.
Lumi -
nometer number is an empiricat factor which provides some indication of the
cleantiness of the flame produced in the combustor, and a vatue greater
than 45 is usuatty required to achieve satisfactory combustor performance
(Ref 47).
Fuels with lower values tend to produce excessive smoke even
when used in wet I-designed combustors.
The smoke gives rise to carbon
deposition and reduces combustor life due to the higher radiant heat trans-
fer from the flame.
The tuminometer number is related to the chemical
composition of the fuet and its hydrogen-to-carbon ratio.
Saturated hydro-
carbons (paraffins), with their high HIC ratio, produce tess smoke than
retativety tow HIC ratio unsaturated compounds such as otefins and aromatics.
The other factors tisted above became of increasing importance as flight
velocity increases.
Most of the fuel properties of interest are interdependent and
often it is necessary to compromise between various factors.
It is not
possible, for example, using hydrocarbons alone, to obtain both a tow vapor
pressure and the high heat content per unit volume desired by the airframe
designer, and at the same time maintain a high luminometer number required
for the combustor.
Thus, there are limits in operating conditions under
which current fuels can operate.
Fuels such as Jet A are satisfactory for
aircraft with flight velocities up to about Mach 2.7.
The Boeing SST wi II
use Jet A and operate at Mach 2.7.
However, above this speed, airframe
requirements cannot be met without resorting to a more highly refined fuel
such as JP-6.
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86
There are more specifications for aviation turbine fuels than
there are fuels available.
They are prepared by engine manufacturers,
mi litary authorities, commercial aircraft operators, the American Society
for Testing and Materials, and other groups.
Fuel producers meet the
various requirements by blending fractions which satisfy more than one
specification.
Consequently, there are available only the four main types
of fuel described earlier.
Normally a turbine engine fuel specification will limit the
value of approximately thirty physical or chemical characteristics result-
ing in overspecification due to the interdependence of the properties.
It
has been shown, for example (Ref 48), that five main properties specified
for the kerosine fuels Jet A and Jet Al can be determined from the experi-
mental measurement of only two of these properties.
The other three
properties can be calculated with an accuracy better than that associated
with one experimental determination.
Typical specifications for aircraft
turbine-engine fuels are shown in Table 33.
Fuels for the Future
Present activity in aviation fuels research is mainly involved
with the development of economical, hydrocarbon fuels for supersonic air-
craft (Ref 50 and 51).
Other activities include the production of
emulsified Jp-4 fuels (Ref 52) with the objective of reducing the fire
hazard in aircraft accidents, and studies of the feasibility of obtaining
fuels from sources other than crude oi 1.
The latter program has two objec-
tives; firstly, to produce fuels with high volumetric heat content for
advanced air breathing systems, and secondly, to study the possibilities
of using liquefied methane (natural gas) or hydrogen in supersonic aircraft.
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87
Attention is turning to nonpetroleum based fuels because of the
operational difficulties that arise in supersonic flight.
At high velo-
cities, air flowing over the aircraft is heated by compression and skin
friction and cannot be used for cooling purposes. Instead, stored fuel is
used for cooling auxiliary systems, such as air-conditioning, hydraulic
fluid, and engine lubrication systems.
At high supersonic velocities,
it may also be necessary to uti lize fuel for cooling certain portions of
the aircraft structure.
In this case, fuels will be required having
greater cooling capacity than those in current use (Ref 53).
Liquefied
methane and hydrogen have large cooling capacities, but problems associated
with their low densities and low boi ling temperatures offset their advan-
tages as coolants.
It is most likely, therefore, that hydrocarbon fuels,
with some modifications, wi 11 be used for all aircraft propulsion for many
years.
Fuel Consumption
The rate of emission of air pollutants by an aircraft engine, as
with other internal combustion engines, is highly correlated with its fuel
consumption rate.
Other factors affect pollutant emission rates, of course,
but engines of the same type operating at simi lar conditions wi 11 emit
pollutants at rates directly proportional to their fuel consumption rates.
Consequently, fuel consumption statistics are relevant to this study.
Consumption of fuel by U. S. aircraft in recent years is shown
in Table 34 and in Figure 10 along with projections for future years.
The
decreasing trend of aviation gasoline consumption is a result of the retire-
ment of piston-engine transport aircraft.
Air carrier aircraft, though
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i
88
constituting only 2 per cent of the U. S. civil aircraft population,
consume approximately 90 per cent of all aircraft fuel used in civil
aviation.
Daily fuel consumption by aviation category, is as follows:
Daily Fuel Consumption by U. S. Civil Aircraft
(Thousands of Pounds - Averaqe Day, 1967)
Aviation Gasoline Turbine Fuels Total
Air Carriers 5,500 74,000 79,500
General Aviation 6,000 2,100 8,100
All Civi 1 Aircraft 11,500 76, 100 87,600
In comparison with fuel consumption by aircraft, dai ly consumption rates
of automobile gasoline in the United States is approximately 1,200,000,000
pounds (Ref 54).
Air carriers dominate the fuel consumption statistics because
the size and engine power levels of air carrier aircraft are so much
greater than those of most general aviation aircraft.
This size disparity
is reflected in a comparison of fuel consumption rates for different en-
gine types as indicated in Table 35 and quantities of fuel consumed during
landing-take-off cycles shown in Table 36.
The LTO-cycle fuel consumption
estimates are based upon the cycle characteristics listed in Table 2 and
the fuel rates listed in Table 35.
It is observed from these estimates
that general aviation aircraft, which are mostly class 6 aircraft, indi-
vidually consume very small quantities of fuel compared to air carrier
transport aircraft (classes 1, 2,4 and 5).
By combining the fuel consumption data from Table 36 with the
aircraft activity levels presented earlier, average dai ly fuel consumption
rates at air terminals have been calculated and are presented in Table 37.
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89
This table shows daily fuel consumption rates for all aircraft operating
from certain air terminals and communities.
Based on the data presented, it is estimated that 20 to 25
per cent of all fuel consumed by U. S. civil aircraft is consumed during
operations at air terminals.
Summary
In this section, we have shown that fuels used in aircraft en-
gines are similar to fuels used for other purposes.
Aircraft piston
engines use aviation gasoline which is similar to automobile gasoline
and, like most automobile gasoline, contains tetraethyllead to prevent
engine knock.
Turbine engines in civil aircraft use aviation kerosine which
is simi lar, in many respects, to fuels used in automotive diesel engines.
Aviation kerosine, however, is subject to more stringent limitations on
impurity levels and smoke-forming tendencies than most other fuel oi Is.
The fuel consumption rates of transport aircraft are large com-
pared to those of general aviation aircraft, and the consumption of
turbine-engine fuels by civil aircraft greatly exceeds that of piston-
engine fuels (aviation gasoline).
Between 20 and 25 per cent of all
aviation fuel used by civil aircraft is consumed during air terminal oper-
ations.
This information on fuel characteristics and consumption rates
is used in the next section to estimate rates of pollutant emission by
aircraft during air terminal operations.
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90
AIRCRAFT ENGINE EMISSIONS
The purposes of this section are to describe the nature of aircraft
engine exhaust emissions, and to indicate the quantities of air pollutants
emitted during aircraft operations.
In the first part of the section, pollu-
tant species contained in engine exhaust gases are described, and other
characteristics of exhaust gases--visual appearance and odor--are discussed.
Methods of measuring concentrations of pollutants and exhaust gas character-
istics are described in Appendix I.
In subsequent parts of this section, the mechanisms of pollutant.
formation and the rates of pollutant emission by individual engines are ~is-
cussed.
Effects of engine design and operating characteristics on emission
rates are presented, to the extent that they are known.
This information
is used to estimate the rates of emission of various pollutants by differ-
ent engine types during various operational modes (take-off, approach, taxi,
etc.).
Finally, estimates of the dai ly rates of pollutant emission at
air terminals are presented.
These estimates are based upon individual
engine emission rates presented in this section, and data on aircraft acti-
vity and fuel consumption presented in earlier sections.
Estimates of pollu-
tant emission during all aircraft operations are presented.
However,
greater emphasis is given to emissions at specific air terminals and in
selected urban areas.
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91
Characteristics of Aircraft Enqine
Exhaust Gases
Composition
The gross composition of exhaust products from typical aircraft
engines is presented in Table 38.
Exhaust gases from both piston and
turbine engines consist mainly of substances which are not regarded as
air pollutants--nitrogen, oxygen, and water.
Pollutant materials are
present in lesser quantities and can be categorized as follows:
( I) carbon dioxide
(2) carbon monoxide
(3) organics
(4) nitrogen oxides
(5) particulates
(6) sulfur dioxide
It is observed that concentrations of these materials are substantially
different in the two engine types and that they also vary with engine
operating conditions.
Pollutant concentrations and rates of emission are
discussed more fully later in this section.
Chemical and Physical Properties
Properties of pollutants are described briefly here with part i-
cular emphasis on those characteristics which are peculiar to aircraft
engine exhaust emissions.
A variety of references are avai lable which
provide more extensive descriptions of properties of pollutants and their
effects (e.g. Ref 57).
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92
Carbon Dio~ide
Carbon dioxide is a colorless, ordorless gas and is a normal
constituent of exhaust gases from all combustion systems which burn
carbonaceous or hydrocarbon fuels, natural fuels such as wood, and most
waste materials.
Since the beginning of the twentieth century, world-
wide atmospheric concentrations of carbon dioxide have been increasing
steadily in a manner related to the increased global use of fossil fuels
(Ref 58).
Carbon dioxide is not often considered to be an air pollutant,
since it produces adverse physiological effects only at relatively high
concentrations and because biological and geochemical processes are known
to provide a natural disposal system.
Its atmospheric increase apparently
reflects an accelerating disparity between the C02 production rate and the
rate of approach to equil ibrium with marine and terrestrial sinks.
Un-
checked increase in the rate of combustion of carbon fuels apparently may
increase world-wide C02 levels eventually to meteorologically significant
However, since C02 is not regarded as a pollutant from the stand-
point of community air qual ity, it has not been included in this study.
levels.
Carbon Monoxide
Carbon monoxide is of interest as an air contaminant primarily
because of its toxic properties.
The highest outdoor levels of carbon
monoxide are often found where vehicular traffic is heaviest.
Indicative
of the increasing urban impact of carbon monoxide is the fact that in the
fall of 1964 during unusually long and severe inversion conditions, carbon
monoxide was monitored in quantities as high as 20 parts per million (ppm)
for eight hours, and higher concentrations (up to 72 ppm) have been reported
for shorter periods of time (Ref 57).
The threshold limit value of CO
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93
(TLV), as adopted by the American Conference of Governmental Hygienists
in May 1967, is 50 ppm.
The TLV refers to the airborne concentration
of a substance to which a worker may be exposed for an eight-hour day,
five days a week without adverse effect.
The problems which arise in the
ambient situation, however, are that exposed individuals are not neces-
sarily workers (e.g. children, elderly people, etc.), are not reimbursed
for their exposure, and may be exposed for periods longer than eight hours.
CO is also a colorless, odorless gas and is chemically stable.
It is oxidized to C02 in the atmosphere, but at very slow rates.
Organics
Organics is a term used to describe substances consisting
mainly of carbon and hydrogen with lesser quantiti~s of oxygen and nitro-
gen.
These mater i a 1 s a 1 50 are referred to as 'Ihydrocarbons", but there
are a number of pollutant species of an organic nature which are nOIDltruly
hydrocarbons.
Organics, as used in this report, include pollutant species
in both gaseous and liquid state.
Most organic materials are not directly harmful at low concen-
trations, but are converted to harmful materials through photochemical
reactions.
The reaction which represents this phenomena is HC+NO +sun-
light.smog.
Haagen-Smit has shown that ozone is also formed during the
photochemical oxidation of organics in the presence of nitrogen dioxides
(Ref 57).
If one were to attempt to catalog organic compo~nds which have
been observed or might be expected to be detectable in contaminated air,
the list would be a very extensive one.
That the chemical composition of
organic air contamination is complex is emphasized by noting some possible
reasons for presence of gas phase organics in the atmosphere. Leakage
Most methods used to measure hydrocarbon emissions from aircraft engines
also respond to non-hydrocarbon, organic compounds. The term organics has
been used throughout this report to describe this pollutant category.
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L-
94
or loss of any gas or I iquid fuel, solvent, etc. would be a direct source
of many organic species.
Both incomplete oxidation and cracking of fuels
in combustion processes can lead to another group of compounds.
To these
primary sources we: need only add the known fact of photochemistry in the
atmosphere, which produces both unknown free radicals and also organic
peroxides, peracids, hydroxyperacids and such nitrogen-containing compounds
such as peroxyacetyl nitrates.
With this variety of sources it seems
reasonable to estimate that with: refinement of observation techniques, many
hundreds of individual organic chemicals could be isolated from the atmo~'
sphere.
The, primary adverse effects of these compounds are physiological
effects on man or an:i,mals, material damage, agricultural damage, and
visibil ity reduction.
Among the more important oxygen-containing organics are the
aldehydes which have been identified repeatedly and which are of intere~t,
in air pollution because of their effect on humans.
At low concentrations,
several of them are very irritating to the eyes and to mucous membranes.
Since the photochemical oxidation of unsaturated olefinic hydrocarbons
results in the formation of formaldehyde, ocrolein, acetaldehyde, pro-
pionaldehyde and 1sobutylaldehyde, these should be present in polluted
air.
Of these, formaldehyde appears to be the most pr.evalent.
The aldehyde
content of air in several United States cities between the years 1946 and
1951 ranged from 0.00 to 0.27 ppm.
In that period the average concentra-
tion varied from 0.04 toO. 18 ppm calculated as formaldehyde.
The report-
ed ~1gh concentration of aldehydes in Los Angeles through 1959 was 1.87
ppm with the usual range being 0.01 to 0.20 ppm with a mean concentration
of 0.04 ppm (Ref 57)., (TLV= 5.0 ppm)
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95
Organic compounds in exhaust products from aircraft engines in-
clude unburned components of the fuel and organic substances formed during
combustion.
A partial listing of organics contained in exhaust gases from
an aircraft turbine engine is presented in Table 39.
Nitrogen Oxides
Of the six commonly encountered oxides of nitrogen - N20 (nitrous
oxide), NO (nitric oxide), N02 (nitrogen dioxide), N203 (nitrogen trioxide),
N204 (nitrogen tetroxide ), and N205 (nitrogen pentoxide) - N02 is consider-
ed of the greatest air pollution interest for three reasons: (1) Most
other oxides of nitrogen react in air in such a way that the principal
product is N02.
(2)
N02 is believed to be one of the chief substances
in the chain of ultraviolet reactions with atmospheric hydrocarbons that
leads to oxidant smog.
(3)
.
Nitrogen dioxide results as a major end pro-
duct of the burning of fuel in engines and furnaces because of air oxida-
tion of the NO formed by high combustion temperatures.
Because of the low
relative toxicity and air pollution significance of N20 and N203 and
N204' only the properties of N02' NO and N205 wi 11 be discussed.
Although particulate matter is the most important factor in
determining the loss of visibility in polluted atmospheres, there has
also been considerable interest in sky color effects, especially the brown
discoloration which occurs as a result of excessive N02 concentrations.
N02 concentrations cause the atmosphere to have a different color because
this gas is strongly absorbent over the blue-green area of the visible
spectrum.
This absorption produces illumination which is overbalanced
toward the yellow-red end of the spectrum and gives N02 mixtures in air
their characteristic yellow-brown coloration in proportion to the N02
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96
concentration.
Light absorption by N02 has been tabulated and demonstrated
graphically from data given by Leighton (Ref 60).
In order to determine
the attenuation effect of N02 at a given wavelength, the gaseous extinction
coefficient is related to the atmospheric concentration.
It is unlikely
that an observer would be aware of a target coloration when the conc~ntra-
tion of N02 is about O. I ppm.
However, at 1 ppm color effects would
probably be quite marked and even at 0.25 ppm would most likely be noticed
if the target wer.e white.
Health effects of N02 and other oxides of nitrogen range from
odor, nose and eye irritation, pulmonary congestion, edema, obliterative
bronchiolitis and pneumonitis to death.
However, mild effects from N02'
such as mucous membrane irritation, do not occur at presently encountered
overall air pollution levels.
However, on a micro scale, such as in an
enclosed area, the concentrations could build to a dangerous level.
The threshold limit value for N02 is 5 ppm.
However, the State
of California, Department of Public Health, has set an ambient air quality
standard for N02 at 0.25 ppm, primarily on the basis of coloration effects
which a concentration of this magnitude would be expected to cause in an
area that otherwise would not be severely affected by pollutants (Ref 61).
N02 concentrations in the ambient atmosphere range from 0.01 to 0.20 ppm
with the mean being approximately 0.04 ppm (Ref 62).
Nitric oxide (NO) is of little toxicological interest as an air
pollutant because of its relatively rapid conversion in the atmosphere to
N02 (2NO + 02 - 2N02)'
It has been shown that 50% of the NO emitted from
the exhaust of an automobile during deceleration (4,000 ppm) is converted
to N02 in 1 minute (Ref 57).
The interest is primarily that of the increase
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97
in NOZ concentration due to NO emission.
In areas where ozone concentrations are high, NOZ is readi ly
oxidized to NZOS (Z NOZ + 03 ~ NZOS+ 0Z) which is subsequently hydrated to
nitric acid.
Nitric acid is also formed in fog by the reaction
4 NOZ + Z HZO + 0z
...
4 HN03.
The effects of nitric acid droplets in the
atmosphere include impairment of health, property damage, and reduction
of visibility.
Oxides of nitrogen emitted by aircraft engines consist primarily
of NO with lesser quantities of NOZ.
Particulate Matter
In this study, the term "particulate" is used to describe
pollutant materials in the solid state.
Pollutants emitted in the form
of liquid droplets are generally organic in nature and are included under
organics.
This method of classification avoids problems associated with
condensation of organic vapors in engine exhaust gases.
The concentra-
tions of organics and solid particulates are not affected by changes in
the physical state of organic materials.
Particulate matter emitted by automobile engines consists
primari ly of lead compounds in a wide range of particle sizes, from O.OZ
to over 1.0 micrometers (Ref 69).
Aircraft piston engines also emit lead
compounds in particulate form since aviation gasoline contains tetraethyllead
and halogenated scavenging agents in quantities similar to those in auto-
mobile gaso line.
To the knowledge of the authors, the physical state of
lead emissions from aircraft engines has not been reported.
It is reason-
able to assume, however, that the particle sizes of lead emissions from
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98
aircraft are similar to those from automobiles, but with higher concentra-
tions of particles in the smaller size ranges.
Since aircraft exhaust
stacks are relatively short, there is less opportunity for particle
agglomeration.
Agglomeration of small particles in the exhaust system
probably is an important mechanism for the formation of particles in the
larger size ranges.
The toxicity of lead and lead compounds is well establ ished.
However, no health effects have been attributed directly to engine emissions.
Nevertheless, considerable concern exists about the possible effects of lead
emissions and a basis is being sought for establishing air quality criteria
with respect to lead compounds.
Solid particulate matter emitted by aircraft turbine engines consists
primarily of carbon particles.
These particles are emitted in particle sizes
in the range of 0.01 to O. I micrometers and are similar to carbon emissions
from other types of combustion equipment.
Pure carbon is considered to
be relatively harmless from the health standpoint, and its principal
effect as a pollutant is reduction of visibility.
Deterioration of visibi-
1 ity as a result of emissions from aircraft turbine engines has been
reported by several workers (Refs 63, 64, 65, and 66).
The visibil ity of
the engine exhaust plume itself is an esthetic problem quite distinct
from the problem of general atmospheric pollution.
(With mil itary air-
craft, exhaust plume visibility is also a tactical problem.)
Exhaust
plume visibility is discussed separately in a later section.
It is recog-
nized that carbon particles can have indirect effects as carriers of
organic materials and odors (see Appendix I I).
However, these effects are
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~
99
complex and not well understood.
The nature of solid particulate matter other than carbon in
turbine engine exhausts has hot been investigated thoroughly.
We are not
aware of adverse effects from such materials except for the physical prob-
lems of visibi lity reduction and soiling.
In this respect, their effects
are simi lar to those of carbon particles.
Consequently, for purposes of
this study, solid particulate emissions from aircraft turbine engines have
been assumed to consist totally of carbon particles.
Sulfur Dioxide
Sulfur dioxide is present in exhaust gases from both aircraft
piston and turbine engines, but in lower concentrations than in gases from
other types of combustion equipment.
It stems from the combustion of
sulfur compounds which are contained in all aircraft fuels as impurities.
S02 is emitted as a colorless gas and can have a variety of adverse effects
on health, including irritation of the respiratory system.
In the atmosphere,
S02 is converted to sulfur trioxide and sulfuric acid.
also is an irritant, but has additional effects including reduction of
The latter material
visibi lity and damage to plants and property.
Visual Appearance
Most of the gaseous components of aircraft engine exhausts are
colorless and, therefore, are not visible.
As mentioned above, N02 is
orange in color, but it is not present in sufficient concentration to
impart color to engine exhaust gases.
. The quantities and physical characteristics of particulate
matter in piston engine exhausts are such that these also are invisible.
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100
Consequently, under most conditions, the exhaust plumes from aircraft
piston engines are not visible.
At idle conditions, these engines emit
a fog of unburned fuel which can be observed from close range, but in
general, their visual appearance is not objectionable.
Exhaust gases from some turbine engines contain sufficient
quantities of particulate matter to render the exhaust plume visible,
even at long range.
The principal offender is carbon which is created
in combustion systems in a form which is highly visible.
The visibility
of the exhaust plume is affected primarily by the concentration of carbon
in the exhaust gases, the arrangement of engines, and the aircraft speed.
As will be noted later, carbon emission is affected by engine design and
operating conditions, with carbon concentration generally increasing with
power I eve 1.
Exhaust gases from engines mounted close together tend to
merge and become more visible than individual plumes.
Simi larly, plumes
from aircraft traveling at low velocities tend to be more visible because
the density of emission along the flight path varies inversely with velo-
city.
As a:result of these various factors, turbine engine exhaust plumes
are most visible during take-off and climb-out operations, and the visibi-
lity of plumes from certain medium-range transport aircraft is aggravated
by the clustering of engines on the fuselage.
Meteorological conditions
also affect e~haust .visibi lity in that the plume is most evident on clear
days and less so in the presence of atmospheric haze.
The visibi lity of an aircraft engine exhaust plume is considered
to be an undesirable factor quite distinct from the contribution by the
aircraft to community concentrations of particulate matter.
Consequently,
reduction of exhaust gas carbon concentrations is a matter of concern from
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101
the standpoint of plume visibility and methods of measuring this character-
istic are discussed along with other measurement techniques in Appendix I.
It should be stressed, however, that an exhaust plume may be rendered
invisible but the emission of particulate matter by the engine may still
be significant from the standpoint of community air pollution.
Odor
Odors resulting from the operation of aircraft turbine engines
frequently are noticeable in air terminals.
These odors are generally
objectionable and are regarded as an adverse sensory effect.
At present,
substances which are responsible for odors from aircraft have hot been
identified precisely, nor are the mechanisms of odor production well under-
stood.
In addition, there are no straightforward methods of measuring
odor intensity.
The response of human subjects is the only method currently
used for measuring odors.
Even though odors at air terminals are associ-
ated with aircraft activity, it does not necessarily follow that odor
intensity is proportional to activity levels.
Thus, it is clear that odor
represents an effect which should be eliminated, but effective approaches
to odor reduction do not exist at the present time.
The characterization
and measurement of odors are discussed in Appendix I I.
Formation of Pollutants in Aircraft Enqines
General
In aircraft engine combustion chambers, and most other internal
combustion devices, the processes by which pollutant species are formed
can be grouped into two general categories.
These are (1) bulk processes,
or "normal" combustion processes, and (2) quenching processes, or "inhibited"
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102
combustion processes.
Bulk processes are those which occur in regions of
the combustible medium which are not directly affected by the presence of
the chamber walls or other factors which could disrupt the chemical and
physical processes leading to complete combustion.
In bulk processes, the
composition of the combustion products, including the concentrations of
pollutants, is determined by the composition and physical conditions
(temperature, pressure, uniformity, etc.) of the initial, unburned mixture,
Quenching processes, on the other hand, are those which occur in
regions of the combustion chamber where combustion is inhibited by various
mechanisms,
The principal inhibiting mechanism is cooling, which occurs
by convection at the walls of the chamber, and by dilution in regions
where cooling air is introduced,
In these regions, combustion processes
are partially or completely inhibited, resulting in a different product
composition, and different concentrations of pollutant species,
Piston Enqines
Aircraft piston engines, like automobile engines, operate at
fuel-rich mixture ratios under all conditions except cruise, and air
terminal activities consist almost entirely of non-cruise operating modes,
As a result, the products of normal combustion, or the bulk processes,
contain a substantial portion of carbon monoxide (CO).
This condition is
even more severe with turbo-charged engines in which excess fuel is used
to reduce exhaust gas temperature,
In these cases, bulk combustion
processes also produce high concentrations of unburned hydrocarbons
(organics) in the exhaust gases,
Nitrogen oxides (NO) also are produced by bulk processes,
x
though the actual mechanisms are not completely understood,
Fuel-rich
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103
operation tends to reduce the output of nitrogen oxides since less oxygen
is avai lable to combine with the nitrogen in the air.
Consequently, the
dependence of NO production on fuel-air ratio, in general, is opposite to
x
that of CO and organic production.
The principal quenching process in piston engines is the cooling
effect of the chamber walls.
During each cycle, a thin layer of fuel-air
mixture adjacent to the wal Is and in confined spaces, such as cylinder-head
joints, does not burn.
The fuel contained within this quenched volume is
discharged to the atmosphere along with the products of normal combustion
and gives rise to a substantial concentration of hydrocarbons.
These sub-
stances pass through the engine largely unchanged and, consequently, their
composition is simi lar to that of the original fuel.
The piston engine produces only small quantities of particulate
material, and a major fraction of what is produced consists of lead com-
pounds.
As with automobile fuels, lead is added to aviation gasoline to
eliminate detonative combustion (knock), and most of the lead added is
emitted to the atmosphere as solid particles of lead chloride, lead bromide,
and other compounds.
Turbine Enqines
In contrast to piston engines, gas-turbine engines operate at
lean over-all fuel-air ratios.
Theoretically, complete combustion can be
obtained and pollutant emissions associated with bulk processes eliminated.
Indeed, it is well-known that emission levels of turbine engines are
substantially lower than comparable piston engines.
However, design
requirements (for example, ease of ignition, stable operation over a wide
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104
range of over-all fuel-air ratio, maintenance of tolerable metal
temperatures by use of only combustor inlet air as a coolant, and
high combus t ion eff i c i ency at cru i se cond i t ions) d i ctal:e th.Jt I oca I
fuel-air ratios and temperature levels be highly non~~jform within the
combustor and vary widely with operating conditions.
As a result~ gas-
turbine combustors generally contain regions of incomp1ete combustion,
the extent of which are highly dependent upon the detailed design of the
combustor as well as the engine operating condition.
A gas-turbine combustor can be conveniently described in terms
.
of three zones, as indicated in the sketch below:
. -
l~~ -~:~-\.
~'. I ~
l;::: zo:~ lZ/
The primary zone of the combustor, in which the fuel is atomized, heated,
mixed with air, and partially burned at near-stoichometric conditions, tends
to contain fuel-rich regions.
This condition leads to partial combustion'
at high temperature and the production of solid carbon particles (smoke)
and carbon monoxide.
In the secondary zone, in which air is added rela-
tively slowly to reduce dissociation losses, further oxidation of incom-
plete combustion products occurs; however, this oxidation is never
sufficient to eliminate carbon particles if they are formed in the primary
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105
zone.
Oxides of nitrogen are formed in both primary and secondary
combustion zones.
Quenching of unburned fuel occurs in the primary zone near the
chamber walls.
However, the amount of unburned fuel produced in this
manner is relatively small since the surface area is small compared to
that in the piston engine.
Quenching of partially-burned fuel and carbon
monoxide can occur in the secondary zone by too-rapid di lution with
secondary air.
However, in current combustors, quenching by dilution
has been reduced to a very low level.
Because of the differences in operation between piston and
turbine engine combustors, the concentrations of pollutants in their
exhaust gases also are different.
Rates of emission of various pollu-
tants are discussed in the next section.
Rates of Pollutant Emission by Aircraft Enqines
In this section, the rates of emission of various pollutants
by individual engines wi 11 be discussed.
To provide a basis for comparing
emissions from different engines and for computing total emissions, the
emission rate of each species is expressed as an emission index as defined
by Sawyer and Starkman (Ref 67).
The emission index is the weight in
pounds of pollutant emitted per 1000 pounds of fuel consumed.
For compari-
son purposes, the use of emission indices can be justified on the basis
that most internal combustion engines have comparable thermal efficiencies,
and thus, the emission index is a measure of pollutant emission per unit
of power output or work done.
From a practical standpoint, the emission
index allows a direct conversion of fuel consumption to pollutant emission.
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i
106
Piston Enqine Emissions
At the present time, very little direct information is avai lable
on the rates of pollutant emission by aircraft piston engines.
During
this study, the only data found on aircraft piston engine emissions con-
sisted of exhaust gas measurements for one engine (Pratt & Whitney R2800)
at two operating conditions (Ref 68).
Consequently, it has been necessary
to rely upon emission data from automotive engines in order to evaluate
pollutant emission from piston-engine aircraft.
The use of automobile
data introduces an uncertainty into the calculated emission loads.
However,
the limited data for aircraft engines appear to be consistent with data
for automobile engines.
Pollutant emission rates for automobiles often are published in
terms of average rates over an extended period of time, distance, or over
a typical cycle of operating conditions.
Such data are not sufficient for
evaluating aircraft emissions since the modes of operation of an aircraft
engine during a landing and take-off cycle differ substantially from th~
operating modes of a typical automobile cycle.
Therefore, it is necessary
to determine emission rates for each of the different operational modes
and to evaluate the pollutant load for each mode separately.
The pollutants of principal concern from piston engines are:
1.
Carbon monoxide
2.
Gaseous organic compounds
3.
4.
Oxides of nitrogen
Particulates
Particulates consist mainly of lead compounds, and, when expressed as a
fraction of the fuel consumed, the rate of particulate emission is directly
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107
proportional to the lead content of the fuel, and is largely independent
of operating mode.
(The latter statement is not entirely true with auto-
mobile engines due to accumulation of lead in the exhaust system during
low-power operation.
However, lead accumulation is far less likely in an
aircraft engine since the exhaust stacks are short and less time. is spent
i f.1:'low-power :modes.)
Report~d values of particulate emission rates for
automobiles range from 0.00078 lb/lb-fuel (Ref 69) to 0.0020 lb/lb-fuel
(Ref 3).
Since the average lead content of aviation gasoline is higher
than that of automotive gasoline, and the retention of lead compounds in
the aircraft engine probably is less, the higher emission rate (0.002 lb/lb-
fuel) is assumed to be representative of aircraft piston engines and has
been adopted for use in this study.
The emission rates of other pollutants are not directly pro-
portional to fuel consumption rate, but are affected strongly by engine
operating conditions.
The principal factor affecting the exhaust gas
composition is the air-fuel ratio.
Data from various sources on emission
rates of CO, organics, and NO
x
as functions of air-fuel ratio are shown
in Figures 11,12 and 13.
These data are from uncontrolled automobiles,
that is, automobiles not incorporating emission control devices.
The CO emission data in Figure 11 show a rapid increase in
emission rate with decreasing air-fuel ratio.
The data are in reasonable
agreement for part load conditions, but emission rates at idle conditions
appear to be substantially lower.
The two operating points for the
PWA R-2800 engine are consistent with the automobile engine data.
Data from various sources on organic emissions do not agree
well, probably because different analysis techniques have been used by
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108
different investigators.
The data on organic emission from the PWA
engine were given in volumetric units with no indication of chemical
composition.
Through chemical element balance computations, the average
carbon number for the organic emission was found to be 3.9.
Assuming an
average composition of (CHZ)3.9 and converting to weight units, the data
for this engine were found to agree well with the data reported by Neerman
and Mi lIar (Ref 76) which were obtained by mass spectrometer analysis.
A
correlation curve has been drawn through the PWA and Neerman and Millar
data from which emission rates have been taken for use in this study.
Fair agreement is found among data from various sources on
nitrogen oxide emission.
At air-fuel ratios less than 10, the emission
rate is assumed to be negligible.
At higher A/F values, the Huls data
(Ref 70) have been used to obtain values for this study.
Air-fuel ratios at various engine operating conditions are shown
in Figure 14 for fuel supply systems for two typical aircraft piston engines
(Ref 8).
Also shown are selected operating points for five radial engines
manufactured by the Pratt & Whitney Aircraft Corporation (Ref 68).
Air-
fuel ratio is plotted against air-flow rate which is approximately pro-
portional to power output.
The data shown are for the "full rich" condition
at which the mixture control adjustment is in the extreme rich position.
Piston-engined aircraft usually are operated at the full rich condition
during operating modes associated with landing and take-off.
The leaning
adjustment is employed during cruise conditions to obtain more economical
air-fuel ratios.
(See Aircraft Fuel Systems).
From Figure 14 it can be seen that wide variations in air-fuel
ratio exist for different engines and-operating conditions.
This is
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109
particularly true under idle conditions.
Since, as we have seen, pollutant
emission rates vary strongly with air-fuel ratio, pollutant emission also
wi 11 vary widely among aircraft.
In this study, in order to determine
pollutant loads at air terminals, it has been necessary to classify aircraft
by type and to assign average rates of pollutant emission to each type.
Using the emission and operating data presented here, typical emission
rates have been selected for use in estimating pollutant loads.
These
typical rates are listed in Table 40.
It must be kept in mind, however,
that emissions by individual aircraft can vary considerably from these
levels.
The operational data presented in Figure 14 were obtained from
large, radial engines.
In assigning emission rates to small piston engines
(class 6 aircraft), it has been assumed that they are operated at conditions
similar to those of the larger engines, and that their rates of pollutant
emission, on a Ib/lb-fuel basis, also are simi lar.
No data on operational
air-fuel ratios or emission rates have been obtained for light engines.
Avai lable information on operating conditions does indicate, however, that
air-fuel ratios at take-off are higher with light, unsupercharged engines
than with heavier engines (Ref 77).
This difference in take-off condition
is included in Table 40, whereas conditions at all other operating modes
are assumed to be simi lar for all piston engines.
It has been pointed out throughout this discussion that uncer-
tainties exist as to the validity of the emission rates which have been
assigned to aircraft piston engines.
An additional source of uncertainty
is the possibi lity of afterburning, that is, spontaneous combustion of the
engine exhaust gases after emission to the atmosphere.
There is reason to
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110
believe that afterburning does occur under certain operating modes, but
the extent of afterburning is unknown.
in automotive engines, injection
of air into the exhaust manifold is found to be an effective method of
reducing CO and organic emissions, while little effect is noted on NO
x
emission
(Ref 73).
Because aircraft piston engines have shorter exhaust
stacks, exhaust gases enter the atmosphere at a relatively high tempera-
ture.
As a result, afterburning may occur during certain operating modes
and the effective emission rates of CO and organics during these operations
may be less than those shown in Table 40.
ConsequentJy~ the emission
rates used in this study for piston engines may be regarded as conservative.
Turbine Enqine Emissions
In contrast to aircraft piston engi~es, considerable information
exists on pollutant emissions from aircraft turbine engines.
Results of
three studies of turbine engine emissions have been published containing
emission
indices for various pollutants (Refs 78, 79, and 80).
In addition
to these data, aircraft engine manufacturers have measured emissions from
their own engines and have provided emission data for use in this study
(Refs 55, 56, 81, 82 and 83).
Pollutants of concern from turbine engines are:
1.
Carbon monoxide
2.
Organic compounds
3.
4.
Oxides of nitrogen
Part icu I ates
5.
Sutfur diox.ide
As with piston engines, the emission indices (lb/lboo Ib-fuel) of CO,
organics, and NO are not constant for turbine engines, but vary with
x
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111
engine design and operating conditions.
Particulate emission also is
variable with turbine engines and consists mostly of carbon (soot).
This
is in contrast to particulates from piston engines which consist mostly of
lead compounds.
502 emission is of concern for turbine engines because
their fuels contain a small, but significant, amount of sulfur.
The 502
emission index is directly proportional to the sulfur content of the fuel
which, for aviation kerosine, is approximately 0.05 per cent.
Using this
value, the 502 emission index is 1.0 lb/1000 lb-fuel.
Emission indices for CO, organics, NO , and particulates, derived
x
from the data from the sources indicated above, are listed in Table 41.
Emission indices are presented for three operating conditions--minimum,
intermediate, and full power--which correspond approximately to the idle,
approach, and take-off aircraft operational modes.
The data are grouped
according to the three basic types of turbine engines--turbojets, turbofans,
and turboshaft engines--and the test conditions and fuels used are included
in the table.
Identification of the engines tested has been omitted at
the request of the Aerospace Industries Association of America, Inc. (Ref 84).
The emission indices in Table 41 are presented graphically in
Figures 15a, b, c and d.
It is apparent from these figures that reported
emission rates vary widely between engine classes and between engines of
the same class.
Variations in emission rates also are observed between
different engines of the same model.
It is likely that these differences
stem partly from differences in sampling and analysis techniques.
In spite of the dispersion of the data, certain trends are
apparent.
For all engine classes, CO and organic emissions are high at
idle conditions and low at part and full power.
This effect is attributable
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112
to a degradation of combustor performance at low power.
NO and particu-
x
late emissions, on the other hand, increase with power level.
These increases
are related to increases in combustor temperature and pressure, but the
exact mechanisms of NO
x
and carbon formation are not known.
No attempt has been made to correlate these emission data with
specific engine operating variables, because, in the opinion of the authors,
no causative relationship exists between the emission index for any pollu-
tant and any of the primary engine operating variables.
Em i s s ion 1 eve 1 s
are dependent upon characteristics of the engine combustion system which
are only indirectly related to the primary variables such as fuel rate,
air rate, or engine speed.
Effects of engine design on pollutant emissions
are discussed later in the section on reduction of emissions.
In selecting emission data for use in calculating emission loads
at air terminals, one engine was selected as representative of each air-
craft class (see Table 1).
In most cases, the engine selected is in ser-
vice in most of the aircraft in its class.
Emission indices for each
representative engine, as reported by the engine manufacturer, were assumed
to be typical of all engines in the same aircraft class and were used to
calculate pollutant emission loads for all aircraft in that class.
This
approach was used in all cases except that average NO
x
emission indices
for all turbine engines were used for aircraft classes 1, 2, 3 and 7, and
indices for CO and organic emission for class 4 aircraft engines were also
used for class 7 aircraft engines.
The approaches used in these special
cases were necessary because of a lack of data or uncertainties in the data
for various engines.
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113
The emission indices used to calculate quantities of pollutants
emitted during aircraft operations are listed in Table 40.
This table
allows a comparison of emission indices for piston and turbine engines.
It is observed that indices for CO and organic emission for turbine engines
are substantially lower than those for piston engines, particularly at
intermediate and high power levels.
However, indices for NO and particu-
x
late emission are of comparable magnitudes for all engine types.
Quantities of Pollutants Emitted by
Aircraft Enqines
Individual Enqine Emissions
Quantities of pollutants emitted by aircraft engines, referred to
here as emission loads, have been calculated from data presented earlier in
th i s report.
The method of approach employed is first to determine the
quantity of pollutant produced by an engine when it is operated through
a set series of operations.
These operations are chosen to represent
those that occur during a typical landing and take-off cycle for an air-
craft employing the engine (see Table 2).
Four major pollutant species
are considered, these being carbon monoxide, organics, oxides of nitrogen,
and particulate matter.
In addition to determining the total quantities
produced during an LTO-cycle, those produced during individual operational
modes are also determined.
The four modes of operation are:
1.
Idle
2.
Taxi
3.
4.
Ground runs on landing and take-off
Approach and climbout
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114
Emissions of sulfur dioxide are considered separately.
It is
emitted in relatively small quantities and only total emission figures are
given.
The aircraft classification system described in Table l,separates
all aircraft into seven categories and indicates the engine present in the
greatest number in each class.
The calculation outlined above has been
carried out for all seven engines.
The results, given in Table 42, show
that large piston engines (class 5 aircraft) produce the greatest quantities
of carbon monoxide and hydrocarbons whereas turbine engines (classes 1, 2,
3 and 7) produce greater quantities of nitrogen oxides.
The relative capa-
bi lities of all engine types to produce pollutants are shown in Table 43
where a comparison is made of emission loads from various engines with
those from a large turbine engine.
Table 43 also contains similar compari-
sons by aircraft type and allows for the difference in number of engines
per aircraft.
Emissions at Air Terminals
Pollutant loads at several air terminals and in certain urban
areas have been determined from the engine emission data presented above.
A count has been made of all aircraft activity by aircraft type occurring
at the air terminals of interest.
From a knowledge of the number of engines
each aircraft contains, it is possible to express activity in terms of the
number of engines of each category that pass through the airport (See Table
24).
It has been assumed that all engines in each class emit pollutants
at the same rate as the representative engine for that class, and total
airport emission loads ~ve been determined by combining the activity levels
with the calculated emission loads for individual engines (Table 42).
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115
Results for an average day during 1967 are summarized in Tables
44, 45, 46, and 47 as follows:
Terminal or Area
Table 44
J. F. Kennedy
Teterboro
New York City Area
Table 45
Washington National
Washington Area
Table 46
Los Angeles International
Longbeach
Los Angeles County
Table 47
All FAA-Controlled Terminals
Terminals included in the urban areas are I isted in Tables 21, 22, and
23.
Emission loads listed in these tables are summarized in Table 48
with emissions during ground and flight operations shown separately.
Total Emissions by Aircraft Engines
The total quantities of pollutants emitted by aircraft engines in
the United States are of interest and can be estimated from the information
presented in this report.
However, our knowledge of aircraft acitivity is
insufficient for an accurate calculation of the total pollution produced
across the nation by aircraft.
Activity at FAA-regulated air terminals
is well documented, but information on activity at mi litary air terminals
is available only in terms of the total number of landing and take-off
cycles per year and not by aircraft type.
Activity at private airports
is not reported at al I, but is bel ieved to represent less than 10 per cent
of the total national activity.
To estimate the total quantities of pollutants emitted by air-
craft, emissions during cruise operations and air terminal operations were
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116
estimated separately.
Fuel consumption data presented earlier indicate
that approximately 80 per cent of all fuel is consumed during the cruise
mode.
Using fuel consumption data and emission indices corresponding to
cruise conditions, estimates of emissions during cruise have been made and
are listed in Table 49.
Emissions from civi I aircraft during air terminal operations were
taken from Table 48.
(Civi I activity at non-FAA-controlled terminals was
neglected.)
Emissions from mi litary aircraft were estimated using pub-
I ished data on mi litary activity (Table 20) and an estimated distribution
of aircraft types presented earlier (see Aircraft Population).
The esti-
mates of emissions from crui~e and air terminal operations are combined
in Table 50 to indicate the approximate rates of pollutant emission by all
aircraft operations in the United States.
Error Analysis
The elements used and the assumptions made in the calculation of
emission loads are listed in Table 51.
Errors resulting from the use of
aircraft activity data and engine fuel consumption rates are believed to
be small, except perhaps in the calculation of pollutant emission at mili-
tary air terminals where the need arises to estimate the distribution of
aircraft by type.
However, more substantial errors could arise from the
assumptions relating to engine emission rates and the duration of the idle
operational mode.
On the basis of the dispersion of pollutant emission
data for both piston and turbine engines, it is estimated that actual
emission rates may exceed those used in this study by as much as 100 per
cent.
It is also estimated that the duration of engine idling operations,
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117
particularly during busy hours (10 am to 10 pm), may exceed the value used
here (1 minute) by factors between 10 and 30.
The effects of these variations
on engine emission loads during an LTO-cycle are shown in Table 52.
Maximum Possible Emission Loads
Previous estimates of emission loads have been based upon average
operating conditions, that is, average activity levels, mean landing and
take-off cycles, and in some cases, mean pollutant emission rates.
Appre-
ciable departures from average activity levels do occur at times at all
terminals.
Table 53 shows the maximum variations that occur at the airports
of interest in this study.
The variations are expressed as ratios of
peak hourly activity to average hourly activity, and values of three are
typical for large air terminals.
Activity ratios can be used together with the error factors pro-
duced in the previous section to estimate the maximum possible emission
loads at the major airports.
Clearly, idle time is a function of relative
activity level and can be expected to increase rapidly as the level in-
creases.
At peak-hour activity, average idle time can increase to 30 minutes.
This figure has been used together with the peak-to-average activity fig-
ure and increased emission indices to determine the maximum possible
emission loads at J. F. Kennedy air terminal.
The results, given in
Table 54, show that it is quite possible for hourly emission loads to ex-
ceed the average loads given in Table 44 by factors ranging from 5 to
nea r 1 y 20.
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118
Future Trends in Aircraft Enqine Emissions
Changes in the nature and extent of aircraft exhaust emissions
in future years will occur as a result of changes in aircraft activity
levels and changes in equipment.
The effects of these changes cannot be
predicted accurately, but certain impending changes can be identified and
their probable effects noted.
Activity levels are expected to increase in all aviation cate-
gories at the rate of approximately 10 per cent per year.
Consequently,
pollutant emission can be expected to increase accordingly on a daily
average basis.
Peak-hourly rates will not follow the same trend at major
air terminals due to limitations on activity levels of conventional, fixed-
wing aircraft.
Limitations on LTO-cycle frequency have been imposed on
several major terminals by the FAA and it does not appear that these limits
wi 11 be lifted in the near future.
Another form of aircraft activity is appearing which will occur
along with conventional activity, and that is STOL and VTOL aircraft acti-
vity.
STOL aircraft are being introduced in the Northeast corridor on an
experimental basis and it is reasonable to expect that they will enter
regular ser~tce in"the near future.
STOL activities probably wi 11 not
displace conventional activities, since they utilize separate landing
areas.
Principal changes in aircraft equipment anticipated in the near
future are:
1.
Retirement of piston-engine, transport aircraft
2.
Introduction of large, turbine-engine, transport aircraft
3.
Increased use of turbocharged, piston engines in general
aviation aircraft
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119
Decreased use of piston-engine transport aircraft will gradually
eliminate the largest individual sources of CO and organic emission among
aircraft.
These will be replaced with current models of turbine-engine
aircraft mostly of the Class 2 category.
The principal effects of this
replacement wi 11 be a decrease in CO and organic emission and an increase in
NO emission during operations at air terminals.
x
New, super-size transport aircraft, such as the Boeing 747,
Lockheed 1011, and McDonnel-Douglas DC-10, will be in service in the early
1970's.
Fuel consumption rates of these aircraft wi 11 be 30 to 40 per cent
greater than those of current transport aircraft.
However, pollutant emis-
sions are not expected to increase accordingly.
Current efforts by engine
manufacturers to reduce exhaust plume visibility will result in a reduction
in particulate emission by individual aircraft.
Also, the use of annular
combustion chambers in the "jumbo-jet" engines will result in reduced CO
and organic emission.
On the other hand, emissions of oxides of nitrogen
by the new aircraft are expected to increase.
There is a trend in the production of general aviation aircraft
toward increased use of turbocharged, piston engines to provide greater take-
off power and higher altitude capability.
CO and organic emission rates
are greater for turbocharged engines at take-off conditions.
Consequent I y, .
emission of these pollutants by general aviation aircraft is expected to
increase.
To indicate the effects of changes in activity and equipment on
pollutant emission by aircraft engines, estimates of emissions from civi 1
aircraft in the year 1979 have been prepared.
These estimates are listed
in Table 55 and are compared with emissions from civi 1 aircraft in 1967.
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120
Emissions from mi litary aircraft have been omitted from these projections
since mi litary activity in 1979 cannot be predicted reliably from current
trends.
The future trends in aircraft emissions listed in Table 55 were
calculated using the following assumptions:
1.
Activity in aircraft classes 1,2,4,5 and 7 will increase
in proportion to FAA projections of air carrier aircraft in those classes
(Table 9), and total activity in these classes will equal projected air
carrier activity in 1979 (Table 20).
2.
Activity in aircraft class 6 wi 11 increase to the lewel pro-
jected by the FAA for general aviation aircraft in 1979 (Table 20).
3.
In 1979, aircraft classes 1 and 2 wi 11 consist of equal num-
bers of current aircraft models and new "jumbo jetsll.
Emission indices
(not emission rates) for the engines of the new aircraft will be one-half
of current values for CO, organics, and particulates, and It times current
values for NO
x
emission.
4.
In 1979, all class 6 aircraft will be powered by turbo-
charged engines and their emission indices will be changed from current
values by the following amounts:
CO - 10 per cent increase, organics - 30
per cent increase, NO - 20 per cent decrease, and particulates - no change.
x
5.
Finally, it has been assumed that no controls on emissions
from aircraft have been insti"tutedby either Federal, state or~local author-
it i es.
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121
. Summary
In this section, the characteristics of pollutants emitted by
aircraft engines have been described, and the mechanisms by which these
materials are formed have been discussed.
The rates of pollutant emis-
sion by individual engines have been presented, and this information has
been used, along with activity and fuel consumption data from previous
sections, to estimate quantities of pollutants emitted at air terminals.
Finally, future trends in pollutant emission by aircraft engines has been
discussed.
Certain pertinent observations have been made from the
material presented in this section and are as follows:
1.
Pollutants of primary concern emitted by aircraft engines
are carbon monoxide, organics, nitrogen oxides, lead compounds, and
carbon (soot).
Sulfur dioxide is emitted in relatively small quantities
by both piston and turbine engines and is of secondary concern.
2.
Aircraft piston engines, on a nationwide basis, account for
most of the emissions of CO and organics by aircraft.
However, at certain
air terminals, turbine-engine aircraft emit greater quantities of these
materials because of the preponderance of activity by these aircraft.
3.
Aircraft turbine engines, individually and collectively,
emit greater quantities of NO than aircraft piston engines.
. x
4.
Anticipated changes in aircraft equipment will change the
rates of pollutant emission from individual engines.
However, the total
quantities of all pollutants emitted are expected to increase substantially
in future years.
The discussion in this section and the observations made pertain
to aircraft engine exhaust emissions only.
Other emissions resulting from
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122
aircraft activity, such as those from auxiliary power units, have not
been included but may be significant.
In the next section, the effects of aircraft emissions on the
public will be discussed.
Quantities of pollutants emitted by aircraft
engines wi 11 be compared with emissions from other sources.
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123
IMPACT OF AIRCRAFT ENGINE EMISSIONS
This section is a report of factors influencing the effects or
impact of aircraft engine emissions, a consideration of the localized
effects of these emissions, and an evaluation of the relative importance
of aircraft engine emissions in total urban air pollution in the Los Angeles,
New York, and Washington metropolitan areas.
In order to provide a quanti-
tative basis for the analysis of impact, a simple emission and diffusion
model for aircraft operations during an LTO-cycle has been developed.
This model has been used to predict concentrations of four major types of
contaminants in air terminal areas and in the immediate neighborhood of
airports.
Also, gross estimates of the importance of aircraft emissions
have been calculated by comparing the amounts of certain pollutants emitted
by aircraft to the amounts of the same pollutants arising from other
sources in the vicinity of air terminals and elsewhere within metropolitan
areas.
An independent measure of the significance of environmental contami-
nation caused by aircraft emissions is avai lable from the records of public
complaints involving air pollution in the vicinity of major air terminals.
Such data are necessari ly subjective, but they can be helpful in the
determination of geographical limits and possible trends in the detection
of undesirable atmospheric conditions by the exposed population.
For the
present study, records of public complaints of air pollution from aircraft
have been analyzed and the results of this analysis are presented in
Appendix I I I.
Changes in land use near air terminals have also been investi-
gated; such changes may indicate an adverse reaction to environmental
quality in these areas.
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124
Factors Influencinq Impact
Locations of Airports with Respect to Homes,
Businesses, and Central Parts of Cities
The location ~f an air terminal relative to other components of
the metropolitan area is important in the determination of the impact of
aircraft engine emissions.
Ambient concentrations of pollutants emitted
from a defined source area (such as an airport) wi II decrease as the dis-
tance from the source increases.
The principal mechanism for diffusion,
and therefore dilution, of air-borne contaminant material is atmospheric
turbulence, or eddy mixing.
The diffusion rate depends upon the intensity
of atmospheric turbulence, and the turbulence intensity in the lowest part
of the atmosphere is determined by the vertical temperature distribution
and by the roughness of the lower boundary (e.g., flat land, tree covered
land, bui Idings, roads, hi lIs, etc.).
The urban area immediately adjacent to an airport is the highest-
risk region for airport-based emissions.
Thus, the possible impact of air-
craft emissions is related to land use in the vicinity of the airport.
When
the airport neighborhood is primarily residential, the local population
wi II be subject to maximum exposure; when the typical land use is commer-
cial or industrial, the projected exposure to the population (e.g., workers,
40 hours per week) is significantly lower.
Obv i ous I y an Ilopen areall of
unused land around airports would minimize the possible impact of aircraft
emissions upon the urban population.
(The statements in this paragraph
illustrate general principles only; they are not intended to suggest the
necessity of land-use controls in the vicinity of existing airports.)
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It is also evident that the possible impact of airport area
emissions upon an urban population is greatest when regions of maximum
population density are relatively near the airport (within five mi les,
for example) and downwind from the airport for the prevailing wind direc-
tions.
However, area-wide emission rates for contaminants at major metro-
politan airports, discussed later in this section, are comparable to, or
less than, the emission rates for the same contaminants elsewhere within
the subject cities.
Thus the specific impact of aircraft area emissions
would be difficult to detect or evaluate at downwind distances greater
than a few mi les.
Table 56 contains a summary of land use characteristics within
approximately three miles of J. F. Kennedy International Airport,
Washington National Airport, and Los Angeles International Airport.
A 1-
though the tabulated information indicates significant land use near the
airport, it should be noted that important open areas exist adjacent to
each airport:
ocean coastal waters in New York and Los Angeles and the
Potomac and Anacostia Rivers in the capital area.
The J. F. Kennedy Airport is located on the south shore of Long
Island 13 mi les southeast of midtown Manhattan and 3-1/2 miles north of the
Atlantic Ocean.
It comprises an area of 7 square miles and is at an ele-
vation of 22 ft MSL.
The airport is bounded on the southeast through
southwest by Jamaica Bay and numerous salt marshes. A range of hills,
100 to 300 ft in elevation, lies east-west along the major axis of Long
Is land; at their nearest point they are 4 miles to the north of the air-
port.
Areas west through north and to the east are heavily populated and
industrialized.
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126
The Washington National Airport, comprises an area of 1 sq mi Ie
at an elevation of 16 ft MSL and is located on the west bank of the Potomac
River 3 mi les south of the urban center.
With the exception of the Potomac
on the east, it is in close proximity to urban activity.
The relatively
flat Atlantic Coastal Plain extends eastward 50 miles to the Chesapeake
Bay and 100 mi les to the Atlantic Ocean.
The nearest mountains, the Blue
Hills 50 mi les to the west, rise to elevations near 2,000 ft and the
Appalachian range is 100 mi les to the west.
There are hi 11s 200 to 400 ft
in height within 4 to 6 miles in most directions from the airport.
Los Angeles International Airport is at 99 ft MSL.
The coastline
is approximately northwest-southeast about three miles west of the airport
center, but it extends west from Santa Monica to the north and southwest
14 mi les to the south.
The main business district of the city is 11 mi 1es
northeast.
Homes and business developments are located 0.5 mi 1es to the
east and 0.3 mi les to the north.
Oil wells and oi 1 refineries are located
south of the airport boundaries.
The terrain slopes gradually down to
Los Angeles Harbor which is 15 mi les to the southeast.
The Baldwin Hills
four mi les to the north-northeast rise to about 600 ft, and low hi lIs about
4 miles east reach elevations of 250 ft.
The Puente Hi 11s, 20 mi 1es to the
east, range from 1400 to 1500 ft and slope upward southeast into the Santa
Ana Mountains.
Twelve mi les south of the airport, the Palos Verdes hi 11s
rise to an elevation of approximately 1200 ft.
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127
Meteoroloqy and Topoqraphy
General Principles
The lateral and vertical extent of the atmosphere available for
waste (air contaminant) disposal is limited and is significantly influenced
by meteorological and topographical effects.
For a consideration of area
source air pollution phenomena (instead of single point source problems)
it is appropriate to express the 'Idilution capacity" of the lower atmo-,
sphere as the product of the local mixing layer depth and the average wind
speed within the mixing layer.
The mixing layer extends from ground level
upward to some height (typically 500 ft) above which vertical mixing rates
are significantly reduced.
The mixing layer depth is controlled primarily
by the local vertical temperature profile.
When the temperature lapse rate
is adiabatic (neutral stability). contaminants introduced to the atmosphere
near ground level wi 11 mix rapidly throughout the neutral stability layer.
When the lapse rate is less than abiabatic or zero (the isothermal case).
the rate of vertical mixing is lower and the depth of the mixed layer is
usually less.
During inversion conditions. mixing is usually suppressed every-
where above the base of the inversion.
When ground level inversions occur
for extended times. nearly all contaminants entering the atmosphere remain
in the lowest few hundred feet above ground level.
The average wind speed in the mixing layer determines the local
"ventilatio n
rate/I,
Ground level wind speeds are typically lower than
elevated winds because of friction drag.
Thus estimates of atmospheric
di lution capacity based upon surface data only are generally conservative.
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Ideally, wind speed data used for estimates of ventilation shou'ld be
obtained from local vertical soundings.
In addition to the transport and dilution ofconta~inants by the
wind field, other processes can change the character of substances after
they enter the atmosphere.
These processes include the photochemical
creation of new species (e.g., N02 + light - NO + 0; 0 + 02 - 03)' other
chemical changes (organic and inorganic) ,.gravitational settling of
larger particulate material, and the washout of material by precipitation.
Topography can induce local flow patterns which may significantly
modify the transport and dilution or accumulation of air pollutants.
Topography or "surface roughness'!, determi nes the generat i on rate for
mechanically induced turbulence in the lower part of the atmosphere, and
surface thermal differences cause variability in the rates of thermally-
induced turbulence.
Some of the topographic influences which are impor-
tant for evaluating the impact of aircraft emissions include the channeling
of flow through valleys, the persistence and intensification of inversions
in valleys, circulations between land and water areas, urban-rural diff-
erences in surface roughness and thermal characteristics, and wind
intensification on hills and ridges.
Recent investigations concerning
topographic and terrain influences upon air pollution phenomena have been
reported by several investigators (Refs 85 through 97).
Because very little air quality data is avai lable for airport
areas,
the analysis of meteorological and topographic effects upon the
emission and transport of contaminants from aircraft engines must be based
upon studies of general urban air pollution phenomena.
It is reasonable
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129
to inquire whether such extrapolations are valid, in view of the special
nature of large airport areas.
For example,
( 1 )
Is the physical setting or size of a large airport, con-
sidered as an area-source of contaminants, unique?
(As
an illustration, most airport emissions occur along the
taxiways and the runways, and these areas are typically
surrounded by flat, source-free land.)
(2)
Are the micrometeorological conditions at an airport differ-
ent from those elsewhere within an urban area?
(3)
Do aircraft emissions, because of special chemical or physi-
cal properties, or because of their release above ground
level, respond to meteorological influences in a unique manner?
(For example, a typical exhaust jet is hot, and therefore
buoyant, but it is directed horizontally or downward during
take-off .
Thus, it is not possible to take advantage of the
momentum of the jet emission to improve vertical mixing and
diffusion.)
(4) Are the transport processes in the atmosphere near an urban
airport influenced primari ly by sma 11 scale (1 oca 1) meteoro-
logical conditions or by the larger scale (urban and synoptic
scale) conditions?
For example, some airports are located on
the fringes of the metropolitan area where the microclimatology
is essentially semi-rural.
Mechanically induced turbulence is
at a minimum, urban heat island effects are absent, and early
morning inversions are pronounced.
The John F. Kennedy Air-
port is semi-rural in these respects (Ref 98).
On the other
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130
hand, Washington National Airport is very close to the center
of the urban heat island for minimum temperatures (Ref 99).
Climatological Summaries
The following summaries describe typical urban and synoptic-scale
meteorological phenomena for New York City, Washington, and Los Angeles.
An
understanding of these larger scale conditions, which influence micro- and
mesoscale transport and dilution processes within the local atmosphere, is
necessary for the evaluation of the possible air pollution risks arising
from aircraft operations within the three cities.
New York
The climate of New York City and nearby areas is a modified conti-
nental type, being influenced more by the land mass to the west than by the
ocean to the east.
It is characterized by a relatively high frequency of
day-to-day weather fluctuations combined with a tempering oceanic effect.
A high frequency of low pressure systems is associated with the
tracks of major storms moving with the prevailing westerly winds.
Coastal
storms are common in the cooler half of the year.
In the months from April
to September, J. F. Kennedy Airport experiences onshore winds in the sector
from south-southwest to south-southeast with a frequency of 32 per cent.
Maritime influences act in several ways.
There is a more uniform
occurrence of precipitation throughout the year than is typical of an inland
regime.
Average minimum temperatures along the coast are higher than in the
interior.
The mid-afternoon sea breeze occurs during spring and summer in
the New York harbor area and along Long Island, but it seldom penetrates
more than 10 miles.
The sea breeze in the New York area has been studied by
Frizzola and Fisher (Ref 100).
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131
The urban heat island of New York City has been studied recently
by Bornstein (Ref 98).
At the surface, the average urban heat island
temperature excess is 2.9 degrees F, measured between urban and rural sites
near sunrise.
Typically, the temperature excess drops to zero at 300 meters
altitude.
Kennedy airport is relatively uninfluenced by the heat island
effect, and the airport area might be classified as non-urban.
Synoptic
soundings at the air.port indicate a relatively high frequency of surface
inversions near sunrise; within the centrat part of New York such inversions
are etevated because of the excess surface heating.
Washington, D. C.
The Washington climate has the nature of both a continental and
a maritime regime.
This is reflected in the bimodal characteristic of the
annuat surface wind direction frequency distribution.
The SW-S lobe of the
annual wind rose reflects the strong maritime influence of the Atlantic high-
pressure cell.
The WNW-NNW lobe represents the continentat regime of
prevailing westerties.
These effects are also seen in the seasonal wind
roses where WNW-NW winds predominate over the southerly flow in winter and
where SSW-S winds are much more common in summer.
During summer, Washington is dominated by the strong southerly
flow of warm, humid air from subtropical latitudes as storm tracks are dis-
placed farther north.
Cold fronts that dip southward deposit more precipi-
tation during uplift over the Appalachian mountains than at Washington
where the downs tope effect is quite noticeable.
Precipitation during this
time of year is derived almost exclusively from showers and thunderstorms
associated with either frontal or squall-like systems, or with air mass instability.
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132
As autumn approaches, storms of tropical origin, including
hurricanes, may pass northeastward along the atlantic coastline to provide
a significant portion (20-30 per cent) of the rainfall at this time of year.
Large high-pressure areas may dominate the region in October or early
November with associated warm, calm days and cool nights.
Stagnating anti-
cyclones occur more frequently during this time of year.
Late autumn and winter storms originating in Texas, the Gulf of
Mexico, or near Cape Hatteras move northeastward and may pass close enough
to Washington to deposit rain or snow.
Polar air masses behind the associ-
ated cold fronts become generally moderate in temperature in their journey
southward.
Significant microclimatological effects at Washington include the
heat island associated with the densely built-up parts of the city, higher
elevations north and west of the city, and the weak moderating influence of
the Potomac River during summer.
Woolum (Ref 99) has summarized the distribution of temperature and
precipitation as recorded at stations in the Washington Metropolitan Area
Climatological Network.
Average minimum temperature isotherms drawn for the
Washington area for a 15 year period ending in 1960 show a significant heat
island.
This temperature anomaly is centered near the Potomac Yards south
of National Airport with a maximum temperature of 49 degrees F compared to a
minimum temperature of 44.5 degrees at Vier's Mill north of the city.
Al-
though the center of the heat island shifts with season, it is characteris-
tically in the vicinity of National Airport, reflecting the distribution of
bu i It-up areas.
Warmer temperatures also occur in a lobe extending northward
beyond the urban center.
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133
The profiles of maximum temperatures during daylight hours are
unlike those for the minimum temperatures; some of this variabi lity is
probably induced by the local wind patterns.
For example, the maximum
temperature anomaly region for September becomes separated into two weak
cells located east and west of the urban center.
Thus the heat island over
the airport region for the minimum-temperature profile is replaced by a
more uniform temperature distribution with much wider separation of the
isotherms.
This would suggest the afternoon moderating influence of the
Potomac.
However, temperatures as much as 7 degrees F lower occur over the
higher elevations north of the city near Vier's Mill.
Total annual precipitation in the metropolitan region is 41 inches.
Locally the total varies by over 4.5 inches between the driest and wettest
parts of the region.
The least precipitation falls in the Potomac valley
at its intersection with the Anacostia River valley; the maximum occurs at
the higher elevations north of the district.
Monthly totals are greater
from May through September when winds are predominantly southerly.
During
the summer, the relatively cool water of the Potomac River stabi lizes the
air by local cooling from below, and shower activity is lessened.
Orographic
lifting of air over the higher elevations north of the city enhances shower
development in that area.
Los Angeles
Los Angeles lies in the Southern California coastal plain with
the Pacific Ocean to the west and south.
The Los Angeles basin is bordered
on the north by the San Gabriel Mountains, on the northwest by the Santa
Monica Coastal Range, and on the east by the Puente Hills and the Santa Ana
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134
Mountains.
The Palos Verdes Hills on the south coast, although not
extensive in area, do reach heights sufficient to exert a deflecting influ-
ence on local windflow.
The maximum annual frequency of wind direction at
Los Angeles International Airport is 37 per cent in the sector from West to
WSW.
Air trajectories originating over the densely populated regions
of the Los Angeles basin early in the day typically extend east of Pomona
by afternoon and frequently reach Riverside and San Bernardino.
A similar
extension into the San Fernando Valley often occurs.
The sheltering influ-
ence of the terrain and the persistence of low winds and atmospheric stabi-
lity make this large population center an area of significant pollution
occurrence.
Large-scale subsidence of air above the ocean-cooled surface layer
is an important feature of the anti-cyclonic circulation around the Pacific
high-pressure cell.
The subsiding air is warmed adiabatically, providing
...
a layer of warm air above the ocean-cooled surface layer.
This stable
stratification dominates in the area during the spring, summer, and fall.
During most days, a layer of cool marine air enters the coast as
a sea breeze, arising because of strong heating over the land surface.
Sur-
face winds are characterized by a dai ly reversal in direction.
On-shore
winds occur during daylight hours, and the flow direction is reversed at
night as cold air drainage from the surrounding mountains filters out to
sea.
The onset of the daytime and nighttime flow patterns lags sunrise and
sunset by intervals varying up to a few hours depending on location.
The strength and depth of the on-shore sea breeze varies dai ly
and the penetration of fresh marine air can often be distinguished by a
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135
measurable contrast in temperature and moisture content along the sea breeze
front.
Excepting days when fresh marine air penetrates deeply into the basin,
the air beneath the subsidence inversion is usually advected back and forth
across the region.
This occurs because the large-scale atmospheric pressure
gradient does not produce sufficient wind movement to carry air completely
out of the basin.
Thus, accumulation of pollutants in the same air frequently
continues for a period of several days.
The inversion base height is also subject to dai ly oscillation.
Along the coast, lowest heights occur in the late afternoon and early even-
ing; inland locations experience lowest heights during early morning hours.
These daily variations in inversion base heights cause significant changes
in the severity of pollution within the marine layer of air.
These basic phenomena are complicated by local orographic features,
by the existing large scale synopic patterns with their associated pressure
gradients, and by fluctuations in the thermal trough over the adjacent conti-
nental area.
Meteorological air trajectories have been summarized by time
and season for this region by DeMarrais, Holzworth and Hosler (Ref 101).
The California meteorological regime has received intensive investigation
(Refs 92, 102, 103, 104, 105, 106, 107, 108, and 109).
In addition to unfavorable venti lation conditions, the Los
Angeles Basin exhibits other features essential to photochemical pollution.
These include strong sun 1 ight, generally clear skies, and reactive emissions
from dense population centers.
Various long-term projects have involved
measurement and analysis of photochemical reactants and by-products within
the Los Angeles Basin.
Trends, seasonal and diurnal variations, and
geographic variabil ity related to land-population usages have been investigated.
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136
Pertinent treatments have been published by various authors (Refs 110, 111
and 112).
Aircraft Operational Procedures
Fuel consumption rates, the duration of emission, the species of
the contaminant emitted, and the altitude of release are determined largely
by the aircraft operating cycle and by variations in flight procedures due
to unusual circumstances.
These factors can be described by following a
typical turbine-engine aircraft operating cycle from engine start-up to
shut-down at destination.
(1)
Enqine Start-up - A quantity of raw fuel due to the start-up
procedure is released from the exhaust nozzle.
Because of
incomplete combustion, high concentrations of hydrocarbons,
carbon monoxide, and particulates are released during this
procedure.
Significant engine and combustion noises also
accompany this operation.
After start-up, the engine operates
in the idle condition which produces the highest carbon monoxide
and hydrocarbon emission rates.
(2)
Aircraft Departure from Terminal Gate - The jet exhaust pro-
ducts are generally directed toward the terminal as the air-
craft turns to leave the loading area.
The aircraft may be
required to wait on the terminal apron with engines at idle
condition before proceeding.
(3)
Taxi - The engines operate under idle conditions during most
of the taxi mode.
The duration of the aircraft taxi period
depends on the distance from the terminal ramp to the end of
the runway.
The taxi speed is determined by the proximity of
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137
parked and moving aircraft.
The holding time at the end
of the taxi period is a function of the time required for
take-off and the number of aircraft awaiting departure.
When a line of aircraft forms on the taxi strip, emissions
are generally directed along the line into the paths of the
aircraft at the rear of the line.
During unfavorable wea-
ther conditions, or during other operational difficulties,
hold-times may exceed one hour.
(4)
Take-Off - The ground run for take-off occurs under maximum
engine power conditions and at the maximum fuel consumption
rate.
Exhaust temperature and velocity are highest under
this maximum power condition.
(5)
Climb-Out and Noise-Abatement Procedure - The first segment
of climb-out occurs at maximum power up to the altitude
specified by noise abatement procedures.
For example, at
Washington the procedure requires a climb to 1500 feet, at
which point power is reduced to an engine setting computed
for hot-day conditions at maximum gross take-off weight to
give approximately a climb rate of 500 fpm.
This reduced
power is maintained until the aircraft is approximately 10
mi les from the terminal.
The power reduction results in
emissions at lower altitudes for longer times over the metro-
politan area; however, emissions rates are also lower.
(6)
Holdinq Prior to Proceedinq on Course to Destination - Hold-
ing whi Ie awaiting instructions to proceed on course generally
occurs within a 10-mi Ie radius of the airport at an altitude
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138
of a few thousand feet.
The engine operates at cruise power
conditions during this time.
(7)
Cruise - The aircraft cruises above 27,000 feet at a cruise
power setting.
Engine efficiency is high and emission rates
for CO and hydrocarbons are minimal.
(8)
Let-Down and Approach - The aircraft reduces altitude to a
certain geographical position prescribed for approach to the
airport.
Fori'Washington National Airport, the aircraft is at
3000 ft when 10 nautical miles away, 2100 ft at 7 mi les, 1500
ft at 5 mi les, and 900 ft at 3 miles.
Thus the aircraft is
usually well within the mixing layer whi Ie over the metro-
politan area.
Engine power during approach is 40 to 60 per
cent of maximum power.
If weather or operational difficulties
require the aircraft to hold before making the approach to
the field, the holding patterns are at higher altitudes and
usually outside of the 10-mile radius from the airport.
(9)
Missed Approach Procedure - An aircraft missing its landing
approach proceeds to a special radial fix and holds at that
fix while awaiting further instructions.
For example, at
Washington the aircraft climbs to 2000 feet and holds at the
Washington, D. C. radio beacon.
At Los Angeles, it cl imbs
to 3000 feet and holds at Kingfish intersection (over the
ocean) until directed to start another approach.
Maximum
power engine operation is employed during the climb to the
holding altitude, and cruise power is used in the holding
pattern.
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139
(10) Landinq - After touch-down the engine power settings are at
idle until thrust reversal, when high power is applied unti 1
a safe taxi speed is realized.
(11) Taxi - Engine conditions are at idle.
Delays are encountered
if taxi strips or the parking area are fully occupied due to
an overload at the terminal area.
(12) Shut-Down - Some raw fuel and odors are emitted momentarily
during the shut-down procedure.
Aircraft FJiqht,Patterns
The horizontal spreading and the vertical angle of flight paths
reduce the impact of aircraft engine emissions occurring in flight below
that inferred from comparisons of emission totals and contamination per unit
of path length for ground and flight operations.
In comparison to flight
operations, ground operations are confined to a fixed (and relatively small)
area.
Major differences among flight patterns exist for the various
terminals.
At ~. F. Kennedy, flight operations are distributed in four
major directions.
Forty per cent of all operations employ the most heavi ly
used sector, the northwest, and nine per cent employ the least used, north-
east sector.
Take-offs to the northwest are constrained by noise abatement
procedures.
There also are constraints imposed on flight paths by noise abate-
ment at Washington National Airport.
Both landing and departing aircraft
are required to follow closely one of the major rivers; thus very little
horizontal spreading of emissions during flight operations can result from
variation in flight paths.
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140
In Los Angeles at least 95 per cent of all take-offs proceed
seaward (west), and a like percentage of landing aircraft approach the
terminal from the city (east).
Over 40 per cent of all landing operations
at Los Angeles follow a westerly gl ide path which begins 15 or more miles
east of the airport near Whittier.
A similar percentage enters this gl ide
path from the north, and the rest from the south, at distances between 3
and 10 miles from the terminal.
Thus almost all of the landing operations
at Los Angeles pass over a zone to the east of the terminal which is not
more than about 1 mile wide.
Number of Flights and Classification of Aircraft
The total number of aircraft operations and the types of aircraft
determine the amount of the aircraft exhaust emissions in the vicinity of
each airport.
Aircraft operations on the ground produce the greatest amount
of contaminants, and these contaminants are distributed within the passenger
terminal area, on the aircraft ramp and taxi strips, along runways and
into the areas surrounding the airport.
Aircraft activity have been tabulated by frequency and c~assifi-
cation earl ier in this report.
A simpl ified aircraft operational cycle
described in Table 2, was used to estimate the relative importance of air-
craft engine emission in total community air pollution.
Estimates of
total emissions at five major air terminals, in three metropolitan areas,
and over the entire nation are summarized in Table 48.
Diurnal Variation of Aircraft Activity
and Meteorological Factors
A diurnal variation of air quality results from the variation of
all emission sources and the variation of the ventilation rate of the
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local atmosphere.
For area-source and transport phenomena, the venti 1a-
tion rate for the atmosphere can be expressed as the product of the local
mixing layer depth and the wind speed within this layer.
In general, aircraft activity begins with the onset of daylight
hours, increases during the day, continuing well into the afternoon, and
decreases thereafter.
This behavior is typical of most man-related acti-
vities; hence other source activity follows a similar pattern.
The diurnal variation of air pollution potential has been
investigated by Holzworth (Refs 113 and 114), who has prepared monthly mean
mixing depths and average wind speeds from morning and afternoon upper-
air soundings at various locations.
The monthly mean ventilation rates for
New York, Washington, and Los Angeles are shown in Figure 16.
Based on
this long-term climatological data, the diurnal range of venti lation rate
is greatest for Washington and least for Los Angeles.
The diurnal range
for New York is intermediate.
Vertical mixing in the lower layers is suppressed during stable
atmospheric conditions such as during early morning inversions and sub-
sidence and frontal inversions.
The height of the mixing layer increases
during the afternoon as a result of solar heating.
During cloudy and windy
days, the diluting power of the atmosphere changes less, and variations in
air quality are more closely related to diurnal variations in the source
emission rates.
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Local Impact of Aircraft Emissions
An Area-Source Model for Pollutant Concentrations
Near Airport Boundaries
Concentrations reaching nearby receptors downwind from the edge
of an airport may be estimated by an airport area-source model.
Emiss ions
caused by low altitude operations from idle to lift-off (but not climb-out)
are assumed to constitute a surface of randomly distributed multiple sources.
For a first approximation, this surface is considered as a uniform area
source with respect to a receptor located 100 meters downwind from the air-
port edge for sampling times exceeding the temporal variations of emission
strength.
The area of the airport includes the loading area, taxi strips
and runways; the area is configured as a rectangle with one side facing
the prevai ling wind.
Each infinitesimal strip of the area normal to the wind direction
is an effective line source.
Integration of the concentration received
from all strips, starting from the windward edge of the airport to the
downwind edge just short of the receptor, provides a relationship for the
concentration at the receptor due to the area source.
For the infinitesimal strip, the line source formula (Ref 115) is
d X (s) = - 2
J27T
iL~
uo""";:
and the integral for a receptor 100 meters from the downwind edge becomes
X =
2
~
(IOO+L
-9.-, ~
u j ()z
) 100
where X is the concentration, Q is the strength of the area source (rate of
mass emission per unit area), u is the wind speed, s is the distance of the
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143
receptor from any infinitesimal strip source, c- is the standard deviation
z
of the plume along the vertical (a function of travel distance from the strip
to receptor), and L is the along-wind dimension of the airport.
In the range of travel distances appropriate to the airport model
(100 to 5,000 meters), the vertical plume dispersion statistics reported by
Slade (Ref 115) may be approximated by
~ = 0.158 s3/4 (meter) for the ne~tral stabi:ity category (D) and
z
3/4
Oiz = 0.06 s (meter) for the stable category (F).
The resulting expression is
8
--
X = ~ 2\\ '
Q
'I
[( 'i OO+L; 4
1
~ 004 ]
au
where "a1i is the appropriate numedca'j ccefficier!~ from :he expressio;1 for
cr.z (either 0.158 or 0.06).
This relationship has beer. applied to John F. Kennedy, Washington
National and Los Ange!e3 ;~~er~ationaJ Airports, w1th an ass~~ed wi~d speed
of 5 mi1es per hour (2.2 meters per second) and with dowr.wind dimensions of
4000, 2400 and 4000 meters respectively.
Emission densities calculated for
average busy hours (~O a~ to 10 pm) have been used; these estimates, and the
airport area data used 1~ developing the estimates, are summarized in
Table 57.
Emissions during the climb-out and approach modes of aircraft
operation have been excluded because the ~odel treats surface level emis-
sions only.
This exclusion is not a serious limitation for the calculation
of concentrations very near the airport bo~ndary.
The choice of wind speed
(5 miles / hour) is arbitrary; it provides a uniform basis for comparison of
of airport size and emission levels.
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144
Table 58 summarizes the concentrations calculated for the three
airports and for the two stability categories.
The effect of atmospheric
stabi lity is evident:
predicted concentrations differ by a factor of
approximately 2.5 between the neutral and stable cases.
Predicted CO
concentrations exhibit the greatest variability, having a maximum for
Washington during stable conditions.
Long-term average concentrations of
certain pollutants in the Washington and Los Angeles Areas also are listed
in the table for comparison with the calculated values for air terminals.
With the assumed dispersion conditions, the model predicts
contaminant concentrations near airports which represent detectable changes
in expected average concentration in urban areas and which are greater than
the sensitivity of the detection methods normally employed.
Consideration
of predicted concentrations should be an integral part of the planning for
preservation of environmental quality in the vicinity of proposed new or
expanded facilities and of the development of programs to improve environ-
mental quality near existing facilities.
Under certain conditions small groups of receptors can be exposed
in a manner not represented by the area source model.
There are a number of
major air terminals at which residential areas are located along an exten-
sion of a runway or within a mile or less of the end of the runway.
When
the runway is in use the wind is generally parallel to the runway axis and
directed toward the neighboring area.
Residents of such an area may experience
concentrations significantly higher than those predicted by the area source
model.
Field studies of air quality conducted to date have not been
directed toward the evaluation of a specific condition or the validation of
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any prediction model (Refs 118, 119, and 120).
Their findings support a
general conclusion that aircraft engine emissions are presently of minor
importance to metropolitan areas or to specific communities, but they did
not attempt an evaluation of localized impact, either on the residents of
areas near an airport or on travelers and employees within the terminal
area.
A considerable quantity of data is avaitable on air quality from
sampling stations in Los Angeles County, operated by the Los Angeles Air
Pollution Control District, including a station (Inglewood - Sta. 76)
located east (generally downwind) and within about 1/2 mile of Los Angeles
International Airport.
A detai led evaluation of this data, together with
operational data for the airport, is suggested as a future task.
At this
time we are unable to report that observations of air quality in the
vicinity of major airports show positive evidence of deterioration due to
aircraft engine emissions, even though we predict that such changes might
be observed.
Impact Within the Airport Neiqhborhood
An extension of the area-source model, for the meteorological and
source conditions assumed, from 100 meters downwind to 1000 meters downwind
of the air terminals considered, results in the prediction of concentrations
approximately one-half of those indicated in Table 58.
These estimates
represent a conservative upper range for concentrations 1000 meters down-
wind from the three subject airports.
The area source model assumes
constant emission density along infinite cross-wind strips, and the finite
lateral dimensions of the airports cannot be considered as "approximately
infinite" for downwind distances as large as one kilometer.
Consequently,
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146
actual concentrations at these distances wi 11 be less than the concentrations
predicted by the area-source model.
Thus it seems unlikely that any measur-
able impact of aircraft engine emissions will be detected at these distances
(Refs 121 and 122).
Improvement and validation of these predictions would
require the design and conduct of a special study to acquire and relate
concurrent values for aircraft operations, micrometeorological variables,
and ambient concentrations for a selected contaminant or a suitable tracer
at several points.
Many authors cite "visible emissions" from aircraft engines as a
major cause of concern.
Our evaluation of complaints by residents of areas
near Kennedy Airport and another major jetport (See Appendix I I I) indicates
a general adverse reaction by this group to "air pollution".
This may be
due in part to obscuration of the observer's low-angle background, an effect
readily seen during peak operating periods.
We have little data to quantify
such an impact, and it is our opinion that whi Ie it is probably real, it is
of minor importance in comparison to the impact of aircraft noise on these
same observers.
Occasional complaints cite, in part, annoyance due to odors, or
due to soot or oi 1 drops settling on property.
We are aware of no field
data in support of this alleged particulate problem.
Nolan (Ref 119)' has
pointed out that the particles emitted from aircraft engines are quite
simi lar in nature to those emitted from other mobile combustion sources.
Further evaluation of this matter should be undertaken.
Although Nolan
was unable to define a community odor problem in his limited study around
JFK Airport, and although our review of complaints of air pollution attri-
buted to jet aircraft does not demonstrate such a problem, it is difficult
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147
to reject the hypothesis that the characteristic odor of jet engine
emissions is sometimes detected in the neighborhoods around major air
terminals.
Jet noise and, perhaps, fears associated with low-altitude over-
flights have greater impact on the population than air pollution near major
terminals.
This is supported by complaint data, newspaper fi les, inter-
views, and by consideration of past and proposed legislative and legal
actions.
Effective actions to reduce exposures of resident populations to
aircraft noise wi 11 also generally reduce the exposure of these same popu-
lations to air contaminants emitted by aircraft.
Pollutant Concentration Variations Within Airports
The preliminary model described above gives no indication of the
spatial and temporal variations in concentration levels within or near an
airport facility.
Contaminant levels at ground and at altitude, and their
relationship to the mode of activity:
idling, taxi, take-off, climb-out,
approach and landing, could be estimated by appropriate models of each activity.
Within terminal areas, in comparison to neighborhoods, different
modes of exposure, different populations, and higher concentrations of con-
taminants must be considered.
The exposed population consists of (1)
transient passengers and visitors, (2) persons such as taxi drivers, pilots
and flight crews, who repeatedly pass through the area, and (3) airline,
terminal, and governmental employees assigned to duty in the terminal area.
In the first and second cases, the exposure is sporadic.
In the third case
and possibly the second case, an occupational exposure is involved.
The
implications of the exposure differ because of the people exposed and be-
cause of their required activities.
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Visible aircraft engine emissions have not been shown to be of
concern to this population.
The dearth of data reflects the absence of
attempts at evaluation, and may also reflect the lack of effective systems
to receive and record indications of impact.
This population should not be
particularly aware of visible emissions which occur during airborne phases,
take-off, and thrust reversal on landing, but are not associated with
operations near the passenger faci lities.
Emissions of odorous material, or of particulates in the forms
of soot, other solids, or liquid drops, might be expected to affect employ-
ees or transients in the immediate terminal area.
Even though aircraft
engine emissions are known to exhibit a characteristic odor which is fre-
quently detectable in these areas, no evidence of expression of concern with
odors on the part of this population was obtained.
This may again be due to
the absence of a readily available system for registering such concern, but
is also probably attributable to motivation or attitude.
Furthermore,
terminal enclosures at some major airports employ air-conditioning systems
which substantially reduce concentration of odorous material in intake air.
Some oral reports of deposits on cars left in terminal areas have been re-
ceived, but no field studies or complaint records are avai lable to support
these reports.
Human exposure in terminal areas is either occupational in nature,
or quite brief and occasional.
In either instance no significant adverse
effects on well-being are suggested by the predicted concentrations of air
-contaminants in these areas.
Greater exposures could occur during some
conditions, and a more detai led consideration of concentrations in terminal
areas, and of public and employee response to these exposures, is indicated.
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Attempts toocalculate concentrations of contaminants expected within
terminal areas are hindered by the variable configurations of buildings
and open spaces within these areas.
Sample calculations for the case of
a four engine turbine aircraft moving slowly away from a terminal building
result in predicted concentrations which are no higher than those summar-
ized in Table 58~
Repeated fumigation of partially or totally enclosed
areas (possibly caused by frequent aircraft departures from the same gate,
for example) might result in the bui ld-up of significant concentrations,
and it would
be worthwhile to sample contaminant levels in a few such high-
risk areas at the major airports.
More refined estimates of concentrations within air terminal
areas await quantitative descriptions of the initial mixing of engine
exhausts with the ambient atmosphere.
Qualitatively, the engine exhaust
trai I may be considered as being composed of the jet phase and the plume
phase.
The jet phase is described by those characteristics of momentum,
heat and buoyancy that are determined by aircraft engine combustion, while
the plume phase is governed primarily by the ambient atmospheric environ-
ment.
Analysis of the jet and plume require knowledge of the rate at
which momentum and buoyancy are reduced by mixing with the surrounding
atmosphere as well as the atmospheric diffusion process.
Aircraft control
structures, such as flaps, and the aerodynamics of wing-tip vortices, also
modify the jet plume.
At some point in the engine exhaust trail, the characteristics of
the plume are determined entirely by atmospheric diffusion.
The lateral and
vertical plume dimensions at this point might be obtained either by measure-
ment, or by calculation from known heat and momentum characteristics of the
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150
,
jet phase where the jet velocity goes to zero and the temperature becomes
ambient.
For purposes of estimating concentrations at points farther
downwind, it is useful to consider the plume as having originated from a
virtual point source ahead of the aircraft.
The extrapolation to the
virtual source is predicated on the dispersion characteristics of the down-
wind plume.
Travel distances downwind are referred to the virtual point
source in subsequent estimates of pollutant concentration.
Methods of
determining virtual source location in the case of aircraft emissions have
not been specified.
Plumes from aircraft in motion present a class of
diffusion problems not usually encountered in the diffusion meteorology
of stationary sources.
A stationary aircraft emitting at idle setting approximates the
continuous point source model used in estimates of industrial stack emission.
Aircraft moving at speeds much greater than the wind may be approximated
by a model designed for the analysis of instantaneous line sources.
Bet-
ween these two extremes, during the taxi mode, the combined effect of air-
craft and wind motion may significantly alter the dispersion.
For example,
a strong headwind acting on an aircraft in taxi will di lute the emissions
at a rate exceeding the no-wind condition.
A tail-wind comparable in
magnitude to the forward speed of the aircraft wi 11 ultimately reverse
the direction of the effluents and act to collect them in a cloud moving
with the plane.
Describing the development of an aircraft engine exhaust plume
by means of a quantitative model is a necessary step toward assessment of
pollutant concentrations within terminal areas.
This task is recommended
as a subject for future research.
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151
Aircraft Cabin Exposures
Dur i ng tax i i ng, i d ling, and even dur i ng take-off, an aircraft
may be directly exposed to the exhaust of a preceding craft.
The di luted
exhaust can be drawn into the airplane through its ventilating system,
exposing both crew and passengers to contamination.
The obvious manifesta-
tion of this exposure is an odor of exhaust fumes.
In order to assess the
potential hazard to either crew or passengers in this event, calculations
of contaminant concentrations in the wake of taxi ing aircraft were carried
out and are summarized in Figure 17.
Estimates of wake volume were based
on field observations of the near-instantaneous expansion of visible em is-
sions during take-off.
For limited exposures, no hazard is indicated by
the concentrations predicted.
However, several aircraft frequently are
aligned behind one another awaiting take-off clearance at the major air
terminals, and total hold time during periods of peak activity is some-
times of the order of an hour.
It would be desirable to carry out a pro-
gram of sampling for CO within typical aircraft cabins, and particularly
within the crew compartments, during such multiple-source exposure conditions.
Except for some concern in the past over visibi lity reduction on
the runway during multiple take-offs of mi litary aircraft using turbojet
engines with water-injection (Ref 123), we found no references to operational
problems created by visible emissions.
In fact, one verbal report was re-
ceived from a pi lot of small, air taxi aircraft that turbulent exhaust plumes
from large turbine-engine aircraft are easier to avoid when they are visible.
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Relative Importance of Aircraft Emissions in
Total Community Air Pollution
Importance of Operations and of Operatinq Modes
A distinction between aircraft operations on the ground and aloft
should be made, and a distinction between types of aircraft drawn.
In this
way the relative importance of various aircraft and operating modes can be
established, and the possibi lities for improvement can be ranked.
Aircraft
classes and operating modes are summarized in Tables 1 and 2, and Table 48
illustrates 1967 dai ly average emission rates for CO, hydrocarbons, NOx and
particulates by all aircraft operating within the three major metropolitan
areas considered in this report.
Tables 44 through 47 further illustrate the relative importance
of certain classes of aircraft and modes of operation to total emissions of
air contaminants by aircraft engines below 3000 ft in metropolitan areas.
In regions with a preponderance of jet traffic (New York and Los Angeles),
ground-level emissions of CO and hydrocarbons are substantially greater
than emissions aloft.
This is due principally to emissions of CO from
taxiing jets.
Where piston-engine traffic dominates (on a national basis
and in Washington, for example), emissions of these contaminants by air-
craft during flight are greater.
In New York and Washington the phasing
out of large piston-engine aircraft (Class 5) would largely eliminate
emissions aloft of CO, but much greater numbers of small (Class 6) aircraft
wi 11 probably be operated in the future.
In Washington, and nationally,
phasing out of Class 5 aircraft will have a similar effect on total hydro-
carbon emissions aloft.
At major jetports handling Class 1 aircraft
(Kennedy, Los Angeles), emissions of CO and hydrocarbons from aircraft operating
on the ground are far in excess of emissions during approach and climb-out.
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Operations associated with these two terminals are responsible for about half
of total contamination from aircraft in the respective metropolitan areas
(Table 48).
Washington National is slightly less important for aircraft-
caused contamination in its metropolitan area.
In each instance operations
at the major jetport result in less than half (about 40%) of total CO emis-
sions from aircraft in their respective metropolitan areas.
For a further evaluation of the relative significance of emissions
during ground and flight operation~ it i~ interesting to compare ~mi~sions
per unit of path length, thus indicating the potential for contamination of
different air masses.
Table 2 illustrates assumed landing and take-off
patterns for all aircraft types, giving path lengths, average velocities,
and elapsed times.
Emissions per unit of path length have been computed
for the paths illustrated, and the results are presented in Table 59,
Taxi
distances differ among airports and within airports on the basis of the
origin or destination of the aircraft, and because of the runway in use.
Further, the speed of taxiing may vary because of congestion or the nature
of the path.
Thus, a "typical" emission per unit of path length based on a
taxi speed of 15 mph, is computed for the taxi mode, using emission rates
previously stated.
Two aircraft classes were selected to illustrate the range
of contaminant "1 inear concentrations" that are produced.
In general, ground
operations cause substantially greater instantaneous concentrations of
pollutants in the aircraft wake.
Since ground operations also provide
greater opportunity for multiple injections of contaminants into the same
air mass, it is expected that contaminant concentrations in and near air-
craft wakes will be greater for wakes or plumes resulting from ground opera-
tions.
Predictions of actual concentrations are not made because the initial
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154
expansion of the exhaust jet has not been established.
Relationship Between Aircraft Emissions and
Emissions from Other Sources
Lemke et al (Ref 3) for Los Angeles County, Nolan (Ref 119) for
J. F. Kennedy Airport, Hochheiser and Lozano (Ref 120) for the New York
metropolitan area, and Johnson and Flynn (Ref 124) for the San Francisco
Bay area, have calculated total emissions of several contaminants from air-
craft engines and have compared these to emissions from other sources in the
respective areas.
Such values and comparisons are germaine to consi.derations
of the relative importance of these emissions to problems of photochemical
smog and atmospheric turbidity in the areas represented.
Aircraft engine
emissions are not uniformly distributed, however, in either the horizontal
or the vertical.
Nolan and subsequently Hochheiser and Lozano also ex-
pressed emissions as a function of the land area of the terminal from, to,
or at which the activity occurred, but assigned the total of emissions from
all operations below an altitude of 3,500 feet, to the terminal area.
We
suggest as a further extension of this approach that the terminal area be
approximated as an area source whose strength is due to aircraft (and other)
operations on the ground, and that operations aloft be considered as distri-
buted more generally throughout the metropol itan area.
"G round operat i onsll
of aircraft include taxi, idle, take-off a.nd landing rolls, and run-up and
other maintenance operations.
(Evaporative and displacement losses from
fuel ing, motor vehicle emissions within the terminal area, and emissions
from housekeeping activities such as generation of power and heat and cook-
ing should be included also.)
This permits a comparison of the terminal
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155
area to its immediate surroundings, as well as a comparison of emissions
from aircraft engines to totals of emissions in metropolitan areas or
selected portions.
"Terminal area" is defined here as the portion of the
land area of the airport used for aircraft operations, and includes runways,
taxiways, aircraft gate and parking areas, and surrounding land not other-
wise used.
It excludes that portion of the airport land area used for
motor vehicles, fuel storage, passenger and freight facilities, other non-
aircraft operations, and that occupied by bui ldings of all types.
Em is s ions
of contaminants (from engines of aircraft during ground operations) expressed
1 -2
as "emission densities" (MT- L ) are compared to emissions, simi larly ex-
pressed, of those contaminants from sources within nearby areas beyond the
airport boundaries.
These comparisons are made in Table 60 for J. F. Kennedy
International, Washington National, and Los Angeles International airports.
Emission densities in the terminal areas are, of course) greater than they
would be if the areas were unused.
However) Table 60 shows that most emis-
sions are less than they would be if presently adjoining types and degrees
of land use had occupied the areas.
Table 53 shows the relationship between present average activity
and peak activity at major terminals, and illustrates the potential for in-
creases in emissions.
Such activity and the concommitant emission increases,
if realized, could result in carbon monoxide and hydrocarbon emission densi-
ties within the terminals which would be as great or greater than present
emission densities in areas adjoining and near to the terminals.
In turn,
air quality (as influenced by CO and hydrocarbon concentrations, and possibly
by the products of photochemical reactions) in and near the terminals would
deteriorate, perhaps to a lower level than is now found in the adjoining areas.
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156
It should be noted that the emission densities shown in Table 60
for regions neqr terminals are averages for the region.
Large variations
exist, of course, and are illustrated in Table 61.
(The data are derived
from the same sources as used in Table 60.)
It is of interest to compare the sum of all contaminant emissions
from aircraft engines to those from other source categories, within a time
period of interest and within a metropolitan air mass.
Table 62 presents
such comparisons, for Los Angeles, New York, and Washington, with respect
to carbon monoxide, hydrocarbons, oxides of nitrogen, and particulates.
This table shows that air contaminant emissions from ai~craft engines are
a small fraction of the sum of such emissions from surface transportation
sources, and are of even less significance with respect to emissions from
all sources, in the metropolitan areas considered.
There is no reason to
assume that circumstances would greatly differ in any major urban center in
any technologically advanced country.
Generally, greater opportunity exists
for di lution and dispersion of emissions from moving airborne sources, as
compared to stationary or moving sources at the ground prior to exposure of
any receptor.
Substantial fractions of aircraft engine emissions occur
aloft in the areas studies (CO, one/third; hydrocarbons, one/third; oxides
of nitrogen, one-half; particulates, two/thirds; all ratios approximate).
Therefore, except for photochemical, condensation, and light-scattering
processes, aircraft emissions are of even less significance than the
percentages shown in Table 62 would indicate.
The importance of reciprocating engine (piston) aircraft
emission for local and community air pollution in comparison to jet engine
emission, and in comparison to other sources deserves note.
Aircraft
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powered by reciprocating engines emit a substantial portion of the total
contaminatinproduced (viz., over 50 per cent of the total carbon monoxide
discharged annually by aircraft in the New York metropol itan area, and all
of the lead discharged by aircraft); however, these emissions are accompanied
by less noise and less smoke than the emissions from turbine engines.
Lead
discharged by piston aircraft engines, while constituting all of the lead
attributable to aircraft operations (11,000 tons per year), is only 6
per cent of the 190,000 tons of lead discharged each year from motor vehicles
(Ref 125).
Most (70 per cent) of the lead from aircraft is discharged during
fl ight and is therefore more widely distributed than is lead discharged from
motor vehicles.
Carbon monoxide from piston aircraft engines represents
about 80 per cent of the total CO from aircraft operations within metropol itan
a rea s .
However, total CO emissions from aircraft are not significant in
comparison to CO emissions from motor vehicles.
Further, CO from piston
engine aircraft is largely (over 65 per cent) discharged during fl ight.
CO emissions were considered for two major "light aircraftll
facil ities, Long Beach Municipal Airport in Los Angeles County, and
Teterboro Airport (PNYA) in New Jersey (N.Y. Area).
Total carbon monoxide
emissions at those facilities were, respectively, 15 per cent and 6 per cent
of the corresponding values for major terminals in the area (LAX or JFK) in
1967.
Therefore operations at airports of the Long Beach or Teterboro type are
not presently considered of importance in influencing community carbon monoxide
levels.
The growth potential at these facilities is large, however.
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Future Trends
It is clear that increases in aircraft activity and other
factors will bring about increases in aircraft emissions in future years.
At the same time, emissions from other sources are expected to be reduced
substantially as a result of control measures.
Current emission rates
from automobiles and aircraft in Los Angeles County are shown below along
with rates anticipated in the next 12 years (Ref 117):
Pollutant Emissions from Automobiles and Aircraft
in Los Anqeles County - 1000 lb/day
Year Source CO Organics NO
--X.
1967 Automobiles 22,000 4,700 1,040
1967 Aircraft 170 39 6
1979 Uncontrolled 30,400 6,500 1,430
Automobiles
1979 Controlled 9,900 1,200 2,200
Au tomobiles
1979 Uncontrolled 270 71 . 26
Aircraft
These projections indicate that the contributions by aircraft to total
emissions of CO and organics in Los Angeles County wi 11 increase from
current levels of less than 1 per cent to 3 to 6 per cent over a ten year
period.
Sensory Effects (Smoke)
Certain emissions from aircraft engines are not regarded as
hazardous to health, but do produce adverse sensory effects.
Such emis-
sions can be regarded as having an esthetic impact.
Aircraft emissions
in this category include visible or smoky exhaust plumes.
Emiss ion of
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159
smoke by turbine-engine aircraft has an impact upon the populace beyond
its contribution to local and community particulate concentrations.
The
quantity of solid material in an aircraft exhaust plume is surprisingly
small.
During its climb-out mode, the plume from a 3-engine, medium-range,
jet transport is estimated to contain 0.2 pounds of carbon per mile of travel.
But, because of the physical characteristics of this material, it is highly
visible even at this low density.
The impact of smoke trails, therefore,
must be regarded as sensory or esthetic.
Nevertheless, smoke must be
taken seriously since it is a source of criticism from the publ ic.
The
fact that its impact has been registered with the aircraft industry is evi-
dent from reports of efforts by engine manufacturers to el iminate smoke trai Is.
Interactions Between Aircraft Safety,
Noise, and Pollutant Emission
There are three aspects of aircraft operations which are of con-
cern to the publ ic and to government regulatory agencies.
These are safety,
noise, and pollutant emission.
Pollutant emission, at the present time, is
of less concern than the other factors.
Consequently, interactions bet-
ween pollutant emission, approaches to emission control, noise generation,
and safety should be identified to assure that emission control measures
are not proposed which would aggravate other problems.
Aircraft engines produce very high noise levels as well as pollu-
tants.
In the past, most attention has been given to reducing the impact of
engine noise upon surrounding areas.
It would, therefore, be undesirable to
reduce pollutant emissions using methods that would increase engine noise.
Fortunately, the rate of pollutant emission for a given engine at a constant
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thrust setting is not related to the noise generated.
Therefore, changes
to the combustion chamber aimed at reducing emissions wi 11 not influence
the noise emitted.
The only interaction between noise and pollution arises
from the need to reduce thrust settings during climb-out from airfields to
comply with local noise abatement procedures.
This reduction in thrust wi 11
reduce the rate of pollutant emissions, but wi 11 increase the time spent
in climbing to 3000 feet.
The percentage changes in emission rates and
climb-out times are small, and the resulting changes in the total quanti-
ties of pollutant emitted, when satisfying local noise abatement require-
ments, are negligible.
Safety considerations receive the highest priority whenever changes
in aircr~ft operations or equipment are contemplated.
Any modification of
engines to reduce pollutant emission must not reduce the reliability of
engine operation .during flight.
Smoke emission from turbine engines is of concern, particularly
during flight operations, and three approaches to smoke-reduction have been
considered.
The safety aspects of these approaches are as follows:
1.
Changes in combustor design could impair inflight engine
relight capabi lity (ability to start an engine while in flight).
2.
Fuel additives could impair the performance and reliabi lity of
the engine over long periods of operation.
.3.
The use of non-hydrocarbon fuels (e.g., hydrogen) consti-
tutes a greater fire hazard than the use of current aviation
fuels.
At the present time only combustor design modifications are thought to be
a practical approach to emission reduction.
It is now accepted that low-smoke
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combustors can be designed without a significant penalty on performance
or altitude relight capability (Ref 129).
Gaseous pollutants from turbine engines are of concern primarily
during ground operations.
Recommended approaches to reducing these emissions
include improved combustor performance at low power settings and curtail-
ment of ground operations.
These approaches are not likely to affect the
safety of flight operations.
With regard to piston engines, certain approaches to emission
reduction are considered to be impractical as they would degrade engine
performance.
However, exhaust gas treatment, which has been proven to be
effective in automobile engines, should be equally applicable to aircraft
engines, without affecting performance or safety.
There are two other possible interactions between pollutants emis-
sions and safety;
1.
Excessive smoke emissions could reduce visibi lity at the end
of runways.
At this time, reduction in visibility due to
aircraft engine smoke is small, and the resulting effect
upon the safety of aircraft is negligible.
2.
Excessive CO and NO levels near stationary aircraft could
x
result in high concentrations of these pollutants in the air-
craft cabin which could impair the performance of the flight
crew.
At this time these levels are not thought to be high
enough to constitute a hazard, but this potential hazard
should be kept in mind in the future.
In general, it appears that interactions between pollutant emis-
sion, noise, and safety are minor, and that certain approaches to emission
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reduction can be introduced without increasing noise or impairing safety.
In fact, in some circumstances, reduced emissions may improve the safety
of aircraft operations.
Summary
At the present time, two aspects or categories of impact of air
pollutants are recognized.
The first of these is the exposure of persons
or property to concentrations of pollutants which could cause injury or
discomfort.
The second aspect is the degradation of the atmospheric environ-
ment.
Whereas the first aspect is concerned with the health of persons and
the maintenance of their property, the second is concerned with esthetic
values associated with life in an urban community.
Aircraft emissions, like
pollutants from other sources, are of concern from both standpoints.
Aircraft emissions having the greatest impact are those released
during air terminal operations because of the concentrations of aircraft
activity and the fact that this activity occurs largely at ground level.
Because of this concentration of activity at air terminals, emissions from
aircraft have local effects which differ from their effects on the over-all
community.
Loca I Impact
In assessing local
impact of aircraft emissions, we are concerned
with the exposure of persons or property to high concentrations of pollutants
as a direct result of aircraft activity.
Persons most I ikely to be affected
include airl ine or air terminal employees, airl ine crews and passengers, and
residents of areas adjacent to air terminals.
These persons are exposed to
atmospheric concentrations of pollutants resulting from the combined effects
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of aircraft operations and the operation of other pollutant sources in the
community.
If the concentrations of aircraft emissions are higher or lower
than concentrations of pollutants from other sources, the impact of these
emissions can be said to be higher or lower than the impact of other
pollutants.
Present Magnitudes
Field studies of air quality have been conducted in urban areas,
including air terminal vicinities.
These studies have not revealed the
presence of unusually high pollutant concentrations near air terminals.
This evidence, though I imited, has led to the conclusion that hazardous
concentrations of pollutants do not exist generally throughout air terminal
areas.
There are, however, circumstances where persons might be exposed to
pollutant levels well above average levels due to concentrations of aircraft
activity, and these circumstances have not been investigated by field test.
Of greatest concern is the concentration of emissions resulting from air-
craft take-off operations.
The combination of aircraft waiting with
engines idl ing and others beginning their take-off runs at low velocity and
with engines at full throttle undoubtedly results in above average pollutant
levels near the runway.
Exposure of aircraft crew members, passengers, and
residents of neighboring areas to emissions from these operations is a sub-
ject yet to be investigated.
Simi larly, concentration of emission sources
occurs in the passenger loading areas.
Here aircraft emissions are combined
with emissions from other sources including auxil iary power units and
automobiles passing through the terminal area.
If pollutant concentrations at air terminals are similar to those
in surrounding communities, as is indicated by field measurements, the impact
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of aircraft emissions cannot be determined directly because they cannot
be distinguished from pollutants from other sources.
Aircraft emissions
contain essentially the same pollutant ingredients as automobile exhaust
gases.
The impact of aircraft emissions can be assessed, however, by
comparing the density of emissions at air terminals with emission
densities in surrounding communities.
Such a comparison is shown in
Table 60.
With few exceptions, this comparison indicates that the
densities of emissions at air terminals from aircraft alone are comparable
to densities of emissions from other sources in adjacent communities.
Another basis for comparing the impact of aircraft emissions
with those from other sources is provided by calculating pollutant con-
centrations at air terminals resulting from aircraft operations.
Such
a calculation requires a knowledge of pollutant emission rates and an
understanding of meteorological dispersion mechanisms.
Calculated levels
of pollutant concentrations are shown in Table 58 for busy hour activity
levels and two different meteorological conditions.
These are compared
with average community concentrations where these data are avai lable.
Comparisons indicate, where they can be made, that pollutant concentrations
from aircraft at air terminals are approximately of the same magnitude as
average concentrations from other sources in metropolitan areas.
On this
basis, it is concluded that the local impact of aircraft emissions is
comparable to the impact of emissions from other sources.
Also included in Table 58 are recommended I imits on atmospheric
concentrations of pollutants in urban areas.
These 1 imits represent
current opinions on pollutant levels which have impact on either the health
or esthetic values of the populace.
It is evident that local concentrations
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of certain pollutants resulting from aircraft activity are comparable to
these recommended limit values.
Future Trends
In future years, quantities of pollutants emitted by aircraft
are expected to increase if no emission controls are adopted.
Concentra-
tions of these pollutants in air terminal vicinities will increase pro-
portionately.
During the next ten years, concentrations of CO, organics,
and particulates are expected to increase by 50 to 100 per cent, and NOx
concentrations will increase by a greater amount.
Consequently, the
impact of these emissions on persons in air terminal vicinities, though
perhaps marginal today, will become serious in the future.
Community Impact
Aircraft exhaust emissions released during ground operations at
air terminals and during low-altitude fl ight operations over a community
mix with emissions from other sources in the community and contribute to
"background" concentrations of atmospheric pollutants.
These background
concent~ations vary with over-all emission rates and with rates of
atmospheric "ventilation'l determined by meteorological and geographical
factors.
Present Magnitude
Aircraft emissions cannot be distinguished from emissions from
other sources when all are mixed together in the community atmosphere.
Consequently, the relative contribution by aircraft can be determined only
by comparing estimates of emission rates from aircraft with rates from
other sources.
Such a comparison is shown in Table 62 for three
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metropol itan areas.
On the basis of estimates of ai rcraft emissions made
during this study and estimates of emissions from al I sources made by
other investigators, aircraft emissions constitute between 0.2 per cent
and 2.3 per cent of all CO, organic, NO , and particulate emission in
x
the areas considered.
Future Trends
It is clear that increases in aircraft activity and other
factors will bring about increases in aircraft emissions in future years.
At the same time, emissions from other sources are expected to be reduced
substantially as a result of control measures.
Future projectJons indicate
that the contributions by aircraft to total emissions of CO and organics
in urban areas will increase from current levels of less than 1 per cent
to 3 to 5 per cent over a ten year period.
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REDUCTION OF AIRCRAFT ENGINE EMISSIONS
This section of the report comprises a description of the various
available methods for reducing the quantities of pollutants that are emitted
by aircraft engines.
Whenever possible the effectiveness of each method
is evaluated.
For discussion purposes emission reduction methods can be
categorized as follows:
1.
Engine modifications
2.
Aircraft modifications
Fuel modifications
3.
4.
Flight pattern modifications
5.
Ground operations modifications
To be regarded as practical, an approach to reducing pollutant emission
must be both effective and feasible.
In other words, the approach must
offer substantial reductions in pollutant emission without imposing un-
justifiable costs on the operator of the source.
Modifications to Enqines
It has been shown earlier that the nature and quantities of
pollutants emitted from piston engines differs markedly from those from
turbine engines.
They will, therefore, be considered separately.
Piston Enqines
The approach taken in this section involves a review of emission
control measures in use in automobile engines, and, subsequently, a dis-
cussion of the practicabi lity of applying simi lar measures to the control
of exhaust emissions from aircraft piston engines.
The subsection dealing
with automobile emission control has been reproduced from Reference 73.
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168
This material, in the opinion of the authors, represents a comprehensive
review of the subject quite pertinent to control of emission from aircraft
piston engines.
Exhaust Emission Reduction in Automobile Engines
Two major sources of air pollutants from the gaso1 ine engine,
the crankcase and the exhaust, are now subject to control.
Crankcase emission control systems have been required by law on
all new cars sold in Ca1 ifornia starting with the 1963 model.
However,
control devices were installed voluntarily by automobile manufacturers start-
ing with the 1961 models on almost all new vehicles produced for the
C'a1ifornia market, and subsequently for the entire country.
Commencing with the 1966 model year, most new cars sold in
California were required to meet standards for content of pollutants emitted
in the exhaus t.
These standards are being app1 ied nationwide to all new
automobiles beginning with 1968 models.
The emission standards for motor
vehicle contaminants are:
Hydrocarbons
--275 parts per mill ion by volume as hexane.
(0.165 mole per cent ca r bon atoms.)
Carbon Monoxide -- I . 5 pe r cent by volume.
The Ca 1 i fo r n i a Motor Vehicle Control Board's compl iance test pro-
cedure, commonly known as the "Cal ifornia Cycle" test, consists of a pres-
cribed sequence of vehicle operating conditions on a chassis dynamometer
using combined samp1 ing of an exhaust gas through an analytical train.
This procedure is designed to simulate an average "trip" in a
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169
metropolitan area of twenty minutes from a cold start.
The test consists
of two parts:
four 7-mode warm-up cycles and three 7-mode hot cycles (5th
cycle not read).
The average concentration of the warm-up cycles and the
hot cycles are combined to yield the reported values.
Exhaust gas concentra-
tions are adjusted to a dry exhaust volume containing 15 per cent by volume
of carbon dioxide plus carbon monoxide.
Hydrocarbons are defined as the organic constituents of vehicle
exhaust as measured by a hexane-sensitive nondispersive infrared analyser
or by an equivalent method.
The basis for the cycle was a field survey, made in Los Angeles
a decade ago, to establish a typical driving pattern.
The use of this
cycle for system development and surveillance has been subject to criticism
because it may not represent a realistic current vehicle use pattern, nor
be applicable outside the urban Los Angeles area.
Nevertheless, it is the
only presently available universal testing procedure for determining and
comparing the performance of exhaust emission control systems.
It is possible through control of certain design and operating
variables to reduce the amounts of unburned hydrocarbons and carbon monoxide
which are produced by an engine.
The most important of these is carburetor
mixture control.
A survey run in California in 1956 showed average un-
burned hydrocarbon emissions were approximately 1400 ppm.
The accuracy of
this value may be open to question because of instrumentation problems
associated with the survey.
It is generally agreed, however, that the
exhaust emission of current model automobiles not equipped with controls
is approximately 900 ppm hydrocarbons.
This suggests that evolutionary
changes in engine design may be responsible for a substantial reduction in
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170
average exhaust emissions from vehicles not equipped with exhaust controls.
Other factors which can reduce e~issions of hydrocarbons are:
decrease in the relative amount of surface per unit volume of the combustion
chamber; decrease in compression ratio; avoidance of dead space and pockets
in the combustion chamber; optimization of ignition timing; the use of an
automatic transmission; increasing average operating temperature; and free-
ing the combustion chamber from deposits.
Three means for reducing exhaust hydrocarbon and carbon monoxide
are presently being uti 1 ized.
The first is engine operation modification
which incorporates leaner and more precisely controlled carburetor mixture
ratios.
This is accompanied by spark adjustment, particularly at low engine
speed.
The second development is the provision of air pumped into the
exhaust manifold and directed into the exhaust gases immediately at the ex-
haust valves.
The last of the three approaches involves design and manufacturing
considerations.
Careful atten~ion is paid to those factors which produce
unburned hydrocarbons as a result of flame quenching or stagnant pockets
and recesses in the combustion space outline.
One example of a manufactur-
ing improvement to reduce emissions is better matching between cylinder head
and gasket.
Prior to the application of control devices, in~5er~ice'vehidLe
exhaust gas hydrocarbon content was me~sured as 900 parts per million and
carbon monoxide was about 3.5 per cent, using a cycle simi lar to the
present Cal ifornia Cycle as the test procedure.
In the average current
production vehicle, these emissions have been reduced to approximately 275
parts per mi II ion of hydrocarbon and 1.5 per cent carbon monoxide as
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prescribed by the California standard.
Controversy exists, however, with
respect to how well the standards have actually been met, both in new cars
as delivered and as tested after a few thousand miles of use.
Information on conformity of present systems to established
standards, other than that from the manufacturers, comes from two sources,
the State of California Motor Vehicle Pollution Control Board and the
National Air Pollution Control Administration, U. S. Public Health Service.
Reports from these two sources indicate that the present systems undergo
progressive deterioration with time and operation.
The systems start out
well within control standards, but emissions are either equal to or exceed
the I imits after 10,000 miles of operation, which is approximately the
average yearly mileage accumulation in Cal ifornia.
Maintenance of carburetor
and ignition adjustment are important factors.
Obviously a system require-
ment which depends upon close maintenance will have more difficulty
achieving long term conformity to a standard which is barely satisfied at
the outset.
Because of variabil ity in production, emissions from new cars
will vary around an average value.
Some of these may and do exceed stated
standards, but certification is based on averages weighted on production
volume.
Obv i ous I y qua Ii ty contro lis a factor wh i ch must be given close
attention.
The data on which the performance of presently installed devices
is based is relatively meager.
The only specific data avai lable at this
time indicates that the hydrocarbon levels in a group of vehicles from the
Los Angeles area have reached 282 parts per million after one year of
operation.
Various reasons for this exceeding of standards have been offered,
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including those of statistical reliability.
These results are important,
however, and if taken as received, they indicate that the average California
vehicle meets the State standard for only a relatively short period of oper-
ation.
There are insufficient data to indicate what might be the ultimate
emission levels for those presently equipped vehicles.
Future Emission Control Methods
Considerable work is in progress in the automotive, petroleum, and
other industrial laboratories, and in Federal installations, directed to-
ward the development of future emission control systems for spark-ignition
gasoline engines.
Four approaches are being followed in this research:
(1) modifications in the design or operating adjustments of engines to
produce minimum emission levels in the exhaust gas leaving the engine cylin-
ders; (2) post-cylinder exhaust treatment of reactive pollutant emissions
prior to their exit from the tai lpipe; (3) recycling of a portion of the
exhaust gas to the engine intake to lower the temperature of engine combus-
tion to reduce the production of nitrogen oxides; and (4) systems to prevent
evaporation of gasoline from the carburetor and fuel tank.
Although it is generally agreed that hydrocarbon and carbon
monoxide reductions are desirable, nitrogen oxide control is not required
by Federal standards, nor is compliance with the California standard of
350 parts per mi 11 ion required unti 1 two or more control devices are tested
and approved.
However, control methods are being studied by industry and
by government laboratories to meet California requirements in case a deci-
sion in favor of Federal nitrogen oxides control should be reached.
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Engine Design
The engine modification (as opposed to air injection) systems for
control I ing hydrocarbon and carbon monoxide emissions, currently in produc-
tion on some 1967 cars in California, rely predominantly on carburet ion and
spark-timing adjustments for their effectiveness.
The use of these procedures
requires either compromise with operational characteristics other than
emissions or engineering improvements in the engine-carburetor system.
Both carburetion and timing were originally optimized for other operational
characteristics.
It has been found possible to improve carburetors and engine
induction systems in general and to satisfactorily engineer spark-timing
changes so that the necessary adjustments could be made.
With engines having
certain basic design characteristics, these adjustments are sufficient to
attain the 1966 California or 1968 Federal emission standards.
Careful fuel control through advanced fuel injection systems as
well as carburetors wi 11 permit optimization of air-fuel ratios for reduced
carbon monoxide and hydrocarbon emissions.
However, these systems increase
cost and introduce design, manufacturing, and adjustment problems.
Other engine design factors which affect hydrocarbon and/or
carbon monoxide emissions are:
displacement per cylinder
compression ratio
combustion chamber surface-to-volume ratio
parasitic volumes in the combustion chamber
combustion chamber surface temperature
valve timing
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174
cyl inder gas motion
Among the vehicle design factors affecting emission levels are:
weight and frontal area
power-to-weight ratio
rear axial ratio
transmission type
By careful optimization of all engine and vehicle design factors,
along with suitable carburetion and spark-timing adjustments, it is 1 ikely
that vehicles averaging 180 ppm hydrocarbon and 1 per cent carbon monoxide
could be manufactured in the future.
It is also 1 ikely that some vehicles
could be manufactured at considerably lower levels, perhaps as low as 100 ppm
hydrocarbons and 0.8 per cent carbon monoxide.
However, if every vehicle
were required to attain such levels by these means, severe 1 imitations on
the variety and versatility of vehicles marketed,would be required, and
many vehicle characteristics now taken for granted would be el iminated.
Many engine design and adjustment changes which effect reductions
in hydrocarbon and carbon monoxide emissions unfortunately increase nitrogen
ox i de em i s s ions.
Almost any modification which increases engine thermal
efficiency also increases nitrogen oxide emissions.
The engine designer
is thus faced with a di lemma if he seeks to simultaneously control all
three emissions.
At present it appears that the only solution to concurrent
control of all emissions by engine design and adjustment factors alone
would be operation with extremely lean combustion mixtures of greater than
18 to 1 air-fuel ratio.
While such operation might be technically feasible,
it is completely non-commercial at this time from the standpoint of a
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175
satisfactorily driveable vehicle.
Simple Air Injection
The exhaust port air injection control systems currently in
production meet the 1966 Cal ifornia and 1968 Federal standards of 275 ppm
hydrocarbons and 1.5 per cent CO, when weight-averaged according to sales
volume.
Although some minor improvements in these systems might result
from further engineering development, e.g., optimized air flow, timed air
injection, and more carburetor and spark-timing optimization, a major
change in approach is required if further significant improvements in
hydrocarbon and carbon monoxide reductions are to be made.
The simple air injection system has no appreciable effect on
nitrogen oxide emissions.
Large Manifold Air Injection Reactors
Several laboratories have demonstrated exhaust emission control
systems which deviate significantly in approach from the simple air injec-
tion systems now in production.
These methods involve large exhaust mani-
folds (reactors) which give the exhaust gases additional residence time for
reaction, and they employ insulation of some form for heat conservation.
By thus providing increased time and temperature for reaction, they al low
considerably better clean-up of hydrocarbons and carbon monoxide than do
the simple air injection systems.
Laboratory demonstrations on individual
vehicles have attained emission levels of 27 ppm hydrocarbons and 0.8 per
cent carbon monoxide.
One such system currently undergoing life testing
and still in operation had maintained hydrocarbons below 50 ppm and CO
below 0.8 per cent for 50,000 miles.
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176
While this demonstration of technical feasibility is certainly
promising, it must be pointed out that there are serious obstacles remaining
on the route to commercial feasibility with this system.
Temperatures above
1000 deg F are required in the reactor to maintain effectiveness, but tempera-
tures above 1700 deg F result in greatly decreased durability even if exotic
and expensive construction materials are used.
Severe damage from engine mis-
firings or backfires can occur.
In addition, the space requirements under
the hoods of cars, as they are designed today, are difficult to meet, and
higher underhood temperatures from some configurations can be a problem.
It
is anticipated that with sufficient development time these problems, and
others yet unknown, can be overcome without unreasonable costs.
The large manifold air injection reactors also have no direct
effect on nitrogen oxide emissions.
However, one combination of systems
has been tried in which rich air-fuel mixtures are supplied to the engine,
giving lowered nitrogen oxide emissions (approximately 500 ppm) but high
hydrocarbon and carbon monoxide emissions.
The hydrocarbon and carbon mono-
xide emissions are then subsequently reduced in the large manifold reactor.
This arrangement puts a heavy heat load on the manifold reactor, and,
causes some loss in fuel economy, but it does present one means of making
simultaneous attacks on all three emissions.
Direct-Flame Afterburner
The direct-flame afterburner is installed.Jn the exhaust system
and provides for flame oxidation of unburned fuel and carbon monoxide.
As
the term is commonly used, it does not include exhaust manifold air injec-
tion reactors.
Afterburners must be provided with a supply of air to support
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177
combustion, and a spark plug and energy source to initiate burning.
These devices have a lean 1 imit below which combustion cannot be
maintained.
For example, an afterburner will not ordinari ly burn with the
amount of chemical energy available in the exhaust with the usual cruising
mixtures supplied to gasol ine engines.
Therefore, carburetor enrichment
has commonly been used or additional fuel added in the afterburner, with
attendant disadvantages and problems.
Catalytic Converters
During the years 1957-1964 considerable work was done in industry
to develop catalytic converters for the reduction of hydrocarbon and carbon
monoxide emissions.
These converters operate quite effectively when new,
but rapidly lose their effectiveness with increased miles of operation due
to deposits from tetraethyl-lead fuel additives which coat the catalyst.
After 12,000 miles of operation most catalytic converters fail to meet the
Cal ifornia standards of 275 ppm hydrocarbons and 1.5 per cent carbon monoxide.
Work on catalytic converters was virtually stopped in 1964 when
it became clear that the engine modification and air injection approaches
were adequate for the 1966 standards.
The 1 imited 1 ife of the catalytic
converters with leaded fuels was considered a serious disadvantage.
Today, when more stringent emission reduction requirements are
a serious consideration, catalytic exhaust treatment is once more competing
for attention since it has good potential for attaining very low hydrocarbon
and carbon monoxide levels.
Levels of 50 ppm hydrocarbons and 0.5 per cent
carbon monoxide have been attained with the use of catalysts uncontaminanted
by lead.
To real ize this control commercially, the lead contamination problem
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178
must be solved, and the most ready solution to this problem is the
marketing of unleaded gasoline.
This, in turn, represents an economic
problem involving increased gasoline cost to the customer and higher capi-
tal investment for the oi I industry.
Lead "fi Iters" or lead removal from
exhaust by reaction ahead of the converter have also been proposed, but
these have not proved successful as yet.
Even with unleaded gasoline, there is sti II some question about
catalyst life.
High temperatures for extended time periods tend to give
"glazing" of the catalyst and reduce surface area.
The effectiveness of
the catalyst is thus reduced according to a time-temperature function, and
some reports indicate lifetimes of less than 25,000 mi les, even without
lead.
Other data suggests that catalysts may run as long as 50,000 mi les
with no deterioration under some conditions.
Since most catalytic converters require the addition of air to
the exhaust for complete effectiveness, the possibility of combining them
with current simple air injection systems is obvious.
Assuming the lead
problem is solved, this arrangement appears quite attractive, although numer-
ous durabi lity, packaging, and cost problems must sti II be overcome before
commercial feasibi lity is proven.
Nitrogen oxide emissions may also be reduced by catalytic means,
although no prototype system has yet been demonstrated on a car under a
wide range of operating conditions.
In general, the most feasible approach
seems to be with rich air-fuel mixtures giving sufficient carbon monoxide
to reduce the nitric oxide with a catalyst.
The nitric oxide reduction
catalyst is then fot towed by air introduction and a second catatyst bed to
eliminate the remaining carbon monoxide and the hydrocarbons.
The system
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179
appears complicated and costly, and its technical and economic feasibility
has not been demonstrated.
Exhaust Recycling
The most effective system for reducing nitrogen oxide emissions
appears to be exhaust gas recycling.
In this system, 10 to 20 ,)er cent of the ex-
haust gas is withdrawn from the exhaust manifold or exhaust pipe and with
suitable flow controls is introduced in the intake manifold of the engine.
This reduces peak cycle temperatures in the cylinder, and the burning rate
is decreased, with significant reductions in nitrogen oxide emissions.
Emissions levels below the California standard of 350 ppm have been attained
by this procedure.
However, problems sti II remain.
The amount of recircu-
lation is critical; too much increases the hydrocarbon and carbon monoxide
and can cause losses in vehicle performance, power, economy, and driveabi lity.
Exhaust recirculation and lean mixture operation for hydrocarbon and
carbon monoxide control appear to be entirely incompatible.
Nevertheless, a combination of exhaust recirculation with air
injection permits simultaneous control of hydrocarbons, carbon monoxide,
and nitrogen oxides within the current California standards with only
driveabi lity, and perhaps durabi lity, as unsolved problems.
These diffi-
culties should be overcome with sufficient development time.
Estimated Attainments for Exhaust Control
In discussing probable attainments of future emission control
systems, it is first necessary to define the present use of the term
IIfeasibi lity.1I
Two levels of feasibi lity are used in this discussion, as
follows:
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180
Demonstrated Technical Feasibility = Emission control at a given
level has been achieved experimentally in the laboratory on at least one vehicle.
Commercial Feasibility = Emission control at a given level is at-
tained on a vehicle which performs the required transportation function, is
manufacturable, and is acceptable to the public in all respects, including
economics, durability, performance, convenience, esthetics, psychology,' etc.
From these definitions, it may be clear tha't itis a long and diffi-
cult obstacle course for any emission control sy~te~ ~b 'travel from techni-
cal feasibility on one vehicle to commercial feasib'ility on approximately
nine million vehicles per year.
Nevertheless, the'~ontrol systems used in
California have surmounted these obstacles, and it i!~ anticipated 'that in time
some of the improved future systems described he'r'ewill also' rea'ch p'roduction.
The table below indicates estimates of the levels of emissions
and times of attainment for spark-ignition gasoline engines.
EsTIMATED CHARACTERISTICS OF FUTURE EMISSION CoNTROL SYSTEMS 1.1
DE.\fOSSTRA TED
TECHNICAL FEASIBIUTY
ULTIMATE FEASIBILITY
Year
1967
Hydrocarbons ppm (as hexane).
Car1:>on Monoxide %.........
Nitrogen Oxides ppm. . . . . . . . .
50
0.7
500
275
1.5
350
Hydrocarbons ppm (as hexane).
Carbon Monoxide %...... ...
Nitrogen Oxides ppm. . . . . . . . .
<25
<0.2S
97'
[IJg
0.5
250
(I) Spark.lgnition gasoline engines tested according to California Standard Cycle Test Procedures lor hydrocarbons and earbon monodde
(bag sample lor nitrogen oxides) and welght-ayeraced ;lccord/nll to yehlcle sales volume.
(Z) Table based on simultaneous attainment 01 tho three (IIC, CO, NOx) emission levell.
The demonstrated technical feasibility section of the table repre-
sents emission levels which have been attained in several laboratories.
It
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181
may be noted, however, that difficulties exist in obtaining simultaneous
low levels of hydrocarbon and carbon monoxide along with low levels of
nitrogen oxides.
Therefore, two possibi lities are listed in the table
depending on the particular combination of levels for the different emis-
sions that are desired simultaneously.
Although serious commercial problems
sti 11 exist with both of the stated combinations, it is believed that these
problems wi 11 be solved in a reasonable manner.
The expected ultimate control figures represent emission levels
demonstrated for single pollutants in laboratory systems, but not levels
which have been demonstrated simultaneously for all pollutants, even in
laboratory systems.
These emission levels may well be reached with suffi-
cient development work some time after 1980.
The commercial feasibility figures for 1967 represent the emission
control systems currently in production for new cars sold in California.
These vehicles have no special control systems for nitrogen oxides.
In
1970 it is believed that two possibi lities exist.
Either hydrocarbon and
carbon monoxide levels can be reduced, and moderate reductions in nitrogen
oxides can be obtained, or hydrocarbon and carbon monoxide can be left at
their 1967 levels, and nitrogen oxide control to the 350 ppm level could be
atta i ned.
In either case, problems with presently unknown solutions must
be resolved in the intervening period.
Beyond 1970, it is anticipated that further commercial problems
wi 11 be solved to the extent that the currently demonstrated technically
feasible control systems can be put in production.
In addition, some further
improvements in carbon monoxide and nitrogen oxide control beyond the 1967
technical feasibi lity level are expected.
If required, these levels could
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182
be attained with adequate notice.to industry as early as 1975, but more
optimized and less costly solutions w.i 11 undoubtedly be avai lable in later
years.
Cost estimates for these future systems are more speculative.
The
1967 systems add $25 to $50 to the vehicle sales price.
It is estimated that,
using the control system approaches described above, the emission levels
in the table for commercial production in 1975-1980 might be attained at
costs of $50 to $300 above that of the normal uncontrolled vehicle.
Application of Automobile Exhaust Emission
Reduction Methods to Aircraft Piston Engines
In the preceding discussion, two "ultimate" approaches to reduction
of most piston engine exhaust emissions have been identified:
1.
Operation at very lean mixture ratios, or
2.
Operation at very rich mixture ratios with auxiliary
exhaust conversion devices.
The first approach is not presently feasible for the automobile and may never
be feasible for aircraft piston engines because it involves a reduction in
power to weight ratio.
The other approach, however, would seem to be parti-
cularly appropriate to aircraft piston engines since, during the LTO-cycle,
they operate at comparatively rich mixture ratios.
At the present time, methods for reducing exhaust emissions from
automobiles can be regarded as interim methods.
They satisfy current emis-
sion control requirements, but wi 11 not be adequate to meet future require-
ments.
In the future, presently used emission reduction methods may be
discarded in favor of improved methods.
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183
Since aircraft piston engines represent a relatively small pollution
source at the present time, it would be impractical for manufacturers of
these engines to follow the same route to emission reduction as is being
followed by automobile manufacturers.
Rather than develop interim reduc-
tion methods, it would be more practical to work directly toward an lIultimatell
approach offering emission
levels which wi 11 meet future control require-
ments.
Current emission loads could be tolerated during the period required
for development of a practical emission reduction method.
The logical, long-term approach to control of emissions from air-
craft piston engines is through exhaust gas conversion or afterburning.
As
mentioned previously, afterburning may occur naturally with aircraft engines
due to the high temperature and fuel content of the exhaust gases.
To the
extent that natural afterburning is not sufficient to reduce emissions to
an acceptable level, auxiliary devices can be employed.
These include:
1.
Exhaust port air injection
2.
Large manifold air injection reactors
3.
4.
Direct-flame afterburners
Catalytic converters
At the present time, exhaust port air injection is the only feasible ap-
proach as the others have not been fully developed.
Air injection could
be adapted to new aircraft piston engines at approximately the same cost
as with automobile engines, and simi lar emission reduction might be expected.
As indicated in Table 38, concentrations of CO and organics J~ aircraft
piston engine exhausts during idle and full power operation are in the follow-
ing ranges:
cO--6 to 12 per cent, and organics--7000 to 11,000 ppm.
Reduc-
tion of these concentrations to levels currently attained in automobiles
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184
(CO--l.5 per cent, organics--275 ppm) would constitute a reduction of CO
emission of nearly go per cent and a greater reduction of organic emissions.
The application of air injection reactors or direct-flame afterburners,
which would require development effort, probably would result in even
greater reductions in emissions.
Use of Alternate Engines
Another approach to reducing certain piston-engine emissions is
the replacement of piston engines with turbine engines.
Replacement is not
feasible at present for light aircraft since turbine engines are not avail-
able in the low power ranges.
Also~ the costs of those which are avai lable
in the medium power range prohibit their use in most private aircraft ap-
plications.
On the other hand, replacement of piston-engine transport air-
craft (class 5) by turbine-engine craft is occurring rapidly.
These aircraft
are being replaced by medium-range aircraft powered by turbofan engines
(c lass 2).
This substitution results in changes in emissions per aircraft
approximately as follows:
co--g6 per cent reduction, organics--95 per cent
reduction, NO --200 per cent increase, particulates--IIO per cent increase.
x
Turbine Enqines
Considerable effort has been directed towards smoke abatement
in aircraft turbine engines, as well as in gas turbines for other uses.
Good descriptions of this work may be found in References 12, 13, 130, 131
and 132.
Durrant (Ref 13) and Toone (Ref 130) describe the approaches taken
at Rolls-Royce, Faitani (Ref 12) describes similar approaches at Pratt and
Whitney Aircraft, and Fiorello (Ref 131) describes the U. S. Navy Smoke
Abatement Program.
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185
On the other hand, reduction of emission of other pollutants has
not been studied extensively.
As described earlier, emission levels of
gaseous pollutants have been measured, but not correlated in a quantitative
manner with engine design parameters.
Durrant (Ref 13) does deal qual ita-
tively with possible ways of controlling gaseous emissions.
For the purposes of this chapter, no distinction wi 11 be made
between turboprop, turbofan, and turbojet engines.
The emission of pollu-
tants is dependent primari ly upon combustion chamber design and operating
conditions, and these do not vary substantially among different turbine
engine types.
Smoke Reduction
It was explained earlier that carbon is formed by combustion of
fuel-rich mixtures.
In combustion chambers, smoke is produced from local
pockets of fuel-rich mixture even though the mixture strength averaged over
the combustion zone may be stoichiometric or fuel-lean.
In a gas turbine
combustor, the main source of carbon formation is in the primary combustion
zone, and to reduce carbon formation, the fuel-air ratio in the primary
zone should be kept to a minimum.
This may be done in practice by increas-
ing the air-flow into the primary zone, and by faci litating the mixing
between the fuel and air.
It is now possible by careful combustor design
to greatly reduce smoke emissions without increasing the cost of the
combustion chamber and without significant performance penalties (Ref 129).
Durrant (Ref 13) states that the new large transport engines will have
barely visible levels of smoke emission.
Four major design approaches to
smoke reduction which have been identified are discussed in the following
paragraphs.
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186
Reduce Primary Zone Fuel-Air Ratio
Durrant states that carbon formation in a Conway engine was
reduced by a factor of 3 when the primary zone was operating at a
stoichiometric fuel-air ratio.
Faitani shows a reduction by a factor
of 2 when the primary zone air-flow is increased from 15 per cent to 30
per cent.
This method does involve certain penalties, however, includ-
ing changes in combustion stabi lity limits and ignition system require-
ments.
Increase Fuel-Air Mixing
Durrant also illustrates the benefits to be gained by increas-
ing the penetration of the primary air jets.
For a Tyne combustor, smoke
reduction factors of 3 were obtained by increasing the pressure drop
across the flame tube wall such that the total pressure loss in the
chamber increased from 3.6 per cent to 4 per cent.
This pressure loss
represents an insignificant increase in specific fuel consumption.
Faitani also found that improving primary zone mixing using directional
tubes reduced smoke by a factor of 2.
This reduction factor increases as
the percentage of primary zone air increases.
Increase Fuel Spray-Cone Angle
Durrant indicates that increasing the spray-cone angle from a
dual orifice injector from 95 degrees to 105 degrees reduces smoke by a
factor of 2.
Changes in Fuel Droplet Size
Faitani found little change in smoke levels with varying droplet
size, whereas Durrant reports an increase by a factor of 2 as the droplets
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187
increase from 50 to 100 microns.
Fiorello (Ref 131) reports that decreas-
ing droplet size increases smoke formation.
These conflicts probably are
due to the effects of differing atomizer and combustor geometries, and to
interactions between droplet size and other combustor variables.
In Refer-
ence 132, it is concluded that large drops may impinge on the walls forming
carbon, whereas very fine droplets do not penetrate the primary zone, and
thus cause local fuel-rich regions, leading to smoke.
Therefore, to re-
duce smoke, small droplets must be accompanied by good mixing with the
primary air.
Substantial reductions in smoke formation can be achieved if com-
bust ion chamber pressures are reduced.
However, pressure reduction is
not a practical solution to the problem.
Not all of the potential reduc-
tion methods can be used simultaneously due to constraints associated with
extinction and stability limits.
However, improved combustor design appears
to be the best approach to reducing smoke formation.
Smoke Reduction Attainable
Several methods of judging smoke density have been used for the
evaluation of carbonaceous emissions in aircraft turbine exhausts (See
Appendix 1).
McDonald (Ref 133) discussed the problem of relating visibi-
lity in the plume to estimates of concentration of particulate matter using
Mie-theory.
More recent 1 y Fa i tan i (Ref 12) has out 1 i ned the use of a
modified "Von Brand Smoke Density" (VBSD) system for estimating exhaust
opacity, and has suggested an opacity of 25 VBSD units (scale of 0-100)
as "acceptab I ell.
This is reported by him to correspond to a concentration
of particulate matter of less than 10 micrograms per liter of exhaust gas.
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188
Rolls-Royce, Ltd. of England, using a "Photo Smoke Meter", has establ-ished
a plume density of about 5 "Photo Smoke Units" (5 PSU), or a concentration
of 5 micrograms of carbon per 1 iter of exhaust gas as the density (or
concentration) associated with the lower limit of visibi lity of smoke
trai Is from aircraft turbine engines (Ref 13).
This plume density is a
highly desirable goal, and emission reductions to achieve it are possible.
Reduction of smoke emission to reduce exhaust plume visibility
wi 11 also reduce the contribution by individual aircraft to community con-
centrations of particulate matter.
At the present time, different engine
models vary widely in their rates of particulate emission, and the degree
of emission reduction required to render exhaust plumes invisible also
varies.
Certain engines wi 11 require a reduction in emission rate of the
order of 80 per cent to reach the goal of 5 to 10 micrograms of carbon per
liter of exhaust gas, while other engines ~eet this goal now.
If all
turbine engines were modified to meet this emission goal, it is estimated
that the over-all reduction in particulate emission from aircraft engines
would be approximately 50 per cent.
Reduction of CO and Organic Emissions
CO and organics can be considered together as they are produced
in a similar manner and their emission rates can be reduced using simi lar
approaches.
As stated earlier, both of these emissions originate in the
outer zone of the combustion chamber where the flame is chi lIed by the
local injection of air needed to cool the liner walls.
Emission rates
decrease as throttle settings are increased such that, for most turbine
engines, CO and organic emissions are negligible at top speed.
The
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189
worst situation exists when the engines are idling.
Under these conditions
Durrant (Ref 13) reports that, for a Tyne engine, organic emissions can be
reduced from 20 per cent to I per cent if the first cooling air strip is
blanked off.
However, this cooling is required to maintain the mechanical
integrity of the walls.
Two practical approaches for reduction of these emissions do
exist.
They are:
( I )
The use of annular combustion chambers.
For a given combus-
tor requirement, the surface area of an annular chamber is
less than for can or can-annular type combustors in current
use, and, therefore, the cooling air requirements are less.
(2)
The use of fuel injectors that reduce the penetration of
fuel towards the walls at the idle conditions.
Neither of the above approaches should add significantly to engine cost.
However, there is insufficient data at this time to state confidently what
emission reduction levels are practically attainable.
Durrant states that
the use of annular combustors can essentially eliminate organics and carbon
monoxide at taxi conditions.
However, the authors feel that a 50 per cent
reduction in emissions is a more reasonable expectation.
This estimate
is based upon a comparison of emission data from one engine with an annular
combustion chamber and emission data from other engines.
(Engine T in
Figure 15 has an annular chamber.)
Reduction of Oxides of Nitrogen
Oxides of nitrogen originate in the combustion chamber in regions
of high temperature.
NO emissions are expected to increase as engine
x
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190
pressure ratios and turbine inlet temperatures increase.
To reduce NO
x
emission, the maximum temperature in the combustor must be reduced.
Durrant
(Ref 13) suggests that this may be achieved by running with a richer pri-
mary zone, but this approach would increase smoke emission.
The maximum
temperature, and therefore NO emissions, can also be reduced by running
x
. the primary zone fuel-lean.
This approach would make ignition problems
more acute, and therefore, it is not.possible at this time to predict
whether the approach would be practical or economically feasible.
.Modifications of Aircraft
In this section approaches to emission reduction through air-
craft modifications are identified and evaluated.
Modifications considered
include changes In basic aircraft design and operational parameters such
as wing loading and aircraft weight.
For all turbine-engine aircraft, the emission of carbon monoxide
and organics during take-off, climb-out, approach, and landing, amount to
10 per cent or less of the total quantities emitted during an LTO-cycle
(see Tab 1 e 42).
The other 90 per cent are emitted when the aircraft is on
the ground and are not affected by aircraft design.
Therefore, aircraft
modifications would not be effective In reducing'CO or organic emissions.
On the other. hand, between 60 and 70 per cent of the emission of CO and
organics by piston engines occurs during the ground runs, approach and
climb-out, and most of this occurs during climb-out.
NO and particulate
x
emission is of most concern from turbine-engine aircraft, and the greatest
I quantities of these materials are emitted during flight operations.
Thus, re-
ducing the duration of flight operations, and particularly the climb-out mode,
would result in reductions in pollutant emission.
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191
Aircraft characteristics which affect its rate of climb most
strongly, assuming that engine thrust is not changed, are weight and wing-
area.
However, changes in these characteristics would result in less-than-
proportionate changes in emissions.
Consequently, the changes which would
be necessary to substantially reduce emissions of pollutants would not be
practical.
Other design variables which affect the durations of operational
modes are thrust and braking power.
Increases in thrust would, however,
increase pollutant emission rates and offset any reduction in duration,
unless accompanied by a reduction in engine specific fuel consumption.
The
braking power only affects the landing-run period which contributes, at
the most, 12.5 per cent of the total NO
x
load for turbine-engine aircraft
(negligible for piston engines), and less than 5 per cent of the other
po 11 utants.
From these observations, it is concluded that aircraft modifica-
tions do not offer practical approaches to reduction of pollutant emissions.
Other approaches, such as engine modification, offer greater effectiveness
and feasibi lity.
Fuel Modifications
If consideration of fuels for aircraft is limited to petroleum
products (hydrocarbons), then little or no effects on the quantities of CO
or organics emitted could be expected from fuel modifications.
Changes in
the character of organic emissions can be achieved, however, and the State
of California currently employs fuel specifications to reduce the photo-
chemical reactivity of organic emissions from automobiles.
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192
Quantities of S02 emitted bY,aircraft could be redu,ced by lowering
the sulfur content of aviation fuels.
. "
However, as stated earlier, the
sulfur content of these fuel.s is very low at present and the costs of fur-
ther reductions are not warranted.
Lead emission by aircraft piston, engines could be reduced, as with
automobiles, by reducing the lead content of gasol ine.
Low-lead or lead-
free gasol ine suitable for automobile engines can be used in most aircraft
piston en~ines, but special fuels may have to be developed for high perfor-
mance aircraft engines if lead is removed.
Particulate emission by aircraft turbine engines could be reduced
by changes in fuel composition.
Smoke formation is found to be less if,
certain fuel constituents are reduced to very low levels, or if lighter,
highly-distilled fuels are used such as naphtha (Ref 131).
These changes,
however; are generally found to be very costly, and in some cases, result.
in an increased fire hazard.
Since effective approaches to smoke reduction
are available through engine modifications, fuel modifications are not,
considered practical at present.
Another approach to reducing smoke emission by turbine engines
involves the use of additives.
Experimental tests with different materials
has revealed that certain metal compounds are effective in reducing smoke
when added to the fuel in low concentrations (Refs 130 and 131).
Howeve r ,
products of combustion of the additive materials are found to cause engine
performance to deteriorate rapidly.
Also, the effects of emissions of
these additive materials in the community atmosphere are largely unknown.
Because of these factors, smoke-reducing adaitives are not considered
practical for general use in turbine engines.
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193
If non-petroleum fuels, such as ammonia or hydrogen, are considered,
emissions of CO, organics, and carbon can, in principle, be eliminated.
How-
ever, conversion to such a fuel would present enormous problems associated
with production, storage, and handling, as well as cost and safety.
Thus,
non-hydrocarbon fuels cannot be considered practical for emission reduction,
at least in the near future.
Finally, we are not aware of fuel modifications which affect
emission of nitrogen oxides.
These pollutants are formed from the normal
constituents of air at the high temperatures existing in engine combustion
chambers.
Thus, there are a variety of approaches to emission reduction
based upon modifications to fuels.
But in nearly all cases, the effective-
ness or feasibi lity of these approaches are less than those of alternative
approaches.
Modifications to Fliqht Patterns
Most aspects of aircraft flight operations are determined by
aircraft performance characteristics or safety considerations, and thus,
are not subject to modification for purposes of emission reduction.
As-
pects which could, at least in principle, be modified include holding time,
noise abatement procedures, and approach angle.
The relationships between
these factors and pollutant emission are discussed in this section.
Influence of Holdin9 Time
All pollutant loads presented in this report are based upon
operations below altitudes of 3000 ft.
Any additional time spent in a
holding pattern below 3000 feet wi 11 add to the pollutant load.
However,
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194
the added CO and organic load due to holding is significant only for piston-
engine aircraft, and the added load represents less than 4 per cent of
the LTO-cycle CO and organic load per minute spent holding below 3000 ft.
The equivalent added load for NO and particulates are higher for turbine
x
engines, representing an additional 15 to 20 per cent load per minute of
ho I din g.
Piston-engine aircraft contribute an additional 6 per cent load
of NO and 2 per cent of particulates per minute of holding.
x
Effects of Noise Abatement Procedures
The added pollutant loads due to constraints imposed by noise
abatement requirements are negligible.
Although the aircraft spends more
time climbing to 3000 ft, this increase in duration is offset, in the case
of NO and particulates, by a reduction in emission rates.
x
Carbon monoxide
and hydrocarbon emissions are insignificant during this mode for turbine
engines, and noise abatement requirements are not applicable to piston-
engine aircraft.
Therefore, noise abatement procedures do not signifi-
cantly affect pollutant loading.
Chanqes in Approach Anqle
The time spent on approach is inversely proportional to the
approach angle.
Therefore, if the approach angle is doubled, the approach
time, and therefore, the emission load during approach is reduced by a
factor of 2.
In this case the following typical reductions can be expected
in the total pollutant loading during an LTO-cycle:
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195
Piston Enqine
Aircraft (Per Cent)
Jet Enqine
Aircraft (Per Cent)
CO
8.0
<:: 1.0
Hydrocarbons
8.0
'< 1.0
NO
x
Particulates
12.5
6.25
12.5
16.0
At this time, most aircraft descend at an approach angle of 3
degrees, and an increase to 6 degrees does not seem to be practicable.
Also, the above data indicate that the pollution reductions resulting from
a change in approach angle are small.
It is concluded from this discussion that, in general, reductions
in emissions attainable through modifications in fl ight patterns are small.
Also, changes in approach and climb-out operations are more likely to
affect the safety of flight operations than other approaches to emission
reduction.
Consequently, modifications to flight patterns associated with
landing and take-off operations are not regarded as practical.
However,
from the standpoint of reducing the impact of emissions from aircraft
engines, unnecessary cruising fl ight at low altitudes over urban areas
should be avoided.
Modification of Ground Operations
Substantial reductions in pollutant emission by aircraft at air
terminals could be achieved by curtail ing taxi operations.
Auxil iary
vehicles could be used to tow aircraft between the runway and the terminal,
or to transport passengers to the aircraft at the runway.
The latter system
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196
is in effect at the Dul les International Terminal serving Washington, D. C.
Pollutant emission by the auxi liary vehicle must be considered as a counter-
balancing factor.
However, a number of low-emission engines are avai lable
for such special service vehicles.
Reductions in emissions also could be achieved by reducing the
duration of operations with engines idling.
Most idling time occurs in the
waiting line at the take-off runway, and the duration of idling time in-
creases rapidly with activity levels.
Substantial reductions in emissions
from idling could be achieved by having aircraft wait for take-off at the
passenger loading area with engines off, thereby eliminating or reducing the
waiting line at the runway.
The following table presents the relative contributions to total
emissions from taxi and idle operations.
These data are for a normal taxi
time of 12 minutes (6 minutes for helicopters) and 1 minute idle.
Per Cent of Total LTO-Cycle Emissions
Occurrinq Durinq Taxi and Idle Modes
Aircraft Class
2
CO Orqanics NO Particulates
~
98 79 14 12
88 83 19 ' 9
95 97 39 20
89 72 45 30
22 17 55 25
39 41 50 25
84 85 14 28
3
4
5
6
7
It should also be noted the quantities of pollutants emitted during the
taxi and idle modes vary linearly with times spent in those modes.
It is
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197
observed from the table that most emissions of CO and organics by turbine-
engine aircraft (classes 1, 2, 3,4 and 7) occur during taxi and idle.
The fractions of NO and particulates from these aircraft, and all emissions
x
from piston-engine aircraft (classes 5 and 6), are less, but sti 11 substan-
t i a 1.
These percentages represent the reductions in total emissions from
aircraft which would be achieved if idle and taxi operations were elimi-
nated.
Nearly complete elimination of these operations could be achieved
through the use of tow vehicles and modified ground operational procedures.
Emission Reduction Attainable
Certain of the approaches described above, if uti lized, would be
effective in reducing certain aircraft emissions from their present levels.
Estimates of the potential reductions attainable at an individual air
terminal and at all FAA-controlled terminals are shown in Table 63.
It is
clear from these estimates that CO and organic emissions at air terminals
can be reduced substantially by using approaches which are currently feasible.
Different approaches vary in their effectiveness among terminals because
of differences in the types of aircraft activity.
Simi larly, a reduction
in particulate emission would be expected, though the indicated reduction
would be partially offset in the future by increases in aircraft activity.
The net effect on particulates would be a reduction of visible smoke, but
little change in total emission.
The major pollutants for which no effective reduction techniques
exist are oxides of nitrogen.
The combined effects of equipment changes,
reduction of other pollutants, and increased aircraft activity wi 11 lead
to a rise in NO
x
em is s ion.
Simi lar trends exist in NO
x
emission from other
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198
sources, including automobiles.
However, no standards or other limitations
on NO emission are in effect at the present time.
x
Reduction of Odors
The absence of information on odor precludes an evaluation of
odor reduction methods.
Nevertheless, certain basic considerations are
discussed below, as an appraisal of the possible effects of control pro-
cedures on odors from aircraft engine emissions.
Greater Dispersal
The primary effect on odors that would be achieved by increased
separation of airfields from densely populated communities, by activated
carbon purification of intake air for passenger terminal bui ldings, and by
simi lar procedures, is that of increased dilution between engine exhaust
and people.
The most recent and reliable series of reports on psycho-
physical scaling of odor intensity (Ref 134) indicate that the intensity
is a power function of the odorant concentration; the exponents varying
approximately in the range 0.5-0.7.
Taking 0.6 as a typical exponent, we
have
Perceived psychological
magnitude
(odor intensity)
0.6
~
odorant cone.
or
0.6
I /'oJ C
Example:
An abatement procedure is 90 per cent efficient in
reducing aircraft engine exhaust odorant concentration.
What is its
"psychological efficiency?"
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199
0.6
+=(+)
2 2
If the odorant concentration is reduced by 90 per cent, then (Cl -C2)/Cl =
0.9 and CI/C2 = 10 (where C] is the initial and C2 the final value). Then
11/12 = 10°,6 = 4, and the "psychological efficiency" (11 -12)/11' is only
75 per cent.
This material-to-psychological transformation itself may not be
too serious.
A problem that is more difficult, and to which there have been
no significant approaches in the air pollution field, is the effect of fre-
quency and duration of exposures to odor on the adverse reactions of people.
Thus, a 90 per cent reduction in odorant concentration that might be ac-
complished by increased physical separation of people from aircraft engine
emissions, resulting in a 75 per cent reduction in perceived odor intensity,
represents an average value over a time span such as 1/2 hour or more.
Under conditions of atmospheric turbulence, these average values may be
exceeded by peaks whose odor impact we have no firm basis on which to evalu-
ate.
More Complete Oxidation of Fuel
To the extent that fuel is oxidized to C02 and H20, its products
are odorless.
Intermediate oxidation products, however, may be more highly
odorous than the fuel.
Some examples are listed below.
Alkane hydrocarbons
Essent~ally odorless after only
minimal di lution.
Alkene hydrocarbons
Typ i ca 1 so-ca 11 ed "gaso 1 i ne" or
'Ihydrocarbon" smell.
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200
Alkylated aromatic hydro-
carbons, especially n-alkyls.
"Oi ly hydrocarbon", or "fuel oi 1"
odors.
-unsaturated acids and
aldehydes from oxygenative
cracking
Pungent, irritating odors
Aryl aldehydes from oxygenative
cracking of substituted aroma-
tics
Sweet, sometimes fruit odors.
Phenolics from oxygenative
cracking of aromatics
Burnt odors
The above list is a very rough classification, but it does serve
to alert the investigator to the fact that not all oxidat'ions improve odor.
Maskinq and Counteraction Methods
It is possible to modify odor quality by adding more pleasant
odors under conditions that do not involve any chemical changes.
Such
processes are called counteraction or cancellation, and odor maskinq or re-
odorization.
There has been some usage of masking agents for diesel exhaust,
but no published scientific evaluation of the responses of people to the
modified odor.
If masking were to be applied as a control procedure for
aircraft engine exhaust, the following considerations would be relevant.
Dispensing
The modifying agent must be dispensed into the exhaust stream
at a point where the temperature is low enough so that the agent would not
be destroyed.
Appropriate equipment procedures would have to be developed.
Di lution
It would be necessary to ascertain that the modifying agent
accompanied the exhaust stream with equivalent di lution to the points where
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201
odors were detected by people.
Evaluation
Measures of intensity and quality are inappropriate for evaluation
of masking agents.
Instead, a survey of acceptability by the affected
populace would be necessary.
Survey methods in the air pollution field,
especially with regard to odor, are only poorly developed.
Reduction of Pollutant Impact
As an alternative to reducing emissions of pollutants by air-
craft engines, methods of reducing the impact of these emissions offer, at
least in principle, a means to the same end, i.e., elimination of the
undesirable effects of air pollution.
Methods of reducing impact, however,
are far more limited than emission reduction methods.
Nevertheless, cer-
tain approaches to impact reduction are worthy of consideration for local
or temporary problems.
The abatement of the impact of aircraft engine emissions upon
receptors within the terminal area, in the absence of effective emission
control as discussed above, can be achieved by imposing barriers between
planes and people in the form of air-conditioned structures with adequate
treatment of intake air.
The technology is well-established, and local
control agencies could specify and enforce air quality standards for inter-
ior spaces, whether "workrooms" or places of public assembly.
Simi lar "barriers" could be provided for receptor populations,
or potential populations, in the vicinity of existing or proposed air-
ports, in the form of air-conditioned homes (Ref 135).
The task would have
greatly different scale and economic aspects, of course, and I'retrofit"
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202
would be a different problem from new construction.
This approach would
not affect pollutant concentrations in the ambient air and thus would not
reduce exposure of individuals while outdoors, but could substantially
reduce the total exposure of a population~
Summary
In this section, methods of reducing quantities of pollutants
emitted by aircraft engines have been identified and evaluated.
Of the
various approaches avai lable, modifications of engines and aircraft ground
operations offer the most practical methods of reducing emissions of pri-
mary concern--carbon monoxide, organics, and carbon.
Pollutants associated
with fuel additives or impurities--lead and sulfur--can only be reduced
by modifications of fuels.
Engine modifications currently used and under development for
automobile engines are equally applicable to aircraft piston engines.
How-
ever, because of the low air-fuel- ratios used in aircraft engines, their
exhaust gases contain high concentrations of organics.
Consequently, emis-
sion reduction methods based upon exhaust gas conversion through combustion
with added air appear to be most practical.
Modifications to aircraft turbine engines which would be effective
in reducing emissions are certain changes in combustor design.
Specific
changes known to be effective are (1) reduction of primary zone fuel-air
ratio, (2) improved mixing of fuel and air in the primary zone, (3) im-
proved fuel injection at low power conditions, and (4) reduction of combustor
surface area.
The first two changes are effective in reducing carbon emis-
sion, and the latter two changes are effective in reducing CO and organic
emissions at low power (idle) conditions.
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203
Since substantial fractions of aircraft engine emissions are
produced during the taxi and idle operating modes, reductions in the dura-
tions of these modes (or reductions in requirements for engine operation)
will be effective in reducing quantities of pollutants emitted.
Approaches
to reducing the durations of these modes which are considered practical
are (1) the use of auxi liary tow vehicles for aircraft, and (2) modifica-
tions of operational procedures which would reduce the time spent by air-
craft with engines idling.
The reductions in emissions attainable by these methods vary
at different terminals because of differences in activity levels among the
various types of aircraft.
At major air carrier terminals where most
activity consists of turbine-engine transport aircraft, the most effective
emission reduction methods would be modifications of ground operations and
turbine-engine combustors.
At general aviation terminals where most acti-
vity consists of piston-engine aircraft, modification or replacement of
piston engines would be the most effective approach.
It is concluded that practical approaches are avai lable for re-
ducing emissions of CO, organics, and particulates from aircraft operations
at air terminals by factors of 60 to over 90 per cent.
On the other hand,
no practical methods for reducing NO emission are presently available.
x
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204
CONTROL OF AIRCRAFT ENGINE EXHAUST EMISSIONS
The two basic aspects of emission control--control requirements
and control methods--are discussed in this section as they pertain to air-
craft engine exhaust emissions.
In dealing with the matter of control, we
are confronted with the interesting question of how to classify aircraft
as an emission source.
Air pollution control agencies generally recognize
two basic source categories--stationary sources and motor vehicles--and
aircraft, at the present time, are included in the latter.
However, an
alternate approach, that of dealing with an air terminal as a stationary
source, offers certain advantages.
Both approaches will be discussed in
this section.
Control Requirements
In determining the degree of emission control required of a
particular source of pollutants, such as aircraft engines, various criteria
can be utilized, depending upon the objective of the control measures.
For
discussion purposes, control objectives and associated criteria can be
classified as follows:
Condition
Control Objective
Control Criterion
1.
Local
hazard
Eliminate local hazard from
specific source.
Reduce source strength suffi-
ciently to eliminate hazard-
ous conditions.
2.
Commun i ty
hazard
Reduce contribution to community
pollution during danger periods.
Eliminate unnecessary oper-
ations.
3.
Local
area
pollution
Reduce contribution to local area
pollution.
Reduce emission levels by
all "effective and feasible"
means.
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205
Condition
Control Objective
Control Criterion
4.
General
community
pollution
Reduce contribution to general
community pollution.
Reduce emission levels by
all "effective and feasible"
means.
5.
Sensory
effects
Eliminate sensory or esthetic
impact.
Eliminate through normal
procedures, as practicable.
The first two categories include severe conditions of a temporary or highly
localized nature, and their control requires prompt action which also may
be temporary or localized.
Categories 3 and 4 pertain to long-term, average
pollutant levels, either in a local area, such as an air terminal, or over
the entire community.
Control of these conditions requires permanent, wide-
spread emission reduction measures.
The last category includes special
conditions of an esthetic nature for which special action is required.
This
classification is general and, as such, is applicable to any type of pol-
lutant source.
A set of criteria such as this is necessary in dealing with
a unique source such as aircraft, for which existing control criteria are
not app I i cab Ie.
Local Hazards
The local hazard condition is defined as including localized
situations of an urgent or emergency nature requiring immediate control
measures.
Local hazards arising from aircraft operations have not been
identified, but investigations of potentially hazardous conditions have
not been exhaustive.
As mentioned previously, it is conceivable that
hazardous pollutant levels could arise as a result of various aircraft
ground operational procedures.
It is concluded that controls on aircraft emissions are not
warranted at present for the purpose of eliminating localized hazards at
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air terminals.
However, monitoring of pollutant levels at certain locations
within terminal areas is advisable.
Locations where the potential hazards
are greatest are take-off runways and passenger loading areas.
If hazardous
pollutant concentrations are encountered, they should be eliminated by
appropriate modifications in aircraft ground operations.
!!'pr,t...>, '. -
Community Hazards
The community hazard condition is a community-wide pollutant con-
dition requiring immediate, but temporary, control action.
Such a condition
is referred to as an air pollution episode and results from peculiar
meteorological conditions wherein community atmospheric venti lation is re-
duced.
When such conditions exist, aircraft operators should be expected
to eliminate unnecessary flights involving aircraft with a high pollutant
emission potential.
Additionally, ground operational procedures at air
terminals should be modified to reduce the duration of operations involving
engine idling.
Specific measures should include:
1.
Curtail unnecessary flights by general aviation aircraft, or,
alternatively, flights by piston-engine aircraft without
emission controls.
2.
Reduce aircraft holding time prior to take-off.
Have aircraft
hold at passenger loading area, with engines shut down, until
clearance is given to proceed to runway for take-off.
3.
Eliminate use of main engines for supplying auxiliary power
during passenger loading.
These measures would require little advanced preparation and should be put
into effect whenever necessary.
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207
Local Area Pollution
Local area pollution is defined here as a long-term pollutant con-
dition existing over a limited area.
Such a condition has local impact as
discussed in the previous section.
With regard to aircraft, the impact of
exhaust emissions in the vicinity of major air terminals is found to be
comparable to the impact in urban areas of pollutants from other sources.
Other sources of pollutants are presently being subjected to emission con-
troIs which wi II become increasingly stringent with time.
As a result, the
impact of emissions from these sources is expected to decrease.
The impact
of aircraft emissions, however, is expected to increase unless control
measures are adopted, and this impact may become serious in the future.
It is clear that controls will be required to reduce aircraft emis-
sions at major air terminals.
Action must be taken by the aviation industry
to reduce emissions by all measures which are effective and feasible, and
such measures should be taken as soon as possible.
Specific measures which
would be appropriate under this criterion are:
1.
Incorporation of emission reduction features in all new air-
craft piston engines, including replacement engines.
2.
Modification of current and new models of aircraft turbine
engines to reduce CO, organic, and particulate emission.
3.
Introduction of tow-vehicles for ground movement of transport
aircraft with uncontrolled engines.
These measures will require equipment development effort, but no
advances in technology.
It is estimated that they could be in effect within
two to three years from initiation of development.
These measures are
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208
considered to be feasible and practical, and, as indicated previously, wi II
be effective in substantially reducing emissions of CO and organics.
General Community Pollution
General community pollution is the result of the mixing of pollu-
tants from all sources and it is manifested as a background pollutant level
existing throughout the community.
To reduce general community pollution,
operators of all sources of air pollutants must reduce these emissions by
every measure which is feasible and effective.
The relative contribution of
a particular source to community air pollution is not a factor in deciding
whether emission reduction should be undertaken.
The magnitude of a source
can only affect an appraisal of the urgency of the emission reduction re-
quirement.
In the case of aircraft, the measures necessary to reduce local
area pollution also wi II be effective in reducing community pollution.
Thus,
the community-wide problem presents additional justification for control of
aircraft emissions.
Sensory Effects
Pollution problems causing sensory effects, but not hazards, should
be dealt with on a practical basis which wi II assure their eventual elimina-
tion, but not at undue cost to the operator of the source.
Smoke trails
and odor from jet aircraft are deemed to fall in this category.
Engine manufacturers have developed the capability of producing
engines whose exhaust trails are marginally visible.
This capabi lity is
expected to improve with time unti 1 engines are produced with near-zero
particulate emission rates.
Exhaust trai Is from these engines wi II be well
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209
below the visibility threshold.
Thus, we can expect that future produc-
tion of current engine models and newly developed engines will be smoke-
free, or nearly so.
Engine manufacturers have the capabi lity to "retrofit" existing
engines with low-smoke burners, and this substitution is expected to take
place gradually as burners are replaced during normal maintenance proce-
dures.
Since the smoke problem cannot be regarded as more than an annoyance,
additional expenditures by aircraft operators to hasten the installation of
low-smoke burners would not be justified.
However, a more compelling rea-
son for leaving the smoke problem to normal maintenance is the desirabi lity
of directing the resources of engine manufacturers and aircraft operators
toward reduction of emissions which constitute more significant problems;
notably, CO, organics, and--in the long run--nitrogen oxides.
Similarly, the elimination of odors from turbine engines is
desirable, but, in this case, odor-reduction methods have not as yet been
developed.
Whenever practical techniques for odor-reduction are available,
they should be adopted by operators of turbine-engine aircraft.
Approaches to Emission Control
Two basic approaches to the control of aircraft emissions are
worthy of consideration.
In the first, aircraft would be treated as motor
vehicles and subjected individually to emission controls.
In the second
approach, an air terminal would be treated as a stationary source and
controls would be applied to total emissions from aircraft within the termi-
nal area.
These approaches are not mutually exclusive.
They could, indeed,
be employed jointly to achieve substantial reductions in aircraft emissions.
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210
The approaches differ, however, in their suitabi lity for use by
different government agencies.
The first approach, that of treating an
aircraft as a motor vehicle, is best applied by the Federal government.
The aviation industry, even more than the automobile industry, is inter-
state in character and a uniform national control system would be desirable.
Also, Federal registration, certification, and inspection procedures, already
in effect, could be utilized to support an emission control program directed
at individual aircraft.
The second approach, that of treating air terminals as stationary
sources,
is more amenable to use by state, regional, or local governmental
agencies.
Control criteria might be established by the Federal government
(NAPCA).
However, imposition of controls would be best accomplished by
local authorities in accordance with local abatement requirements.
Aircraft as Motor Vehicles
Approaches to Emission Control
Approaches which can be taken by the Federal Government to reduce
the emission on the impact of pollutants from aircraft engines fall into
six categories.
These are listed below with the most direct approaches list-
ed first.
(a)
(b)
Specification of exhaust emission standards
Regulation of aircraft applications
(c)
(d)
Regulation of aircraft operations
Taxation
(e)
(f)
Government procurement
Research and development funding
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211
Each of these categories is discussed in the following paragraphs.
Specification of standards iS'the most direct approach to exhaust
emission reduction.
It is being used by the Federal government for the con-
trol of emissions from many types of pollutant sources, including automobiles.
In principal, an emission standard can be very effective in that it simply
prohibits the sale or operation of sources which do not conform to the stan-
dard.
In actual practice, however, the circumstances under which standards
can be effective are limited.
limitations stem from the ability of operators
of pollutant sources to conform to the standards, and the abi lity of govern- ,
ment agencies to enforce the standards.
In the case of aircraft emissions, various pollutant types could
be controlled by the application of standards to either engines or fuels.
Standards on emission of CO, organics, and particulates could be imposed
on new aircraft engines, provided that engine manufacturers were given suf-
ficient lead time to incorporate the necessary modifications in engines
currently in production.
There is, however, no basis at present for setting
a standard on emission of oxides of nitrogen from aircraft engines.
If engine emission standards are established, they would logically
be based upon total emissions during a landing-take-off cycle.
This approach
would be consistent with the current controls on automobile emissions which
are based upon a standard operational cycle.
Also, it would be more practi-
cal to impose standards on emissions by engines rather than aircraft since
the numbers of engine manufacturers and engine models in production are far
fewer than the corresponding numbers of aircraft manufacturers and models.
Standards could be imposed on aircraft fuels to control emission
of S02 and lead.
Because of the basic simi larity of aviation and automobile
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212
gasolines, they are amenable to simi lar standards.
If standards are
established on the lead or sulfur content of gasoline, the standards should
apply to both automobile and aircraft fuels.
Aircraft turbine fuels do n9t
contain lead, and their sulfur content is limited to .relatively low values
to prevent corrosion of engine elements.
The costs associated with further
reductions of sulfur content could not be justified.
Requlation of aircraft applications is an approach avai lable to
the Federal government through its aircraft certification and registration
procedures.
Conceivably, aircraft which are strong sources ,of air pollutants
could be denied certification for types of service involving high rates of
activity in metropolitan areas.
At first glance, this approach is appealing
in that it appears to be selective toward aircraft making the greatest con-
tribution to urban pollution.
There are very few aircraft types, however,
that do not regularly or occasionally operate from urban air terminals.
Consequently, the effect of this approach would be the same as that result-
ing from the establ ishment of emission standards applicable to all aircraft.
Aircraft certification and registration procedures wi II be most useful in
the enforcement of emission standards or in providing a basis for pollution
emission taxation.
These procedures offer no unique advantages as primary
control measures.
Requlation of aircraft operations is an approach which could be
used, at least in principle, to reduce emissions at FAA-controlled air
terminals.
The FAA establishes operational procedures during the approach
and climb phases of an aircraft LTO-cycle.
To the extent that these pro-
cedures can be varied without compromising factors such as safety and noise
abatement~ they might be manipulated to reduce the aircraft emission load.
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213
H,owever, emission reductions attainable by this approach are small, and it
does not appear that the Federal government can deny an aircraft access to
a terminal on the basis of its emission chracteristics.
Therefore, opera-
tional regulation does not offer the Federal government a means to effective
pollutant control.
On the other hand, control of ground operations could
be an effective approach by local government agencies.
Taxation as a means of air pollution control can be effective in
circumstances where an aircraft operator has a choice between options which
result in different pollutant contributions.
Such options might include
equipment types, fuel types, or air terminals.
In any of these categories~
taxation could be used to encourage the operator to choose the alternative
involving the lower pollutant load potential.
Taxation offers the addi-
tional advantage of providing revenue useful for the support of pollutant
control programs.
Taxes on equipment could be imposed as sales taxes or as use taxes
in the form of increased registration fees and could be based upon pollutant
emission rate.
Taxes on fuels would logically be imposed as sales taxes
and would be based upon lead or sulfur content.
Taxes on air terminal
usage could take the form of increased landing fees also based upon pollu-
tant emission.
However, since the assessment of such fees is performed by
the air terminal operator, this approach could not be adopted readily by
the Federal government.
Thus, it appears that taxation might be uti lized to induce the
same reductions in emissions which might otherwise be achieved by the
establishment of emission or fuel standards.
There are two considerations
dictating against taxation, however.
The first and foremost is that taxation
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214
does not assure emission reduction unless tax rates are prohibitively high.
In this case, the effect would be the same as creating standards and impos-
ing penalties for noncompl iance.
The second consideration is that taxation
has not been used to date in the United States as anair pollution control
method and it seems inappropriate to establ ish a precedent for taxation by
applying it to a minor source of pollutants such as aircraft.
Government procurement has been used by the Federal government as
a means for inducing automobile manufacturers to incorporate certain safety
features in automobiles.
By specifying such features on cars purchased by
the government, the manufacturers have been forced, as a practical matter,
to incorporate the same features in their entire production.
A comparable
situation exists in the aircraft industry to a I imited extent.
The Federal
government is a major purchaser of aircraft turbine engines.
By specifying
emission standards for government purchased engines, the emission loads from
mil itary aircraft could be reduced, and the technology would exist for re-
ducing emissions from civilian versions of the same engines.
A precedent
for this approach is being establ ished by the U. S. Navy in proposing stan-
dards on smoke emission from its engines.
The Federal government does not
purchase significant numbers of aircraft piston engines, and thus, cannot
exercise the same leverage in bringing about a reduction in piston-engine
emissions.
However, the Federal government is a substantial consumer of
aircraft fuels, and by this approach could reduce emissions which are asso-
ciated with fuel composition.
Research and development funding wil I be necessary to provide
the techniques for reducing pollutant emission rates below levels currently
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215
attainable.
Rand D will be required on piston-engine emissions, turbine-
engine emissions, and fuel modifications.
The Federal government should
participate in the funding of such activity.
Air Terminals as Stationary Sources
Classification of an air terminal as a stationary source of air
pollutants provides a basis for control of aircraft emissions by local author-
it i es.
Control measures would consist of restrictions on aircraft operations,
or engine operating time.
Criteria for such control measures should be
establ ished by the NAPCA and based upon differences in engine pollutant
emission as determined by standardized measurement techniques.
A distinct
advantage of this approach is th~t the degree of control can be varied with
time and with terminal location in response to local air qual ity conditions.
Implementation of the control of emissions at air terminals re-
quires that emission standards be defined.
A logical basis for such a
standard would be an average emission density over the terminal area.
That is, the rate of emission of pollutants per square mile of land area
would be 1 imited.
The 1 imit on emission density might be set to be con-
sistent with 1 imits imposed on other urban areas, or might be selected on
some other basis.
Steps which can be taken by the air terminal operator to comply
with emission 1 imits have been described earl ier.
These include:
1.
Curtailment of all activities by aircraft with high emission
ra tes .
The basis for such curtailment might be emission
per passenger rather than simply emission per aircraft.
2.
Reduction of engine operating time during aircraft ground
movements.
Reduction could be accompl ished by changes in
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216
operating procedures, or by provision of auxil iary tow
vehicles.
3.
Reduction of emission from other sources associated with
aircraft operations including auxi liary power sources, and
deicing and maintenance procedures.
Minimization of pollutant emission has not been a factor in the establ ishment
of air terminal operational procedures.
Thus, it is expected that considerable
reduction of emissions can be accompl ished through revisions of operations
without seriously affecting passenger and cargo transportation.
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217
RESEARCH NEEDS
During the course of this study, a number of subject areas have
been identified wherein further research is required to reduce uncertain-
ties in the assessment of pollutant emissions by aircraft and their impact.
Research also is required to evaluate approaches to the reduction of pollu-
tant emission by aircraft.
These research needs have, in many cases, been
identified in the text of this report.
This section contains a summary of
these needs which is suggested as a basis for planning of future research
on aircraft emissions and their control.
Aircraft Emissions and Emission Reduction
Piston Enqine Emissions
1.
The nature and extent of piston engine emissions should be
determined as affected by engine size, type, and operating
condition.
Of particular interest are differences in the
character of aircraft emissions from those of automobile
emissions.
2.
The degree of afterburning occurring naturally with piston
engine emissions should be determined as it is affected by
engine type, size, and operating condition, and by aircraft
configuration and operating mode.
3.
The effectiveness of emission control methods as applied to
aircraft piston engines should be determined.
Particular
emphasis should be placed on exhaust gas conversion techniques.
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218
Turbine Engine Emi~sions
1.
Further study of turbine engi'ne emissions is necessary to
reduce uncertainties in rates of emission, particularly during
taxi and idle modes.
The nature of organic and particulate
emissions from turbine engines also warrants further study.
2.
Mechanisms of formation of hitrogen oxides in turbine engine
combustors should be studied.
The results of such studies
should lead to methods of correlating NO emission with engine
x
design and operating variables, and to methods of reducing
emission.
3.
NO
x
Research on turbine engine combustor design should be c~ntin-
ued to determine effective approaches to emission reduction.
Particular emphasis should be placed upon low power operation
for application to current problems.
However, ultimate solu-
tions to long-term problems also should be studied.
4.
A study of sampling and analysis techniques is required for
characterizing organic emissions from aircraft turbine engines.
The objective of this study should be to develop techniques
applicable to exhaust gases containing organic compounds of
high molecular weight and low volatility.
5.
Studies of ground operations at air carrier terminals are
warranted to determine modifications in ground operational
procedures which would be effective in reducing emissions.
Other Sources
1.
Studies of other sources of air pollutants associated with
aircraft operations are necessary to determine total pollutant
-------
219
emissions at air terminals.
Sources of concern not included
in this study are auxiliary power units, service vehicles,
fuel transfer and storage faci lities, and aircraft servicing
operations such as painting, cleaning, and deicing.
Impact of Aircraft Emissions
I.
The initial mixing process by which the high temperature,
high velocity exhaust stream is reduced to ambient atmospheric
conditions should receive special study.
This 'Itransition
zonell mixing wi 11 generally be determined by the exhaust velo-
city and temperature, exhaust nozzle design, engine grouping,
aircraft configuration, aircraft velocity, and meteorological
conditions.
When the mechanics of this transition zone mixing
can be described, it wi 11 be possible to model subsequent
dispersion of the exhaust products.
Analytical studies of
initial mixing and subsequent transport of exhaust products
is recommended for three cases:
a.
Fumigation of terminal bui lding and neighboring work
areas by aircraft near passenger loading areas.
b.
Contamination of intake air for crew and passenger cabins
in aircraft waiting for take-off.
c.
Repeated exposure of land areas immediately adjacent to
runways at major air terminals.
2.
Field measurements should be made of pollutant concentrations
at ground level within and around major air terminals.
Such
data are required to verify and improve models of pollutant
-------
220
dispersion from individual aircraft and from air terminal
operations involving many aircraft.
3.
Studies of measurable effects of aircraft emissions on persons
and property should be conducted.
Related Areas
Effort should be continued on studies of pollutant emission
problems which are not unique to aircraft engines.
Such problems include:
1.
Emission and effects of lead compounds
2.
Emission of odors
3.
Complaint behavior of persons exposed to air pollutants
The need for study of these problems has arisen as a result of pollutant
emission from automotive vehicles as well as aircraft.
Solutions to these
problems, when they are developed, will be appl icable to both types of
sources.
-------
221
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231
TABLES
-------
TABLE I - AIRCRAFT CLASSIFICATION SYSTEM FOR ASSESSING EXHAUST EMISSIONS
Representative engine
~i rcraft Aircraft Manufacturer Maximum thrust
class type Examples and mode! Type or power
I Long-range Boeing 707 Pratt & Whitney Turbofan 18,000 Ib-t
jet transport Douglas OC-8 JT30
2 Medium-range Boeing 727 Pratt & Whitney Turbofan 14,000 Ib-t
, jet transport Douglas DC-9 JT8D
3 Business jet Lockheed Jetstar Pratt & Wh i tney Turbojet 3,000 Ib-t
North Ameri can JTI2
Sabreliner
4 Turboprop Lockheed Electra Allison Turboprop 3,750 eshp*
transport Fai rchi Id Hi Iler 501 -D 13
FH-227
5 Piston-engine Douglas DC-6 Pratt & Whitney Radial 2,500 hp
transport Convair 440 R-2800 pi ston
6 Pi ston-engi ne Cessna 210 Continental Opposed 285 hp
utility Centuri on lO-S20-A piston
Piper 32-300
Cherokee Six
7 Turbine-engine Sikorsky S-61 General E I ec t ri c Tu rbosha ft I ,400 hp
helicopter Vertol 107 CT58
*eshp = equivalent shaft horsepower
N
Vol
Vol
-------
234
TABLE 2 - AIRCRAFT PERFORMANCE CHARACTERISTICS DURING
LANDING AND TAKE-OFF OPERATIONS
Approach Landing I
I'
A B C
Aircraft at Touchdown Stop
3000 ft
SAB Distance A to B SBC Distance B to C
VAB Average Velocity A toB VB Touchdown Velocity
tAB Time to Travel A to B tBC Ti me to Travel B to C
SAB VAB tAB SBe VB tBC
Class Mi 1 es iE2. min feet ~ mi n
9.4 230 3.6 2800 227 O.L~
2 9.0 264 3.0 1900 213 0.3
3 6.0 330 1.6 1900 147 0.4
4 10.3 202 4.5 1700 191 0.3
5 9.0 172 4.6 2330 135 0.6
6 5.0 117 3.8 1000 100 0.3
7 15.0 200 6.5 0 0 0
Durations of idle and taxi modes assumed to be I and 12 minutes respectively
for classes 1 through 6, and 1 and 6 minutes for class 7 (he 1 i copters).
-------
TABLE 2 - AIRCRAFT PERFORMANCE CHARACTERISTICS DURING
LANDING AND TAKE-OFF OPERATIONS (CONTINUED)
Take-Off
D
I
I
E
Lift-Off
Ai rcraft at
3000 ft
Cl imb-Out
Start Take-
Off .
SDE Distance D to E SEF Distance E to F
VE Velocity at E VEF Average Velocity E to F
tDE Time to Travel D to E tEF Ti me to Travel E to F
SDE VE tDE SEF VEF tEF
Class feet ~ mi ns mi les ~ mins
9300 305 1.0 8. I 320 2.2
2 6075 265 0.8 6.5 300 1.9
3 2800 235 0.4 1.6 285 0.5
4 3280 178 0.6 10.6 260 3.6
5 3150 187 0.6 14.8 260 5.0
6 1545 120 0.4 6.3 220 2.5
7 0 0 0 15.0 200 6.5
Assumed Conditions: (a) Runway at sea 1evel
(b) Zero runway slope
(c) Temperature 60 deg F
(d) Zero wind
(e) Aircraft at maximum load
235
-------
236
TABLE 3 - AIRCRAFT REGISTERED WITH FAA BY TYPE:
JANUARY 1, 1967
TYlje of ai rcraft Total EI i gi bJe I ne 1 i q i h 1 pi
Total 155,132 107,085 48,047
Fixed-wing airplane 150,948 104,556 46,392
Turbojet 1 ,547 1 ,423 124
I-engine 69 6 63
2-engine 513 462 51
3-engine 287 287 --
4-engine 678 668 10
Turboprop 904 863 41
I-engine 42 40 2
2-engine 618 583 35
4-engine 244 240 4
Piston 148,497 102,270 46,227
I-engine 130,723 88,653 42,070
100 hp and less 42,186 23,543 18,643
101-200 hp 50,292 36,942 13.350
201-350 hp 32,965 25,997 6,968
351-500 hp 3, 273 1 ,387 1 , 886
501-700 hp 915 429 486
Over 700 hp 1 , 092 355 737
2-engine 16,895 13,010 3,885
800 hp and less 12,099 9,984 2,115
801-2,000 hp 2,341 .1 ,527 814
2,001-4,000 hp 1 , 284 823 461
Over 4,000 hp 1,171 676 495
3-engine 29 9 20
1,000 hp and less 6 5 1
Over 1,000 hp 23 4 19
4-engine 850 598 252
5,000 hp and less 36 18 18
5,001-6,000 hp 95 27 68
6,001-10,000 hp 318. 263 55
Over 10,000 hp 401 290 11 J
Rotorcraft 2,740 1 ,652 1 , 088
Turbine 126 88 38
Piston 2,614 1,564 1 ,050
G 1 ide rs 1,348 841 507
BJ imps 6 2 4
Ba 11 oons 90 34 56
Source: Reference 14
-------
237
TABLE 4 - U. S. POPULATION OF ACTIVE. CIVIL
AIRCRAFT. PAST AND FUTURE
Fixed-Wing Aircraft
Year Total
(As of Active Total Rotor-
Jan 1) Ai rcraft Fixed-Wing Turbine Piston craft Other
1960 70.747 69.681 377 69.304 543 523
1961 78,760 77 , 730 546 77 , 1 84 659 371
1962 82,853 81,603 748 80,855 823 427
1963 86,287 84,795 851 83 , 944 985 507
1964 87,267 85.541 972 84,569 1. 138 588
1965 90,935 88.962 1 .118 87,844 1,325 648
1966 97,741 95,407 1,624 93.783 1.525 809
1967 107,085 104,556 2,285 102,270 1,652 877
1968~': 114,400 111,700 3,000 108,700 1 ,750 950
1969~': 122.600 119,600 3,800 115,800 2,000 1,000
1970~'( 130,600 127,400 4,400 123,000 2,200 1,000
1971 ~': 138,900 135,400 5,000 130,400 2,400 1,100
1972~': 146,900 143,200 5.500 137,700 2,600 I, 100
1973~': 155,100 151,100 6,200 144,900 2,800 1,200
1974~': 163,100 158,900 6,900 152,100 3,000 1,200
1979~': 206,900 201 ,200 10,700 190,500 4,200 1,500
,
.'.
"Estimated
Sources:
References 14 and 16
-------
238
TABLE 5 - ACTIVE, CIVIL AIRCRAFT BY YEAR OF
MANUFACTURE AS OF JANUARY 1, 1967
Year of Number of Per Cent of
Manufacture Aircraft Total
1966 11 ,893 11. 1
1965 9,388 8.8
1964 7,200 6.7
1963 5,544 5.2
1962 4,769 4.5
1961 4,586 4.3
1960 5,161 4.8
1959 5,671 5.3
1958 4,421 4. 1
1957 3,686 3.4
1956 and 44,766 41.8
prior years
Total 107,085 100.0
Source:
Reference 14
-------
239
TABLE 6 - COMPOSITION OF THE U. S. AIR CARRIER
FLEET, PAST AND FUTURE
Year Fixed-Wing Aircraft Rotorcraft
(As of Total Turbojet
Jan. I) Aircraft Total Piston Turboprop and Fan Piston Turbine
1960 2,135 2,112 1,812 216 84 23 0
1961 2,135 2, 110 1,678 230 202 24 1
1962 2,104 2,085 1,505 261 319 19 0
1963 2,047 2,027 1,368 262 397 12 8
1964 2,079 2,059 1,360 267 432 8 12
1965 2,081 2,061 1,221 276 564 7 13
1966 2,125 2,104 1,067 312 725 6 15
1967 2,272 2,251 873 372 1,006 5 16
1968 2.452 2,430 642 444 1,344 5 17
1969~o( 2,583 2,561 368 407 1,786 5 17
1970~'( 2,730 2,704 287 430 1,987 5 21
1971 ~o( 2,860 2,834 260 405 2,169 5 21
1972~'( 2,990 2,962 240 404 2,318 5 23
1973~o( 3.170 3,141 223 396 2,522 5 24
1974~o( 3,320 3,290 201 393 2,696 5 25
1979~o( 3,860 3,820 151 380 3,289 0 40
~'(Est imates
Sources:
References 14 and 16
-------
240
TABLE 7 - AIRCRAFT OF THE U. S. AIR CARRIER
FLEET (JANUARY 1968)
Fixed-Winq Aircraft - Turbine
Aircraft
Manufacturer
Boeing Company
British Aircraft
Corporation
Canadair
Convair
Dassault-Sud
DeHav i II and of
Canada
Fairchild Hiller
Grumman
Hawker-Siddeley
Lockheed
Douglas
Nihon
Nord
Pilatus
Aircraft Engine Number Number Aircraft
Model Series and Model in Service
707 4 PW JT3C, JT3D, JT4A 338
720 4 PW JT3C, JT3D 135
727 3 PW JT8D 410
III 2 RR Spey 506, 510 57
V-745 4 RR Dart 510 38
CL-44D 4 RR Tyne 515 19
240T (600) 2 RR Dart 542 29
340T (580) 2 A I 501- D 13 77
340T (640) 2 RR Dart 542 8
880 4 GE CJ805-3 45
990 4 GE CJ805-23 14
SE-20 2 GE CF700 3
Twin Otter 2 UAC PT6A-20 3
F-27 2 RR Da r t 51 1, 528, 532 49
FH-227 2 RR Dart 532 58
159 2 RR Dart 529 2
650 4 RR Dart 526 5
100 4 Al 501- 022 9
188 4 Al 501- D 13 125
1329 4 PW JT12A 1
Dc-8 4 PW JT3C, JT3D, JT4A 173
DC-9 2 PW JT8D 148
YS-ll 2 RR Dart 542 2
262 2 Tu Bastan VIC 12
PC-6A 1 Tu Astazou XII 3
PC-6B 1 UAC PT6A-20 4
-------
241
TABLE U. S. AIR CARRIER
CONTINUED
Aircraft Aircraft Engine Number Number Aircraft
Manufacturer Model Series and Model in Service
Short SC-7 2 Tu As tazou X I I
Sud Caravelle 2 RR Avon 532R 20
Fixed-Winq Aircraft - Piston
Aircraft Ai rcraft Engine Number Number Aircraft
Manufacturer Mode 1 Ser i es and Model in Service
Aero Commander 680E 2 Ly IGSO-540
Convair 240 2 PW R2800 12
340/440 2 PW R2800 78
28-5ACF 2 PW R1830 4
Curtis C-46, 20T 2 PW R2800 63
Douglas DC-3, 3A 2 PW R1830 107
DC-4 4 PW R2000 10
DC-6 4 PW R2800 133
DC-7 4 Wr R3350 55
Fa i rch i 1 d C-82 2 PW R2800 4
Grumman 21, 21A 2 PW R985 18
44A 2 Ly 0-435 2
73 2 PW R-1340 2
SA 16 2 Wr R1820 2
Lockheed 12 2 PW R985 1
049/149 4 Wr R3350 5
749 4 Wr R3350 7
1049 4 Wr R3350 54
1649 4 Wr R3350 1
Martin 202A 2 PW R2800 2
404 2 PW R2800 57
Piper 31 2 Ly TlO-540 4
18 1 Ly 0-320 3
Cessna 180/185 1 Co 0-470 10
206 1 Co 10-520 1
-------
242
TABLE 7- AIRCRAFT OF THE U. S. AIR CARRIER
FLEET (JANUARY 1968) (CONTINUED)
Aircraft
Manufacturer
Aircraft
Model Series
Engine Number
and Model
Number A i rcr;:~ft
in Service
DeHavi11and
of Canada
DHC- 2
1 PW R-98S
3
Pi latus
pc-6
1 Ly GSO-480
3
Rotorcraft - Turbine
Aircraft
Manufacturer
Aircraft
Mode 1 Ser i es
Engine Number
and Model
Number Ai rcr;1ft
in Service
Sikorsky
S-61
S-62
2 GE CTS8
1 GE CTS8
2 GE CTS8
9
1
Verto1
107-11
7
Rotorcraft - Piston
Aircraft
Manufacturer
Aircraft
Model Series
Engine Number
and Model
Number Aircraft
in Service
Sikorsky
S-ss
S-S8C
1 PW R 1 340
1 Wr R1820
2
3
Sources:
References 6, 14, 17, 18, 19, and 20
-------
.
,-
243
TABLE 8 - U. S. AIR CARRIER BY COUNTRY
OF MANUFACTURE JANUARY 1968
Number of Aircraft
Fixed Wing
Country Turbine Piston Rotorcraft Total
U. S.A. 1621 636 22 2279
Canada 22 3 0 25
Great
Britain 101 0 0 101
France 35 0 0 35
Japan 2 0 0 2
Sw i tzer 1 and 7 3 0 10
Total 1788 642 22 2452
Sources:
References 14 and 17
-------
244
TABLE 9 - COMPOSITION OF THE U. S. GENERAL AVIATION
FLEET, PAST AND FUTURE
Fixed-Wing Aircraft
Year Total Single-Engine Multiengine Rotor
(Jan.!) Aircraft Piston Piston Turbine Craft Other
1960 68,727 61,844 5,957 77 525 324
1961 76,549 68,301 7,129 114 634 371
1962 80,632 71,006 8,241 160 798 427
1963 84,121 73 ,456 8,978 213 967 507
1964 85,088 73,626 9,458 245 1171 588
1965 88,742 76,136 10,346 306 1306 648
1966 95,442 81, 134 11,422 574 1503 809
1967 104,706 88,621 12,671 915 1622 877
1968;'( 112,000 94,500 13,600 1220 1730 950
1969;'( 120,000 100,400 15,000 1600 2000 1000
1970;'( 128,000 106,500 16,250 2000 2200 1050
1971;'( 136,000 112,600 17,500 2400 2400 1100
1972;'( 144,000 118,700 18,750 2800 2600 1150
1973;'( 152,000 124,700 20,000 3300 2800 1200
1974* 160,000 130,700 21,200 3850 3000 1250
1979;'( 203,000 163,800 26,500 7000 4200 1500
;'(Est imates
Sources:
References 14 and 16
-------
245
TABLE 10 - ACTIVE. GENERAL AVIATION
AIRCRAFT BY TYPE
Aircraft (Jan. 1967) Hours Flown (1966)
Aircraft Type Number Per cent Number (000) Per cent
Total, all types 104,706 100.0 21,023 100.0
Fixed-Wing, Total 102,207 97.8 20,463 97.4
Fixed-Wing, Piston 101,292 96.9 20,040 95.3
Single-Engine,
1-3 places 35,681 34.1 5,847 27.8
100HP or less 26,753 25.6 4,394 20.9
Over 100 HP 8,928 8.5 1,453 6.9
Single-Engine, 4
or more places 52,940 50.5 10,335 49.1
200 HP or less 27,907 26.7 5,751 27.3
Over 200 HP 25,033 23.9 4,584 21.8
Mu1tiengine 12,671 12.1 3,858 18.3
800 HP or less 9,957 9.5 2,748 13. 1
801-2000 HP 1,531 1.5 602 2.9
Over 2000 HP 1, 183 1.1 508 2.4
Fixed-Wing Turbine 915 0.9 423 2.0
Single-Engine 38 - NA -
Mu1tiengine 877 0.8 NA -
Rotorcraft 1622 1.5 492 2.3
G 1 i ders, ba 11oons,
etc. 877 0.8 68 0.3
Source:
Reference 14
-------
246
TABLE 11 - U. S. DEPARTMENT OF DEFENSE
INVENTORY OF ACTIVE AIRCRAFT
Service
No. of Active Aircraft
Ju ly 1, 1967 Jan. 1, 1968 July 1, 1968
(Estimated)
Army 9,375 9,803 10,671
Navy 8,417 8,603 8,942
Air Force 15,017 15,343 15,127
000 Total 32,809 33,749 34,740
Sources:
References 17 and 23
-------
247
TABLE 12 - TURBINE ENGINES IN THE U. S. AIR CARRIER
FLEET (JANUARY 1968)
Manufacturer Model ~ Max. Power or Thrust Number in Use
AI1ison Division 501-D13 Turboprop 3750 eshp 654
General Motors 501-D22 Turboprop 4050 eshp 36
Corp.
Genera I Electric
Co. CJ805-3 Turbojet II ,650 I b- t 180
CJ805-23 Turbofan 16, I 00 I b- t 56
CT58-110/140 Turboshaft 1250/1400 shp 33
C F700 Turbofan 4125 I b- t 6
Pratt & Whitney
Aircraft Division JT3C-6/7 Turbojet 13,500/12,000 Ib-t 160
United Aircraft
Corp. JT3D-I/3 Turbofan 17,000/18,000 Ib-t 2048
JT4A-9/11 Tu rboj et 16,800/17,500 Ib-t 376
JT8D-1 ,5,7,9 Turbofan 12,250-14,500 Ib-t 1526
JTI 2A Turbojet 3000 Ib-t 4
Ro II s-Royce L td. Avon 29 Turbojet I 2,080 I b- t 40
Dart 6,7,10 Turboprop 1670-3025 eshp 468
Spey 3/4 Turbofan 10,410/11,000 Ib-t 114
Tyne 12 Turboprop 5500 eshp 76
Societe
Turbomeca Astazou XII Turboprop 731 eshp 3
Bastan Vlc Turboprop 1065 eshp 24
United Aircraft
of Canada PT6A-20 Turboprop 579 eshp 10
Total Engines
5814
Sources:
References 6, 19 and 24
-------
21+8
TABLE 13 - PISTON ENGINES IN THE U. S. AIR CARRIER
FLEET, JANUARY 1968
I
Manufacturer Mode 1 Ser i es Type. Max. Power No. in Usej
0-320 I
Avco Lycoming Div. Opposed 150 HP 3
Avco Corp. 0-435 Opposed 260 HP 4
GSO-480 Opposed 270 HP 3 I
IGSO-540 Opposed 380 HP 2
T10-540 Opposed 310 HP 8
Continental 0-470 Opposed 225 HP 10 I
Motors Corp. 10-520 Opposed 285 HP 1
Pratt & Whitney R-985 Radial 450 HP 41 I
Aircraft Div., R-1340 Radial .600 HP 5
United Aircraft R-1830 Radial 1200 HP 218
Corp. R-2000 Radial 1450 HP 40 I
R-2800 Radial 2400 HP 964
Wright Aeronautical R-1820 Radial 1425 HP 7 I
Div. , R-3350 Radial 2700+ HP 488
Curtiss-Wright Corp.
Tota 1 Eng i nes 1804
I
Sources:
References 6, 18, 19 and 20
-------
249
TABLE 14 - AIRCRAFT PRODUCTION IN THE UNITED STATES
Calendar Commercial Commercial General Mil i tary Total
Year Transport Rotorcraft Aviation Aircraft Aircraft
Aircraft Aircraft & Rotorcraft
1963 100 411 7644 1970 10,125
1964 163 450 9440 2439 12,492
1965 233 388 11 ,922 2806 15,349
1966 344 390 15,543 3600E 19,877E
1967 480 455 13,725 4000E 18,660E
1968 555* 500~'( 14, 900~'(
- ' . -
,,.- - - .
1969 4 30~'( 17 , OOO~'(
1970 2 75~'( 18 , 600~'(
1971 240~'( 20, 200~'(
1972 230~'( 2 1 ,800~'(
1973 225~'( 23 ,400~'(
1974 215~'( 25 , OOO~'(
1979 280~'( 32, 200~'(
I
E - Estimate
~.( Forecast
Sources:
References 16 and 17
-------
250
TABLE 15 - MAJOR UNITED STATES MANUFACTURERS OF CIVIL AIRCRAFT
Commercial transport General aviation -
Manufacturer 1967 Production Manufacturer 1967 Production
-
Boeing 237 Alon 50
Douglas 196 Beech 1 , 260
Fai rchi ld Hi 11 er 38 Bellanca 86
Lockheed 9 Cessna 6,233
Champion 267
Total 480 Grumman 52
Lake 15
Lear 34
Lockheed 19
Rotorcraft Mau 1 e 43
Manufactu rer 1967 Production Mooney 642
North American 386
Bell 316 Pi per 4,490
Brantley - 17 Other 148
Enstrom 7
.
Fa i rch i I d Hill er 53 Total 1 3 , 725
Hughes 48
Sikorsky 14
Total 455
Total 1967 production, all categories - 14,660
Source:
Reference 17
-------
Manufacturer
Aermacchi
Beagle
British Aircraft corp.
Britten-Norman
Canadair
Dassault-Sud
DeHavi Iland, Canada
DeHaviliand, G. B.
Dornier
Handley-Page
Hawker-Siddeley
Mitsubishi
Nihon
Nord
Pilatus
Short
Sud
TABLE 16 - FOREIGN-MADE AIRCRAFT DELIVERED TO
U. S. CUSTOMERS
Aircraft
AL-60
B-206-2
BAC- 111
Viscount
BN-2
C L-44D
SE-20
Twin Otter
DHC-2
DH-l04
D028-Al
Herald 200
137
101
HS 125
Dove
Heron
MU-2
YS- 11
262
PC -6A
PC-6B
pc-6
SC7
Carave I Ie
EnQines
I Ly. 10-720
2 RR-Con.
2 RR Spey
4 RR Dart
I Ly.0-540
4 RR Tyne
2 GE CF700
2 UAC PT-6A-20
I PW R-985
2 DeH.
I Ly. 0-540
2 RR Dart
2 Tu Astazou
4 RR Dart
2 RR Viper
2 RR Gipsy
4 RR Gipsy
Tu or AR
2 RR Dart
2 Tu Bastan
I Tu, Astazou
1 UAC PT6A
1 Ly. GSO-480
2 Tu Astazou
2 RR Avon
Note:
List not complete and numbers are approximate.
EnQine Type
Piston
Piston
Turbofan
Turboprop
Piston
Turboprop
Turbofan
Turboprop
Piston
Piston
Piston
Turboprop
Turboprop
Turboprop
Turboj et
Piston
Pis ton
Turboprop
Turboprop
Turboprop
Turboprop
Turboprop
Pis ton
Turboprop
Turboj et
251
Aircraft Deliveries
ThrouQh 1967
6
14
62
92
52
24
80
52
67
86
6
3
1
7
61
62
3
I
10
13
21
4
5
5
21
Sources:
References 6, 20, 22, 24, 25, 26 and direct corresponderice with.~anufaiturersi..
-------
252
TABLE 17 - AIRCRAFT ENGINE PRODUCTION IN
THE UNITED STATES
Calendar C ivi.l Aircraft Engines Military Ai rcraft Eng i nes
Year Piston Turbine Piston Turbine Total
<
1963 11,322 473 155 5,235 17,185
1964 13,346 859 175 5,205 19,585
1965 17,018 1,169 92 5,099 23,378
1966 21,324 1,938 75E 6,000E 29,337E
1967 18, 100 2,624 75E 6,450E 26,747E
1968 20,600;', 2,700;',
1969 23,000;', 2,300;',
1970 25, 200-k 1 , 700;',
1971 26,500;', 1 ,600;',
1972 29,700;', 1,650;',
1973 3 1 ,800;', 1,650;',
1974 33,900;', 1,650;',
1979 43,900;', 2,400;',
E - Estimate
;', Forecas t
Sources:
References 16, 17 and 27
-------
253
TABLE
18 - MAJOR UNITED STATES AIRCRAFT ENGINE MANUFACTURERS
Manufacturer
Enqine types
1967 Production
civil aircraft enqines
Continental Motors Corp.
Piston
7,845
260
General Electric Co.
Turbine
Lycoming Division
Avco Corporation
Piston
9 , 841
Pratt & Whitney
Aircraft Division
United Aircraft Corp.
Turbine
2,276
a
Other
Piston and Turbine
502
Total
20,724
Sources:
References 17 and 27
a
Includes:
Allison Division, General Motors Corp.
AiResearch Manufacturing Co., Garrett Corp.
Franklin Engine Co., Inc. .
Wright Aeronaut I ca I Di vi s i on, Curt i ss-Wri ght
Corp.
-------
254
TABLE 19 - FOREIGN MANUFACTURERES OF AIRCRAFT ENGINES
SOLD TO U. S. CIVIL AIRCRAFT MANUFACTURERS
Engine
Manufacturer
Rolls-Royce Limited
England
United Aircraft of Canada Ltd..
Div. United Aircraft
Corporation
Sources:
References 26 and 28
Engine
~
Sales to U. S. Parties
Through Sept. 1968
Turboprop
Turbofan
Turboprop
877
352
893
-------
255
TABLE 20 - ANNUAL U. S. AIR TERMINAL TRAFFIC ACTIVITY
(LANDING-TAKE-OFF CYCLES - MILLIONSt
Total Ai r General Mi 1 i tar
Calendar C ivi 1 Carrier Aviation FAA-Controlled Military
Year Activitv Activitv Activitv Terminals Terminals
1960 11.0 3.6 7.4 1.9
1961 11.3 3.5 7.8 1.9
1962 12.2 3.5 8.7 1.9
1963 13.7 3.7 10.0 1.9
1964 15.2 3.7 11.5 1.9
1965 17.2 3.9 13.3 1.7 9.1
1966 20.8 4.1 16.7 1.7 12.3
1967 23.3 4.7 18.6 1.7 14.8
1968~'~ 27.0 5.3 21.7
1969~'~ 30.8 5.9 24.9
1970~1~ 34.1 6.3 27.8
197 J;'~ 38.0 6.7 31.3
1972~'~ 42.4 7.2 35.2
1973~'~ 47.1 7.6 39.5
1974~'~ 52.0 8.0 44.0
1979~lr 82.5 10.3 72.2
~'r Projections
Sources:
References 16, 29 and 30
-------
256
TABLE 21 - 1967 AIR TRAFFIC ACTIVITY' AT MAJOR AIR TERMINALS
IN THE NEW YORK CITY METROPOLITAN AREA
(LANDING-TAKE-OFF CYCLES - THOUSANDS)
Term i na b':f::. Total Ai r General Aviation Mi 1 itary
C vc 1 es Carrier Total Itinerant Local Total Itinerant Local
J. F. Kennedy 241 202 38 38 0 1 1 0
Laguardia 165 103 61 60 1 1 1 0
Newark 130 97 33 33 0 0 0 0
Teterboro 144 3 141 62 79 0 0 0
Naval Air 23 0 2 0 2 21 4 17
Station
Bridgeport 101 3 95 45 50 3 1 2
Morr i s town 86 1 85 45 40 0 0 0
"'hite Plains 125 3 121 66 55 1 1 0
Total 1015 412 576 349 227 27 8 19
Sources:
References 29 and 30
* Includes FAA-controlled terminals and military terminals in the New York Inter-
state Air Quality Control Region.
-------
257
TABLE 22 - 1967 AIR TRAFFIC ACTIVITY AT MAJOR AIR TERMINALS
IN THE WASHINGTON, D. C., METROPOLITAN AREA
(LANDING-TAKE-OFF CYCLES - THOUSANDS)
I Total Ai r General Aviation Military
lerminal~'" Cvcles Carrier Total Itinerant Local Total Itinerant Local
Nationa1 167 119 46 45 1 2 2 0
Du lIes 106 25 47 21 26 34 7 27
Pentagon 4 0 0 0 0 4 4 0
t\ndrews AFB 104 0 1 0 1 103 60 43
~uantico MCAS 19 0 6 0 6 13 2 11
Ft. Belvoir 40 0 0 0 0 40 7 33
Total 440 144 100 66 34 196 82 114
Sources:
References 29 and 30
* Includes FAA-control1ed termina1s and active military termina1s in the Nationa1 Capito1
Interstate Air Qua1ity Control Region.
-------
258
TABLE 23 - 1967 AIR TRAFFIC ACTIVITY AT AIR TERMINALS
IN THE LOS ANGELES METROPOLITAN AREA
(LANDING-TAKE-OFF CYCLES - THOUSANDS)
Total' Air . General Aviation Military
Terminal, Cycles Carrier Total I tiner-ant: Local Total Itinerant Lac
Los Angeles 241 192 44 39 5 5 5 0 .
Long Beach 242 3 225 119 106 14 3 11
Van Nuys 248 2 244 135 109 2 2 0
Santa Monica 178 1 177 69 108 0 0 0
La Verne
(Brackett) 109 0 109 54 55 0 0 0
Burbank 119 9 109 72 37 1 1 0
Hawthorne 148 0 148 76 72 0 0 0
Torrance 186 0 185 65 120 1 0 I
Palmdale 59 0 31 8 23 28 6 22
Non-FAA
Terminals 285 0 285 NA. .NA 0 0 0
Total 1815 207 1557 51 17 34
Sources:
References 3, 29, and 30
-------
I
1---
259
TABLE 24 - AIRCRAFT ACTIVITY LEVELS BY AIRCRAFT CLASS
AT VARIOUS TERMINALS AND METROPOLITAN AREAS
Average Number of LTO Cycles Per Day in 1967b
Aircraft Class
Area I 2 3 4 5 6 7 Total
J. F. Kennedy 256 183 I 49 13 105 53 660
Terminal (4.0) (3.0) (c) (3.5) (3. 1) (1.4) (2.0)
Teterboro 0 0 0 0 0 395 0 395
Terminal (1.4)
a 303 459 37 178 61 1624 118 2784
New York IAQCR
(4.0) (2.8) (c) (3. I) (3.3) (1.4) (2.0)
Washington 3 132 3 123 69 127 0 457
Nat i ona I (4.0) (2.6) (c) (3.3) (3.0) (1.4)
Terminal
National capital 37 155 265 208 126 380 26 1197
IAQ,CRa (4.0) (2.7) (c) (3.2) (3. I) (1.4) (2.0)
Los Angeles 263 156 7 45 17 126 46 660
International (4.0) (2.9) (c) (2.9) (3.2) (1.4) (2.0)
Terminal
Long Beach 0 0 19 6 4 623 2 654
Terminal (c)
Los Angeles 276 181 70 69 29 4286 54 4967
County (4.0) (3.0) (c) (3.0) (3. I) (1.4) (2.0)
Total nation 2444 4202 2300 4203 2820 52091 615 68675
(FAA-cont ro 11 ed (4.0) (2.7) (c) (2.8) (3.0) (1.4) (2.0)
terminals)
alAQCR = Interstate air qual ity control region
b
Numbers in parentheses are average numbers of engine per aircraft.
cClass 3 activity at these terminals is mostly mil itary aircraft.
Mil itary engine estimated to be equivalent to six civil aircraft
engines used in class 3 aircraft.
-------
260
TABLE 25 - 1967 AIR TRAFFIC ACTIVITY RATES AT
MAJOR AIR TERMINALS IN THE NEW YORK CITY
METROPOLITAN AREA
Daily Rate Hourly Rate
(LTO Cycles/Day) (LTO Cycles/Hour)
Terminal Average Peak,;', Average Pea k,;',
J. F. Kennedy 660 810 27.5 75
Laguardia 452 760 18.8 79
Newark 356 507 14.8 45
Teterboro 395 720 16.4 92
Naval Air Station 63 NA 2.6 NA
Bridgeport 277 822 11.5 94
Morristown 236 582 9.8 62
White Plains 342 770 14.3 68
-'-
AEstimates based upon 1965 peak-average ratios
Sources:
References 29, 30, and 34
-------
'1-
261
TABLE 26 - 1967 AIR TRAFFIC ACTIVITY RATES AT MAJOR
AIR TERMINALS IN THE WASHINGTON, D. C.,
METROPOLITAN AREA
Da i Iy Rate Hour I y Rate
(LTO Cycles/Day) (LTO Cycles/Hour)
Terminal Average Pea k,;', Average Pea k,;',
Na t i ona I 457 620 19.1 60
Dulles 291 595 12.1 109
Pentagon 10 NA 0.4 NA
Andrews Air
Force Base 286 540 1 1.0 97
Quant ico MCAS 52 NA 2.2 NA
Fort Belvoir 110 NA 4.6 NA
.'.
"Estimates based upon 1965 peak-average ratios
Sources:
References 29, 30, and 34
-------
262
TABLE 27 - 1967 AIR TRAFFIC ACTIVITY RATES AT AIR
TERMINALS IN LOS ANGELES COUNTY
Daily Rate Hourly Rate
(LTO Cycles/Day) (LTO Cycles/Hour)
Terminal Average Peak~': Average Pea k~':
Los Angeles 660 1160 27.5 94
Long Beach 654 1305 27.7 160
Van Nuys 680 1515 28.4 157
Santa Mon ica 488 1020 20.3 94
La Verne
(Brackett) 295 . NA 12.5 NA
Burbank 325 535 13.5 111
Hawthorne 408 615 17.0 66
Tor rance 510 1455 21.2 99
Palmdale 162 423 6.7 104
Non- FAA
Terminals 780 NA 32.6 NA
,'.
"Estimates based upon 1965 peak-average ratios
Sources:
References 3, 29, 30, and 34
-------
263
TABLE 28 - SCHEDULED AIR CARRIER AND AIR TAXI
ARRIVALS AT J. F. KENNEDY INTERNATIONAL
TERMINAL MAY I, 1968
Hour
Aircraft C I ass 1 2 3 4 5 6 7 8 9 10 11 12
1 9 3 4 6 2 2 15 4 8 6 9 8
2 4 8 4 1 2 4 3 5 9 3 7 7
4 - - - - - I 2 2 2 2 4
5 I - - - - - - - I - - -
6 - - - - - - I 4 4 I 4 4
7 - - - - - - - 3 3 5 3 3
Hour Da i 1 Y
Aircraft Class 13 14 15 16 17 18 19 20 21 22 23 24 Total
1 13 17 14 21 29 36 21 19 22 19 15 8 310
2 8 8 9 17 14 14 11 8 II 9 7 - 173
4 2 2 - 2 4 I 3 3 I 3 3 2 39
5 - - I - - - I - - - - - 4
6 3 3 6 2 4 4 6 4 5 3 2 - 60
7 5 5 6 7 7 5 9 6 3 4 2 - 76
Total Scheduled Arrivals 622
Sources:
References 35 and 36
-------
264
TABLE 29 - SCHEDULED AIR CARRIER AND AIR TAXI
ARRIVALS BY AIRCRAFT TYPE, MAY I, 1968
WASHINGTON NATIONAL TERMINAL
Hour
Aircraft Class I 2 '3 4 c; 6 7 8 9 10 11 12
I - - - - - - - - - I - -
2 - - - - - - - 9 17 10 14 11
4 1 1 - 1 - - 1 1 2 5 5 3
5 - 2 - - - - - - 3 4 4 1
6 - - - - - - - 3 4 I 1 -
7 - ---..- - - - - - - - - - -
Hour
Da i 1 Y
Aircraft Class 13 14 1 s 16 17 18 19 20 21 22 23 24 Total
i I
1 - - -! - ! - - - 1 - - 1 - I 3
,
I
2 11 12 11 14 13 10 13 13 14 16 6 1 195
4 4 4 8 5 4 5 3 5 5 3 6 2 74
5 3 5 2 4 1 4 3 2 5 3 4 1 51
6 1 - - - 3 5 1 1 2 - - - 22
7 - - - - - - - - - - - - 0
!
Total Scheduled Arrivals 345 I
Sources:
References 35 and 36
-------
265
TABLE 30 - SCHEDULED AIR CARRIER AND AIR TAXI
ARRIVALS BY AIRCRAFT TYPE. MAY 1. 1968
LOS ANGELES INTERNATIONAL TERMINAL
Hour
Aircraft Class 1 2 3 4 5 6 7 8 9 10 11 12
1 6 5 4 3 5 1 4 5 12 8 26 20
2 - - - 2 3 1 4 7 9 11 16 11
4 1 - - - - 1 2 4 2 5 6 1
5 - - - - - - - 1 1 - 1 1
6 - - - - - - - - - - - -
7 - - - - - - 2 3 5 2 3 5
Hour
Da i 1 Y
Aircraft Class 13 14 15 16 17 18 19 20 21 22 23 24 Total
1 12 10 18 10 15 14 15 20 22 13 18 5 271
I i
,
2 9 14 8 11 7 8 14 18 13 6 7 3 182
4 4 7 3 3 6 7 7 6 3 4 1 - 73
5 1 - - 2 1 - I 1 1 1 - - 12
6 - - - - - - - - - - - - 0
7 5 5 2 4 4 4 3 5 2 4 3 1 60
Sources:
References 35 and 36
-------
Knock value, min, octane
number, lean rating
Knock value, min, octane
number, rich rating
Color
Dye content:
Permissible blue dye,
max, mg per gal
Permissible yel low dye,
m~x, mg per gal
Permissible red dye,
max, mg per gal
Permissible orange dye,
max, mg per gal
Tetraethyllead, ma~, ml
per ga I
Net heat of combustion,
min, Btu per Ib
TABLE
Grade
80-87
80
87
Red
0.5
none
8.65
none
0.5
18 720
1 - SPECIFICATIONS FOR AVIATION GASOLINES
-TAKEN FROM REFERENCE 41
Grade
91-98
91
Blue
5.7
none
none
none
2.0
18 720
98
Grade
100-130
100
Isooctane plus
1.28 ml of
tetraethyllead
per gallon
Green
4.7
7.0
none
none
3.0
18 720
Grade
108- 1 35
Isooctane plus 0.22
ml of tetraethyllead
pe r ga lIon
Isooctane plus 1.68
ml of tetraethyl lead
per ga lIon'
Brown
3.1
none
2.7
6.0
3.0
18 800
Grade
115-145
Isooctane plus 0.47
ml of tetraethyllead
pe r ga lion
IV
(j"\
(j"\
Isooctane plus 2.8
ml of tetraethyl lead
pe r ga lion
Purple
4.7
none
3.27
none
4.6
18 800
i,
-------
TABLE 31 - SPECIFICATIONS FOR AVIATION GASOLINES
(TAKEN FROM REFERENCE 41) Continued
Requirements for All Grades
Distillation temperature,
10 per cent evaporated,
50 per cent evaporated,
90 per cent evaporated,
90 per cent evaporated,
deg F
max
max
niin
max
158
221
212
257
338
Final boil ing point, max, deg F
Sum of 10 and 50 per cent evaporated temperatures,
min, deg F (deg C)
307
Distillation recovery, min, per cent
97
Distillation residue, max, per cent
1.5
1.5
Distillation loss, max, per. cent
Acidity of distillation residue
Shall not be acid
Vapor pressure, max, Ib
7.0
Potential gum (5 hr aging gum), max, mg per 100 ml
6
Visible lead precipitate, max, mg per 100 ml
3
Sulfur, max, per cent
0.05
Freezing point, max, deg F (deg C)
- 72 ( - 58 )
Water tolerance
Volume change not to
exceed + 2 ml
Permissible antioxidants, max, lb per 1000 bbl
(42 ga 1)
4.2
N
(J"\
-....J
-------
268
TABLE 32 - PROPERTIES OF AVIATION TURBINE FUELS
Property
Composition
Hydrocarbon Constituents
Paraffins~ per cent vol
Naphthenes, per cent vol
0lefins, per cent vol
Aromatics, per cent vol
Naphthalenes, per cent vol
Carbon-to-Hydrogen Ratio, mass
Molecular Weight, approximate
Impurities, per cent mass
Sulphur, total
Sulphur, mercaptans
Gum, existent
Gum, potential
Physical Properties
ASTM Distillation Temps, degF
In it i a 1 Bo i 1 i ng Po in t
10 per cent recovery
50 per cent recovery
90 per cent recovery
End point
Vapor pressure at 100 deg F,
psia
Flash point (PM), deg F
Dynamic Viscosity, Ibm per
ft sec
At-30 deg F
At 0 deg F
At 100 deg F
Specific Gravity at 60 deg F
Freezing Point, deg F
Specific Heat, Btu per Ibm
deg F
At 100 deg F
Combustion Properties
Lower Calorific value
Btu per 1 bm
Btu per cu ft
Stoichiometric Air-Fuel
Smoke Point, mm
Luminometer Number
Rat io
Other Specification
Bromine Number
Anil ine Point, deg F
Copper Strip Test at
Indices
212 deg F
Sources:
References 43 and 44
Type A
-
-
o
17
-
-
164
0.046
0.0002
0.010
0.010
354
373
412
477
509
-
117
0.0048
-
-
0.8105
-52
-
Jp-4
-
-
0.8
11
-
-
112
0.04
0.0001
0.006
0.014
154
221
274
378
462
2.6
-
0.0016
-
-
0.756
-78
-
-18,569 18,752
938,000 885,000
-
22
49
-
140.5
1
-
31
78
-
133
1
JP-5
-
-
0.9
13.3
-
-
170
0.039
0.001
0.010
0.010
368
389
419
465
501
0.0
144
0.0055
-
-
0.813
-62
-
Fuel
Jp-6
36
47
1
16
o. 1
6. 1
146
0.04
0.0001
0.001
0.001
334
342
364
428
492
0.2
126
-
0.0017
0.00063
0.7972
-76
0.48
18,564 18,594
942,000 923,000
- 14.7
25 25
51 47
-
145.6
lA
1.3
137
lA
JP-150
92
5
2
1
0.1
5.35
120
0.002
0.0001
0.001
0.001
196
217
247
304
340
1.8
80
-
0.0006
0.0003
o. 71 54
-76
0.51
19,040
849,000
15. 1
50
138
0.02
158
2A
Deca 1 i n
o
98
o
2
O. 1
6.63
138
0.003
0.0002
0.001
0.001
361
364
366
369
384
0.0
146
-
0.0048
0.0013
0.8888
-76
0.46
18,282
1 ,01 2,000
14.4
24
47
O. 1
95
1
-------
269
TABLE 33 - SPECIFICATIONS FOR AVIATION TURBINE FUELS
Property Jet A Jet A-I Jet B
Gravity, max, deg API
(mi n, sp gr) 51 (0.7753) 51 (0.7753) 57 (0.7507
Gravity, Olin, deg API
(max, sp gr) 39 (0.8299) 39 (0.8299) 45 (0.8017)
Distillation temperature,
deg, F (deg C)
10 per cent evaporated, max 400 (204.4) 400 (204.4) -
20 per cent evaporated, max - - 290 (143.3)
50 per cent evaporated, max 450 (232.2) 450 (232.2) 370 (187.8)
90 per cent evaporated, max - - 470 (243.3)
Final boil ing point, max, deg F
( deg C) 550 (287.8) 550 (287.8) -
D i s till at i on residue, max,
per cent 1.5 1.5 1.5
Distillation loss, max, per cent 1.5 1.5 1.5
Vapor'pressure, max, I b - - 3
Flash point, Olin, deg F (deg C) 110 (43.3) 110 (43.3) -
Flash point, max, deg F (deg C) 150 (65.6) 150 (65.6) -
Freezing point, max, deg F I -30
( deg C) ( - 38) -54 (-48) -56 ( - 40 )
Viscosity at -30 F (-34.4 C),
max, cs 15 15 -
Net heat of combustion, Olin,
Btu per 1 b 18 400 18 400 I 18 400
Total acidity, max, mg KOH I
per gram O. I O. I i -
Sulfur, max, per cent 0.3 0.3 I 0.3
Mercaptan sulfur, max, per cent 0.003 0.003 I 0.003
I Water tolerance, vol change, I
not !
to exceed, 011 +1 +1 I +1
1
- I - -
Existent gum, max, mg per 100 011 7 ! 7 I 7
Total potential residue, 16 hr, I
max, mg per 100 011 14 14 14
Thermal stability at 300 to 400 F
(148.9 to 204.4 C):
Filter press drop, max, in
of Hg 12 12 12
Preheater deposit less than Code 3 Code 3 Code 3
Combustion properties. One of the
following requirements shall be
met:
( I) Luminometer number, Olin 45 45 50
or (2) Smoke point, Olin 25 25 -
(3) Smoke point, Olin 20 20 -
or Burning test, 16 hr
i '
,
-------
270
TABLE 33 - SPECIFICATIONS FOR AVIATION TURBINE FUELS
(CONTINUED)
Property Jet A Jet A-I Jet B
(4) FSmoke point, min 20 20 -
or ~Naphthalenes, max, per
cent 3 3 -
or (5) Smoke volati I i ty index,
min - - 54
Aromatics, vol, max, per cent 20 20 20
Olefins, vol, max, per cent - - 5
Source:
Reference 49
-------
271
TABLE 34 - UNITED STATES CONSUMPTION
OF AIRCRAFT FUELS, PAST AND FUTURE
Annual Consumption (Mill ions of Gallons)
Piston - Eng i ne Fuel s Turbine - Engine Fuels
Fiscal Ai r General Ai r General
Year Carrier Aviation Mil ita ry Carrier Aviation Mil ita ry
1963 635 245 1,230 2,250 25 4,790
1964 615 255 1,040 2,561 36 4,520
1965 557 277 1,030 3,058 61 5,050
1966 464 333 950 3,907 109 5,540
1967 335 371 850 4,568 129 6,600
1968,'. 190 415 - 5,560 150 -
1969'" 100 440 - 6,840 175 -
I 970,', 70 470 - 7,470 195 -
1971,'. 60 500 - 8,010 210 -
1972,'. 60 530 - 8,620 225 -
1973,', 50 560 - 9,500 240 -
1974,'. 40 590 - 10,350 265 -
I 979,', 30 780 - 16,450 440 -
,'.Est imates
Sources:
References 15 and 54
-------
272
TABLE 35 - FUEL CONSUMPTION RATES FOR
REPRESENTATIVE ENGINES
Fuel Rates
Aircraft Representative (lbs per hour per engine)
Class Engine Taxi Idle land i ng Take-Off Approach C 1 i mb-Out
1 Pratt & Whitney 1084 1084 5467 9510 4970 7608
JT3D
2 Pratt & Whitney 920 920 3218 7765 2925 6212
JT8D
3 Pratt & Whitney 540 540 1940 3350 1765 2680
JT12
4 All i son 594 516 981 2036 892 1629
501-D13
5 Pratt & Whitney 360 162 528 2100 480 1680
R-2800
6 Continental 28 25 28 140 42 112
10-520-A
l General Electric 370 180 590 880 540 700
CT58
Data obtained from engine and aircraft manufacturers.
Fuel rates estimated where manufacturers. data not available.
-------
273
TABLE 36 - FUEL CONSUMPTION DURING LANDING
AND TAKE-OFF OPERATIONS FOR REPRESENTATIVE ENGINES
Fuel Consumed
(Ibs per Engine)
Total
Aircraft Representative Take- CI imb- LTO-
Class Engine Tax.i. Idle Landing Off Approach Out Cycle
1 Pratt & Whitney 217.4 18. I 36.4 158.5 298.2 279.0 1007.6
JT3D
2 Pratt & Wh i tney 184.0 15.3 16. I 103.5 141. 3 196.7 656.9
JT8D
3 Pratt & Whitney 108.0 9.0 12.9 22.3 47. I 22.3 221.7
JT12
4 All ison 118.8 8.5 4.9 20.4 66.9 97.8 317.4
501-D13
5 Pratt & Whitney 72.0 2.7 5.3 21.0 36.8 140.0 277.8
R-2800
6 Continental 5.6 0.4 O. I 0.9 2.7 4.7 14.4
10-520-A
7 General Electric 37.0 3.0 0.0 0.0 59.4 77.0 176.4
CT58
-------
274
Table 37- AIRCRAFT FUEL CONSUMPTION DURING AIR TERMINAL OPERATIONS
Estimated average daily consumption in 1967,
I 000 I bs
Aviation Turbine All
Ai r termi nal Qasoline fuels fuel s
John F. Kennedy 13 1,472 I ,485
International
Teterboro 8 0 8
(Gene ra I A v i a t i on)
All FAA-cont ro II ed 89 2,336 2,425
and military terminals
in New York IAQCRa
Washington National 60 373 433
A II FAA-cont ro II ed 116 992 1 , I 08
and military terminals
in national capital
IAQCRa
Los Angeles 17 1 , 453 1 , 470
I nterna t i ona 1
Long Beach (General 17 31 48
Avi at ion)
All terminals in Los 111. 1 ,637 1 , 748
Angeles County
A II FAA-cont ro 11 ed 4, 1 08 24, 340 28,448
terminals in United
States
a'AQCR = interstate air quality control region
-------
TABLE 38 - COMPOSITION OF EXHAUST PRODUCTS
FROM TYPICAL AIRCRAFT ENGINES
Exhaust Composition
Exhaust Concentration Rad i a 1- Pis ton I
Species Units Engine Turbofan Engine
Idle Take-Off Idle Take-Off
I
N2 Vol. cent 70.9 65.9 78.5';', 78.0';', I
per I
02 II 0.8 0.8 18.4,;', I 16.3,;',
H20 II 11.4,;'( 8.4,;\- 1.5-;'\ ' 2.8,;',
I
H2 II 2.5 7.7 ...,'(.;'( ! ...,,\...,'(
8.3 4.6 I 2.84
C02 II 1. 52
I
I
CO II 5.5 11.6 0.0390 0.0018
Organics
(As CH4) II 0.6 1.0 0.0132 0.0015
NOx Vo 1. ppm ';\-;\- ",,'("k 12.1 27.9
S02 II ...,'(';'( ...,'(";': 1.0 0.4
,
Part I cu'l ates mg/m 3 i'c...,,( i'nl, 5.5 43.8
Sources:
References 55 and 68
';\-
Estimated values
'irk
Values not reported, assumed to be small or negligible
275
-------
276
TABLE 39 - DETAILED ANALYSIS OF ORGANIC EMISSIONS
FROM A TURBOJET ENGINE
t
Exhaust Composition
Exhaus t Concentration
Species Units Idle Approach Take - Off
Total Organics ppm by vo I. 224.0 144.0 71.0
as C02
Formaldehyde ppm by vol. 29..0 6.0 60.0
Acetaldehyde II. 1.5 1.5 " 0.6
Propionaldehyde II 3.0 3.0 L..0.6
Butanaldehyde II ~ 0.6 ~0.6 .t... 0.6
Pentanaldehyde II <: 0.6 L..0.6 L 0.6
Ethylene II 30.0 21.5 L. 0.15
Propylene II 10.0 7.0 ~0.3
Acetylene II 8.5 6.0 "'-.0.3
Methane II 26.0 20.0 3.0
Ethane II 2.0 1.5 1.5
Propane II 0.3 L..0.3 ~ 0.15
Butane II ~ 0.3 LO.3 L... 0.3
Hydrocarbons
above C5 ppm by vol. 37.0 28.0 2.0
as C02
Other Species
CO ppm by vo I . 750 590 50
NO II 12 21 210
x
C02 % by vo 1. 1.095 1.190 2.090
Particulates mg/m 3 0.5 0.5 27.0
Source: Reference 56
-------
277
TABLE 40 - EMISSION INDICES FOR
AIRCRAFT ENGINES
"
Emission index (1 b/ 1000 lb fuel)
Aircraft Operating
Class Mode A/F CO Organics NO Part i cu I ates SO
x 2
I Idle & 133 174 75 2.0 0.3 1.0
Taxi
~pproach 103 8.7 16 2.7 1.1 1.0
Land
jrake-Off 75 0.7 0.1 4.3 0.6 1.0
~ 1 imb-Out
2 Idle & 132 50 9.6 2.0 0.6 1.0
Taxi
Approach 108 6.6 1.4 2.7 2.7 1.0
Land
Take-Off 69 1.2 0.6 4.3 2.5 1.0
C 1 i mb-Out
3 Idle & 127 118 11.5 2.0 O. I 1.0
Taxi
Approach 91 II 0.6 2.7 0.4 1.0
Land
Take-Off 58 4 0.3 4.3 0.3 1.0
Climb-Out
4 Idle & 106 24.8 8.1 3.7 0.6 1.0
Taxi
Approach 133 1.6 0 2.9 1.0 1.0
Land
Take-Off 57 2.3 3.2 3. 1 0.8 1.0
Climb-Out
-------
278
TABLE 40 -EMISSION INDICES FOR
AIRCRAFT ENGINES (CONTINUED)
Aircraft Operating Emission index (Ib/IOOO Ib fuel)
C I ass Mode A/F CO Organics NO)( Ftarticulates S02
5 Idle 10.0 600 160 0 2 0.2
Taxi 11.5 900 90 3 2 0.2
Approach 12.0 800 60 5 2 0.2
land
Take-Off 9.5 1250 190 0 2 0.2
Climb-Out
6 Idle 10.0 600 160 0 2 0.2
Taxi 11.5 900 90 3 . 2 0.2
Approach 12.0 800 60 5 2 0.2
land
Take-Off 11.0 1050 110 1 2 0.2
Climb-Out
7 Idle & III 118 11.5 2.0 1.0 1.0
Taxi
Approach 75 11 0.6 2.7 1.5 1.0
Climb-Out 63 4 0.3 4.3 1.5 1.0
-------
279
TABLE 41a - TURBINE ENGINE EMISSION DATA
IDLE CONDITION
Em I S S I on ' I n d ex
. . . lb per lb fuel X1000)
Fuel Flo\'\ Organics NO
Engine Fuel F/A 1 b/hr CO (as CH4) x Particulates
(as NO)
Turboj ets
A - 0.0064 1120 63.0 4. 2~'~ 1.5 12. 5~'~
B - 0.0061 - 58.5 26.3 2.2 -
C Jp4 0.0052 890 24.3 16.2 2.6 -
D Jp4 0.0065 1140 90.2 69.'6 0.4 0.3
E JP5 0.0065 1220 98.3 62.4 0.4 0.1
F Jp4 0.0061 1697 76.2 41.6 0.7 0.3
G JP5 0.0065 1678 166.8 82.2 0.6 0.7
H Jp4 0.0079 542 117.5. 11.5 0.5 o. I
I JPS 0.0086 568 103.6 12.1 0.4 0.1
J Kerosine 0.0099 1140 - 11.4 0.5 1.1
K Kerosine 0.0125 600 - - - 0.4
Turbofans
L Kerosine 0.0089 - 33.3 12.8 2.4 -
M Jp4 0.0065 1000 29.2 60.0 1.8 2.4
N Jp4 0.0075 1087 74.4 75.1 0.2 0.3
o JP5 0.0087 1212 24.7 56.0 o. I 0.4
P Jp4 0.0076 918 49.9 9.6 1.5 0.6
Q JP5 0.0092 850 67.4 9.2 0.4 0.8
R Kerosine - - - - j '- 1.0
S Kerosine 0.011 936 28.2 19.1 2.2 O. I
T Jp4 - - 30.0 5.0 0.7 <.0.5
~urboprops
U Jp4 0.008 675 13.3 7.0 1.6 -
V Kerosine 0.009 180 - - - 1.0
W JetAI 0.0094 516 24.8 8. I 3.7 0.6
X JetAl 0.0094 514 - - - 0.7
y Kerosine 0.0078 741 31.3 1.5 5.9 o. I
.'.
"Particulate emissions reported include organic materials condensed
during sample collection.
-------
280
TABLE 41b .. TURBINE ENGINE EMISSION DATA
,
APPROACH MODE
Em i's s i on' Index
Ib per Ib fuel XIOOO)
Fuel Flow Organics NO
En~ine Fuel F/A Ib/hr CO (as CH4) x Particulates
(as NO)
Turboj .ets'
A - 0.0084 3820 8.0 <3.5;'(' 3.9 7,-5";'(
B - .. .. .. - - -
C Jp4 .. .. - - - -
D Jp4 0.0092 3807 8.7 3.2 1.3 0.9
E JP5 0.0092 3864 11.4 11.0 1.7 1.0
F Jp4 0.0084 4784 8.7 3.5 1.5 0.6
G JP5 0.0089 4565 12.3 8.6 1.9 1.3
H Jp4 O. OliO 1766 11.5 0.6 1.7 0.4
I JP5 0.0110 1768 10.8 0.8 1.5 0.5
J Kerosine - .. .. .. - -
K Kerosine 0.0128 .. .. - - 0.5
,
Turpofans'
L Kerosine - .. - . - - -
M Jp4 0.0119 5290 2.5 . 1. 9 1.3 2.0
N Jp4 0.0097 4970 8.7 15.9 1.9 1.1
o JP5 0.0102 5080 7.1 9.8 1.9 1.6
P Jp4 0.0093 2824 6.6 1.4 2.2 2.7
Q JP5 0.0114 3370 5.0 0.6 1.8 2.8
R Kerosine .. .. .. - - -
S Kerosine 0.011 3350 11.0 0.0 1.9 1.1
T Jp4 .. .. .. - - -
Tur,bopr,O,ps .
U Jp4 0.0143 1515 2.7 O. I 2.0 -
V Kerosine 0.0133 540 .. .. .. 1.5
W JetAI 0.0075 892 1.6 0.0 2.9 1.0
X JetAI 0.0145 1718 .. - - 0.6
Y Kerosine 0.009 780 34.8 2.5 7.0 0.0
*Particulate emissions reP9rted include organic materials condensed during
sample collection.
-------
TABLE 41c - TURBINE ENGINE EMISSION DATA
TAKE - OFF MODE
Emiss ion' Index
(lb per I b fue I X 1000')
Fuel Flow Organics NO
Engine Fuel F/A Ib/hr CO (as CH4) x Particulates
(as NO)
Turboj ets
A - 0.017 13000 6.5 <:.. I. 5;'( 1.3 I 3. 5;'(
B - 0.0143 - 0.8 1.2 5.3 -
C Jp4 0.0143 8300 2.2 0.2 4.3 -
D Jp4 0.0164 10174 1.0 O. I 2.4 0.6
E JP5 0.0166 11387 0.9 0.4 2.8 0.8
F Jp4 0.0158 14102 0.6 0.5 0.8 0.6
G JP5 0.0161 13953 1.1 0.1 0.8 1.5
H Jp4 0.0172 3334 3.9 0.3 1.1 0.3
I JP5 0.0174 3353 3.8 0.3 1.0 0.4
J Kerosine 0.0144 8310 - 0.0 5.3 1.8
K Kerosine 0.0183 2900 - - - 0.4
Turbofans
L Kerosine 0.0164 - 2.4 2.9 5.0 -
M Jp4 0.0133 8550 0.5 0.3 2. I 1.9
N Jp4 0.0133 9510 rO.7 0.1 1.2 0.6
o JP5 0.0135 9400 0.7 0.3 1.0 0.9
P Jp4 0.0145 7766 1.2 0.6 1.9 2.5
Q JP5 0.0181 10050 1.1 0.2 3.0 2.2
R Kerosine 0.0149 9035 - - - 2.0
S Kerosine 0.0202 7745 4.8 0.6 21.8 2.1
T JP4 - - 1c1.0 O. I 2.0 1.0
Turboprops
U Jp4 0.0184 1970 1.8 0.2 2.5 -
V Kerosine 0.0158 730 - - - 1.5
W JetAI 0.0175 2035 2.3 3.2 3. I 0.8
X JetAI 0.0201 2349 I 0.4
- - -
y Kerosine - - I - - - -
, !
I j ,
~~ .
~Water injection used. Particulate emissions reported include organic
materials condensed during sample collection.
281
-------
282
TABLE 42 - ENGINE EMISSION LEVELS DURING
A LANDING AND TAKE - OFF CYCLE
. i
Pollutant Specie I
I Ai rcraft total flow in Ibs per engine I
I
class Mode* CO HC NO Particulate
x
1 1 37.83 16.30 0.43 0.07
2 3.15 1.36 0.04 0.01
3 0.14 0.02 0.84 0.12
4 2.79 4.80 2.00 0.50
Total 43.91 22.48 3.31 0.69
2 1 9.20 1.77 0.37 O. 11
2' 0.77 0.15 0.03 0.01
3 0.14 0.07 0.51 0.30
4 1. 1 7 0.32 1.23 0.87
Total 11 . 28 2.31 2.14 1.29
3 1 1 2. 74 1.24 0.22 0.01
2 1.06 0.10 0.02 0.0
3 0.14 0.01 0.15 0.01
4 0.61 0.03 0.22 0.03
Total 14.55 1.38 0.61 0.05
4 1 2.95 0.96 0.44 0.07
2 0.21 0.07 0.03 0.01
3 0.06 0.08 0.08 0.02
4 0.33 0.31 0..50 0.15
Total 3.55 1.42 1.05 0.25
5 1 64.80 6.48 0.22, 0.14
2 1.62 0.43 0.0 0.01
3 32.88 5.00 0.0 0.05
4 204..44 28.81 0..18 0.35
Total 303.70 40.72 0.40 0..56
6 1 5.04 0.50 0..02 0.01
2 0.24 0.06 0..0 0.01
3 1.04 O. 11 0.0 0.0
4 7.10 0.68 0.02 0.02
Total 13.42 1.35 0.04 0.04
7 1 4.37 0.43 0.07 0.04
2 0.35 0.03 0.01 0.04
3 ---- ---- ---- ----
4 0.96 0.06 0.49 0.21
Total 5.68 0.52 0.57 0.29
I
Source: Reference 4
*1 - taxi, 2 - idle, 3 - landing and take - off, 4 - approach and
c 1 i mb"out
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283
TABLE 43 - RELATIVE EMISSION LOADS
BY ENGINE AND AIRCRAFT TYPE
C'1ass CO HC NOx Pa r t.
1 1.0 1.0 1.0 1.0
2 0.27 0.10 0.65 1.87
3 0.35 0.06 o. 18 0.07
4 0.09 0.06 0.32 0.36
~ 5 7.29 1.81 0.12 0.81
6 0.32 0.06 0.01 0.06
7 0.14 0.02 0.17 0.42
(a) By Engine Type
Class Aircraft E CO HC NO Part.
x
l 707 4 1.0 1.0 1.0 1.0
2 727 3 0.20 0.08 0.49 1.40
3 Sabre 1 i ner 2 0.17 0.03 0.09 0.04
4 Electra 4 0.09 0.06 0.32 0.36
5 DC6 4 7.29 1.81 0.12 0.81
6 Cessna 210 1 0.08 0.015 0.003 0.015 .
7 He 1 i copter 2 0.07 0.01 0.085 0.21
Vl07
(b) By Aircraft Type
-------
284
TABLE 44 - AIRCRAFT EXHAUST EMISSIONS AT
NEW YORK AREA TERMINALS - 1967
Aircraft Operating Average Emissions
Terminal Type Hode (lb/day)
CO Organics NOx Part i cu 1 ates
,J. F. Kennedy Turbi ne ' ' Taxi 44,900 17,900 730 150
: I nternat iona 1 (Classes) Idle 3,700 1,500 60 20
I 1,2,3,4,7) Land, Take-Off 200 100 1,160 290
'
I Approach, Climb-Out 3,700 5,100 2,870 1,040
Total Cycle 52,500 24,600 4,820 1,500
Piston Taxi ,! 3,300 300 10 10
(C 1 asses Idle 100
6 & 7) Land, Take-Off, 1,500 200
Approach, CI.imb-Out 9,200 1,300 10 20
Total Cyc1e 14,100 ' 1,800 20 30
All Types Tota1 Cycle 166,700 26,400 4,840 1,530
Teterboro Turbine Taxi (Turbine - engine aircraft
(New Jersey) (C lasses Idle activity assumed to be
1,2,3,4,7) Land, Take-Off neg 1 i g i b 1 e.)
Approach, Climb-Out
Total Cycle
Piston Taxi 2,800 300 10 10
(C 1 asses Idle 100
6 & 7) Land, Take-Off 600
Approach, Climb-Out 3,900 400 10 10
Tota.l Cyc 1 e 7,400 700 . 20 20
All Types Tota1 Cycle 7,400 700 20 20
A 11 Haj or Turbine Taxi 63,400 23, 100 1,310 280
New York Area (C 1 asses Idle 5,300 1,900 110 40
Terminals 1,2,3,4,7) Land, Take-Off 400 200 1,760 540
Approach, Climb-Out 5,400 6,400 4,450 1,860
. Total Cycle 74,500 31,600 7,630 2,720
Piston Taxi 24.500 2,400 90 50
(Classes Idle 900 200 30
6 & 7) Land, Take-Off 9,000 1,300 10
Approach, Climb-Out 57,200 7,300 80 110
Total Cycle 91 ,600 11,200 170 200
All Types Total Cycle 166, 100 42,800 7,800 2,920
-------
285
TABLE 45 - AIRCRAFT EXHAUST EMISSIONS AT
WASHINGTON AREA TERMINALS - 1967
Aircraft Operating Average Emissions
Terminal Type Mode (lb/day)
CO Organics NO Particulates
x
fWash i ngton Turbine Taxi 5,000 1,200 320 70
;Nat i ona 1 (C I asses Idle 400 100 20 10
I 1,2,3,4,7) Land, Take-Off 100 220
100 110
Approach, Climb-Out 600 300 660 370
Total Cycle 6,100 1,700 1,220 560
Piston Taxi 14.200 1,400 50 30
(C I asses Idle 400 100 - -
6 & 7) Land, Take-Off 7,000 1,000 - 10
Approach, Climb-Out 43,400 6,100 40 80
Total Cycle 65,000 8,600 90 120
All Types Total Cycle 71 ,100 10,300 1,310 680
A II Maj or Turbine Taxi 31,800 5,800 860 120
Washington (Classes Idle 2,600 400 70 30
Area 1,2,3,4,7) Land, Take-Off 400 100 630 200
Terminals Approach, Climb-Out 2,100 1,100 1,510 620
Total Cycle 36,900 7,400 3,070 970
Piston Taxi 27,900 2,800 100 60
(Classes Idle 800 200 - 10
6 & 7) Land, Take-Off 13,300 2,000 - 20
Approach, Climb-Out 83,300 11,600 80 150
Total Cycle 125,300 16,600 180 240
All Types Total Cycle 162,200 24,000 3,250 1,210
-------
286
TABLE 46 - AIRCRAFT EXHAUST EMISSIONS AT
LOS ANGELES AREA TERMINALS - 1967
Aircraft Operating . Average Emissions . ----l
Terminal Type Mode (Ib/day)
CO Organics NOx Particulates
Los Angeles Turbine Taxi 46,000 18,400 710 140
International (C I asses Idle 3,900 1,500 60 20
1.2,3.4.7) ~and. Take-Off 300 100 1.150 270
Approach, Climb-Out 3,700 5.300 2,840 990
Total Cycle 53,900 25,300 4,760 1,420
Piston Taxi 4,400 400 20 20
(C I asses Idle 100 - - -
6 & 7) Land, Take-Off 1,900 300 - -
Approach, Climb-Out 12,300 1,700 10 20
Total Cycle 18,700 2,400 30 40
All Types Total Cycle 72,600 27,700 4,790 1,460
Long Beach Turbine Taxi 1,500 200 30 -
(C I asses Idle . 100 - - -
1,2,3,4,7) Land. Take-Off - - 20 -
Approach. Climb-Out 100 - 40 10
Total Cycle 1,700 200 90 10
Piston Taxi 5,600 500 20 20
(Classes Idle 300 100 - 10
6 & 7) Land, Take-Off 1,400 200 - -
Approach. Climb-Out 9.300 1.000 20 20
Total Cycle 16,600 1,800 40 50
A 11 Types Total Cycle 18,300 2,000 130 60
All Turbine Taxi 53.200 19.700 870 160
Los Angeles (C I asses Idle 4,400 1,600 70 20
County 1.2,3.4,7) Land. Take-Off 300 100 1,280 300
Terminals Approach, Climb-Out 4.200 5,600 3,130 I, 100
Total Cycle 62, 100 27,000 5,360 1,580
Piston Taxi 36,100 3,600 140 70
(G 1 asse.s Idle 1,600 400 - 60
6 & 7) Land, Take-Off 9,200 1.100 - 10
Approach. Climb-Out 61.000 6,700 140 150
Total Cycle 107.900 11.800 280 290
All Types Total Cycle 170,000 38,800 5,640 1,870
-------
287
TABLE 47 - AIRCRAFT EXHAUST EMISSIONS AT ALL
FAA - CONTROLLED TERMINALS - 1967
Averaoe Emi ss ions
Aircratt Operational (10 0 lb/day)
Class Mode CO Organics NO Particulate~
x
I Taxi 370 160 4.2 0.7
Idle 31 13 0.4 o. t
Land, Take-Off I - 8.2 1.1
Approach, Climb-Out 27 47 19.6 4.9
Total Cycle 429 220 32.4 6.8
2 Taxi 105 20 4.2 1.3
Idle 9 2 0.4 0.1
Land, Take-Off I I 5.8 3.4
Approach, Climb-Out 13 3 14.0 9.9
Total Cycle 128 26 24.4 14.7
3 Taxi 176 17 3.0 0.2
Idle 15 2 0.3 -
Land, Take-Off 2 - 2. I O. I
Approach, Climb-Out 8 - 3.0 0.4
Total Cycle 201 19 8.4 0.7
4 Taxi 35 II 5.2 0.8
Idle 2 I 0.3 o. I
Land, Take-Off I I 0.9 0.2
Approach, Climb-Out 4 4 5.9 1.8
Total Cycle 42 17 12.3 2.9
5 Taxi 713 71 2.4 1.5
Idle 18 5 - O. I
Land, Take-Off 362 55 - 0.6
Approach, Climb-Out 2250 317 2.0 3.9
Total Cycle 3343 448 4.4 6. I
6 Taxi 368 36 1.5 0.7
Idle 17 4 - 0.7
land, Take-Off 76 8 - -
Approach, Climb-Out 518 50 1.4 1.5
Total Cycle 979 98 2.9 2.9
7 Taxi 5 I O. I O. I
Idle I - - -
land, Take-Off - - - -
Approach, Climb-Out I - 0.6 0.3
Tota I Cyc I e 7 I 0.7 0.4
All
Classes Total Cycle 5129 829 85.5 34.5
-------
288
TABLE 48 - POLLUTANT EMISSION BY AIRCRAFT
DURING AIR TERMINAL OPERATIONS - 1967
Estimated Average Dai ly Emissions
(1000 lb/day)
Air Term i na 1 b' CO 'Organ i cs NO I Par tic u 1 ate sl
Operat ions.
I ! x
r
[
J. F. Kennedy Ground 54 20 1.9 0.4
International Fl i ght 13 6 2.9 1.1
Total 67 I 26 4.8 1.5
I
Teterboro Ground 3 I 0.3 0.01 0.01
(General Aviation) Fli ght 4 0.4 0.01 0.01
Total 7 i 0.7 0.02 0.02
,
i
All FAA - contro 11 ed Ground 103 I 30 3.2 0.9
and mi litary terminals F light 63 I 13 4.6 2.0
in New York IAQCRa Total 166 I 43 7.8 2.9
Washington National Ground 27 I 4 0.6 0.2
FI i ght 44 I 6 0.7 0.5
I
Total 71 j 10 1.3 0.7
All FAA - contro 11 ed Ground 77 I II 1.6 0.4
and mi litary terminals F light 85 13 1.6 0.8
in national capital Total 162 24 3.2 1.2
IAQCRa
Los Angeles Ground 57 21 1.9 0.5
International FI i ght 16 7 2.9 1.0
Total 73 28 4.8 1.5
Long Beach Ground 9 I 0.07 0.03
(General Aviation) FI i ght 9 1 0.06 0.03
Total 18 2 0.13 0.06
All terminals in Ground 105 27 2.3 0.7
Los Angeles County Flight 65 12 3.3 1.2
Total 170 39 5.6 1.9
All FAA - controlled Ground 2316 408 39.0 11.8
terminals in the Fl i ght 2813 421 46.5 22.7
United States Total 5129 829 85.5 34.5
a .
IAQCR = Interstate
bGround Operations
Flight Operations
air quality control region
= taxi, idle, take-off and landing runs
= approach and climb-out
-------
TABLE l~9 - AI RCRAFT EXHAUST EMISSIONS
DURING CRUISE
Emission Indices at Cruise (lb/IOOO Ib fuel>.:
Engine Type CO Orqanics NOx Particulates
Piston
(A/F = 15) 100 15 50 2
Turbine 0.5 4
Fuel Consumption - 1967 (106 I b) :
Fuel Type Air Carrier General Aviation Mil ita ry
Av. Ga so line 1,380 2,190 5,400
Turbine Fuels 27,000 760 26,600
Total Emissions .,. 1967 (106 I b) ~.~:
CO Organics NOx Particulates
Air Carrier 180 34 166 25
General Av. 176 26 90 4
Mil ita ry 45L} 75 300 30
Total 810 135 556 59
.'.
"80 per cent of all fuel assumed to be consumed during cruise.
289
-------
290
TABLE 50 - TOTAL EMISSIONS IN THE UNITED STATES
FROM AIRCRAFT (1967)
Emissions - 1967 (106 lb)
,
Operations CO Organics NO Particulates
x
At FAA - Controlled
Terminals 1860 302 31 12
At Military Terminals 2079 257 38 7
Cruise 810 135 556 , 59
Total 4749 694 625 78
I I
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291
TABLE 51 - ELEMENTS USED AND ASSUMPTIONS MADE IN
CALCULATION OF EMISSION LOADS
Elements Used
Assumptions Made
1. Aircraft Activity by
Aircraft Type
2. Aircraft Operations
3. Engine Fuel Consumption
Rates
4. Pollutant Emission Rates
a. Air carrier activity, other than certifi-
cated route air carriers, consists en-
tirely of class 1 and class 2 aircraft.
b. General aviation activity consists en-
tirelyof class 6 aircraft with average
power of 400hp.
c.
Mil itary activity at urban air termi-
nals consists of aircraft classes
3(50%), 4(15%), 5(1~1o), 6(20%) and
7(5%).
a.
All aircraft
low the same
air terminal
Table 2.
within a given class fol-
operational cycle during
operations as defined in
a. Wherever fuel consumption rates were
not reported by engine manufacturers
for specific operational modes, the
following relationships were used:
Taxi rate = Idle rate
Climb-out rate = 0.8 Take-off
rate
Landing rate = 1.1 Approach
rate
a. Emission indices for CO, organics and
NOx for aircraft piston engines are e-
qual to emission indices for automobile
engines. (Assumed to vary similarly
with A-F ratio.
b. Emission index for particulates from
aircraft piston engines assumed equal
to 2.0 lb/IOOO lb fuel.
c. Emission indices and emission rates for
all civi 1 aircraft engines within a giv-
en aircraft class are equal to those of
the representative engine for that class.
-------
292
TABLE 51 - ELEMENTS USED AND ASSUMPTIONS MADE IN
CALCULATION OF EMISSION LOADS (CONTINUED)
Elements Used
Assumptions Made
d.
Emission rates for mi litary class 3
craft are six times as great as the
of emission from the representative
3 engine.
air-
rates
class
.e.
For turbine-engine aircraft, emission rates
in the taxi mode are equal to those at idle.
-------
293
TABLE 52 - ERROR FACTORS FOR
AIRCRAFT EMISSION LOADS
Error Factor for Total LTO - Cycle
(Maximum Load/Average Load)*
Idle
Aircraft Time CO Organics NO Particulates
Class (Minutes) x
I 10 3.3 3. I 2.2 2.3
30 6.4 5.5 2.7 2.8
2 10 3.2 3.2 2.3 2. I
30 6.0 5.8 2.8 2.4
3 10 3.3 2.6 2.6 2.0
30 6.2 6.2 3.9 2.0
4 10 3. I 2.9 2.5 2.7
30 5.4 4.9 3.7 4.3
5 10 2. I 2.2 2.0 2.3
30 2.3 2.6 2.0 3.0
6 10 2.3 2.8 2.0 6.5
30 3.0 4.6 2.0 16.5
7 10 3. I 3.0 2.3 4.5
30 5.6 5.3 3.0 10.0
* Average load is the value of the total load per engine
per LTO - cycle used in this analysis and listed in Table
42. Maximum load is based upon increased idle time from
one minute to value shown, and emission indices increased
by 100 per cent over those listed in Table 40.
-------
294
TABLE 53 -AIRCRAFT ACTIVITY DURING BUSY AND PEAK HOURS
Activity Ratios
Air Terminal
Busy Hour (1)
Avg. Hour
Peak Hour
Avg. Hour
J. F. Kennedy International
1.58
2.91 (2)
3. 14 (2)
Washington National
Los Angeles International
1. 50
1.48
3.42 (3)
5.61 (3)
5 . 78 (3 )
Teterboro
Long Beach Municipal
( 1 )
Busy hour activity = average hourly rate between 10:00 AM and
10:00 PM
(2)
(3)
FAA - Proposed rates used
FAA - reported data for FY 1965.
(Ref 34)
-------
295
TABLE 54 - MAXIMUM POSSIBLE EMISSION LOADS
AT J. F. KENNEDY AIRPORT DURING 1967
Aircraft Pollutant Specie
Type CO HC NOx Particulates
Jet Average Load 2092 1026 201 63
~'~Sca Ie-up Factor 17.5 16.2 9.5 8.4
Piston Average Load 588 76 I I
~'~Sca Ie-up Factor 6.7 7.6 5.8 8.8
Max Load
Ibs per hr 40500 17200 1900 542
- Peak ()
*Scale-up Factor - Average Hourly Activity Factor Table 53
x Max Error Factor
The following assumptions are made in calculating the maximum error
factor:
Idle Time = 30 minutes
Emission indices equal to twice those given in Table 40.
-------
296
TABLE 55 - EMISSIONS BY CIVIL AIRCRAFT AT ALL FAA~CONTROLLED
TERMINALS - 1967 & 1979
... - -..~._.._----~.__..._.~- __'M-___".-.--"----
Emissions (1000 Ib/day)
Ai rcraft ---. CO Organics -NOx Particulates
Class I 1967 1979 1967 1979 1967 1979 1967 1979
1 429 1195 220 613 32.4 169.0 6.8 18.9
2 129 356 26 72 24.4 126.2 14.7 40.6
3 0 0 0 0 0 0 0 0
4 35 36 14 14 10.3 10.6 2.4 2.5
5 2795 475 375 64 3.7 0.6 5.1 0.9
6 963 4860 97 565 2.9 11.3 2.9 13.5
7 5 12 0.4 1 0.5 1.2 0.2 0.5
Total 4356 6934 732 1329 74.2 318.9 32.1 76.9
Per Cent
Change +59 +81 +330 +139
Method Used to Forecast 1979 Emissions:
1979 Emissions = (AR) (ER) (1967 Emissions)
AR = Ratio of 1979 activity (LTO - cycles per year) to 1967
activity by aircraft class.
Ai rcraft Class
AR
1
3.5
2
3.4
3
4
1.0
5
0.2
6
3.9
7
2.5
Total
3.5
ER = Ratio of emission per LTO cycle in 1979 to emission per LTO
cycle in 1967 as affected by equipment changes.
ER =
ABC + (I -C )
where A = ratio of fuel consumption/LTO cycle, 1979 to 1967
B = ratio of mean emission index, 1979 to 1967
C = fraction of aircraft in class affected by change
-------
297
TABLE 55 - EMISSIONS BY CIVIL AIRCRAFT AT ALL FAA-CONTROLLED
TERMINALS - 1967 & 1979 (CONTINUED)
Assumptions
Aircraft
Class Pollutant A B C ER
I and 2 CO 1.3 0.5 0.5 0.8
Organics 1.3 0.5 0.5 0.8
NO 1.3 1.5 0.5 1.5
x
Particulates 1.3 0.5 0.5 0.8
5 CO I .2 I . I 1.0 1.3
Organics 1.2 1.3 1.0 1.5
NO 1.2 0.8 1.0 1.0
x
Particulates 1.2 1.0 1.0 1.2
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298
TABLE 56 - LAND USE NEAR J. F. KENNEDY, WASHINGTON
NATIONAL, AND LOS ANGELES INTERNATIONAL AIRPORTS
Distance from
Airport (mi les) JFK~~ DCA LAX~I(
0-1 Sparse residential, Sparse residential Dense residential,
1 i ght residential and commercial commer i ca 1; 1 i ght
and commercial and heavy industrial
1-2 Dense residential Dense residential Dense residential
and commercial light commerical, and commerc i a 1 ;
and government 1 i ght industrial
offices
2-3 Dense residential Dense commercial, Dense residential
and commercial government offices and commercial;
and residential 1 i ght industrial
* From Reference 119
-------
299
TABLE 57 - SOURCE DATA USED WITH THE
AIRPORT AREA-SOURCE MODEL
Emmision Densities (g/m2/sec Ai rport
A rea~'~
Airport CO Organics NOx particulates (mi 2)
J. F. Kennedy
International 25 9.2 0.92 0.21 4.5
Washington
National 62 8.8 0.95 0.53 0.9
Los Angeles
International 39 15.0 1.3 0.32 3.0
*Estimated area used for aircraft operations less than total
airport area.
-------
300
TABLE 58 - COMPARISON OF CONCENTRATIONS OF AIRCRAFT
EMISSIONS AT AIR TERMINALS WITH
COMMUNITY CONCENTRATIONS
Concentration
'
CO Organics NO Particu~ates
Location ppm CH2 x
ppm ppm ~g/m
J. F. Kennedy
Terminal
a 1.5 1.2 0.04 15
Neutral
a 4.1 3.0 0.09 39
Stable
Washington National
Terminal
Neutral 3.0 0.8 0.03 27
Stable 7.9 2.2 0.09 78
Washington, D.C. - 2. 1 b
1965 Avg (Ref 73) 3.7 0.07 NA
Los Angeles Inter-
national Terminal
Neutral 2.3 1.8 0.04 21
Stable 6.1 4.8 0.12 56
Los Angeles - 1966
Avg (Ref 116) 10 NA 0.09 NA
Recommended community
1 imit values
(Refs 61, 73, 136) 15-30 3-4 0.25 80-120
a refers to meteorological conditions
b .. k
composition un nown
c concentrations at air terminals calculated using airport area
source model and following assumptions:
(I) receptor 100 meters downwind of airport
edge,
(2) wind speed 5 mi les per hour.
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301
TABLE 59 - EMISSIONS PER UNIT OF PATH LENGTH
Contaminant Emissions
(lbs/1000 feet of travel)
Aircraft Operating
C 1 ass)'c Mode)~'c CO HC NO Particulates
X
l 1 9.6 4.12 .12 .016
3 .046 .007 .28 .04
4 .023 .21 .09 .022
5 1 16.4 1.6 .05 .04
3 .23.9 3.7 - .04
4 6.5 .92 .01 .01
* Class 1 - large turbine engined aircraft
Class 5 - large piston engined aircraft
)~'c Mode 1 - tax i
Mode 3 land/take-off
Mode 4 - approach/climb-out
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302
TABLE 60 - DENSITY OF AIRCRAFT EXHAUST EMISSIONS AT AIR TERMINALS
COMPARED WITH EMISSIONS IN SURROUNDING REGIONS
Average Emission Density in 1967d
1000 1b/day per sq mi
Land Area
.c
sq ml
Region
New York City:
J. F. Kennedy
Terminal
Queens County
(Refs 120,
CO Organics
International
4.5
12.0
4.4
126 & 127)
30.2
8.4
113
Kings County
(Refs 120, 126 & 127)
76
25.4
7.2
National Capital:
Washington National
Terminal
Arlington County
(Ref 128)
0.9
30.0
4.4
25.8
32.6
5.2
Alexandria City
(Ref 128)
Washington, D. C.
(Ref 128)
'24.0
6.0
15.7
61.4
32.0
8.0
Los Anqelesa:
Los Angeles International
Terminal
Los Angeles County
(Ref 117)
Los Angeles Basinb
(Ref 117)
18.7
3.0
7.3
4,083
5.0
1.3
16.2
4.3
1,250
NOx
0.44
5.72
6.00
0.67
1.86
4.70
3.80
0.67
0.39
1.29
Particulates
0.11
I. 10
2.48
0.22
0.54
1.00
1.20
o. 17
0.05
O. 16
arule 62 period
b
90 per cent of
Angeles Basin
c . d
estimate area used for aircraft operations; less than total airport area
(summer months)
Los Angeles County emissions assumed to occur in Los
d
based upon emissions during ground operations only
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303
TABLE 61 - VARIATIONS IN EMISSION DENSITIES
I N URBAN AREAS
Em is s ion Densit~
(tons/day per m i )
CO Particu1ate
avg avg
Region max near min max near mi r.
val airport va1 va1 airport val
New York City:
Queens County 42.5 16 0.8 14 .21 o. 16
Kings County 69 30 1.2 27 1.5 .07
National Capital:
Ar I i ngton Count\ 29 28 4.2 0.6 0.6 o. I
Alexandria City 37 37 7.6 0.5 0.5 0.3
Washington, D.C 107 - 5 2. 1 - O. 1
-------
TABLE 62 - AIRCRAFT ENGINE EMISSIONS COMPARED WITH EMISSIONS FROM
OTHER SOURCES (1967 AVERAGE DAILY EMISSIONS)
;
CO Orqanics NOv Particulates
1 .000 lb/dav % of Total I 000 Ib/dav % of Total 1.000 Ib/day % of Total I 000 Ib/dav % of Total
a
New York IAQCR
Aircraft operations 166 0.6 43 7.8 2.9 0.2
Ground - JFK 54 20 2.0 0.5
Ground - All term- 103 30 3.2 0.9
inals
Fl ight 63 13 4.6 2.0
Surface transporta- 27,800 95.0 189 15.0
tion
Stationary sources 1,290 4.4 1 ,070 84.8
All sources 29,300 100.0 1 ,260 100.0
National capital I AQCRa
Aircraft operations 162 2.3 24 1.4 3.2 0.4 1.2 0.6
Ground - Washingtor 27 - 4 0.6 0.2
National -
Ground - all term- 77 11 1.6 0.4
inals
Fl ight 85 13 1.6 0.8
Surface transporta- 6,800 96.5 1,510 88.3 285 38.6 32 16.9
tion
Stationary sources 88 1.2 176 10.3 450 61.0 156 82.5
All sources 7,050 100.0 1 ,710 100.0 738 100.0 189 100.0
Los Angeles County
Aircraft operations 170 0.8 39 0.7 5.6 0.3 1.9 1.0
Ground - LAX 56 22 1.9 0.5
Ground - All term- 105 27 2.4 0.7
inals
Flight 65 12 3.2 1.2
Surface transporta- 19,950 98.3 3,740 69.5 1,800 67.3 92 47.5
tion b
Stationary sources 190 0.9 1,600 29.8 520 32.4 100 51.5
All sources 20,310 100.0 5,380 100.0 1 ,610 100.0 194 100.0
Sources:
References 117, 120, 126, 127 & 28.
aintprstate air Dualitv control reglilrL
bnnf", 62 pt:"1 iod !,,>ummeTlTlDnth'i,/
I..»
o
.po
-------
laule 6~ - £STTMAT£D REDUCTIONS IN AIRCRAtT EXHAUST EMISSioNS
ATTAINABLE BY VARIOUS METHODS
305
Total emissions in
1967 (Ib per day)
Piston-engine exhaust
treatment (a)
Replacement of piston-
engine transport air-
craft by medium-range
fanj ets
Turbine-engine low-
smoke combustors (b)
,
Turbine engine annular
combustors (c)
Auxiliary ground pro-
pulsion (transport
aircraft)
Total reduction by all
.methods combined
Total emissions in
1967 (tons per day)
Piston-engine exhaust
treatment (a)
Replacement of piston-
engine transport air-
craft by medium-range
fanj ets
Low-smoke turbine-
engine combustors (b)
Annular turbine-
engine combustors (c)
Auxiliary ground pro-
pulsion (transport
aircraft)
Total reduction by all
methods combined
John F. Kennedy International Terminal
CO orQanlCs NO IPartlcuTates
,..
66,645 26,441 4,847 I ,538
-200h -6% 0 0
-18% -6% +1% +2%
o 0 +7 -50%
-39% -47% 0 0
-79% -75% -16% -11%
-98%
""0
-600h
- 9 OOh
r.n.
All FAA-controlled air terminals
nrn:lnics NO ParticulAtes
,..
2,550 415 43 17
-75% -600h 0 0
-63% . -51% +22% +23%
o 0 +7 -50%
-8% -17% 0 0
-25% -34% -20% -14%
-85%
"'8]Oh
+7
-60%
NOTES: (a) estimated effectiveness: 90 per cent reduction of CO and
organic em i s s i on
(b) estimated effectiveness: 50 per cent reduction of particu-
late emission
(c) estimated effect'l veness: 50 per cent reduction of CO find
I-;r'l{~~' '}I:I 'L;.'7'""LI
-------
307
'"
FIGURES
-------
LEn FUEL TANK
RIGHT FUEL TANK
SELECTOR
VALVE
TO . .,,,,.,.,...
ENGINE ....d.
:f.
"'
.":
CODE
£II FUEL SUPPLY
o VENT
.~
,.
~:
- -.I--tr"r)
- - 'f'"'"L.lJ
-- THROTTLE
.1:
-- ~
--
--
MIXTURE
CONTROL
ICNOB
--- MECHANICAL
UNKAGE
..
TO
ENGINE
Cessna Mode1 172 with Lycoming
0-320-E2D Engine
LEFT FUEL BAY
RIGHT FUEL BAY
. .
CHECK V"LVE t
VENT
AUXILIARY
FUEL PUMP
CODE
~@~;~:" FUELSUPPLY
IIIII!IIIIIIIJJ EXCESS FUEL
II VAPOR RETURN
r::::::J VENT
ENGINE
FUEL PUMP
THROTTLE
---~
,. ~
,.,."
~~------~
FUEL
CON1'ROL UNIT
MIXTURE
CONTROL
Cessna Model 210 with Continental
10-S20-A Fuel Injection Engine
FIGURE' - TYPICAL FUEL SYSTEMS FOR LIGHT, PISTON-ENGINE AIRCRAFT
COURTESY OF CESSNA AIRCRAFT COMPANY (REFS 10 AND 11)
\AI
o
\D
-------
310
,--
. ---~
- ----,.
''--''-'-'1
I
- j
.---"....--..--'
---..---.J
'J
-
....
ContnII
-
-
~
FMOI,.."
--
SIIII
'''''-.
~
......-
-------~==
(Reproduced from Reference 9 with
permission of the Hayden Book Co., Inc.)
FIGURE 2 - TYPICAL FUEL SYSTEMS FOR NON-AFTERBURNING
TURBINE ENGINE
, .
.
-------
Fuel
(Main) -P
Fuel
(Pr imary}"P
a.
Dual-Orifice Atomizer
Atomizing
Air
b.
Airspray Fuel Atomizer
(Taken from Reference 13)
FIGURE 3 - TURBINE-ENGINE FUEL INJECTORS
311
/
,
-
"
~
/
-------
312
4000
3000
.....
...
1'0
L.
U
L.
«
4-
o
2000
L.
a)
.D
E
::J
Z
1000
,.
;'
/' "
,/ ",.
,/.
/' .
/ ,/
/ ~fc"if' /'
~~ / ~y /
, '\~ /
.I /
/ /
/ /
I I
/
I
I
/
o
. Report Date
/
,
Turboprop
.-.-.-.-.---.-. -.-.
'_Piston-Engine Aircraft
--
---
---'----.
60.
64
62
66
68
74
76
78
70
72
Year
FIGURE 4 - COMPOSITION OF THE UNITED STATES
. AIR CARRIER FLEET
-------
313
200
/
/
/
/ /0
/ / °
,
Total / /
150 Aircraft ,
/ 0/
If) / /
"C
c: /"
III /
If) /0 Single-Engine
::J /
0
~ / /' Pi ston
....
/'
4..1 /0/0
\I-
III 100
L
U
L
<
\I-
0
L
Q)
..Q
E
::J
Z
50
--
--
--
--
--
-
Multiengine
Piston
Turbine
o
60
62
64
66
68
70
72
74 -
76 - 78
Year
FIGURE 5 - COMPOS I'T ION OF THE UN I TED STATES
GENERAL AVIATION FLEET
-------
314
100
75
V1
C
0
I
I
I ~
I
J..
IU
Q) 50
>
J..
Q)
0.
V1
Q)
-
u
>-
(.J
I
0
...
....I
/
11/
/ /
11/
/ ,/
Total ;I ,;I
Civi 1* ;I /
/ /'
/ /' General
/ ' Aviation*
/ ./
/ ./
/
./'
--
--
--
-- ..... --- .
- - - - A I r Ca rr i er
62
68
74
76
64
66
72
.70
Year
*At FAA-Controlled Terminals Only
FIGURE 6 - ANNUAL AIR TRAFFIC ACTIVITY AT .
UNITED STATES AIR TERMINALS
78
-------
NUMUR OF
'UGHTS
NUMBER OF
FUGHTS
ire NEW YORK
.J\
f \
, \
, ,
, ,
, ,
, ,
.
.
.
.
.
.
.
,
.
.
.
.
f
.
to
4D
o
60
«I
20
IX! 01 02 03 04 os 06 07 08 r:1I 10 II 12 13 14 15 16 17 18 1920 21 2223
EAStERN STANDARD TIME
N\JM8ER OF
FLIGHTS
LOS ANGELES
NUMBER Of
'UGHT5
CHICAGO
eo
CI
60
o
WASHINGTON
-ARRIVALS
---DEPARTURES
111213141516 17181920212223
SAN FRANCI SCO
60
40
20
40
PACIFIC STANDARD TIME
(Reproduced from Reference 31)
o
PACifiC ST 'NDAI!D 11.\1i:
\oN
V'I
FIGURE 7 - HOURLY VARIATION OF AIRCRAFT ACTIVITY IN FIVE METROPOLITAN
AREAS - MAY 1967 (SCHEDULED AIR CARRIER AND AIR TAXI ACTIVITY ONLY)
-------
316
Crude
Oil
i&..
en
-8 600
..
G)
L.
::J
+'
I'D
L.
8. 400
E
G)
l-
e
o
+'
~ 200.
+'
en
Q
800
Refinery Gas
Gasoline
Hydrocarbon
Gases r- - -.-
I
I
.
I
I
I
Gasoline
4
Polymer
Gasol ine
Kerosine
Gas Oi 1
~-
I
:a; ~i~
3
Light Gas Oi 1
I
I
I
t
L~=.sl~!
( Lubr i cants
Fue 1 0 i 1
Tars
1 .
2. .
3.
4.
Atmospheric Distillation
Vacuum Distillation
Catalytic Cracking
Catalytic Polymerization
a.
Process Flow Sheet
Approximate Temperature
f
Gas and Diesel Oils
~
f
Kerosines
!
Ranges
o
Gaso 1 i nes
!
t
and Gases
o
10
40
50
20
30
Fraction of Crude Oil, per cent
b.
Products from the Atmospheric Distillation of Crude Oil
FIGURE 8 - PRODUCTS FROM A TYPICAL CRUDE
OIL REFINING OPERATION
-------
317
100
90
e D
80 ~'(.
70 ~<~
L..
Q) 60
.0
E
:J 0
Z 0
L..
Q) 50 0
~
Q)
E
0 . {'?'\.. 0
c: 40 . ~ \
E I\~'\..e{ '\..\01\
:J ."a
i . '?'\..\
\)\
30
Crude Source
20
Africa-
10 South North Middle
America America East
0
0 10 20 30 40 50 60 70 80 90 100
Per Cent Paraff ins in Saturate Fraction
*
Smoking tendancy decreases as 1uminometer
number increases.
FIGURE 9 - LUMINOMETER RATING OF AVIATION KEROSINES
AS A FUNCTION OF CRUDE OIL SOURCE
~TAKEN FROM REFERENCE 40)
-------
318
22
/
.
Turbine-Engine Fuels /~ /
" .. /
Tota1 ~. ~
./. /
./ /
./ /
./
/ /
~.
. . /~iVi1
/' AviatlOfl
/'
/
/
/
I 18
I
I
I 16
I "
I
I 14
I
C1\
I
0 12
x
III
c::
0
- 6
I1J
c.:J
4
2
0
60
C1\
I
O
x 3
s...
IV
Q)
>- 2
s...
Q)
a.
III
c:: -
o
IV
c.:J 0
60
66
68
74
76
72
Years
Piston-Engine Fuels
.-
Tota1 -.--.--
8........." ----.
.-.........-
Civi 1 AvUU:.i~ --
-- ---- -. - --- ~ --- ----
Years
FIGURE 10 - NATIONAL CONSUMPTION ~TES OF AVIATION
FUELS. YEARS 1960-1979
78
-------
-
-
1400
1200
Q)
::J
~
I
.J:1
1000
o
o
o
-
"'-
.J:1
800
)(
C)
~
t:
600
t:
o
III
III
E
LLI
400
200
o
8
o
Take-Off
"
~ " Correlation Curve
........X used for Aircraft
~ "Engines at Part
" load
~
"
"'-" Id~~
" :+ \:
"', '\
"
o "+\ ~
"'-, Idle "'- \
" , ~
"'-",~---=-~~~===-
Idle~', /IJ. "\.. '" "-
'''', A""" "'-
, A . \ " ~Part load
,A ~"-.
'.. ~ "-....
--- --- Engine Test
---- - Engine Test
----- Auto T€st
--- Auto Average
---- Auto Average
+ Auto Survey
. Auto Survey
~ P&WA R-28oo
(Ref 70)
(Ref 71)
(Ref 72)
(Ref 3)
(Ref 73)
(Ref 74)
(Ref 69)
(Ref 68)
9
17 ~
\D
14
15
16
10
11
12
13
Ai r- Fue 1 Ra t i 0
FIGURE 1 I - CARBON MONOXIDE EMISSION BY PISTON ENGINES
-------
-
-
Q)
~
~
I
..c
o
o
o
-
.......
..c
'-"
x
Q)
~
c:
c:
o
CII
CII
-
E
L&J
--:::: - -A-
--- -- - --- ~
------- ~
A ---
280
--
Engine Test, Two
Ana1ysis Methods
Engine Test (Ref
240
---
~
200
160
<:>
Id1e
120
80
40
--
o
9
10
(Ref 11)
12)
11
--- Auto Average (Ref 3)
---- Auto Average (Ref 73)
+ Auto Survey (Ref 74)
A Auto Survey (Ref 69)
B Auto Test (Ref 75)
~ Auto Test, Id1e (Ref 76)
a P&WA R-2800 (Ref 68)
----------
----------- -
A
+
++
~+
+
m m
Corre1ation Curve
~used for Aircraft
ngines
12
14
15
16
13
Ai r-Fue1 Ratio
FIGURE 12 - :1 SSION OF ORGANICS BY PISTON ENG NES
\.oJ
N
o
17
-------
/
/
/
A. /
-8 -~
AI
A/
A
/
50
40
Engine Test (Ref 70)
- - Engine Test .(Ref 75)
- - - Auto Average (Ref 3)
---- Auto Average (Ref 73)
. Ii. Auto Survey (Ref 69)
-
4)
:J
....
I
JJ
30
o
o
o
-
.......
JJ
--
-
)(
Q)
"
c:
20
A
c:
o
VI
VI
E
~
10
fA
A ~
0 A
8 9 10 II 12 13 14 15 16 17
Ai r- Fuel Ratio
"'"
N
FI GURE 13 - EMISSION OF NITROGEN OXIDES BY PISTON ENGINES
-------
322
o
.-
.jJ
10
a::
Q)
:J
1L.
I
L.
c:( , 10
Id1e
13
12
11
'-""" /
V
j
. II
\ /'
\ ,,I
'r1
/ ,GFJ 0
I '
I .'
,
.
I
.
I
,
,
.
I
9
o
Cruise
Climb and Take-Off
o
000
20
40
100
60
80
Per Cent of Maximum Air-Flow
(Full Ridh Condition)
0' PWA Data - 5 Radial E~9ines (Ref 68)
----- Fuel System Performance (Ref 8)
FIGURE 14 - AIR-FUEL RATIO CURVES FOR
TYPICAL AIRCRAFT PISTON ENGINES
-------
140
5
0
- 120
Q)
::J
'+-
I
.c
0
0 100
0
-
........
.c
-
X
Q) 80 T J - Turbojet
"'C
c: TF - Turbofan
c: TP - Turboprop
o
III
III
E 60
UJ
(Data points identified
40 in Table 41)
y
c
20
o
TJ TF TP TJ TF TP TJ TF TP
Idle Approach Take-Off
Power Level
FIGURE 15a - TURBINE ENGINE EMISSION DATA. CARBON MONOXIDE
180
160
323
N
G
-------
324
90
80
70
........ 60
-
Q)
:)
4-
I
.J:J
0
0 50
o
-
'-
.J:J
'-'
X
Q) F
""0 40
c
c
0
III
III
E 30
1&1
20
10
o
G
N
T J - Turboj et
TF - Turbofan
TP - Turboprop
(Data points identified
in Tab1e 41)
TP
TJ
TF TP
TJ TF
Idle
TP
TJ
TF
Take-Off
"FIGURE 15b - TURBINE ENGINE EMISSION DATA.
ORGANICS AS CH4
Approach
Power Level
-------
325
8
7
y
21.8 t
6
y
-
Q) BJ
::J
4- 5
I
.c
a
a
a
~ c
.......
.c 4
......
x: w
Q)
"0
c:
c: I
o 3
VI
VI
E
UJ
2
u
o
(Data points identified
in Tab1e 41)
TJ
TF
Id1e
TP
TJ
TF
TP
TJ
TF TP
Take-Off
Approach
Power Leve1
FIGURE 15c - TURBINE ENGINE EMISSION DATA.
NITROGEN OXIDES AS NO
-------
2.0
-.
Q)
::J
4-
I
.D
0 0
0 v i
o 1.5
"
.D
"-"
x: I
Q)
"'0
C I
HS
c
0 1.0 .
w
en
en
.5
326
3.0
2.5
0.5
M
o
x
(Oata points Identified
'A Tn1e 41)
TJ
TF
Id1e
TP
TF
TJ
TP
TJ
TF
TP
Approach
Take-Off
Power Leve1
FIGURE 15d - TURBINE ENGINE EMISSION DATA. PARTICULATES
-------
,....
u
(I)
VI
........
N
VI
L..
(I)
~ 10
(I)
E
"'"
0
-
-
(I)
~
I'D
~
c:
0
~
I'D
.....
0-
~
c:
(I)
>
327
Ventilation Rate = Mixing Depth x Wind Speed
Data shown for non-precipitation cases
Sources: References 113 and 114
5
Wash., D.C. Afternoon ~A ...
Morning ~-~
Afternoon {--.....
15 New York Morning
..0-.---0-
Afternoon f. .
Los Angeles Morning ..---+
\
.
\
\
.
h..-.
~...,
/~ ~--~ ~
~ . , ~
.o--~,-Q...... P
~---- ""-- '... ,
_.~' ~ ~ A ,
. . .0-'" ,...... - -1::1:- - -.... .... ...6.- ~- -- -.Q. ....
-' -tJr-:t. -=:--o-----o--_:~ '-,
o
J
F
'A
S
o
N
D
A
M
J
Month
J
M
FIGURE 16 - MONTHLY MEAN VENTILATION RATES FOR
NEW YORK. WASHINGTON. AND LOS ANGELES
-------
328
-
~
[-4
~ 200
-
:>
t.
=
~ 100
-
~
J.c
CI)
~
CD 50
'5
Pot .
2.5
.
Meters per Second
7.5
12.5
5
10
500
Wake Area
[ 100 Nf
X~E = 100 gm/sec 500 M2
1000 M2
E = 20 gm/sec, A = 100 -Nl'
. -
. x
--------
'M-)(
)(
.-.-8
o
0_8
20
)C
10
5
10
15
20
25
Miles per Hour
Predictions at various taxi speeds for
Class 1 aircraft (CO Emission = 100 gm/sec)
Class 2 aircraft (CO Emission = 20 gm/aec)
FIGURE 17 - CARBON MONOXIDE CONCENTRATION IN THE
WAKE OF TAX II NG AIRCRAFT
1.0
0.5
0.25 J.c
CI)
~
CI)
~
o
-
~
- 0.1
q)
w
m
J.c
0.05 --
0.025
30
-------
329
APPENDICES
-------
331
APPENDIX I
SAMPLING AND MEASUREMENT METHODS
Exhaust Sampl inq Techniques
The measurement of concentrations of pollutants in engine exhaust
gases can, in some cases, be accompl ished by direct observation of the
exhaust gas stream, or by collection of an exhaust gas sample with subsequent
analysis of the sample.
Direct observation is not commonly used in measuring
aircraft engine exhaust emissions.
Instead, most measurements, including all
those presented in this report, are obtained by analysis of exhaust gas
samples.
The primary objective in exhaust gas sampling is obtaining a
representative sample of exhaust gas of a known quantity or at a known
flow rate.
Apparatus used for sampling generally consists of a probe, sampl ing
1 ine, a flow measuring device, a pump capable of drawing the desired flow rate
through the system, and collection devices for capturing pollutant samples.
The design of the sampling probe is not critical in measuring con-
centrations of gaseous pollutants.
However, in measuring concentrations of
particulates, it is desirable that the probe be designed to achieve isokinetic
sampling which is defined as a condition wherein the gas velocity at the sampl-
ing inlet nozzle matches the velocity of the stream being sampled.
Departures
from this condition may cause errors in sampl ing for particulates whose diameter
is greater than 3 to 5 micrometers.
However,
isokinetic sampl ing is not con-
sidered to be necessary in measuring aircraft engine emission since particulates
from these engines are generally less than l;4m in diameter.
The sampl ing line, which conveys the gas sample from the probe to the
collection and measurement apparatus, must be designed such that no changes in
-------
332
sample composition or physical state occur during transit.
The 1 ine must be
constructed of materials which do not adsorb or react chemically with pollutant
materials, and the 1 ine must allow free passage of particulate materials.
In sampling engine exhaust gases, it is also necessary to maintain the sampl-
ing line temperature at a level at which condensation of organic vapors does
not occur.
This requirement is more severe with turbine engines than with
gasol ine-fueled piston engines.
Turbine engine fuels, which have higher
boil ing points than gasol ine, give rise to organic emissions which also have
high boiling points.
The requirement for heating the sampl ing lIne often is
neglected.
A notable exception is the sampl ing technique devised by the Los
Angeles County Air Pollution Control District (Ref 1-1).
With this technique,
the entire sampl ing system is located near the engine so that the sampling
line length is minimized.
The design of the sampling pump and flow measuring device usually
is not critical since these units normally are installed downstream from the
collection equipment.
If they are upstream, however, they must also be
designed so as not to change the nature of the exhaust gas sample.
The types of pollutant collection devices to be used in a sampl ing
system depend upon the measuring techniques to be employed.
Many measuring
techniques do not require pollutant collection, but indicate pollutant con-
centration directly by measuring some property of the gas sample.
These
techniques are utilized either by connecting the measuring device directly
to the sampl ing system, or by collecting a gas sample in a container (grab
sample) and transporting it to the measuring device.
Many other analysis techniques require that the pollutant species
being measured be extracted from the gas sample and concentrated in order to
determine the concentration of the pollutant in the exhaust gas.
These methods
-------
333
of pollutant collection are tailored to the analysis methods with which they
are used and are described in the next section.
Methods of Analysis
Particulates
Collection
With particulate analysis techniques which require sample collection,
filters or impingers generally are used.
These devices effectively separate
sol id particles from the sample and pass the gaseous components on to other
devices downstream.
However, if the gas sample contains vapors of low
volatility, as is often the case with engine exhaust gases, these vapors may
condense in the collecting device and be captured along with solid particulate
matter.
In this event, the indicated particulate concentration wil I be greater
than that actually existing in the engine exhaust stream, and the organic con-
centration will be correspondingly less.
Vapor condensation can be avoided by
maintaining a high temperature throughout the sampl ing and collecting system.
Mass Analysis
The total mass of particulates is most easily determined by gravimetric
analysis.
,
This analysis is performed in two ways depending on the method used
for collection.
If the particles are collected using a filter paper or cloth
bag, the filter is dehumidified and weighted before sampl ing.
After collection,
it is dehumidified again and weighed to determine the mass collected.
If the
collection device is a dry impinger, the collected material is removed
from the impinger and weighed directly.
If a wet impinger is used, after
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334
sampling, the liquid slurry is passed through a pre-weighed, dried, absolute
f i Iter.
After re-drying it is weighed, yielding a net collected mass.
Both
of these methods of weight analysis have proven efficient and accurate and
will probably continue to be used.
Collected particulates are classified as:
1.
Insolubles which are determined by filtering the impinger
solutions or, In :the case of a dry filter collection, by
simply extracting the soluble solids with methyl chloroform
and weighing the solid cake retained by the fi Iter paper.
2.
Solvent solubles which are determined by weighing the residue
remaining after evaporating the combined solvent extract by
a stream of dry air at room temperature.
3.
Water solubles remaining in the fi Itrate which are determined
by adding water and weighing the residue left after evaporat-
ing the filtrate at a maximum temperature of 105 deg C.
Size Analysis
One of the major gap areas in aircraft exhaust emission sampl ing
is in the measurement of discrete particle sizes and particle size distribu-
tions.
Several techniques which appear to be applicable have not been
.
investigated.
One potential technique is Light Detection ,and Ranging (LIDAR)
(Ref 1-2).
LIDAR is basically a tool for remotely detecting the presence
and range of particulate scattering inhomogeneities.
This capability has
been used to measure cloud heights and to detect hazes and fogs.
LIDAR has
also been used to monitor industrial sources such as smoke stacks.
Reagan
(Ref 1-3) suggests that LIDAR might be employed to map the dispersal of
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335
insecticides dumped from aircraft or to track the airborne flow of wastes
released by explosions.
Atmospheric scientists are presently investigating the possibi lity
of using LIDAR in a more quantitative way to determine the quantities of
particulates in the atmosphere.
Basically the problem involves inverting
back scatter measurements to infer the size distribution and number density
of the scatterers producing the received signal.
Obtaining such information
is extremely difficult, however, because a scattered signal depends in a
compl icated way on several properties of the light scattering medium.
This
dependency necessitates making certain assumptions relative to the size
distribution and index of refraction of the particles.
In view of recent
experimental results presented by Barrett and Ben-Dov (Ref 1-4), it appears
that it might be possible to obtain useful estimates of the quantities of
particulates in a given volume of gas by making such assumptions.
A second particle counting device which may have application is
the Illinois Institute of Technology Research Institute (IITRI) particle
counter (Ref 1-5).
This instrument is a light-scattering, single particle
counter which classifies particles into six size ranges from 0.35 to 2.8 "l(m
i n d i am e t e r .
Unfortunately the concentration of particulates issuing from
an aircraft engine is higher than the instrument is capable of analyzing.
Dilution devices are avai lable which may enable this instrument to operate
in higher concentration ranges (Ref 1-6).
Gordon and Dennis (Ref 1-7) report the successful use of a single
stage boundary layer diluter in conjunction with a Royco Instrument Co.
PC200 automatic light scattering particle counter when high concentrations
of aerosols (0.3-10 ~m) are encountered.
The results of a series of tests
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336
at di lution ratios varying from 5/1 to 353/1 correlate well with simultaneous
cascade impactor samples and mass balance techniques.
Gussman (Ref 1-8) reports use of a condensation nuclei counter
based on a design by Pollak, that will accurately measure number concentra-
tions in the submicron particle size range.
These submicron particles, known
as condensation nuclei, are generally considered to be in the size range
between 10-3 and l)U m.
Because of their size, the nuclei cannot be directly
observed.
Their presence can be demonstrated by causing them to grow into
droplets.
This is accomplished by drawing air containing the nuclei into
a wet wall chamber and allowing the vapor pressure to reach saturation.
When
the saturated air is adiabatically expanded to a lower pressure, there will
be a drop in temperature dependent on the pressure ratio.
At this lower
temperature, the air wi 11 be super-saturated and the water vapor wi 11 con-
dense upon the active nuclei in a matter of milliseconds.
Because of the
physical nature of the process, the particles all tend to grow to the same
final size regardless of their initial distribution.
A light beam directed
through the chamber onto a sensitive photocell is obscured by the droplets
and the degree of obscuration may be cal ibrated to indicate the number of
particles present per unit volume.
This type of instrument may also be used
to determine the size distribution of the submicron aerosol when the device
is used in conjunction with a diffusion battery (Refs 1-9 and 1-10).
The
diffusion battery is a device which wi 11 remove the particles from a flowing
air stream with an efficiency dependent upon the particle's diffusional
mobility.
By operating the battery in accordance with the method of Fuchs
. (Ref 1-9), it is possible to determine the median diameter and standard
geometric deviation of a submicron aerosol distribution.
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337
There are several automatic particle sizing and counting devices
available.
There are no reports of these types of instruments being used,
but, with certain modifications for proper di lution, these devices could be
useful in determining the size and quantity of aircraft engine particulates.
Analysis of Light Obscuration Characteristics (Smoke)
Smoke has been defined as the visible by-product of the combus-
tion process.
Smoke is a complicated phenomenon and the physical nature
of a smoke cloud cannot be defined uniquely by anyone parameter.
Visibility
of smoke results from changes in light transmission, and the parameters
which describe smoke visibility have been related in Bouguer's equation
(Ref I - 11 ) .
There are various techniques, known .as stained fi Iter paper sys-
tems, for taking smoke samples and indirectly determining a "smoke number".
All of these systems have the following common traits.
The smoke sample is
extracted from the smoke source with a probe, and the sample is transported
through a sample line to the smoke filtering instrument.
This instrument
filters a certain volume of smoke through a selected area of filter paper.
(Whatman No.4 is frequently used.)
The mass of carbon collected on filter
paper is a function of the sampling volume and the carbon concentration of
the smoke sample.
The optical density of the stain on the fi Iter paper is
related to the quantity of carbon collected per square inch of stain area.
Diffuse reflectometers are used to measure the optical density of stains on
the fi Iter paper.
Stained filter paper systems presently avai lable include the
Bacharach system which is described in detai I in ASTM specification
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338
ASTMD-2-156-65 entitled "Standard Method of Test for Smoke Density in the
Flue Gases from Distillate Fuels", the Bosch system which is similar to the
Bacharach system approved as American Standard Zll. 182-1965 by ASA LDC
665.52:662.615.533.1, the Von Brand Meter System, (Reflectance Unit of Dirt
System), proposed by Gruber (Ref 1-12), and the G. E. Smoke Number System
(Ref 1-13).
A system which uses Millipore filter paper instead of Whatman
No.4 and a proposed smoke number (PSN) is under study by the Aerospace
Industries Association (AlA) for standardizing all reported smoke levels.
A technique for estimating smoke density directly by comparing
the visual appearance of smoke with a standardized density scale was
developed by Ringlemann (Ref 1-14).
The Ringlemann scale is an accepted
smoke density standard for public health service agencies.
The scale spans
0.5 units and is used to indicate the light transmission properties of
plumes.
A Ringlemann number of 0-1 is approximately equal to 80-100 per cent
transmission, 1-2 is 60-80 per cent transmission, 2-3 is 40-60 per cent trans-
mission,
3-4 is 20-40 per cent transmission and 4-5 is 0~20 per cent trans-
mission.
This technique, although useful, has severe 1 imitations.
1 tis
primarily used for black smoke, and the changing background conditions
result in errors in smoke density readings.
A method of obtaining plume transmittance by means of contrasting
targets also has been used.
Luminance measurements are made with a telephoto-
meter on a black target and a white target through the plume and at the side
of the plume.
The transmittance of the plume is calculated by dividing the
difference in luminescence between the black and white targets as measured
through the plume by the difference in luminance measured clear of the plume.
To date, no satisfactory method has been developed for making this system
operat i ona 1.
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339.
Fiorello (Ref I-IS) of the Naval Air Propulsion Test Center claims
liTo date there has been no suitable light transmission or light scattering
method found to measure smoke emission of the entire exhaust stream using a
direct light transmission and light scattering method through the plumell.
He describes several methods including a Rolls Royce meter which is a modifi-
cation of the principle used in the B. T. Hartridge meter.
This method
does not collect smoke on a fi Iter but draws a sample of gas through a tube,
one end of which is a light source and the other end a photocell.
Changes
in the output of the photocel I correspond to the amount of smoke present in
the exhaust air sample.
Faitani (Ref 1-16) reports the use of an electron microscope in
conjunction with a Von Brand reflectance meter to determine the quantity of
smoke as well as the particle size.
It appears that the advent of an instrument which will remotely
measure the opacity of a jet exhaust is desirable and would enable testing
of an aircraft in flight as opposed to one engine mounted in a test cell or
on an airplane on the ground.
This is a difficult requirement because of the
lack of a uniform background, and because of atmospheric density, tempera-
ture, and humidity changes which occur with changes in altitude.
Oxides of Nitroqen
There are three commonly used batch methods for the quantitative
determination of nitrogen dioxide concentration in a gas sample:
1.
The Jacobs and Hochheiser method (Ref 1-17) can be used in the
presence of high concentrations of sulfur dioxide.
Ai r is
aspirated through a fritted bubbler in a sampling train
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340
containing a nitrogen dioxide absorbing alkaline solution.
The absorbed nitrogen dioxide is determined colorimetrica]ly
as the azo dye.
Nitrogen dioxide concentrations of the order
of parts per hundred million in air can be determined by
this method.
2.
Another method used is based on the absorption of nitrogen
oxides by a solution of mixed reagent consisting of sulfani ]ic
acid, o(-naphthylamine, and acetic acid in a glass bubbler
(Ref 1-]8).
A color is produced which may be compared to
standards or observed spectrophotometrica]ly at a wavelength
of 550 nanometers (nm).
ASTM designation E1607, issued in
]958, is a modification of the above principle, the major
changes being the substitution of N-], naphthylethy]ene diamine
dihydroch]oride for ~:naphthy]ene as the coupling agent and
the use of a fritted bubbler instead of an ordinary glass
bubbler.
Again the resultant color can be read with a spectro-
photometer set at 550 nm.
3.
The third and most commonly used method for the determination
of nitrogen dioxide and nitric oxide is the Saltzman method
(Ref 1-19).
This method is intended for manual determination
of nitrogen dioxide in the atmosphere in the range of a few
parts per billion to about five parts per million.
The sample
is obtained by drawing air through fritted bubblers and
nitrogen dioxide is absorbed in Griess-Saltzman reagent.
A
stable pink color is produced and may be read visually or
spectrophotometrically at 550 nm.
This method is also applicable
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341
to the determination of nitric oxide after it is converted
to an equivalent amount of nitrogen dioxide by passage through
a permanganate bubbler.
These three methods are batch type analyses which are slow and
which do not yield continuous data.
Some investigators have incorporated
these techniques into a continuous analyzer by using a spectrophotometer
and appropriate valving, and these devices do yield continuous results.
Ganz and Kuznetsou (Ref 1-20) have developed an automatic record-
ing gas analyzer based on measurement of the PH of a solution which varies
with the concentration of oxides of nitrogen in the gas passing through it.
It is based on the principle that the interaction of nitrous gases with the
absorbent (5% hydrogen peroxide) yields a weak nitric acid solution and that
the change in concentration of the acid is dependent on the specific gravity
and concentration of gas passing through the solution.
Unfortunately the
manufacturers do not indicate the sensitivity or specificity of the instru-
ment.
Smith (Ref 1-21) describes an instrument to determine NO concen-
tration which uti lizes an ultraviolet spectrophotometer technique developed
at the University of California at Berkeley.
Its accuracy is claimed to
be ~IO% over a range of 50-2500 ppm and has been used to sample the exhaust
from gas turbine combustors.
Nitric oxide and nitrogen dioxide have been measured continuously
with a modified Beckman Model K-75 Acralyzer employing modified Saltzman
solution.
The potassium permanganate solution normally used for oxidizing
nitric oxide to nitrogen dioxide is found to result in losses of nitric
oxide of up to 50 per cent (Ref 1-22).
This solution may be replaced with
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342
a tube containing chromic oxide impregnated glass fiber fi lters which
oxidize essentially 100% of the nitric oxide.
A cold trap is inserted
prior to the oxidizer to prolong its life.
In addition, the N(l-naphthyl)
ethy1enediamine hydroch1oride NEDA norma11y used as the coup1ing compound
is replaced with N(1-naphthyl, acetyl) ethylenediamine (ANEDA).
The former
reduces approximately 10% of the nitrogen dioxide to nitric oxide, thus
giving 10w results for nitrogen dioxide and high results for nitric oxide.
This reduction is only 1-2% with ANEDA.
The absorbtances of theresu1ting
solutions are measured with a Bausch and Lomb Spectronic-20 spectrophoto-
meter.
Carbon Monoxide
The quantity of carbon monoxide found in the exhaust of a jet
engine is very low compared to other sources such as the piston engine.
This fact negates the use of an Orsat type analysis, which is a widely used
technique for measuring high concentrations of CO, C02 and 02 in gas streams.
Several methods are present1y avai lable for quantitatively ana1yz-
ing the carbon monoxide content in a gas sample.
One of the most common
and least expensive tools is the carbon monoxide indicator tube.
When
highly purified si1ica ge1, impregnated with ammonium molybdate and a so1u-
tion of palladium or pal1adium oxide, is digested in sulfuric acid, it
forms a silicomo1ybdate and upon being exposed to carbon monoxide forms a
molybdenum blue.
The depth of color in the detector tube varies from
faint green to a deep b1ue in proportion to the amount of carbon monoxide
present in the air being sampled.
This method has been used on a continuous
basis for sampling carbon monoxide in the range of 1:2 parts per mi llion
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343
by aspirating a metered flow of air through the tube at a constant rate
and observing the change of color with respect to time.
It has been used
for sampling aircraft jet engine exhaust with some degree of success
(Ref I-I).
An instrument often used for monitoring carbon monoxide is a
pressurized, non-dispersive, infrared (NDIR) spectrometer.
This instru-
ment has been used in studies by the National Air Pollution Control Adminis-
tration (Ref 1-23).
The instrument is a selective non-dispersive type
infrared analyzer comprising a source of radiation, a beam chopper, sample
and comparison, a beam combiner, a detector, preamplifier, control box,
and readout.
It is in wide use for the monitoring of carbon monoxide and
is considered to be reliable and accurate.
In an NDIR analyser, two Nichrome fi laments are used as sources
of infrared radiation.
Beams from these fi laments pass through parallel
gold-plated stainless steel ce1ls.
One beam traverses the sample cell, and
the other a comparison cell.
The emergent radiation is directed into the
signal detector cell.
As the gas in the detector absorbs radiation its
temperature and pressure increase.
An expansion of the detector gas
causes a condenser microphone membrane to move.
This movement, when
converted and e1ectrically amplified, produces an output signal.
Between the source and the cel1s~ a semicircu1ar beam chopper
a1ternately blocks the radiation of the samp1e cell and the comparison cel1.
When the beams are equal, an equa1 amount of radiation enters the detector
from each beam.
The amplifier is tuned so that only variations in light
intensity occurring at the desired frequency produce an output signal.
Therefore, when the beams are equal, the output is zero.
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When the gas to be analyzed is introduced into the sample cell,
it absorbs infrared energy and thus reduces the radiation reaching the
detector from the sample beam.
As a result, the beams become unequal and
the radiation entering the detector pulses as the beams are alternated.
The detector gas expands and contracts in accordance with the pulse and
causes the membrane to move in response.
The membrane movement varies the
condenser microphone capacity and the variation in capacity generates an
electrical signal which is proportional to the difference between the two
radiation beams.
The signal is then amplified and fed to an indicating
meter.
This type of device may be specifically sensitized to a single
component in a multi-component stream.
Normal variations of background
components generally effect analysis signals less than one per cent of full
scale range.
Scott (Ref 1-22) reports the use of a Beckman Model 513AL Non-
Dispersive Infrared Analyzer to monitor carbon monoxide continuously in
the range of 0-50 ppm.
This analyzer contains an optical fi Iter to elimi-
nate the interference from atmospheric moisture which wi II otherwise pro-
duce high readings.
Scott also utilizes an Aerograph Model 1532-26 Chromatograph
with dual helium ionization detectors.
This instrument is used to verify
the results from the infrared analyzers measuring carbon monoxide.
The
instrument is claimed to determine carbon monoxide concentrations to plus
or minus 0.1 ppm in the 0.0-10.0 ppm range and to plus or minus 1 per cent
of the component value from 10-100 ppm.
It has an ultimate capability
of detecting as little as I ppb carbon monoxide.
This sensitivity is not
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345
required for aircraft analysis but the accuracy of ~I per cent is a great
asset.
Both of these instruments are calibrated with "close tolerance",
pre-analyzed gas mixtures.
A spectrophotometric method has been used which relies on the
reduction of a si Iver salt of an acid to give a sol.
This method is claimed
to be very sensitive and possibly has an application in jet exhausts (Ref 1-
24) .
Another method from the same source is an electrochemical method uti-
lizing the oxidation of carbon monoxide at a vibrating electrode in a
solution of borax.
A type of wet chemical analysis using iodine pentoxide is gener-
ally not sensitive enough for measuring the concentrations of carbon monoxide
found in the ambient atmosphere and can be used only when the levels are
sufficiently high as in piston engine exhaust analyses (Ref 1-24).
Wilson (Ref 1-24) reports a simple but precise instrumental
method which makes use of the temperature changes in the air stream when
carbon monoxide is oxidized over a catalyst.
This method is useful when
a continuous monitor is desired.
The problems of measuring a small tempera-
ture rise may be complicated, however, in an engine exhaust by the high
temperatures already present.
Carbon Dioxide
Several methods are currently avai lable for monitoring carbon
dioxide, both on a continuous and a batch basis.
One of the most common
methods presently in use is the Orsat type analysis.
This is a batch analy-
sis method which has been applied successfully to exhaust sampling in
stationary engines (static tests) (Ref 1-23).
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346
Workers at Pratt and Whitney Aircraft have reported the use of
a gas chromatograph for measuring the volume of C02'
This device also
measures 02' CO and CH4'
This method requires a grab sample which has an
inherent drawback in that the sample must be analyzed within a short period
of time after collection due to C02 diffusion to the walls of the exhaust
gas sample container.
High range C02 detection tubes also have been used at Pratt and
Whitney Aircraft with some degree of success as indicated by comparison with
the chromatographic method.
Although this testing was on a batch basis, it
is felt that by constant aspiration a continuous sample could be obtained
and analysed.
Wilson (Ref 1-24) speaks of Parsons' use of an interference
filter photometer at 4,290 ~m to continuously measure C02 in the 1% -
18% range.
This technique has been applied in the analysis of the C02 in
the exhausts of motor vehicles.
C02 can also be monitored using a non-dispersive infrared analyzer.
This is an accurate, continuous device which utilizes the principle of
infrared analysis to monitor carbon dioxide down to 1-2 ppm (see previous
sect ion).
There are several other techniques available for the quantitative
measurement of carbon dioxide in the ambient atmosphere, but in general,
these methods are used for measuring minute quantities of carbon dioxide.
This does not preclude the use of a di lution device to enable these techni-
ques to be applied, but the techniques already described fulfi 11 the analysis
requirements.
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347
Orqanic Compounds
In this report, a distinction is made between hydrocarbons and
other organic compounds.
Saturated hydrocarbons are not very reactive and
many of the reactions described in the literature as involving "hydrocarbons",
actually occur with oxygenated organic compounds or with unsaturated or
aromatic hydrocarbons.
Total Organic Measurements
George and Burlin (Ref I-I) report collecting gas samples in eva-
cuated two-liter glass flasks.
The gases were analyzed with an infrared
spectrophotometer at the 3,450~m wavelength absorption band.
Lozano (Ref 1-23), whi Ie monitoring jet engines of various types
in a test cell, continuously monitored organics with a flame ionization
detector.
Jacobs (Ref 1-18) reports the use of a selective, nondispersive
type, infrared analyzer which can be used to determine the organic concen-
tration in the atmosphere.
The instrument is calibrated using hexane, and
the results obtained must be interpreted in this light.
This instrument has
been successfully adapted for use in the measurement of organics emitted
from jet engines.
Total organics have been monitored with Beckman Model I08A and
I09A flame ionization detectors, and Wi II iamson (Ref 1-2) reports the use of
a flame ionization detector for use in measuring total organics on an auto-
matic basis.
This device operates on the principle that a pure hydrogen
flame burning in air produces a negligible quantity of ions whi Ie oxidized
organics produce large quantities.
The number of ions produced bears a
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348
direct relationship to the number of carbon atoms present in the sample.
The
ion charged flame is placed in an electric field which permits ion collec-
t ion.
The resulting electric current is recorded.
Wi lliamson's major contri-
but ion was in automating the system to enable continuous analyses every 30
seconds by use of intricate manifolding, timing, valving and analyzing sys-
terns.
Specific Organic Measurements
A Perkin-Elmer Model 900 Gas Chromatograph with dual flame
ioniza-
tion detectors and a sub-ambient temperature accessory has been used to
analyze for individual organics (Ref 1-22).
The separation of the components
is accomplished with a 150 ft by .01 in ID column coated with Versalube.
The sample is concentrated directly on the column at -650C or lower.
Linear
temperature programming is used to elute all individual organics from C] to
CIO in less than 45 minutes.
The sensitivity is less than one part per
bi 11 ion (ppb).
An electronic digital integrator-printer is used to tabulate
the concentrations of the 150-200 peaks (compounds) which result from each
sample injection.
Some of these peaks are not immediately identified but
their organic class may be determined by subtractive techniques.
Th i s me-
thod is recommended for exhaust analysis by the Coordinating Research Counci 1.
McEwen (Ref 1-25) reports the use of a gas chromatograph for
analyzing organics in automobile exhausts which also appears to be applicable
to aircraft emissions.
This method was developed to analyze the complete
range of organics in both raw and highly di luted exhausts.
A commercial
chromatograph was modified to include a separate oven for thermostating a
gas sampling valve and a flow switching valve, a subtractor column for
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349
removing unsaturated hydrocarbons, and an absorption column in dual arrange-
ment with a capillary column.
Exhaust gases were analyzed successfully at
all operating modes.
This technique is similar to that reported by Scott
(Ref 1-22)
Korth (Ref 1-26) reports the use of a programmed chromatographic
technique for analyzing the exhaust emissions from a gas turbine automobile
with success.
Klosterman (Ref 1-27), in investigating the organics found in
automotive exhausts, approached the problem with a simple analytical method
by adapting existing organic analyzers so that the resulting system analyzes
classes of compounds in groups according to their reactivity in the atmo-
sphere.
In Klosterman's method, a sample of dilute automobile exhaust is
passed through a system of scrubbers to remove components selectively.
One
column removes olefins, and another removes olefins and aromatics except
benzene.
By subtraction from the total, the organics are reported accord-
ing to reactivity class.
The scrubber system is external to the analyzer
and no modification of the instrument is required.
A flame ionization
analyzer was used for measuring total organics.
An automatic cycling
timer was incorporated to regulate the several components of the analysis.
Polynuclear Hydrocarbons
Polynuclear hydrocarbons are a group of polycyclic hydrocarbons,
some of which have been shown to have carcinogenic properties.
Considerable
interest has been expressed in the determination of the amount of such
substances in the air.
There are three commonly used methods for deter-
mining concentrations of polynuclear hydrocarbons.
Most of the methods
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350
used involve sampling of air by absorption or condensation techniques.
One method, the Quinon test developed by Sawicki and Mi ller (Ref 1-28),
is a color test for the detection of polycyclic compounds.
A bri Iliant dark
blue color is obtained with pyrene and benzo(a)pyrene and the concentration
is determined by prior cal ibration.
A second method reported by Jacobs (Ref 1-18) is the benzal
chloride test.
Lipmann and Pollack noted many years ago that polynuclear
hydrocarbons give characteristic color reactions when concentrated sulfuric
acid and benzal chloride are added.
These colors are not very stable.
Sawicki
substituted trifluoracetic acid for the sulfuric acid and achieved greater
stabi lity by the use of chloroform as a solvent.
In many instances Sawicki
found that it was necessary to add sulfuric acid to obtain a positive test.
A third test is the piperonal chloride test, and Sawicki, Miller
and Hauser (Ref 1-29) describe a test for polynuclear hydrocarbons using
piperonal fluoride.
These tests are simi lar to that using benzal chloride.
At present, no investigators have reported the measurement of
polynuclear hydrocarbons from jet engines, but polynuclear hydrocarbons have
been found in measurable quantities in the exhaust gases of piston engines.
Aldehydes
Wi Ison's paper (Ref 1-24) contains a review of the determination
of aldehydes in air.
A fluorometric determination based on reaction with
acetyl acetone is claimed to detect O.OI~g.
A method claimed to be specific
and accurate to 5-l~!o in the~g range involves reaction with phenylhydrazine
and oxygen in an alkal ine medium to give a product read by a colorimeter.
Rayner and Jephcott describe a method in which Schiff's reagent is used with
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351
acetone to increase the color intensity and stabi lity.
They claim a
sensitivity of five parts per bi Ilion (ppb) in 1.5 liters of air and a
72 per cent collection efficiency for an impinger using .005N hydrochloric
acid sampling air at 1 CFM.
Another method for measuring aldehydes at the ppb level involves
the use of acid-bleached para-rosanaline and dichlorosulfitomercurate
complex, and has been used successfully in a mobile laboratory for over
four years (Ref 1-29).
A red color is developed by oxidation with
potassium hexacysuofferate in detector tubes using si lica gel impregnated
with phenylhydrazine hydrochloride.
The only method presently avai lable which successfully analyzes
aldehydes on a continuous, automatic basis is the Technicon Auto Analyzer
wet chemical technique.
A non-dispersive infrared technique is promising,
but is not yet avai lable.
Rounds and Pearsall (Ref 1-30) found that it is sometimes neces-
sary to distinguish between total aldehydes and formaldehyde in a sample.
They did this in an attempt to find correlations between the odor and
irritant properties of diesel engine exhaust gases.
An absorbing agent,
phenylhydrazine hydrochloride in solution, was used.
This method depends
on the formation of an intense magenta color when di lute solutions of
formaldehyde hydrazones are treated with potassium ferricyanide solution
in the presence of excess hydrochloric acid.
The depth of color is pro-
portional to the concentration of formaldehyde present.
This method has
been found to have the disadvantage that the color produced is not stable.
Jacobs (Ref 1-18) altered the preparation of the reagents and changed the
order of the addition of the reagents and obtained a stabi lized color.
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352
The concentration is determined by light absorption with a photoelectric
colorimeter.
The method used by Lozano (Ref 1-23) in his study of jet engine
exhausts in test cells is the 3-ethyl-2-benzothiazolone hydrazone hydrochlo-
ride (MBTH) method.
This method is applicable to the determination of
total water soluble aldehydes (measured as formaldehyde) in an atmosphere.
Formaldehyde, acrolein and total aliphatic aldehydes have been
analyzed by collecting samples from motor vehicles in bubblers for one hour
periods (Ref 1-22).
The chromotropic acid method is used for formaldehyde
analysis.
The 4-hexylresorcinl method is used for acrolein and the
3-methyl-2-benzothiazolone hydrazone hydrochloride (MBTH) method is used
for total aliphatic aldehydes.
The absorbtances of the resulting solu-
tions are measured with a spectrometer using I-inch diameter curettes to
insure sensitivity of less than 5 ppb for each analysis.
Peroxyacetyl Nitrate (PAN)
Peroxyacetyl nitrate may be determined by using an Aerograph
Hy-Fi III Model 1220-1 Gas Chromatograph with an electron capture detector.
A packed column is used for initial separation.
Scott anticipates the
development of a capillary column in the near future, which wi 11 permit
analysis for higher homologs such as peroxypropionyl and peroxybutyryl
nitrate.
It is also hoped that the atmospheric presence of peroxybenzoyJ
nitrate, which was recently isolated in chamber studies by General Motors
Research, can be determined.
This compound was reported to be 200 times
as powerful an eye irritant as formaldehyde.
The Hy-Fi 1220-1 is designed
for capi llary use and has linear temperature programming.
The fact that
-------
353
lower column temperatures are needed with capi Ilary columns than with
packed columns should overcome the current problem of decomposition of
peroxyacetcl nitrates at room temperatures which are required for separat-
ing and eluting the entire series with packed columns.
-------
354
1-1.
1-2.
1-3.
1-4.
1-5.
1-6.
1-7.
1-8.
1-9.
1-10.
I-II.
1-12.
REFERENCES
George. R. E. and Burlin. R. M.. Air Pollution from Commercial Jet
Aircraft in Los Anqeles County. Air Pollution Control District. County
of Los Angeles. Apri I. 1960.
Williamson. R. C. and Russell. J. A.. liOn Line Gas Analysis of Jet
Eng i ne Exhaus tll, SAE paper #670945 presented at the Comb i ned Fue I s
and Lubricants Powerplant and Transportation Mtgs.. Pittsburgh. Pa..
October 30-November 3. 1967.
Reagan. John A.. "App 1 y i ng LI DAR as an Atmospheric Probe". Lasar
Focus. June. 1968.
Barrett. E. W. and Ben-Dov. 0.. "Application of the LIDAR to Air
Pollution Measurements". J. Appl. Meteorol.. vol. 6.1967. pp. 500-
515.
Lieberman. A.. "Composition of Exhaust from a Regenerative Turbine
System". Ai r Pollut. Control Assn. J.. vol. 18. March. 1968. p. 3.
Bi Ilings. C. E.. et al. Open Hearth Stack Gas Cleanin~ Studies.
Semi-Annual Report (SA-16). Harvard Univ. School of Public Health.
Boston. Mass.. February. 1962.
Gordon. D. and Dennis. R.. "Use of a Single Stage Boundary Layer
Di luter in Conjunction with the Royco particle Counter". paper pre-
sented at the Joint Tech. Mtg. of the APCA-AIHA-HPS. Auburn. Mass..
May. 1965.
Gussman. R. A..
ment of Aerosol
ing Conference.
1961.
et al. "Factors in Condensation Nuclei for Measure-
Agllomeration". presented at the 7th USAEC Air Clean-
Brookhaven National Laboratory. New York. October.
Fuchs. N. A.. et al. liOn the Determination of Particle Size Distribu-
tion in Po1ydisperse Aerosols by the Diffusion Method". Brit. J. Appl.
Phys .. vo I. 13. 1962.
Twomey. S. and Severynse. G. T.. "Measurements of Size Distributions
of Natural Aerosols". J. Atm. Sciences. vol. 20. 1963.
Connor. W. D. and Hodkinson. J. R.. A Study of the Optical Properties
and Visual Effects of Smokestack Plumes, Co-operative Study Project,
Edison Elec. Inst. and U. S. Public Health Service. 1963.
Gruber. C. W. and Schumann. C. E.. "Soi ling Potential--A New Method
for Measuring Smoke Emissions". J. Air Pollut. Control. Assn.. vol.
16 . 1966. p. 5.
-------
1-13.
1-14.
1-15.
1-16.
1-17 .
1-18.
1-19.
1-20.
1-21.
1-22.
1-23.
1-24.
1-25.
1-26.
1-27.
1-28.
355
Shaffernocker, W. M. and Stanforth, C. M., "Smoke Measurement Techniques",
presented at the SAE Air Transportation Mtg., New York, N. Y., 1968.
Ringlemann, I., "Ringlemann's Smoke Chart", U. S. Bureau of Mines
Information Circular 8333, 1967.
Fiorello, S. C., The Navy1s Smoke Abatement Pro~ram (SAE Paper No.
680345), Society of Automotive Engineers, Air Transportation Meeting,
New York, Apri 1, 1968.
Faitani, J. J., Smoke Reduction in Jet En~ines Throuqh Burner Desiqn
(SAE Paper No. 680348), Society of Automotive Engineers, New York.
Jacobs, M. B. and Hochheiser, S., Anal. Chem.
1958, p. 426.
(AC No.3), vol. 30,
Jacobs, M. B., "The Chemical Analysis of Air Pollutants", Interscience
Publ., New York, London, 1960.
Saltzman, B. L, "Selected Methods for the Measurement of Air Pollu-
tants", Public Health Service Publ. No. 999-AP-ll, 1965.
Ganz, G. and Kuznetsou, I., "Automat i c Gas Ana 1 yzer for Ox i des of
Nitrogen''', Ind. Lab. (IL No.1), vol. 33, 1967, pp. 126-128.
Smith, D., et aI, "Oxides of Nitrogen from Gas Turbines", Air Pollut.
Con t ro 1 As s n. J., vo 1. 18, 1968, p. 1.
Scott Research Labs., Inc., Private Communication, Perkasie, Penn.,
July, 1968.
Lozano, L R., et aI, Ai r Pollut. Control J., vol. 18, 1968, p. 392.
Wi lson, H. N. and Duff, G. M. S., "Industrial Gas Analysis.
ture Review", The Analyst, vol. 92, December, 1967, p. 1101.
A Litera-
McEwen, D. J., "Automobile Exhaust Hydrocarbon Analysis by Gas
Chromatography'l, Anal. Chem., vol. 38, 1966, pp. 1047-1053.
Korth, M. W. and Rose, A. H., Jr., "Emission from a Gas Turbine Auto-
mobile",.SAE paper #680402, presented at the Midyear Mtg. of Soc. of
Automotive Engineers, Detroit, Michigan, May 20-24, 1968.
Klosterman, D. L. and Sigsby, J. E., Jr., "Application of Subtractive
Techniques to the Analysis of Automotive Exhaust", J. Environ. Sci.
& Tech. (JES&T No.4), vol. 1, Apri 1, 1967, p. 309.
Sawicki, E. and Miller, R. R., Detection of Puriene, Benzo(a)pyrene
and Other Polynuclear Hydrocarbons, Sanitary Engineering Center, U. S.
Public Health Service, Cincinnati, 1957a.
-------
356
1-29.
1-30.
Sawicki, E., et aI, Depiction of Polynuclear Hydrocarbons and
Phenols with Benzal and Piperonal Fluorides, Sanitary Engineering
Center, U. S. Public Health Service, Cincinnati, 1957b.
Rounds, F. G. and Pearsall, H. W., "Diesel Exhaust Odor",SAE
National Diesel Engine Mtg., Chicago, 1966.
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357
APPEND IX II
THE ORIGIN AND MEASUREMENT OF ODOR IN
AIRCRAFT ENGINE EXHAUST EMISSIONS
Odor Mechanisms
The literature on the measurement, control, and theory of odor.
no t e s
repeatedly that a compound must be volatile to be odorous.
This
assumption forms part of the basis of current ideas on olfaction, which
have recently been reviewed by Roderick (Ref I I-I).
It is also sometimes
inferred that the transfer of odorous material from a solid or liquid
source to a human sensor always occurs by vaporization of the source
material, and by subsequent diffusion or convection of the gaseous odorant
unti 1 it reaches the nasal cavity of the subject.
There is evidence,
however, that this picture is incomplete, and that particulate matter
can playa role in the transfer and/or perception of odors by humans.
Since the production of particulate matter is a significant occurrence in
aircraft engine exhaust, it wi II be helpful first to consider what these
possible effects might be.
Odors Possibly Due to Particles in
Aircraft Enqine Exhaust
No study has ever rigorously defined the upper limit of particle
size for airborne odorous matter.
Particles up to about O.S.or I nm in dia-
meter are considered to be molecules that can exist in equilibrium with a
solid or liquid phase from which they escape by vaporization.
The vapor
pressure decreases as the molecular weight increases, and particles above
about lnm do not generally exist in any significant concentration in
equi librium with a bulk phase; hence we do not consider them to be "vapors".
, '\
-------
358
Nonetheless, it is possible that odorant properties do not disappear when
particle sizes exceed those of vapor molecules.
Our knowledge about
particles in the size range of 1 ~5 nm (up to about the size of small
viruses) is relatively meager, and we do not know whether or not they can
be odorous, nor what the effect of an electrical charge on their odorous
properties might be.
Larger particles may also be intrinsically odorous,
although their more significant role may be to contribute to odor by
absorbing and desorbing odorous gases and vapors.
Odors Possibly Due to Desorption of
Gases from Particles
Goetz (Ref 11-2) has treated the kinetics of the interaction
between free gas molecules and the surface of airborne particles.
His
theoretical considerations were directed to the question of transfer of
toxicants by particles, but are also applicable to odors.
If we assume
that a given aerosol is intrinsically odorless, then it can act as an
odor intensifier if it has a sorptive capacity for the odorant large
enough to produce an accumulation on the particle surface, but smaller
than the affinity of the odorant for the nasal receptor.
In such case,
the aerosol particles wi 11 concentrate molecular odorous matter on their
surfaces, but the particles wi 11 not retain the odorous matter when they
reach the olfactory receptors.
Instead, the odorous matter wi 11 be trans-
ferred to the receptor sites in a higher concentration than would exist
in the absence of the aerosol.
The resulting effect will be synergistic.
If, on the other hand, the affinity of the molecules for the particles
exceeds that for the receptor surface, then the transfer of odorous matter
to be nasal receptors is impeded and an attenuation of the odor wi II occur.
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359
Odors Possibly due to Volatile Particles
Liquid or even solid aerosols may be sufficiently volatile so
that when they enter the nasal cavity, their vaporization produces enough
gaseous material to be detected by smell.
Such aerosols may be relatively
pure substances, like particl~s of camphor, or they may be mixtures which
release their more volati Ie components.
The odor intensity associated with
volatile aerosols wi 11, of course, depend on the prevailing temperature and
on the length of time they are dispersed in air.
In a cold atmosphere,
the temperature rise accompanying inhalation will accelerate the production
of gaseous odorant.
The idea that odors are associated with particles is supported
by observations that fi ltration of particles from odorous air stream can
reduce the odor level.
Rossano and Ott (Ref 11-3) showed that the removal
of particulate matter from diesel exhaust by thermal precipitation effected
a marked reduction in odor intensity.
Thermal precipitation was selected
for the good reason that this method provides minimal contact between the
collected particles and the gaseous components of the diesel exhaust stream.
In this way, the effects that could be produced by a filter bed, such as
removal of odorous vapors by absorption in the fi Iter cake, were eliminated.
Thermal precipitation does not remove gaseous or vaporous material, and
the observed odor reduction must therefore, have resulted directly from
the removal of particulate matter.
The particles collected by Rossano
and Ott were aggregates of spherical balls about 0.04-0.05 micrometers
(400-500~) in diameter.
It is possible that anyone or a combination of
the three possible aerosol odor effects described above could have been
responsible for the observed results.
Particulate matter from diesel exhaust
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360
collected on glass fiber filters by Linnell and Scott (Ref 11-4) yielded
a heavy "diesel" odor.
Analysis of the particulate matter showed that it
contained no acrolein or formaldehyde, although it did release N02 on being
heated to 1000C.
The authors conclude that "no appreciable gas phase concen-
tration changes for acrolein or formaldehyde wi II result from particulate
removal".
Other more or less casual observations on the role of particu-
late matter in community odor nuisance problems appear occasionally in
the literature.
The association of particulate matter with outdoor odors is also
implied by the fact that predictions of odor intensities based on gas phase
dispersion of an odor source are often in gross error (Ref 11-5).
These
discrepancies between calculated di lutions and odor measurements may there-
fore be caused by one or more of the possible particle effects noted above.
Odor Measurement
General
"Odor measurement" may imply the chemical analysis of odorous
substances, or the sensory evaluation of odor stimuli, or a combination of
both methods of appraisal, with some establishment of relationships between
the two sets of results (Ref 11-6).
In the case of exhaust from combustion
of hydrocarbon fuels, chemical analysis alone, even if it were to be qual ita-
tively and quantitatively complete, would be uninformative with regard to
odor, because identification of components does not establish their rele-
vance to the odor of the mixture.
The eventual determination of odor rele-
vances of the components of aircraft engine exhaust is a valid objective,
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. 361
however, because such information would make it possible to predict sensory
effects from chemical analysis.
Discriminatory sensory evaluations of odors are concerned with
odor intensity or odor quality; affective evaluations measure odor accepta-
b i 1 i t y (Ref I I -7) .
The development of odor acceptability ratings (so-called
"hedonic scaling") has been applied mainly to flavors of foods and beverages
(Refs 11-8 and 11-9), and only very little to odor problems associated with
air pollution (Ref 11-10).
The translation of a hedonic, or like-dislike
scale, to an action scale, that rates affective properties of odors in terms
of the anticipated behavioral response of people, has been applied only to
food acceptance (Ref 11-11).
The relevant action response for odors asso-
ciated with foods is eat-not eat, or buy-not buy.
For odors associated with
air pollution, the action responses may well be much more complex; in any
event, no such scaling has yet been reported.
Therefore the only sensory
evaluations that will be considered in this report are discriminatory
ones--odor intensity and odor quality.
Samplinq for Odor Measurement
General
When odors are perceived at some distance from the aircraft engine
exhaust such that the odor intensities are tolerable, at locations such as
terminal buildings, aircraft passenger gat~ areas, and the community areas
adjacent to airfields, sensory odor judgments are best made by direct expo-
sure of the judges to the odorous atmosphere without prior sampling.
Such
atmospheres usually vary in odor intensity from time to time, depending on
variations in number and proximity of aircraft, and in wind velocity,
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362
direction, and turbulence.
Therefore, an adequate sampling program would
be very costly.
Furthermore, outdoor ambient odor samples are difficult
to preserve in containers, because even a small amount of absorption on
the walls detracts seriously from the samples.
The fact that odor levels
under such conditions vary in intensity from time to time, however, consti-
tutes an advantage for direct sniffing by the observers, because the vari-
at ions usually provide adequate opportunity for recovery from olfactory
fatigue between judgments.
Each judge is, in effect, making a measurement
with each sniff, without being fatigued during the times that he is not
detecting odor.
An observer may also move about from place to place in an
area of suspected odor, either by foot or automobile, and spend most of
his time making judgments at locations where the odor levels are highest.
There are some instances, however, in which it is advantageous
or necessary to collect a sample of odorant before presenting it for
sensory measurements.
The most significant instance of this type will be
the direct sampling of engine exhaust for sensory odor evaluation, where
cooling and dilution will necessarily precede exposure of judges.
Other
instances may involve the necessity of moving an odor sample to a special
location for testing, away from aircraft engine exhaust backgrounds.
When
chemical analysis of odorants is to be carried out, sampling with concen-
tration may be necessary.
Grab Sampling
A grab sample places a volume of odorant at barometric pressure
into a container from which it can subsequently be presented to judges for
evaluation.
Grab sampling of odorants is subject to some severe limitations:
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363
(a)
If the odorant is close enough to the engine so that it is hot,
condensation may occur on cooling.
The condensate will probably contain
odorous material at the expense of the concentration in the gas phase.
(b)
During the time between collection and evaluation, odorous material
may be sorbed on the walls of the container or on particulate matter in
the air sample.
(c)
Chemical interactions among the exhaust components'
may alter the odorant.
Containers for grab sampling should therefore be inert to the
odorant material, and should have a large volume-to-surface ratio.
If the
odorant being sampled is not at ambient temperature, the investigator must
assure himself that condensation wi II not occur on cooling.
Grab sampling is carried out by allowing the air to fill an
evacuated or collapsed container, or to displace a fluid from a container.
Suitable materials of construction may include stainless steel, glass, or
plastics such as Mylar, Teflon, and Saran (Refs 11-12 and 11-13).
Any
container, however, together with its auxi liary tubing and equipment like
air moving devices, must be tested for suitability for the specific engine
exhaust odorant in question, especially with regard to extraneous back-
ground odor of the airport area, and to depletion of sample by adsorption
or absosption effects.
When the grab sample is to be evaluated, it must be expelled
from the container into the space near the judge1s nose.
This expulsion
may be effected by displacement of the sample with another fluid, or by
collapsing the container.
The following example is given as an illustra-
tion of grab sampling.
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3~
Example 1.
A sampling probe of 111 diameter Teflon tubing
is mounted so that its inlet end is close to the upstream side of a central
activated carbon purification unit in an aircraft passenger terminal build-
ing.
A blower of suitable capacity draws air through the probe and discharges
it into a collapsed Mylar bag of about 2 ft.3 capacity.
The sampling pro-
cedure is repeated on the downstream side of the carbon unit at different
times during the life of the carbon bed.
The samples are then removed to
a suitable test room where a panel of judges can appraise them by sensory
measurements such as those elaborated in subsequent sections.
Sampling with Di lution
Di lution procedures for sampling aircraft engine exhaust can
reduce concentrations and temperatures to levels suitable for human expo-
sure without permitting condensation of the odorant material.
The di lution
ratio must be specified and can be determined on the basis of either pressure
or volume.
The material of choice for dilution of a sample of aircraft
engine exhaust is stainless steel.
A suitable device is a 1000 cu. in.
stainless steel tank fitted with a flow control inlet valve, a constant
differential type flow controller and two additional valves, one between
the flow controller and the tank, and the other at the opposite end of the
tank (Ref 11-14).
Before use in sampling, the tank is evacuated, and the
inlet valve is adjusted to the desired flow rate, as indicated on a flow-
meter.
Once the adjustment is made, the handle is removed from the inlet
valve and its stem is sealed with wax so as to insure against accidental
tampering; the tank is then reevacuated and the two seal valves are closed.
For sampling, it is necessary to open only the seal valve between the flow
controller and the tank and to record the time during which the odorant is
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365
being sampled.
The total volume of sample wi 11 be equal to the time of
sampling multiplied by the flow rate through the inlet valve.
The flow
controller assures that this rate wi 11 be constant over the sampling
period if the tank is not filled beyond about 75% of its capacity.
As
an alternate method, the flow control system is omitted and the end oppo-
site the sampling probe is fitted with a vacuum gage; the partial pressure
of the odorant is then the difference between the vacuum readings before
and after sampling.
The method is further illustrated by the following
example.
Example 2.
For direct sampling of jet exhaust odorant, a stain-
less steel tank fitted with a length of stainless steel tube probe is
evacuated to a pressure of 50 torr.
The steel probe is inserted in the
exhaust and a sample is drawn into the tank until the pressure reaches 60
torr.
At this point the temperature of the gas mixture in the tank is
28°C.
The tank is now pressurized with odor-free air to 3.00 atmosphere
(2.28 x 103 torr).
The dilution ratio then is
The final temperature is 22oC.
2.28 x 103 torr
(273
(60-50) torr (273
+ 22)" = 233
+ 28)
The diluted sample in the tank is then removed to a test room
where judges can draw samples for sniffing simply by opening the valve.
A sequence of samples taken from the engine exhaust under different condi-
tions can be used for comparative tests.
Sampling with Concentration
If it becomes necessary to correlate sensory odor measurements
with chemical analysis at places where people are directly exposed to aircraft
-------
366
engine exhaust odors, a grab sample may be too dilute for adequate chemical
characterization.
For example, a grab sample taken near a passenger gate
area would probably show only a generalized hydrocarbon response when examined
by infrared spectrometry.
This information would be inadequate even for
purposes of comparing infrared profiles under different conditions.
Other
analytical responses are likely to be even less informative.
Analytical
characterization of odorants can be highly improved by concentrating them
during sampling.
Freeze-out, adsorptive, and absorptive sampling have all
been used.
In freeze-out sampling (Refs 11-15 and 11-16), the odorant
air
stream is passed through a cold trap that freezes and holds the odorous
substances but does not retain the major non-odorous components.
Unfortu-
nately, the trap retains water.
The coldest permissible refrigerant is
usually liquid air.
Liquid nitrogen may condense oxygen in the trap, thus
creating a hazard of pressurization when the trap is sealed and the refrig-
erant is removed.
The trap should accommodate the relatively large quantity
of ice that is collected, and a filter for the aerosol matter that is usu-
ally formed.
The designs of Shepherd (Ref 11-16) and Turk (Ref 11-17) both
provide these features.
Freeze-out sampling for odorants is advantageous
because interactions among the concentrated components are minimized at
low temperatures.
A serious disadvantage is the icing of practically all
the water in the air being sampled.
Of course, a desiccant can be placed
before the cold trap, but the desiccant may adsorb or absorb odorous matter
and invalidate the sampling (Ref 11-18).
In adsorptive sampl ing (Refs 11-19, 11-20 and 11-21), the odorant
air stream is passed through a bed of activated carbon, si lica gel, or
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367
(much less frequently) some other adsorbent to concentrate the odorous
mater i a 1.
Activated carbon is advantageous because it adsorbs organic
matter in preference to water, and excessive aqueous dilution of the
collected odorant therefore does not occur (Ref 11-22).
Activated carbon
is so retentive to most odorous matter, however, that recovery may be diffi-
cult.
Desorption of the odorant from the carbon iD vacuo into a cold trap
is effective, but may involve isomerization or other chemical changes
(Refs 11-17 and 11-23).
Solvent extraction of the odorant is a less drastic
method but may yield much less recovery (Ref 11-24).
When the degree of
concentration needed is small enough, and the ambient air is dry enough so
that water collection is not a serious problem, silica gel may be used in
place of carbon, with the advantage that milder conditions for odorant
recovery can be used (Refs 11-25, 11-26 and 11-27).
Absorptive sampling is sometimes advantageous when one desires
to concentrate and hold an odor sample easily and with minimum manipula-
tion of equipment.
If the concentration factor need not be known precisely,
it may be convenient to use an odorless solvent, like mineral oil, carried
on a relatively inert material like absorbent cotton.
A wad of such
absorbent material may be suspended in an odorous space and subsequently
removed for odor evaluation.
Odorants may be collected by equilibration in a stationary liquid
phase, from which they can be subsequently released (for example, into a
gas chromatograph) by heating (Ref J 1-28).
The most recently described
system of this type uses a fluidized bed of Teflon powder coated with
Apiezon L stationary phase (Ref 11-29).
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368
Odor Intensity
The intensity of an odor is the magnitude of the stimulus
produced when a person is exposed to an odorant.
In measurements of
odors involved in air pollution, the usual practice is to use threshold
measurements as an index of odor intensity, with the assumption that more
intense odors have lower threshold values~
In fact, the one reported jet
engine emission odor study (Ref 80) utilized odor dilution threshold
measurements.
Other very recent reports are also concerned with threshold
methods (Refs 11-30 and 11-31).
It is therefore important to consider
what information on odor intensity can be obtained from threshold measure-
ments.
The odor threshold is the minimum concentration at which an
odorous substance can be distinguished from odor-free air ("detection
threshold") or at which its quality can be recognized ("recognition
threshold", or "minimum identifiable odor", MIO).
The latter is the high-
er value.
Odor threshold levels depend on the nature of the substance and
on the sensitivity of the judge.
The "50% threshold" is the concentration
at which the odor can be detected (or recognized) by 50% of the population.
Threshold data, strictly speaking, can be used to predict the
conditions under which a given substance will be odorous or odorless.
Such
predictions provide a basis for calculating (a) the degree of dilution,
by ventilation or outdoor dispersal, that is needed to deodorize a given
odor source, (b) the proportion of odorant that must be removed from a
space, by methods such as activated carbon adsorption, to effect deodori-
zation, (c) the amount of a substance that must be injected into a space
to odorize it, or (d) the volume of air that can be odorized by a given
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369
amount of substance.
Threshold concentrations are not, however, direct
measures of odor intensity at supra-threshold levels.
The threshold values reported in the literature scatter over
-4
wide ranges, for example 3.2 x 10 p.p.m. to 10 p.p.m. for pyridine.
Such
variances have been assumed to result from impurities, differences in mode
of presentation of odorants, differences in subjects (Ref 11-31), calibra-
tion errors (Ref 11-32), and the like.
More serious is the supposition
that the "threshold value" is not a specific property of an odorant sub-
stance at all, to be approached more and more closely as our techniques of
sensory evaluation grow more precise (Ref 134).
Instead, it is a property
that depends heavily on the motivations and expectations of the observers,
and that can be manipulated by rewards and punishments.
These findings lead
to the conclusion that threshold values will always be a shaky index on
which to base supra-threshold measurements of odor intensity.
The threshold level, C , is often measured by quantitative dilu-
t
tion of a given volume, V, of odorant of known concentration, C.
Then C ~ W/V,
and Ct = W/Vt' where W is the quantity of odorant and Vt is the volume of
sample after it is diluted to threshold level.
Dividing and solving for C ,
t
Ct = CV/Vt
The same procedure can be applied to characterize an odorant or odor source
of unknown concentration.
The then threshold dilution ratio, Vt/V = C/Ct'
This ratio, also called the threshold odor number, or the odor pervasiveness
(Ref 11-33), can be used as a basis for the same calculations as those pre-
viously cited for the odor threshold concentration.
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370
A related unit, called the "odor unit", is defined as one cubic
foot of air at the odor threshold (Ref 11-34).
A cubic foot of odorant that
must be di luted to n cubic feet to reach the odor threshold level is said
to contain ~ odor units.
The odor concentration of an odorant is then ex-
pressed in terms of "odor un its per cub i c foot'l.
This nomenclature is un-
fortunate in that the meaning of "concentration" is foreign to chemical
usage, but it wi 11 be recognized that it is identical with the threshold
di lution ratio, with volumes being expressed in cubic feet.
Di lution methods have been described by several workers (Refs 11-30,
11-35, 11-36, 11-37 and ~~-38) and the general principles were explained
earlier.
In the light of the gross variances in odor threshold data, it
must be assumed that nominal dilution factors, calculated from ratios of
volumes or flow rates in a dilution system, are unreliable.
An absolute
method for establishing the reliability of a di lution method involves recon-
centrating the odorant and verifying the reestablishment of the original
concentration.
The maximum error in such a procedure can be calculated on
the following basis:
Assume that an initial concentration of odorant, C.,
I
is sufficiently high so that it can be determined accurately by a reliable
method of analysis.
The odorant is then di luted by a factor, Fd' that is
nominally determined by volume or flow ratios in the system, to a lower
concentration Cd' . Now, using some method such as freeze-out trapping, the
diluted odorant is reconcentrated by a factor, F , to recover a high con-
r
centration, C , which, like C., can be determined accurately.
r I
Now, the
value for the concentration of the di luted odorant that is calculated with-
out a confirming analysis from the applied dilution factor is
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371
C = C F
d(calc.) i d
The reconcentrated value is
Cr = CdFr' and Cd = Cr/Fr
Now, the error in measuring Cd is
Error (fractional) =
C -C
d(calc.) d
C
d(calc.)
=
C/d - C/Fr
CiFd
= 1 -
C
r
C. FdF
I r
If Fd = l/Fr' that is, if the original concentration is nominally restored
after dilution, the Error = 1 -
C
r .
C.
I
Note that in this calculation it is assumed that recovery of the diluted
odorant is complete and that all the error lies in the dilution procedure.
If some loss occurring during reconcentration is thus erroneously ascribed
to the di lution, then the calculated di lution error is too high.
There is
no way to resolve this question except to state that the calculated error
is a maximum value, and that the real error therefore cannot be any greater
than that obtained by this procedure.
Turk, Edmonds, and Mark (Ref 11-32)
have shown that a tracer gas like SF6 can be used to explore inherent errors
in a gas di lution system.
In any dilution method, important consideration must be given to
the d i 1 uent.
When di lutions are carried out in the field, the di lution air
is ambient air purified by passage through activated carbon.
The "Scento-
meter" (Barnebey-Cheney Co., Columbus, Ohio) is a simple, portable device
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372
of this kind that uses a carbon bed to supply di lution air.
However, it
cannot be assumed, without further check, that di lution air prepared in
different ways wil I have equal effects on determined threshold values.
Odor intensity can be measured on a scale (called a psychophysical
scale) whose reference points are fixed in some physical way.
The most con-
ventional physical standards are odorant substances of known and repro-
ducible composition and concentration.
Because odor, like other sensations,
is a logarithmic or power function of the stimulus (Ref 11-39), it is
appropriate for the concentrations of the reference odor standards to be
distributed along some exponential scale; a convenient scale is based on
exponents of 2.
The procedure is illustrated by the following example.
Example 3.
The intensity of a series of odors caused by raw jet
fuel is to be measured.
The reference standards are the vapor phases in
equi librium with an exponential concentration series of octyl benzene solu-
tion in odorless mineral oi I at 250C.
The solutions are:
D i I uti on # Concentration of octyle benzene
in mineral oi 1
Strong E ( I 00%)
1/2 (50%)
1/4 (25%)
4 1/8 ( 12. 5%)
Moderate 5 1/16 (6.25%)
6 1/32 (3. I 3%)
7 1/64 ( I. 56%)
S light 8 1/128 (0. 78'>10)
9 1/256 (0.39%)
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373
About 25-30 ml. (1 fl oz) of each solution may be placed in a 4 oz plastic
squeeze bottle.
A judge sniffs the odor standard when he squeezes the bottle
to expel about half (50 ml) of the vapor phase in equi librium with any given
solution.
Instructions are given to the judges as follows:
liThe samples
1 ined up in front of you all contain solutions of a fuel odor in mineral oi 1.
They differ from each other in odor strength, the most intense odor is on
the left, and the intensity gradually gets less from sample to sample to-
wards the right.
You are to judge the jet fuel odor intensity of the unknown
sample by picking the standard solution that matches its intensity most
closely."
The example above uses n-octylbenzene because it is found that
this is a stable substance which provides a good reference for this odor
measurement (Ref 11-40).
It is available commercially, but must be analyzed
(gas chromatography) and, if necessary, redistilled to remove impurities.
It has been suggested (Ref 11-41) that n-butanol may be used as
an odor reference standard for all airborne odors, even though they differ
markedly from it in quality, but we do not know to what extent such diver-
gence is disadvantageous.
Judges may make subjective estimates of magnitude between points
that are represented by reference standards.
It is also possible for a
judge to estimate intensity ratios that are based on only one reference
point.
Thus, a judge may estimate that a given phenolic odor is five times
as strong as that of a standard phenol odorant.
Measurements set up in this
way are called ratio scales.
Some odor intensity scales are not anchored in specific reference
standards at all, but instead are defined by descriptions like liS light",
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374
"moderate", I'strong", and "extreme".
Such,adjectives are actually implied
reference standards, because an odor judge, even without instructions, wi II
refer to his experience.
Thus, for example, a fragrant odor of "moderate"
intensity may be taken to mean the typical odor level in a level in a
florist shop.
Such scaling can be grossly imprecise.
Odor Qua Ii ty
The quality of an odor is its character described in terms of
resemblance to some other odor.
Descriptions of quality include words like
"burnt", "oi Iy", "musky", and "phenolic".
If a general description of odor
qualities could be set up, it would be possible to describe any odor in
terms of a number of primary odor standards (Refs 11-42, 11-43, 11-44 and
11-45) .
Taking the Crocker-Henderson system as an example of this sort,
odors are classified according to four primary qualities:
fragrant, acidic,
burnt, and caprylic (goaty or rancid).
Each quality is also rated on an
odor intensity scale from 0 (none) to 8 (strongest).
Thus, acetic acid is
described by the number 3803, which implies that the odor is moderately
fragrant, highly acidic, not burAt, and mildly caprylic.
Systems of this
type, though they date from 1895 or earlier and are described in standard
psychological texts have not become useful methods of odor measurement in
air pollution problems.
The reason is that no conceptual system has yet
been devised which accurately predicts odor quality from the chemical compo-
sition of the odorant, especially from such complex mixtures as outdoor
pollutants, or vice versa, or explains the detai led mechanism of odor per-
ception.
As a result, the odor quality classifications are largely empirical
and are usually compromises between high specificity, which requires many
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375
reference qualities, and convenience, which implies that the reference
qualities should be few and universally recognized.
An empirical approach that does not entai I any assumptions con-
cerning primary odor types can be realized by using specific odor quality
descriptors that are represented by odor quality reference standards.
In
this method, the group of odors to be judged is defined in terms of a few
(usually 3 to 8) qualities that seem reasonable in the light of subjective
associations and chemical analysis.
The selections are made by people who
are fami liar both with the odors in question and with the analytical findings,
even though the latter may be incomplete.
Then an odor quality reference
standard is made up to represent each quality description.
The chemicals
used in a reference standard represent the best choice avai lable on the
basis of odor, stability, lack of toxicity, and correspondence with consti-
tuents that are known or suspected to exist in the odorant.
Each reference
standard may then be expanded into a dilution scale using a suitable odorless
di luent (as mentioned above).
For convenience, and in order not to overload
the judges' capacity for yielding informative responses, the number of
points on the di lution scale should correspond to the following relation-
ship:
No. of quality stds. x No. of intensity stds. per quality; 10 to 32.
Then an odor to be appraised may be described in terms of intensities of
the various qualities by proper matching with the reference standards, as
in the Crocker-Henderson system.
Such a description is called a quality-
intensity profile.
This procedure is illustrated by the following example:
Example 4.
Diesel exhaust is to be appraised in terms of its
quality-intensity profile (Ref 11-40).
It is found that the odor can be
characterized in terms of four descriptors:
burnt/smoky, oi ly, pungent/acid,
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376
and aldehydic/aromatic.
The odor quality reference standards are made up of
the following components:
(burnt), oil of cade (Juniper tar), guaiacol,
carvacrol, and acetylenedi-carboxylic acid; (Qily), n-octylbenzene; ,
(punqent/acid), crotonic acid and propiolic acid; (aromatic/aldehyde), a
mixture of aromatic hydrocarbons and aromatic and aliphatic aldehydes.
Each
reference standard is diluted in mineral oil, with benzyl benzoate added if
necessary for solubilization, to four different concentrations representing
different levels of intensity.
The resulting kit of sixteen reference
standards is used as a basis for quality-intensity profi ling of diesel ex-
haust odors.
There have been several other recent approaches to the problem of
characterizing odor quality.
One is that of Woskow (Ref 11-46) who has
shown that estimates of similarities among various odors can be used to
locate the odors in a psychological "space", such that the closeness between
any two odors in the "spacell is a good relative measure of the degree of
simi larity expressed by observers.
Furthermore, he finds that a good repre-
sentation can be obtained with as few as three dimensions, one of which is
pleasantness, and the other two are rather difficult to define.
The method
is structurally capable of describing any odor by specifying its position
in the space, but it has not yet been shown whether this objective can be
rea I i zed.
Another method is that of Harper (Ref 11-47), who has classified
odor qualities by the responses of experienced and inexperienced subjects
who refer to a list of,44 suggested quality descriptions.
The result is a
glossary in which each odorant is characterized in terms of the various
descriptions elicited in these responses.
The method has been reported only
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377
for pure odorants, not for mixtures, and is unlikely to be usable, in its
present form, for informative quality descriptions of aircraft engine
exhaust odors.
Selection and Traininq of Odor Judqes
Although many procedures for the statistical analysis of sensory
measurements have appeared in the literature (Ref 11-8), the simplest and
most satisfactory for selection of odor judges for discrimination panels
are those of Wittes and Turk which have been used in various diesel studies
and which are recommended for studies of aircraft engine exhaust odors.
If only odor intensities are to be measured in a given study, the test for
quality may be omitted.
It is particularly important, in odor studies in-
volving aircraft, to rule out potential panel members whose responses may
be impaired by the extra distractions that may be encountered in airfield
areas.
Screening tests should be conducted at low levels of statistical
confidence (~25%), with one of two objectives:
(a) If a large panel is to
be used (over 15), the procedure should rapidly accept most of the able
candidates while rejecting the very obviously unsuitable ones.
(b)
If a
small panel is to be used, the screening procedure should rapidly eliminate
most of the unsuitable candidates, even though some potentially able ones
wi II thus be lost.
The first step in the training procedure should be the repetition
of the screening tests, with group discussion and evaluation of results,
until a high performance plateau is reached (1-2 days).
The subsequent
steps should be patterned very closely after the actual experimental designs
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378
to be followed in the tests.
If reference standards are to be used, the
panel members should learn them.
If these are to be conducted in airport
areas, the panel members should be exposed to field conditions.
During this
period, additional screening should take place, with el imination of unsuit-
able judges.
Correlations between Instrumental Analysis and
Sensory Properties of Odors
Odorants, like other substances, are amenable to chemical analysis.
Hydrocarbon fuels are complex substances because they contain many components.
Combustion products of hydrocarbon fuels are much more complex because of
the additional components introduced by cracking and by partial oxidation
processes.
Since the specific chemical and physical determinants of odor
are not yet known, a chemical analysis of itself, no matter how complete,
is not a measurement of odor.
To co~relate the chemical with the sensory
properties of an odorant, it is necessary to assign odor intensity and
quality attributes to the various components that the analyst has identi-
fied, and possibly to consider interaction effects.
Very few complex
odorous substances have been carefully investigated in this way.
Those
for which satisfactory instrumental-sensory relations have been worked out
have been food odors and essences, such as those of apple, cucumber, and
banana (Ref 11-6).
There have been attempts to accomplish simi lar results
with diesel exhaust odors (Refs 11-48 and 11-49), and work in this area
is still in progress in several laboratories, but results have not approached
the point where analytical information can predict sensory properties.
It
is not likely that work with aircraft engine exhausts would be any easier.
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379
Dravnieks and Krotoszynski (Ref 11-29) have recently reported on
procedures for establishing "odor relevance" of specific components of an
odorous air sample, which involves sensory evaluation of components that
correspond to individual peaks from a gas chromatographic trace.
Procedures
of this kind have been used before, especially in the various food odor
studies cited above.
However, the possibi lity that some odor-relevant
components of hydrocarbon combustion are labi Ie in air (for example, carbon
suboxide), and could be destroyed during examination, adds to the difficulty
of the problem.
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380
II-I.
11-2.
11-3.
11-4.
11-5
11-6.
11-7.
11-8.
11-9.
REFERENC ES
Roderick, W. R., J. Chem. Educ. (JCE No. 10), vol. 43, October, 1966,
p. 510. .
Goetz, A.,
Inti I. J. Air & Water Pollution, \toli 4,1961, p. 168.
Rossano, A. T.,
and Particulate
Meeting Pacific
Control Assoc.,
Jr. and Ott, R. R., liThe Relationship between Odor
Matter in Diesel Exhaust," presented at the Annual
Northwest Internatl I. Section of the Air Pollution
Portland, Ore., November 5-6, 1964.
Linnell, R. H. and Scott, W. E., IIDiesel Exhaust Composition and
Odor Studies", Air Pollut. Control Assoc. J. (APCA No. 11), vol. 12,
November, 1962, p. 10.
Wohlers, H. C., "Odor Intensity and Odor Travel from Industrial
Sources", Inti I. J. Air Water Pollut., vol. 7,1963, p. 71.
American Society for Testing and Materials, Correlation of Subiective-
Objective Methods in the Study of Odors and Taste, STP-440, June, 1968a.
Schu tz, H. G., "Recent Advances in Odor", Anna 1 s N.. Y. Acad. Sc i ence
(AN.Y.AS, Art. 2), vol 116, 1964, p. 517.
A. D. Little, Inc., Flavor Research and Food Acceptance, Reinhold
Pub 1. Corp., New York, 1958.
American Society for Testing and Materials, Manual on Sensory Testinq
Methods, STP-434, June, 1968b.
11-10. Medalia, N. Z. and Finker, A. L., "Community Perception of Air Quality:
An Opinion Survey in Clarkston, Washington", Public Health Service
Publ. No. 999, AP-10, 1965.
11-11. Schutz, H. G., J. Food Sci., vol. 30, 1965, p. 365.
11-12. Clemons, C. A. and Altshuller, A. P., J. Air Pollut. Control Assn.,
vol. 14, 1964, p. 407.
11-13. Connor, W. D. and Nader, J. S., Am. Ind. Hyqiene Assn. J., vol. 25,
1964, p.' 29 I.
11-14. Collins, G. F., et ai, Air Pollut. Control Assn. J., vol. 15, 1965,
p. 109.
11-15. American Society for Testing and Materials, Recommended Practice for
Sampl inq Atmospheres for Analysis of Gases and Vapors, D-1605-60,
1960.
-------
11-16.
11-17.
11-18.
11-19.
11-20.
11-21.
11-22.
11-23.
11-24.
11-25.
11-26.
11-27.
11-28.
11-29.
~/
11-30.
/'
/,/
/ 11-31.
,/
,/
.,,-/
/
I
11-32.
11-33.
381
Shepherd, M., et aI, J. Anal. Chem., vol. 23, 1951, p. 143l.
Turk, A., et aI, Anal. Chem., vol. 34,1962, p. 561.
McKee, H. C., et aI, Paper presented at 136th Nat' I. Mtg., Am.
Chem. Soc., Atlantic City, New Jersey,' September, 1959.
Chiantella, A. J., et ai, Am. Ind. Hygiene Assn. J., vol. 27,1966,
p. 186.
Turk, A., et ai, "Determination of Gaseous Air Pollution by Carbon
Adsorption", Am. Ind. Hygiene Assn. Quart., vol. 13, 1952, p. 23.
Turk, A. and Mehlman, S., "Correlations Between Instrumental and
Sensory Characterizations of Atmospheric Odors. Correlation of
Subjective-Objective Methods in the Study of Odors and Taste", Amer.
Society for Testing and Materials (ASTM, STP-440), 1968a, p. 27.
Turk, A. and Van Doren, A., Agr. Food Chem., vol. I, 1953, p. 145.
Turk, A., et aI, Ai r Pollut. Control J., vol. 16, 1966, p. 383.
Brooman, D. L. and Edgerly, E., J. Air Pollut. Control Assn., vol.
16, 1966, p. 25.
Adams, D. F., et ai, IAffl, vol. 43, 1960, p. 602.
Altshuller, A. P., et ai, Am. Ind. Hygiene Assoc. J., vol. 23,1962,
p. 164.
Campbell, E. E. and Ide, H. M., Am. Ind. Hygiene Assn. J., vol. 27,
1966, p. 323.
Dravnieks, A. and Krotoszynski, B. K., J. Gas Chromatography, vol.
4, 1966, p. 367.
Dravnieks, A. and Krotoszynski, B. K., J. Gas Chromatography, vol.
6, 1968, p. 144.
Hemeon, W. C. L., J. Air Pollut. Control Assn., vol. 18, 1968, p. 166.
Leonardos, G., et ai, Paper 68-13, Air Pollut. Control Assn. 61 Mtg.,
June, 1968.
Turk, A., et ai, Environmental Sci. Tech., 1968b, p. 44.
Turk, A., "Odor Measurement and Control", Chapter 13 in Air Pollution
Abatement Manual, Manufacturing Chemists' Assn., Washington, D. C.,
1960.
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382
11-34.
11-35.
11-36.
11-37 .
11-38.
11-39.
11-40.
11-41.
11-42.
11-43.
11-44.
11-45.
11-46.
11-47.
11-48.
11-49.
American Society for Testing and Materials, Method of Measurement
of Odor in Atmosphere (Di lution Method), D-139l-57, 1962.
American Society for Testing and Materials, Standards on Methods of
Atmospheric Sampling and Analysis, 2nd ed., 1962, pp. 40-43.
Gordon, D. and Dennis, R., "Use of a Single Stage Boundary Layer
Di luter in Conjunction with the Royco Particle Counter", paper pre-
sented at the Joint Tech. Mtg. of the APCA-AIHA-HPS, Auburn, Mass.,
May, 1965.
Mateson, J. F., "Olfactometry: Its Techniques and Apparatus", Air
Pollut. Control Assn. J., vol. 5,1955, p. 167.
Nader, John S., "An Odor Evaluation Apparatus for Field and Labora-
tory Use", Am. Ind. Hyqiene Assn. J., vol. 19, 1958, p. 1.
Stevens, S. S., Psychol. Rev., vol. 64, 1957, p. 153.
Turk, A., Sele c tion and Traininq of Judqes for Sensory Evaluation
of the Intensity and Character of Diesel Exhaust Odors (PHS Publ.
No. 999-AP-32), 1967.
Krotoszynski, B. K. and Dravnieks, A., Paper 68-17 in Air Pollut.
Control Assn. 6lst mtg., June, 1968.
Amoore, J. E., Ann. N. Y. Acad. Sci. (Art. 2), vol. 116, 1964, p. 457.
Crocker, E. C. and Henderson, L. F., IIAnalysis and Classification of
Odors", Amer. Perfumer, vol. 22, 1927, pp. 325-356.
Foster, D., "A New Method of Predicting the Qualities of Flavor
Mixtures", Instit. of Food Technoloqists, January, 1952.
Henning, H., Der Geruch, Leipzig, 2nd ed., 1924.
Woskow, M. H., "Multidimensional Scal ing of Odors'l, In Theories of
Odors and Odor Measurement, Robert College Research Center, Istanbul,
Turkey, 1968, p. 147.
Harper, R., et aI, A Glossary of Odor Stimuli and Their Qual ities,
Perfumery & Essential Oil Record, London, 1968.
Holtz, J. C., et aI, U. S. Bureau of Mines, R. I. 3508, May, 1940.
Reckner, L., Diesel Exhaust Composition, Odor and Eye Irritation,
Scott Res.' Lab.,' U'. 5."Publ ic 'Health Service,' Contract PH' 86-63':'60,
Apri 1 22, 1966.
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383
APPENDIX I I I
ANALYSIS OF COMPLAINTS CONCERNING
POLLUTANT EMISSION BY AIRCRAFT
The investigation upon which this analysis is based was conducted
by making contact with those agencies that are apt to receive complaints
about air pollution or about aircraft.
In the three metropolitan areas
studied--Los Angeles, New York, and Washington, D.C.--these are the local
air pollution control agencies and the airports.
Other agencies such as
local units of government tend to refer complaints to these agencies.
The Handlinq of Aircraft Air Pollution Complaints
The Los Angeles Air Pollution Control District receives (and
files) complaints about "smog'l from aircraft; however, it makes no direct
use of these complaints in its abatement efforts.
Rather than attempting
to respond to complaints directly, the District maintains a program of air-
craft engine research designed to reduce effluents.
For example, tests are
now being conducted to assess the effectiveness of fuel additives in reduc-
ing exhaust pollutants.
Currently, the Los Angeles Air Pollution Board
(County Board of Supervisors) has ordered a tightening of standards for
aircraft emissions and of the enforcement of present standards (Ref I I 1-1).
Los Angeles International Airport (LAX) receives complaints about
aircraft, both in its Public Relations and Sound Abatement Departments.
When the Sound Abatement Department receives a complaint about air pollution
from aircraft, the complainant is referred to a study made by the Los Angeles
Air Pollution Control District (Ref 3) showing that aircraft are minor con-
tributors to the total amount of pollution.
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384
In the Washington, D. C. area, responsibil ity for air pollution
abatement is scattered among a number of city and county units in
Maryland and Virginia, and the Air Pollution Control Division of the
District of Columbia Department of Publ ic Health.
These agencies have
recently adopted a uniform method for handl ing and recording air pollution
complaints through their joint efforts in the Metropol itan Washington
Council of Governments; 1968 will be the first full year using the new
system.
Complaints about aircraft around Washington, D. C., center at the
Federal Aviation Administration Bureau of National Capital Airports, which
operates Dulles and National airports.
No separate count is kept of complaint~
about air pollution from aircraft, but when people do not make such complaints,
thc; are told that recent findings (Ref 120) show that aircraft account for
:e~s than 1 per cent of all air pollution.
In the New York City area, contact was made with the New York City
Department of Air Pollution Control, but not with air pollution control
agencies in neighboring counties of New York and New Jersey.
The New York
City Department indicates its records do not include any information about
aircraft.
The Port of New York Authority, as operator of J. F. Kennedy,
LaGuardia, and Newark airports, receives a majority of the complaints
concerning aircraft in the New York City area.
Telephone complaints to
an airport are taken by the airport's sound crew; complaints, either by
phone or by letter, which come directly to the Port Authority or are refer-
red to it by another agency, such as the Mayor's office, are handled by
the Authority's Aviation Publ ic Service Division.
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385
An Overview of Complaint Data
One characteristic of aircraft air pollution data is its
inaccessibility.
No air pollution agency that we contacted reports air-
craft complaints as a separate category, and no airport reports air pollu-
tion complaints as a separate category.
Aircraft are considered by many to
be minor contributors to air pollution and air pollution is a minor reason
for complaining about aircraft; hence, aircraft air pollution tends to be
lightly regarded.
While we obtain no estimates of the magnitude of aircraft air
pollution complaints for the Los Angeles area, the Air Pollution Control
District did mention that persons who complain about smog from aircraft
often complain about their noise also.
The District of Columbia Air Pollu-
tion Control Division reported receiving two complaints about aircraft in
1967, while the Bureau of National Capitol Airports had received "a few"
air pollution complaints.
The New York City Department of Air Pollution
Control reports no complaints about aircraft in their 1967 records.
The
Port of New York Authority received 26 complaints from 19 persons about
air pollution from aircraft in 1967.
The Interpretation of Complaint Data
"Complaint data," that is, complaints on file, may not be a good
representation of "complaints," even of official complaints.
Complaints
which go to an agency which has not instituted a complaint procedure or
to an officer who may be outside the established complaint network, or
which use a medium such as a personal visitation or a meeting, rather than
mail or telephone, for which complaint routines have not been established,
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386
often never find their way to the files.
Some fi les are never analyzed,
and again, these tend to be those that fall outside the routines.
Thus,
"complaint data" not only may underestimate "complaint behavior," but may
lead to misinterpretation.
Complaint behavior may not accurately represent the seriousness
of the situation which engenders it.
In the Boston area where airport
complaint files are currently (November, 1968) under study, 88 complaints
were recorded in the calendar year 1967, whi Ie 330 were recorded from
January I to October 15, 1968.
Air traffic has neither increased nor
changed its pattern appreciably, but the senior United States Senator from
the area held hearings about the airport early in the calendar year, a
number of local office holders have interested themselves in the problems
of nearby residents, and the airport itself has publicized its unlisted
"complaint" telephone number for the first time in several years.
Thus,
increased hope of abatement and a known mode for complaining seem to have
increased the number of complaints.
Characteristics of complainers may have simi lar effects.
Longer
residence in one's neighborhood and high occupational status (Ref I I 1-2),
more frequent exposure to mass communications, and a more urbane outlook
on life (Ref 111-3) seem to increase people's likelihood of complaining
about air pollution.
However, despite these sources of individual varia-
tion, complaints about air pollution are evoked by polluted air, and some
relation may be expected to hold between the two.
Thus, meaning can be derived from a study of complaint data,
but relations between complaint data and complaints, annoyance, community
action, or the degree of environmental degradation are apt to be very
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387
complex.
Hence, the data must be interpreted with great care, and a much
more systematic study of the relations between complaints and background
factors must be made before complaints can confidently be employed as
social indicators of known significance and reliability.
The Siqnificance of Aircraft Air Pollution Complaints
In assessing the significance of complaints about air pollution
from aircraft, it must be recognized that no complaints are to be expected
concerning emission of invisible and nonodorous pollutants.
The publ ic
is not directly aware of the quantities of CO, organics, or NO
x
em i tted
by aircraft, or of the contribution by aircraft to community pollution
levels.
Consequently, complaint analysis is not an effective approach to
evaluating the impact of these emissions on the community.
On the other hand, the publ ic is aware of odor and visible
smoke emission by aircraft.
Since the principal effects of these emissions
are offenses to the senses, complaints directed at these effects might
well be regarded as a significant measure of impact.
This study of
complaint data has revealed that the number of complaints about air
pollution from aircraft is very small in comparison to complaints
about other sources.
Consequently, despite the caveats entered above
about the interpretation of complaint data, we feel safe in concluding
that the sensory effects associated with aircraft exhaust emissions are
not of pressing concern to the public.
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388
III - I
III - 2
III - 3
REFERENCES
Los Angeles Times, September 16, 1968.
Medalia, 'JCommunity Perception of Air Quality", U. S. Department
of Health, Education and Welfare, Publ ic Health Service, Division
of Air Pollution, Cincinnati, Ohio, Report #999-AP-IO, 1965.
Van Arsdol, "Social Organization and Air Pollution"~ Paper pre-
sented at meeting of the Air Pollution Control Association, Cleve-
land, Ohio, June, 1967.
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