1. Sabrina Groth, Judith Rosenow and Hartmut Fricke
Aviation-induced nitrogen oxide emissions and their effect on the energy budget of the Earth-atmosphere system Identification of climate optimized trajectories
Sabrina Groth, Judith Rosenow and Hartmut Fricke

2. Structure
1. Introduction 2. Calculation of NOx emissions 2.1 Aircraft Performance Model 2.2 Calculation methods 3. Optimization of flight trajectories 3.1 Modelling approach for trajectory optimization 3.2 Qualitative optimization strategies 3.3 Assessment of NOx calculations 3.4 Recommendations for eco-friendly trajectory design 4. Conclusion

3. 1. Introduction
air transport is assumed to be one of the key roles in international mobility and provides the only worldwide transportation network1
since 2009 the number of passengers worldwide has increased by 29%2
global fuel consumption increases
aviation-induced emissions of pollutants
Air Transport has a significant impact on environment, it influences the natural composition of the atmosphere
- Also, air transport takes a special role because it´s the only emitter of pollutants in the upper troposphere and lower stratosphere.
- Therefore, air transport has a significant impact on the environment and climate change, which will also continue to grow.
Though, it influences the natural composition of the atmosphere
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1ATAG (Air Transport Action Group), “The economic & social benefit of air transport,” Joint Workshop 2005, p.2
2DLR, „DLR- Institut für Flughafenwesen und Luftverkehr,“ [Online]. Available:

4. 1. Introduction Direct emissions CO2 NOx H2O SO2 HC C
Influence on atmosphere2:
Direct emissions
CO2
NOx
H2O
SO2 HC C
Atmospheric processes
Ocean uptake
Chemical reactions
Microphysical processes
ΔCO2
ΔCH4
ΔO3
ΔH2O
ΔAerosol
Contrails
Changes in radiative forcing components
ΔClouds
Changes in temperatures, sea level, ice/snow cover, precipitation etc.
Climate change
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2DLR, „DLR- Institut für Flughafenwesen und Luftverkehr,“ [Online]. Available:

5. 1. Introduction
Aviation changes not only the natural composition of the atmosphere, but also influences the climate change
securing sustainability and protection of climate and environment represent a global challenge
Institute of Logistics and Aviation at TU Dresden started the research project MEFUL3
Objective: Implementation of an ecologically friendly and safe air transport system to ensure the sustainability of aviation as mode of transport
Not only the reduction of emissions but also their influence on the atmosphere and e.g. radiation budget are required.
In recent years, the environmental awareness grew especially in the industrialized countries.
….which has to be faced by politics and economics
This ambitious goal is already one of the objective of research programs e.g. SESAR and NextGen.
….and the German Federal ministry of Economic Affairs and Energy ….
To realize this, …
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3 MEFUL: Minimizing Flight Emissions while Sustaining Guaranteed Operational Safety as a Contribution to an Environmental Friendly Air Transport System

6. 1. Introduction Focus of this work: Nitrogen Oxide emissions NOx
Effects influence diverse and complex chemical processes in the atmosphere
Short-term: O3
inducing an increase of the troposphere's ozone production
𝑁𝑂 2 + 𝑙𝑖𝑔ℎ𝑡⇒𝑁𝑂+ 𝑂
𝑂+ 𝑂 2 +𝑀⇒ 𝑂 3 +𝑀
Long-term: CH4
decrease of the troposphere's methane concentration
𝐻𝑂2 +𝑁𝑂⇒𝑁𝑂2+𝑂𝐻
𝐶𝐻4+ 𝑂𝐻⇒𝐶𝐻3+𝐻2𝑂
Long-term: O3
decreasing ozone concentration as result of less methane- Primary Mode Ozone (PMO)

7. 1. Introduction ΔCH4 Δ RFCH4 ↓ NOx Δ RFNOx ΔO3 Δ RFO3 ↑
contrary processes are accomplished
difficult to calculate and measure
different results in terms of the extent of the compensating effect
Identifying trajectories with minimal impact of NOx on atmospheres radiation budget within MEFUL.
NOx
ΔCH4
Δ RFCH4 ↓
Δ RFNOx
ΔO3
Δ RFO3 ↑
Contrary Processes are accomplished by emitted nitrogen oxide emissions.
These are very difficult to measure and calculate.
So far, there are a lot of different results in terms of the extent of the compensating effect.
The aim of this work was to identify trajectories with minimal impact of nitrogen oxide emissions on the radiation budget of the atmosphere within the MEFUL project.
This leads me to my next point…

8. 2. Calculation of NOx emissions
2.1 Aircraft Performance Model
Aircraft Performance Model COALA for generating vertical flight trajectories
aircraft type Airbus A320 with engine type CFM56-5A3 (2x111,2 kN)
temporal discretization ds=1s
Assumptions:
Continuous Climb with maximum climb gradient up to altitude of ft
Maximum climb rate until cruise altitude
Thrust Rating T/O- 100%
C/O- 85%
Continuous descent operations
maximum thrust at a certain level and the fuel flow are calculated with BADA of EUROCONTROL
- …for the determination of the impact of NOx emissions it is necessary to calculate the amount of emitted nitrogen oxides.
- Therefore, it is essential to generate flight trajectories.
- It is based on the integration of a dynamic equation which results from the flight mechanics and includes the decrease in the mass of the aircraft due the fuel flow.

9. 2. Calculation of NOx emissions
vertical trajectories with different distances and cruise altitudes were generated
Opt. Cruise Altitude m, different altitude means increasing fuel consumption
Ranges [km]
2.000
3.000
4.000
5.000
6.000
Max. Altitude [m]
EINOx
7.000
8.000
9.000
10.000
11.000
12.000
13.000
Max. Specific Range
- To calculate the nitrogen oxide emissions different vertical trajectories were generated.
Therefore,…..
- For all generated trajectories the emission index, which means the total emitted amount, for nitrogen oxides has been calculated.

10. 2. Calculation of NOx emissions
2.2 Calculation methods
Methods for calculation of EINOx
Fuel Flow Methods
EINOx,ref published by ICAO
Correlation Models
Correlation of actual parameters, e.g. fuel flow, with reference values
Simplified physic-based Models
- Due to the complexity of other methods, correlation models were used for the calculations.
- All used models use reference values measured at sea level.
- These data are published by the ICAO in the ICAO emissions database
- Also actual parameters are involved in the calculation like the actual fuel flow.
- This is related to the corresponding reference values on the ground by use different correction factors.
- For the determination of the reference values EINOx,ref the actual emissions on the ground are measured for the 4 different thrust levels.
CFD Models

11. 2. Calculation of NOx emissions
Döpelheuer
𝐸𝐼𝑁𝑂 𝑥 𝐸𝐼𝑁𝑂 𝑥,𝑟𝑒𝑓 = 𝛿 𝑡 𝑎 ∙ 𝜃 𝑡 𝑏
(2) Boeing Fuel Flow Method 2
𝐸𝐼𝑁𝑂 𝑥 = 𝐸𝐼𝑁𝑂 𝑥,𝑟𝑒𝑓 𝛿 1,02 𝜃 3,3 𝑒 𝐻
(2) DLR Fuel Flow Method
𝐸𝐼𝑁𝑂 𝑥 = 𝐸𝐼𝑁𝑂 𝑥,𝑟𝑒𝑓 𝛿 𝑡 0,4 𝜃 𝑡 3 exp(𝐻) qt
correction factor for temperature dt
correction factor for pressure a
0,4;temperature exponent b
3; pressure exponent
humSL
humidity at ground level
humFL
humidity at flieght alttitude
All three use the actual fuel flow which was output of the aircraft performance model
In all methods it is necessary to correct the fuel flow to get the emission index on reference level
The certified emission index is correlated with the fuel flow which is corrected for flight conditions
Also, all use a correction factor for the temperature θ(theta) and for the pressure δ(delta)
For the Boeing Fuel Flow Method, the fuel flow needs an additional correction due to the not contained installation effects
Furthermore, for BFM and DLR Fuel Flow Method a correction factor for the humidity is required which forms the difference between the specific humidity at ground level and on flight level

12. 3. Optimization of flight trajectories
3.1 Modelling approach for trajectory optimization
effects of aviation-induced NOx on climate and radiation budget can be reduced by eco-friendly planning of flight trajectories
contribution to climate change can be sustainably reduced by exploiting several optimization potentials simultaneously
3 different approaches:
Technical
Operational
Regulatory
- To prevent a high contribution to global warming…have to be considered.

13. 3. Optimization of flight trajectories
Implementation directly by reduction at source
Innovative technologies e.g. higher load factor, fuel-optimized flight trajectories, alternative fuels, lower-cruise speeds
Impact of Non-CO2 emissions can be reduced by changing cruise altitudes and eco-efficient flight trajectories
non-CO2 emissions have much shorter lifetime than CO2
highly dependent on chemical and meteorological ambient conditions
- This means a reduction of the absolute emission due to lower specific emissions.

14. 3. Optimization of flight trajectories
optimization of flight trajectories regarding the effects of NOx requires a cost function which depends on several parameters
climate impact depends on:
Time of emission (daytime and season)
Location of emission:
altitude h
latitude φ
longitude λ
The climate impact of these depends on the time of emission the daytime as well as the season because of the differences in radiation and photochemical activities.

15. 3. Optimization of flight trajectories
NOx are emitted in upper troposphere and lower stratosphere (UTLS)
pollutants have much higher residence time than on ground
washout much more slowly and the ozone Radiative Forcing (RF) reaches its maximum
Climate impact can be reduced by operational change in cruise altitude towards a lower flight level (FL).
Especially, the NOx emitted during the cruise flight in the upper troposphere and lower stratosphere have a significant relevance.

16. 3. Optimization of flight trajectories
design of eco-efficient flight trajectories can be implemented by a cost function (CF) which depends on location, altitude and time of emission
CF determines climate impact of a unit emission for each space and time
calculation by an integral over the total emissions of a flight trajectory
climate impact reaches its minimum if the integral reaches minimum by varying the trajectory
minimization of climate impact is accompanied by an increase in operational costs
This approach is similar to the determination of flight trajectories with minimal operational costs just with different parameter which means flight time, fuel consumption and operational costs.

17. 3. Optimization of flight trajectories
INPUT
OUTPUT
Flight Data
Model for generating Flight Trajectories
Eco-optimized Flight Trajectories:
climate impact
fuel consumption
operational costs
Black Box
Emission Model
To optimize trajectories with regard to the impact of NOx on climate change, an access to different data and models is absolutely necessary.
At first, all flight data are required.
all existing air links have to be extracted
airport origins, destinations, aircraft and engine types, departure times, reference trajectories based on minimal operational costs
The Model for generating Flight Trajectory
- simulation environment of the air traffic flow.
- 4D trajectories can be generated for any flight regarding origin and destination airport and possible restrictions on the flight path
- considering various cost functions and optimization intentions
- minimization of climate impact requires the implementation of a climate cost function.
The third needed element is the Emission model.
- determines the actual fuel consumption as well as the emitted amount of nitrogen oxides depending on the type of aircraft type/engines for the chosen flight trajectories.
The next required part is the model of the global atmosphere, a chemistry transport model.
- chemical, physical and meteorological characteristics and processes within the atmosphere
- tropospheric and stratospheric properties as well as the interaction with oceans, continents and anthropogenic influences
Also, the definition of a globe-spanning grid is essential.
- low resolution to cover as many points all over the globe.
- For each grid point various levels of altitudes has to be defines to cover the standard cruise altitude as well as altitudes up to ft above and ft below.
 - temporal division of the day is necessary to evaluate the climate impact depending in daily variations
- hourly division is recommendable to cover all individual influences such as changing radiation and the associated photo-chemical activity in the atmosphere
- designated elements have to be combined to determine consequently trajectories and their climate impact, first based on minimal operational costs and subsequently based on minimal climate impact.
- This is accomplished by the use of the climate cost function, I´ve already mentioned.
- Finally, alternative routes with less climate impact are calculated based on trajectories with optimal operational costs
Model of Global Atmosphere
Grid Model

18. 3. Optimization of flight trajectories
3.2 Qualitative optimization strategies
general strategies for generating trajectories with reduced climate impact of NOx
Vertical variation
Decreasing standard flight altitude:
Fuel consumption ↑ RFO3 ↓
NOx ↑ RFCH4 ↓
O3 ↓ RFNOx ↓
CH4 ↓
Altitudes with minimal climate impact for transatlantic region:
Westbound: FL 310 (9448 m)
Eastbound: FL 320 (9753 m) 3
These will lead to a reduction of climate impact of NOx emissions.
- In general, fuel consumption decreases with an increasing altitude and the amount of emitted nitrogen oxides decreases
- reduction of cruise altitude a contrary development applies
- consumption increases and an increase of NOx applies
the impact of an equal amount of NOx on the radiation budget at standard cruise altitude is higher than ft below
- caused by a decreasing NOx background concentration and temperature with increasing altitude
- In general, a low NOx background concentration leads to a more effective ozone production.
- That means, the ozone production increases with an increasing altitude and decreases with a decreasing altitude.
- Also the increasing life time of ozone precursors with increasing altitudes, due to slower washout, contributes to this effect.
Furthermore, the reduction of methane is higher with a decreasing altitude
the radiative forcing for methane and ozone increases with increasing altitude which leads to a higher total radiative forcing of nitrogen oxides.
- if the standard cruise altitude decreases the Radiative Forcing for Methane, ozone and of course for NOx decreases which leads to a lower climate impact.
- transatlantic region exact statements for an altitude with minimal climate impact were estimated.
- differences between Westbound and Eastbound flights caused by the consideration of wind systems.
- altitudes with a minimal climate impact are ft beneath the altitude for minimal economic costs.
- Detailed calculations like this have to be considered for all regions to derive eco-efficient flight altitudes for each region on earth.
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3 Grewe et al., “Reduction of the air traffic´s contribution to climate change: A REACT4C case study,” Atmospheric Environment 94, pp , 2014

19. 3. Optimization of flight trajectories
(2) Lateral and longitudinal variation
Lateral variation
Low latitudes:
O3 ↑ RFO3 ↑
CH4 ↓ RFCH4 ↓
RFNOx ↑ (dominating O3–effect)
same amount of NOx emission leads to lower RFNOx in higher latitudes than in lower latitudes
- NOx emissions in higher latitudes have longer lifetimes causes by a slower washout
- Also the production of ozone is lower, because of the lower solar radiation and photochemical activity at higher latitudes.
- In addition, the changes caused by methane and PMO are more effective.
- Therefore, the radiative forcing is often negative in higher latitudes.
- The warming ozone RF almost compensates the cooling methane and PMO RF.
- Emissions at low latitudes are leached more quickly which leads to a shorter lifetime but in general the ozone production increases.
- The lower the latitude or the closer to the equator, the efficiency of O3 production per emitted NOx molecule and the lifetime of methane increases.
- But the effect of increasing O3 dominates which induces a positive rate of change for low latitudes.
- This results in a higher warming potential.
- That means, the same amount of emitted nitrogen oxides leads to a lower radiative forcing in higher latitudes and to higher RF in lower latitudes.

20. 3. Optimization of flight trajectories
(2) Lateral and longitudinal variation
Longitudinal variation
same amount of NOx with longitudinal difference of 30° over north atlantics induces different RF
weather dependence- air mass movement in different directions
one air parcel is transported in tropical regions and the other remains in mid-latitudes - RFNOx in tropical region 7 times larger than in mid-latitudes
Shifting centers of trajectories in the transatlantic region:
Westbound: South and West direction
Eastbound: North and East direction3
- In order to reduce climate impact, also for the lateral and longitudinal variation exact measures for the transatlantic region have been researched.
The climate impact of Westbound flights will be reduced by shifting the center of trajectories in South and West direction.
For eastbound flights the opposite applies, so the centers have to be relocated towards east and north direction.
- Also detailed studies need to be conducted for all remaining regions of the world to include all wind systems and to be able to make recommendations of this kind for all regions.
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3 Grewe et al., “Reduction of the air traffic´s contribution to climate change: A REACT4C case study,” Atmospheric Environment 94, pp , 2014

21. 3. Optimization of flight trajectories
(3) Variation of oceanic and continental air corridors
O3 production efficiency significantly higher above oceans than over continental regions
in Northern hemisphere difference goes up to 34%
lower concentration of NOx in atmosphere above oceans because of less contamination
Oceanic air corridor:
NOx background
concentration ↓ RFO3 ↑
O3 ↑ RFNOx ↑
Avoiding oceanic air corridors if there are alternative flight paths above continental regions
- There are differences between the induced climate impact above oceans and continents.
- As I already explained, a lower background concentration leads to a higher efficiency of ozone production
- That’s why the radiative forcing for ozone is higher above oceans than for the same amount of emitted NOx above continents which leads to a higher total radiative forcing for nitrogen oxides.
- Consequently, the avoidance of oceanic regions during the cruise flight if there are alternative flight corridors above continental regions, offers a potential to reduce the climate impact of NOx.

22. 3. Optimization of flight trajectories
3.3 Assessment of NOx calculations
evaluation of determined amounts of NOx for the applied emission models
from a variety of emission models Döpelheuer, Boeing Fuel Flow Method 2 and DLR Fuel Flow Method were selected because they reflect the state of the art
models use different parameters for the calculation which indicates different distributions of total amount of emitted NOx
-….for the individual models and flight altitudes

23. for an altitude of 13.000 m flight time increases again
flight time decreases continuously with increasing altitude from to m
for an altitude of m flight time increases again
engines are not designed for efficient operating in low altitudes like or m
fuel consumption reaches minimum at cruise altitude of m
This figure represents the fuel consumption and the flight time for the ranges of and km depending on the altitude.
For and altitude of m the flight time increases again because each engine operates most efficiently in terms of operational costs at a certain altitude and the A320 is not designed for such high cruise altitudes.
Fig. 1: Fuel burn and flight time for flight distances and km depending on cruise altitudes

24. maximum values at altitude of 13.000 m
minimum of emitted amount of NOx for flight distances 2.000, 3.000, and km at a cruise altitude of m for all models
for km same location of minimum for BFM2, for DLR and DH it is located at altitude of m
maximum values at altitude of m
Emission models show consistent position of minimum and maximum and general distribution of emission amounts
This figure presents the profiles for the determined nitrogen oxides for all three models exemplary for the flight distances of and km.
It shows clearly the differences between the amounts depending on the applied correlation model.
The 3 curves at the top show the distribution for the range of 4000 km and the 3 curves at the bottom represent the range of km.
These curves and even the distribution for two further considered flight distances, for and km, represent a Minimum of emitted nitrogen oxides at a cruise altitude of m.
In general, the considered
This leads me to me next point….
Fig. 2: Emitted NOx for Boeing Fuel Flow Method 2 (BFM), DLR Fuel Flow Method (DLR) and Döpelheuer (DH) for flight distances and km depending on cruise altitude

25. 3. Optimization of flight trajectories
3.4. Recommendations for eco-friendly trajectory design
Decrease of standard cruise altitude
Lowering the standard flight altitude to m represents not only the least pollution of the atmosphere and also of the environment in terms of emission quantity but also a minimum with respect to the climate impact.
(2) Lateral trajectory optimization towards higher latitudes
(3) Avoidance of oceanic air corridors
..general recommendations for an eco-friendly trajectory design
- A flight altitude of m represents not only the least pollution of the atmosphere and also of the environment in terms of emission quantity, like I´ve just explained on the last presentation slide, but also a minimum with respect to the climate impact.
- This means, the derived recommendation from the evaluation of the calculated emitted amount of NOx is content-wise based by former research results with regard to the minimum of the climate impact.
As well, the…. Offer the potential to reduce the climate impact of nitrogen oxides, as I recently explained.

26. 4. Conclusions
possible approaches for reducing NOx climate impact through changed trajectories were examined
air traffic is the only emitter of pollutants in UTLS
3 emission models were considered which require knowledge of various engine parameters
exact knowledge of the processes in atmosphere and specific characteristics and weather conditions are absolutely necessary
influence of winds on the amount and distribution of nitrogen oxides in the atmosphere should be considered in a further study
- Just a quick recab: During this work, …
- Air traffic has a special contribution,
- To know the exact impact on the climate the calculation of the exact amount of emitted NOx is required.
Furthermore, exact….., which includes solar radiation and photochemical activities.

27. 4. Conclusions
The horizontal and vertical variation of trajectories as operational approach to minimize the climate impact offers the potential in order to protect the environment and the climate sustainably.
in future it will be more important to know the interaction between all emitted pollutants
optimization with respect to one specific emission may bring disadvantage for another
environmental awareness in aviation has to increase to implement new eco-friendly slight operation strategies despite financial disadvantages
All in all,…
- All airlines are operating very close a fuel and operating costs optimum
- This means, a variation of trajectories regarding to minimal climate impacts always implies an increase of operational costs.
- For this purpose, the environmental awareness in aviation industry has to increase to implement eco-friendly flight operation strategies despite financial disadvantages.
This brings me to the end of my presentation.

28. Thank you for your attention.
Thank you all for listening and your attention, it was a pleasure to be here today.