Calculation of odour emissions from aircraft engines at Copenhagen Airport

www.elsevier.com/locate/scitotenv

Science of the Total Environm

Calculation of odour emissions from aircraft engines at

Copenhagen Airport

Morten Winther a,*, Uffe Kousgaard a, Arne Oxbøl b

a National Environmental Research Institute, Frederiksborgvej 399, 4000 Roskilde, Denmarkb FORCE Technology, Park Alle 345, 2605 Brøndby, Denmark

Received 10 February 2005; received in revised form 15 July 2005; accepted 4 August 2005

Available online 27 September 2005

Abstract

In a new approach the odour emissions from aircraft engines at Copenhagen Airport are calculated using actual fuel flow and

emission measurements (one main engine and one APU: Auxiliary Power Unit), odour panel results, engine specific data and

aircraft operational data for seven busy days. The calculation principle assumes a linear relation between odour and HC emissions.

Using a digitalisation of the aircraft movements in the airport area, the results are depicted on grid maps, clearly reflecting aircraft

operational statistics as single flights or total activity during a whole day. The results clearly reflect the short-term temporal

fluctuations of the emissions of odour (and exhaust gases). Aircraft operating at low engine thrust (taxiing, queuing and landing)

have a total odour emission share of almost 98%, whereas the shares for the take off/climb out phases (2%) and APU usage (0.5%)

are only marginal. In most hours of the day, the largest odour emissions occur, when the total amount of fuel burned during idle is

high. However, significantly higher HC emissions for one specific engine cause considerable amounts of odour emissions during

limited time periods. The experimentally derived odour emission factor of 57 OU/mg HC is within the range of 23 and 110 OU/mg

HC used in other airport odour studies. The distribution of odour emission results between aircraft operational phases also

correspond very well with the results for these other studies. The present study uses measurement data for a representative engine.

However, the uncertainties become large when the experimental data is used to estimate the odour emissions for all aircraft engines.

More experimental data is needed to increase inventory accuracy, and in terms of completeness it is recommended to make odour

emission estimates also for engine start and the fuelling of aircraft at Copenhagen Airport in the future.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Odour emissions; Aircraft engines; APU; HC; NOx

1. Introduction

Traditionally, environmental impact assessments of

airports are focusing on the local noise and air pollution

levels (e.g. Fenger et al., 1996; Miljø-og Energiminis-

teriet, 1996; Berkowicz et al., 1999). The most impor-

tant sources considered for air pollution inventorying

and modelling are aircraft engines, airport GSEs

0048-9697/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.scitotenv.2005.08.015

* Corresponding author. Tel.: +45 4630 1297; fax: +45 4630 1212.

E-mail address: [email protected] (M. Winther).

(Ground Service Equipment) and the contribution

from road traffic in the surrounding road network.

Along with air pollutant emissions, the use of different

kinds of combustion engines causes varying levels of

odour nuisances.

The investigation of the nuisances of odour caused

by aircraft activities is made using questionnaire sur-

veys, air quality measurements of known odour caus-

ing hydrocarbon substances, or by setting up regular

odour emission inventories as input for dispersion

modelling. Until now not many studies have been

ent 366 (2006) 218–232

mailto:[email protected]

http://dx.doi.org/10.1016/j.scitotenv.2005.08.015

M. Winther et al. / Science of the Total Environment 366 (2006) 218–232 219

published in this specific field of research. Results,

however, clearly point out that aircraft engine related

odour nuisances in varying degrees occur in the vi-

cinities of airports.

In Hamburg Airport (Fuhlsbuttel) a questionnaire

survey was conducted to investigate the nuisances in

the airport vicinity caused by odour (TUV-Nord-

deutschland, 1987). Here, a serious odour annoyance

was found in small areas around the airport, predomi-

nantly caused by jet engines and auxiliary power unit

(APU) emissions. In another questionnaire survey made

in Amsterdam Airport (Shiphol), the percentage of

people reporting serious odour annoyance caused by

odour was 5% within a radius of 25 km centring the

airport. The share of people reporting the effect in-

creased to 16% within a 10-km radius (TNO-PG and

RIVM, 1999).

At Boston Airport (Logan) a 4-year database of

odour complaints from the surrounding areas was

used for odour investigation purposes (Chng Environ-

mental, 1996). A relatively good correlation was found

between odour complaints, the level of aircraft activi-

ties, the specific runways used, and meteorological

conditions. Prior to this survey, measurements of

known odour causing hydrocarbon components above

the critical 50% recognition odour concentrations was

made outside Boston Airport. The results suggested that

jet exhaust was likely to be the odour problem (Tech

Environmental, Inc., 1992; Wayson, 1995).

In Bahmann et al. (1994) and ArguMet (2004) odour

emission factors derived from measurements, expressed

as odour units per mg organic carbon, was used for

odour emissions calculations at the airports of Dussel-

dorf and Frankfurt, respectively. The product of the

average odour emission factor and the aircraft specific

hydrocarbon emissions gave an estimate of the total

odour emitted. The subsequent dispersion calculations

were based on the hourly odour emissions for each of

the line sources (three dimensional line source system)

comprised in the odour inventories. Dispersion results

for both airports showed that exceedances of the odour

threshold limits occurred in certain areas close to the

airport. Calculations for Hamburg Airport using the

same approach (and odour data from the Dusseldorf

inventory) gave similar conclusions (Huttig et al.,

1996).

The odour inventories at the airports of Dusseldorf,

Hamburg and Frankfurt make up a fine platform for

environmental impact assessment (EIA) work. The

weakness of the studies is, however, that they use rather

low geographical and temporal resolutions. More de-

tailed and accurate results are produced if instantaneous

odour emissions are obtained for each grid cell the

aircraft passes.

In the present paper a new approach is described to

quantify the odour emissions at Copenhagen Airport

originating from the use of aircraft engines. The subse-

quent work made to determine the odour concentrations

using the actual odour emissions and meteorological

data in dispersion modelling will be published in a

subsequent paper (J. Fenger, personal communication,

2005). The present approach uses actual odour and

emission measurements for one main aircraft engine

and one APU engine in combination with engine spe-

cific fuel consumption and emissions for all aircraft.

The aircraft movements and emissions are described in

a GIS (50�50 m resolution) with a temporal resolution

given in seconds.

One specific advantage of this new approach is that

the instantaneous emission modelling gives a detailed

picture of the time and place for the emissions of

odour in Copenhagen Airport. In this way, the present

odour emission survey can be used as an input to

future odour limitation strategies in the airport, and

in addition may serve as an inspiration for similar

work in other airports.

Due to a lack of experimental and operational data,

the odour emissions from engine start and the fuelling

of aircraft, as well as from stationary sources and the

use of GSEs in the airport, and road traffic contribu-

tions in general are excluded from the present survey.

2. Method

In the airport the aircraft engines use maximum

thrust on the runway during take off and initial climb

out, and idle thrust on taxiways and during arrival and

departure from the gate. The aircraft also use APUs

(Auxiliary Power Unit) for purposes such as the gen-

eration of electricity, air conditioning and for main

engine start up.

Based on emission measurements and odour panel

results the initial step is to determine the odour emis-

sions per mg HC from a representative aircraft engine.

The next step is to gather engine specific fuel consump-

tion and emission data for all aircraft using Copenhagen

Airport. Here, information is obtained by joining data-

base information of tail number/engine ID, and data-

base information of engine IDs, fuel consumption and

emissions figures.

Subsequently, the odour emissions per engine are

calculated using a linear relation between odour and HC

emissions. In parallel, the aircraft movements are digi-

tised using a digital map and aircraft operational data

M. Winther et al. / Science of the Total Environment 366 (2006) 218–232220

for the airport. The final odour inventory is made up by

combining the instantaneous odour emissions and the

geographical positions for each aircraft during opera-

tion at the airport.

2.1. Main digitalisation principles and assumptions

Copenhagen Airport has provided a digital map

covering the airport area, and aircraft operational data

for seven busy working days in 2002. Data consist of

aircraft type, tail number, gate, off/on block time, spec-

ification of start/landing, time of start/landing and run-

way specification. The selected days are not

consecutive days. Instead they are selected in consid-

eration to the further dispersion modelling work, so that

operational data are available with the preferential use

of each of the six runways as defined by meteorological

conditions.

The documentation behind noise monitoring at

Copenhagen Airport is used to map out the aircraft

taxiways (Svane et al., 1997). No infrastructural

changes have been made in Copenhagen Airport in

the time after the taxiway analysis was carried out,

and consequently the results are still valid for today’s

situation (P. Schøn, Copenhagen Airport, personal com-

munication, 2003).

In Fig. 1, the 133 airport gates are marked as violet

coloured points. The taxiways are coloured red going

from the gates to the shared taxiways (green on the

map). The black points are knots in the digitised road

system. The six runways 22L, 22R, 04L, 04R, 12 and

30 are numbered in the compass direction and the

notifications for left (L) and right (R) distinguish

between parallel lanes and the same direction of

movement.

In order to determine the time span in each of the

grid cells for the aircraft during operation, the location

of gates, taxiways and runways on the electronical map,

and the off/on block and start/landing times are used,

together with appropriate assumptions for aircraft mo-

tion during the different phases of operation.

2.1.1. Taxiing

An average (standard) taxi speed of 8 m/s is reported

by Copenhagen Airport (B. Mikkelsen, personal com-

munication, 2003). For each operation, the taxi speed is

also calculated using the data for off block and take off

time, and taxiway length. For calculated taxi speeds

smaller than 8 m/s, the difference in the taxi periods

derived from the standard and the calculated taxi

speeds, is counted as queuing time at the runway start-

ing point. When exceeding 8 m/s, the calculated taxi

speed is used. After landing, the taxi speed is calculated

using the runway exit time, on block time and taxiway

length. If queuing occurs, the calculated taxi speed

becomes proportionally lower.

2.1.2. Take off and landing

The airport provides information on six MTOW

(Maximum Take Off Weight) classes of the runway

distance used during take off, and on the final speed

when the aircraft leaves the ground. A constant accel-

eration is assumed. For each runway the landing spot

is the same as the starting point during take off. For

landing a constant deceleration is assumed, numerical-

ly equal to the take off acceleration, until a speed of

20 m/s is reached. After this the aircraft continues in a

constant speed until the first exit turn appears.

2.1.3. Climb out and approach

The odour survey includes the aircraft movements

up to 100 m above ground level. The selected threshold

height is rather arbitrary, however, it is assumed that

odour emissions that take place above this height, have

only a marginal influence on the ground level odour

concentrations. During climb out and approach a con-

stant aircraft speed is assumed and horizontally the

aircraft motion is described as a linear prolongation of

the runway. For the six MTOW classes the climb out

gradients range from 8% to 18%, in increments of 2%,

as MTOW decreases (B. Mikkelsen, Copenhagen Air-

port, personal communication, 2003). Depending on

aircraft MTOW the line source extension becomes

between 556 and 1250 m horizontally, when the vertical

dimension is included in the project. The approach

gradient is 3% for all aircraft, which corresponds to

extending the considered line source with 3333 m

horizontally.

2.1.4. Use of APUs

For environmental reasons the use of APUs at the

airport is restricted during parking at the gate. Based on

airport information a 5-min use before off block and 5-

min use after on block is assumed.

2.2. Measurements of odour, fuel flow and emissions

To obtain inventory basis data, measurements of

odour, fuel flow and emissions have been made on a

JT8D-219 engine fitted to a MD80 aircraft, the most

frequently used aircraft type at the airport. The mea-

surements have been conducted at the Volvo laboratory

in Bromma Airport (Sweden). During the laboratory

tests, three sets of measurements were obtained for the

Fig. 1. Grid map of Copenhagen Airport showing gates, taxi and runways.


engine operational phases idle and take off. The corre-

spondent engine power settings were 7% and 100%.

In terms of emissions, the JT8D-219 and the most

commonly used JT8D-217C engine are almost identi-

cal, and have emission performances close to the over-

all average for the jet engines used at Copenhagen

Airport. Also in terms of operations a good represen-

tation is reached. Totally, the JT8D-217C and JT8D-

219 engines are used in 26% of the take offs and

landings covered by operational data, cf. Table 2.

Table 1

Bag analysis results and fuel flows during tests for the JT8D-219 and APU engines

Engine Power

setting

Fuel flow

(ff), kg/s

Total HCa,

mg C/m3

NOx,

mg NO2/m3

NO2b,

mg/m3

CCO2c,

g/m3

Odour

(odour panel),

OU/m3

Odour (from measured

NO2), OU/m3

Odour character

JT8D-219 Idle 0.13 2.0 3.8 0 0.55 200 0 Wash, smoke,

chemicalIdle 0.13 2.3 3.8 0 0.54 170 0

Idle 0.13 2.1 3.8 0 0.56 130 0

Avg. 0.13 2.1 3.8 0 0.55 170 0

JT8D-219 Max. 1.4 4.0 31 17 1.3 720 580 Chlorine, smoke,

chemicalMax. 1.4 2.9 33 19 1.3 720 640

Max. 1.4 3.9 33 17 1.4 720 580

Avg. 1.4 3.6 32 18 1.3 720 600

APU Normal 0.013 8.0 48 40 13.8 830 1342 Chlorine, gas oil,

gas, gasolineNormal 0.013 6.3 48 40 13.3 970 1342

Avg. 0.013 7.2 48 40 13.5 900 1342

a Measured using infrared photoacustic spectroscopy (Bruel and Kjær Gas Monitor 1302).b Measured using chemiluminescense (NOx-monitor CLD 700 El).c Measured in vol. % using non-dispersive infrared light absorption (Monitor Labs CO/CO2 monitor) and recalculated to g carbon in CO2

emissions per m3 (g CCO2/m3).


Their correspondent fuel use share is 37% of all fuel

used, according to additional calculations.

In addition measurements have been made at Copen-

hagen Airport on an APU engine1 installed in a SAS

Airbus 321-200 aircraft. This APU engine is also used

by the common SAS B737 and MD90 aircraft types,

and is thus regarded as an overall representative for

APUs. A description of the JT8D-219 and APU mea-

surements are given by Oxbøl (2003a,b).

During the tests the exhaust gas has been collected

in sample bags made of Nalophan for subsequent chem-

ical analysis and odour panel tests, and the engine fuel

flows have been measured simultaneously. It was not

possible to take samples directly from the engine ex-

haust, and thus diluted exhaust samples were taken in a

test cell.

The subsequent odour analysis has been made less

than 24 h after the collection of exhaust samples by

persons in an odour panel constituted according to the

regulations from the Danish EPA (Vejledning nr. 4,

1985) and European standards (EN 13725). The

odour panel test approach is to let the panel members

smell to strongly diluted samples of the exhaust gas

collected. By gradually reducing the dilution ratio until

50% of the panel members indicate a smell, a critical

concentration is determined. This critical concentration

defines one odour unit (OU; At a concentration of 1

OU, 50% of the panel members indicate a smell).

In Table 1 the results of the sample bag analysis

(truncated values) are shown for the JT8D-219 and the

1 Honeywell GTCP 131-9A, 131 HK.

APU engine together with the fuel flows during the

actual laboratory tests. Due to different dilution ratios

during tests, the concentration results cannot be com-

pared between the different engines/engine power set-

tings. For CO2 the measured concentrations are

corrected for the atmospheric background concentra-

tion (approx. 400 ppm). No corrections are made for

HC and NO2, since the background concentration

levels for these substances under normal conditions

are too low to have an influence on the measurement

results.

From the engine manufacturers side a general NO2

share of between 5% and 10% of total NOx emitted is

expected at maximum engine thrust (P. Madden, Rolls

Royce, personal communication, 2005). For this part of

the experiments the NO2:NOx ratio is 0.56 and there-

fore most likely a chemical transformation of NO to

NO2 has occurred in the sample bags from the time of

the filling of the bags to the moment of bag analysis.

For the APU engine measurements the NO2:NOx ratio

of 0.83 is also considered to be unrealistically high.

Again, most likely a considerable amount of NO has

been chemically transformed into NO2 after the filling

of the bags.

It is very likely that the created NO2 is dominating

the odour results. The odour panel test persons most

predominantly characterise the odour as chlorine like,

and this is the odour character that is empirically given

to NO2. Based on the experience from FORCE Tech-

nology the empirical critical odour level (1 OU) is

reached when the NO2 concentration is 0.03 mg/m3.

A theoretical odour contribution for NO2 (Table 1) is

then found as the measured NO2 concentration (Table

Table 2

Engine IDs most commonly used at Copenhagen Airport (seven busy working days)

Engine ID Typea Take off/

Landings [No.]

%-share Idle thrust Maximum thrust

EI HC [g/kg fuel] Fuel flow [kg/s] EI HC [g/kg fuel] Fuel flow [kg/s]

JT8D-217C MTF 1074 19.5 3.3 0.14 0.28 1.32

PW150A TP 547 9.9 18.1 0.04 0.50 0.29

JT8D-219 MTF 372 6.7 3.5 0.13 0.27 1.35

CFM56-3C1 TF 296 5.4 1.4 0.12 0.03 1.15

CFM56-7B20 TF 284 5.2 3.1 0.10 0.10 0.91

PW120 TP 271 4.9 0.0 0.03 0.00 0.13

LF507-1F TF 257 4.7 4.7 0.05 0.01 0.36

CF34-3B1 TF 193 3.5 4.7 0.05 0.06 0.40

PW125B TP 168 3.0 3.6 0.03 0.00 0.15

PW127F TP 146 2.6 2.7 0.03 0.00 0.17

CFM56-7B26 TF 137 2.5 1.9 0.11 0.10 1.22

V2525-D5 TF 133 2.4 0.1 0.13 0.04 1.05

AE3007A1 TF 109 2.0 3.1 0.05 0.26 0.38

V2533-A5 TF 108 2.0 0.1 0.14 0.05 1.43

CFM56-7B22 TF 100 1.8 2.5 0.11 0.10 1.02

a MTF: Mixed Turbo Fan; TF: Turbo Fan; TP: Turbo Prop.


1) divided with the critical NO2 concentration. Thus for

maximum engine thrust the theoretical odour contribu-

tion from NO2 is 80% of the odour panel result, and for

the APU engine the theoretical odour contribution

becomes larger than the odour panel results.

Due to the large odour impact of the subsequently

transformed NO2 in the sample bags for maximum

engine thrust for the jet engine and for the APU mea-

surements as such, it is decided to leave out these

measurements from the experimental input to the

odour inventory calculations.

For idle power, the measured NO2 concentrations

are very low (truncated value: 0). Thus only a marginal

(if any) transformation of NO to NO2 has taken place

after the filling of the bags, and for these measurement

results HC is believed to cause the perceptible odour.

These conditions are more in line with real ambient air

conditions, and consequently these measurements are

used in the further odour emission calculations. Using

the experimental figures for odour and mg C (Table 1)

and by taking into account a general carbon/total hy-

drocarbon ratio of 0.73 in the combustion products

(Huttig et al., 1996), the HC related odour emission

factor becomes:

OU=mg HC ¼ 0:73C=total HCð Þd OU=m3ð Þmg C=m3ð Þ ð1Þ

The obtained odour emission factor of 57 OU/mg

HC is within the range of 31 and 150 OU/mg CHC

(~23 and 110 OU/mg HC) used in the Dusseldorf and

Hamburg airport studies and at Frankfurt Airport,

respectively.

The odour emission rate (OU/s) for the APU engine

is found using the odour emission factor of 57 OU/mg

HC, and taking into account the APU engine fuel flow

and the specific sample bag concentrations of CCO2 and

CHC.

The mass rate of carbon (C) in the CO2 emissions (g

CCO2/s) is calculated from the fuel flow (Table 1)

assuming a 99% complete combustion and a carbon

share of 0.86 in the fuel (assumed to be CH2):

g CCO2=s ¼ 0:99d 0:86C=CH2ð Þd ff ð2Þ

The ratio of mg HC and g CCO2 in the sample bag is:

mg HC=g CCO2¼ mg CHC=m

3=0:73

g CCO2=m3

ð3Þ

The odour emission rate is then expressed as:

OR¼ g CCO2=s

� �dmg HC=g CCO2

d OU=mg HCð Þ ð4Þ

The odour emission rate for the APU engine is 462

OU/s.

The uncertainty of the determination of the odour in

the exhaust gas is approximately F60% (95% confi-

dence interval), whereas the uncertainties of the HC

measurements are F10% (95% confidence interval),

see Oxbøl (2003a,b).

2.3. Fuel consumption and emission data

To facilitate the further calculations fuel consump-

tion and emission data are gathered for each aircraft

(per aircraft registration number). Aircraft specific en-

gine IDs are found in the global database bjp airline-


fleets international 2003/2004Q (Klee, 2003). Engine

specific fuel consumption and HC emissions are taken

from the ICAO Engine Exhaust Emission Database

(ICAO; jets) and from FOI (Swedish Defence Research

Agency; turboprops and small jets) for idle and maxi-

mum engine power settings. For turboprops and small

jets most of the data are also available in EMEP/COR-

INAIR (2003).

Table 2 shows the most commonly used engines at

the airport. Their fuel flows and HC emission indices

(HC EI) are used in the final odour calculations together

with data for the remaining engines used. More than

98% of all aircraft have been allocated accurate engine

data. The remaining aircraft have been assigned repre-

sentative engine data from a similar aircraft type.

The fuel use and emission data in the ICAO database

are engine certification data, and the database is con-

tinuously updated as new engines enter into service.

The FOI database for turboprop aircraft is from 2003.

Also in this case updates are made whenever new

engine information becomes available.

Because of very high safety standards for aircraft in

general, the engine maintenance levels are high as well.

This means that engine components are checked regu-

larly and if necessary are replaced according to a strict

maintenance scheme. Even though there may be small

deterioration effects for fuel burn and emissions, the

effects are cyclic as engines are overhauled at regular 3

or 4 years intervals (P. Madden, Rolls Royce, personal

communication, 2005).

Consequently, neither ageing effects nor fuel use and

emission differences from one engine to another of the

same mark are considered as real problems in relation

to inventory input data. The general uncertainties on

ICAO and FOI emission data are assumed to be F2%

(L. Hawkins, Rolls Royce, personal communication,

2005).

Table 3

The odour emission inventory for Copenhagen Airport divided into

aircraft operational phases

Operation Power setting Results

OU [109] OU share [%]

Taxi (arrival) Idle 36.8 26.6

Taxi (departure) Idle 40.8 29.5

Queing (departure) Idle 49.0 35.3

Approach Idle 3.6 2.6

Runway (deceleration) Idle 2.9 2.1

Runway (taxi) Idle 2.4 1.7

Runway (take off) Maximum 1.8 1.3

Climb out Maximum 0.5 0.4

APU APU 0.7 0.5

Total 138.5 100.0

3. Calculation method

The total odour emission from an aircraft in a grid

cell at a given time is calculated as the product of the

measured odour emission factor, the number of engines

fitted to the aircraft, the specific engine HC emission

index and fuel flow, and the time interval for the aircraft

in the cell:

DOUAircraft;X t; ið Þ¼ OU=g HCð Þd NEd EIHC;Xd ff Xd Dt t; ið Þð5Þ

i=grid cell, t=time (s), DOUAircraft,x(t,i)=odour emis-

sions from an aircraft with an engine, X, in grid cell, i,

and time, t, during the time interval Dt, NE=No. of

aircraft engines, ffX=fuel flow (kg/s) for a given en-

gine, X, figure from ICAO/FOI, EIHC,X =HC emission

index (g/kg fuel) for a given engine, X, figure from

ICAO/FOI, Dt(t,i)= the time interval for the aircraft in

grid cell i.

For APU engines the total odour emissions per

engine are calculated as product of the odour emission

rate from (4) and the time interval for the aircraft in the

cell:

DOUAircraft;APU t; ið Þ ¼ ORAPUDt t; ið Þ ð6Þ

The odour emission rate used for APU engines is

very low compared to the odour emission rate of 32,000

that can be derived for the JT8D-219 measurements.

Thus APUs are regarded as marginal sources of odour

emissions, and the uncertainties introduced in the final

results by using the same odour emission rate for all

APUs are equally small.

The total odour emissions from aircraft activities in

the seven days covered by operational data are found by

summing up the expressions (2) and (3) for all aircraft,

grid cells and time intervals. For further dispersion

modelling the odour emission figures calculated in (2)

are used in a Gaussian dispersion model (OML model),

see Olesen (1995).

4. Results

The odour emission results for the different phases

of aircraft operations are shown in Table 3. Taken as a

whole, the idle phases taxiing, queuing and landing

accounts for almost 98% of the total odour emissions.

The odour emission share for take off and climb out is a

little less than 2%, whereas the odour emissions from

APU are only marginal (0.5% of total). The uncertainty

on the odour determination by the odour panel is far

0

2

4

6

8

10

12

14

16

18

0-1

2-3

4-5

6-7

8-9

10-1

112

-13

14-1

516

-17

18-1

920

-21

22-2

3

Hour interval

Od

ou

r u

nit

s [1

08 /h

ou

r]

Total odour emissions

Fig. 2. Total odour emissions at Copenhagen Airport (hourly average).


higher than the uncertainties for the remaining calcula-

tion parameters, and consequently the general uncer-

tainty of the odour emission results is assumed to be

60%.

The odour results for Copenhagen airport are calcu-

lated for 7 not consecutive days, and since the distri-

bution of operational data in terms of times in modes,

runways used, etc., will not be the same for a full year

period, no effort is made to extrapolate the results into

year estimates. Bearing this in mind, the percentage

shares between the different aircraft operational phases

can, however, be compared with the shares from other

studies derived from year totals.

The percentage shares for approach (as a single

source), the remaining low idle phases, and the take

off/climb phases, are in harmony with the results from

the Dusseldorf, Hamburg and Frankfurt airport odour

investigations. In the latter studies the odour shares for

Fuel burn (

0

1

2

3

4

5

6

7

8

0-1

2-3

4-5

6-7

8-9

10-1

112

Hour i

[To

ns/

ho

ur]

Fig. 3. Fuel burn at Copenhagen Airport for ai

APU are approximately 5 times higher than the present

figure, corresponding to a similar difference in odour

emission factors used.

In Fig. 2 the diurnal variation of the odour emission

rate is shown as average values of the 7 days comprised

in the aircraft operational data. Since almost all odour

are emitted during engine idle conditions, in practical

terms Fig. 2 also show the diurnal variation of the

odour emission rate for low engine power modes. The

diurnal variations of the fuel burn rate in Copenhagen

Airport for idle and maximum engine power are shown

in the Figs. 3 and 4, respectively. The fuel burn rate

variations reflect the fluctuations of the aircraft activi-

ties in the airport.

For most of the hour intervals the largest odour

emissions (Fig. 2) occur during periods when the en-

gine fuel burn rate is high during idle (Fig. 3). The

largest odour emission contributions are calculated be-

idle power)

-13

14-1

516

-17

18-1

920

-21

22-2

3

nterval

rcraft operating at idle (hourly average).

Fuel burn (take off and climb out)

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

0-1

2-3

4-5

6-7

8-9

10-1

112

-13

14-1

516

-17

18-1

920

-21

22-2

3

Hour interval

[To

ns/

ho

ur]

Fig. 4. Fuel burn at Copenhagen Airport for aircraft operating at maximum thrust (hourly average).


tween 7 and 8 a.m., 9 and 11 a.m., 2 and 5 p.m., and

8 and 10 p.m.

The high odour emissions between 7 and 8 a.m. and

between 8 and 10 p.m., are particularly due to the odour

emissions during idle for the aircraft type Antonov 26B.

The engine (Al-24VT) has a HC EI of 281 g/kg fuel in

this situation. Aircraft operations made with Antonov

26B are scheduled flights in Copenhagen Airport, and

so it becomes sensible to include the odour results for

this specific aircraft type in the final odour inventory

and in the subsequent dispersion model runs.

The odour emissions from the eleven Antonov 26B

departures between 7 and 8 a.m. (average per day) are

around 0.8 billion OU, and in particular the taxi phase

related to take off carries great weight in the calcula-

tions (Fig. 2). The average odour emissions from the

Antonov 26B arrivals between 8 and 9 p.m. (six arri-

vals), and between 9 and 10 p.m. (seven arrivals) are

around 0.4 and 0.6 billion OU, respectively. Most of the

Odour emissions (ta

0

5

10

15

20

25

30

35

0-1

2-3

4-5

6-7

8-9

10-1

1

Hour

Od

ou

r u

nit

s [1

06 /h

ou

r]

Fig. 5. Total odour emissions at Copenhagen Airpo

odour emissions come from the taxi phase after landing.

Leaving out Antonov 26B from the odour emission

totals, the diurnal variation of the odour emission rate

(Fig. 2) and the fuel burn rate for idle engine power

(Fig. 3) become almost similar.

The diurnal variation of the odour emissions for take

off and climb out, shown in Fig. 5, is approximately the

same as for the fuel use rate during maximum engine

power (Fig. 4). Consequently, periods with many take

offs and/or the use of large aircraft correspond to peaks

in odour emissions, when the take off/climb out situa-

tion is regarded separately. It must be noted, however,

that the contributions to total odour emissions are very

small for maximum engine thrust.

In Figs. 6 and 7 the odour emissions are depicted as

minute values for the hour between 10 and 11 a.m.

(30th of April 2002) for idle and maximum engine

thrust, respectively. The corresponding average minute

values of odour emissions are also shown, as horizontal

ke off and climb out)

12-1

314

-15

16-1

718

-19

20-2

122

-23

interval

rt for take off and climb out (hourly average).

Odour emissions (idle power)

0,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

1 4 7 10 13 16 19 22 25 28 31 34 37 40 43 46 49 52 55 58

Minutes

Od

ou

r u

nit

s [1

08 /m

in]

Fig. 6. Minute values of odour emissions for an exemplary hour at Copenhagen Airport (idle engine power).


lines. The figures clearly show the characteristic fluc-

tuations of the emissions of odour (and exhaust gases)

in an airport during the lapse of an hour.

Throughout the whole hour period odour is emitted

from engines during idle power conditions (taxi, queu-

ing and landing) and the use of APU. For maximum

engine thrust the emissions of odour drop to zero in

the minute intervals where no take offs are made, or in

a few cases when EI HC database values are report-

edly zero. For both engine power modes, the peaks in

odour emissions are generally due to relatively high

fuel burn levels. However, in a few cases the odour

emission peaks also rely on relatively high aggregated

HC EIs.

Fig. 8 displays the calculated odour emissions from

a MD80 aircraft departuring from gate C36 (including 5

min of APU use before off-block time), and using

runway 30 for take off (before take off: 2 min queuing

Odour emissions (t

0,0

1,0

2,0

3,0

4,0

5,0

6,0

1 4 7 10 13 16 19 22 25 28

Mi

Od

ou

r u

nit

s [1

06 /m

in]

Fig. 7. Minute values of odour emissions for an exemplary h

time). It should be noted that the top stage of the odour

scale in Fig. 8 covers a large interval. The taxiway

differs slightly from its most logical course, with a

detour to the so called b7-starQ.The taxi related odour emissions fluctuate between

grid cells due to a non-parallelism between the taxi-

way course and the orientation of the grid cells. The

highest accumulated odour emissions are in the run-

way 30 take off starting point, and reflect the 2 min

queuing time prior to take off. During the beginning

of take off, the odour emission levels are in the mid-

range of the odour scale due to the increased fuel burn

and the low aircraft speed. However, the emitted

odour quantities soon drop to a very low level as

the aircraft accelerates along the runway and finally

begins its initial climb.

In Table 4 the operational data is given for the 30th

of April 2002 at Copenhagen Airport. On this day the

ake off and climb out)

31 34 37 40 43 46 49 52 55 58

nutes

our at Copenhagen Airport (maximum engine power).

Fig. 8. Odour emissions for the aircraft type MD80 (one departure) from gate C36 and using runway 30 for take off.


take offs and landings are mainly made using the run-

ways 22R and 22L, respectively. The distribution of the

accumulated odour emissions is shown in Fig. 9. The

runway exit turns are marked with a black symbol. On

Fig. 9 it is important to note that the odour scale is non-

linear with significantly increasing levels of odour. By

relating the colouring of the map to the odour scale

specifications the general picture gives that the domi-

nant part of the odour is emitted on the taxiways

relatively close to the terminal area.

Table 4

Operational data for Copenhagen Airport (30th of April 2002)

Operation Runway No. of operations

Landing 04L 7

Landing 22L 358

Landing 22R 14

Take off 22L 34

Take off 22R 340


The landings on the runways 22R (14 landings) and

04L (7 landings) give small, but visible, odour emission

contributions during approach,. The larger number of

landings on runway 22L (358 landings) give corre-

spondingly more odour emissions. It is clear from

Fig. 9, that many (smaller) aircraft use the exit turn

relatively close to the point of landing on 22L. Fig. 9

also shows that fewer and fewer aircraft (the largest

aircraft) use the exit turns, as the distance to the landing

point gradually increases.

On Fig. 9, there is a visible odour emission related to

the aircraft taxiing before take off (340 in all) on

runway 22R. At the take off starting point the queuing

of aircraft cause odour emissions in the highest range of

the odour scale on Fig. 9. The odour emission levels on

runway 22R after the take off starting point a sum of the

odour contributions from the 340 take offs and 14

landings. At the end of runway 22L, Fig. 9 shows a

visible (but much smaller) odour emission contribution

coming from the 34 take offs.

During taxi, the odour emissions increase on the

taxiways as the aircraft approach the b7-starQ. Here,

the odour emissions are on the maximum level. In the

GIS taxiway system, the aircraft moving from and

arriving to the gates at the fingers A, B and C, cross

the b7-starQ as defined in the noise/taxiway documen-

tation report for Copenhagen Airport (Svane et al.,

1997).

5. Discussion

Different operational issues, such as aircraft engine

loads and the temporary aircraft positions, the experi-

mental basis for odour emission data, the model

assumptions used for odour calculations and inventory

completeness, all have an impact on the accuracy of the

final odour inventory results.

The calculations become more uncertain if there is a

discrepancy between the actual aircraft engine loads in

Copenhagen Airport and the standard ICAO power set-

tings for idle and take off. In Fleuti and Polymeris

(2004) the fuel consumption differences were examined

for the actual vs. the ICAO LTO cycle in Zurich Airport

(Kloten). During airport ground taxiing and take off the

power settings were found to be somewhat smaller than

the 7% and 100% given in the ICAO engine certification

cycle (J. Polymeris, personal communication, Swiss

International Airlines, 2005). The fuel flow becomes

lower for reduced engine thrust, whereas the HC emis-

sion indices tend to increase. In the odour inventory

these two developments tend to outbalance each other,

since both parameters enter into the odour calculation

product. However, at present it is not possible to quan-

tify to what extent this equalisation takes place.

The aircraft taxi speeds and the route and queuing

definitions used in the model will in some cases vary

from the actual situation in the airport. As a conse-

quence, odour emissions in some cases refer to queuing

where no queuing actually occurs and vice versa. How-

ever, the error concerns only the allocation of odour on

the distances between departure gate/take off starting

point and runway exit point/arrival gate and thus the

total odour emissions remain unchanged. Since it only

affects the allocation of odour, the potential error is

regarded as small, not least because high odour levels

already prevail in the airport area of consideration, cf.

Fig. 9.

As mentioned in Section 2.2, it was decided to

exclude a part of the odour measurements for the

JT8D-219 engine (maximum engine thrust) and the

APU engine. In general it is essential to carefully

plan the test site measurement conditions and the sub-

sequent storage of the obtained sample bag before

odour panel tests. If the NO concentrations are high,

a chemical reaction takes place between NO and oxy-

gen in the sample bag leading to the formation of NO2.

Consequently, there is an increase of odour in the

sample bag compared to what the odour impact of the

same chemical reaction would be in the airport ambient

air. To minimise the NO-oxygen reaction in question, a

high dilution of the exhaust is needed during the test.

Under real conditions, the dilution of the engine ex-

haust gases almost immediately reaches a level, so that

the amount of subsequently created NO2 becomes min-

imal. The further transformation of NO to NO2 in the

atmosphere to a large extent depends on the ozone

concentrations in the ambient air.

As regards the extent of the experimental tests, more

measurements of odour emissions would in general

reduce the uncertainties of the odour emission factor

basis. However, operational data reveals some degree

of representativity by the measured engine and the

almost identical JT8D-217C engine type. In all, 26%

of all take offs and landings are made with aircraft

fitted with these two engines, and the corresponding

Fig. 9. Accumulated odour emissions for 1 day at Copenhagen Airport (30th of April 2002).


fuel use share is 37% of the total fuel used. If additional

emission tests could be conducted it would be expedi-

ent to obtain measurements from the engine type

PW150A, which is the most frequently used turboprop

engine at the airport.

New research results for Frankfurt Airport pro-

duced after the finalisation of the present study sug-

gest that the amount of unburned fuel released from

the main engines during the engine start phase is a

significant source of odour (ArguMet, 2004). An


odour share of 26% of total odour calculated is

reported. The latter study also finds the percentage

odour contribution from the fuelling of aircraft to be

in the order of 7% of total odour emitted. If an odour

estimate was made for Copenhagen Airport by using

the odour emission factors for unburned hydrocarbons

from the Frankfurt Airport study, roughly 15% and

4% more odour would be added to the inventory as

such, coming from engine start and aircraft fuelling,

respectively.

The assumption of a linear relationship between

odour and HC emissions has been used in the Dussel-

dorf, Hamburg and Frankfurt airport odour studies. This

investigation principle seems intuitively reasonable, the

weakness of this method is, however, that only some of

the HC components are odour active. The concentra-

tions of these components are engine specific, and the

inter-engine concentration variations are different from

the variations in total HC emissions. For the further

dispersion modelling, no chemical reactions involving

hydrocarbons are assumed to take place from the mo-

ment of emission to the moment of odour perception by

people in the airport surroundings. It is however likely

that on this time-scale no chemical reactions of rele-

vance will be taking place (e.g. Seinfield and Pandis,

1998).

Due to a lack of specific knowledge in terms of

odour active emission components and measurement

data, it has been decided here to use the linear odour-

HC dependency bearing in mind the uncertainties as-

sociated with this method of calculation.

6. Conclusion

In a new approach the odour emissions from aircraft

engines at Copenhagen Airport are calculated using

actual fuel flow and emission measurements (one

main engine and one APU), odour panel results, engine

specific data and aircraft operational data for seven

busy days. The odour calculation principle assumes a

linear relation between odour and HC emissions.

Using a digitalisation of the aircraft movements in

the airport area, the results are depicted on grid maps,

clearly showing the size of odour emissions during

each phase of a single flight departure. The aircraft

operational statistics are also reflected for a whole

day in terms of runways used during take offs and

landings, and the taxiways used during arrival and

departure from the gates. During the lapse of an

exemplary hour, the results clearly show the charac-

teristic fluctuations of the aircraft activities in an

airport.

The aircraft operational phases using low thrust

(taxiing, queuing and landing) account for almost

98% of the total calculated odour emissions, and the

dominant part is emitted on the taxiways relatively

close to the terminal area. The odour emission share

for maximum thrust during take off and climb out is

very small (less than 2%), and for APU the share

becomes even smaller (0.5%). The overall uncertainty

of the odour results is around 60%.

The experimentally derived odour emission factor of

57 OU/mg HC is within the range of 23 and 110 OU/

mg HC used in the odour studies at the Dusseldorf,

Hamburg and Frankfurt airports. In general, the distri-

bution of odour results between aircraft operational

phases corresponds very well with the findings from

the three German airports, whereas a difference in

odour emission factors for APU cause a similar differ-

ence in the odour emission estimates.

During the day, the highest odour emissions are

calculated between 7 and 8 a.m., 9 and 11 a.m., 2

and 5 p.m., and 8 and 10 p.m. The odour emission

fluctuations correspond to the total fuel burned during

aircraft idle, except for the periods between 7 and 8 a.m.

and 8 and 10 p.m. Here, the odour emission peaks are

caused by one specific aircraft type using an engine

with significantly high HC emissions.

The present study uses experimental data for an

engine directly representing 26% of all landings and

take offs, and 37% of all jet fuel burned in Copenhagen

Airport. In spite of the good engine representation, the

uncertainties become large when the experimental data

is used to estimate the odour emissions for all aircraft

engines. Therefore there is an urgent need for more

experimental data in order to understand the relative

importance of all the different odour sources and to

obtain a more robust picture of their actual levels. More

measurement data would not only be an advantage for

Copenhagen Airport, but in addition would enhance the

odour emission factor basis for odour investigations in

other airports. In terms of completeness, it is recom-

mended in the future to include the odour emission

sources engine start and the fuelling of aircraft in the

odour inventory for Copenhagen Airport.

Acknowledgements

The work was funded by Copenhagen Airport and

the authors acknowledge their support and provision of

background data material. Thanks should also be given

to Jytte Illerup and Ruwim Berkowicz, National Envi-

ronmental Research Institute, for many fruitful discus-

sions during the writing of this paper.


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Calculation of odour emissions from aircraft engines at Copenhagen Airport

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