Greenhouse gas emissions from international aviation and allocation options

8 Aircraft emission inventories and reporting guidelines

8.1 EMEP/CORINAIR reporting guidelines
8.2 ANCAT/EMCAL reporting guidelines
8.3 EUROSTAT/EUROCONTROL&TRENDS emission inventory
8.4 Global emission inventory models
8.5 Discussion on emission inventories

This chapter gives a brief summary of some main methodologies for calculating emissions from air transport, focusing mainly on the European CORINAIR methodology.

8.1 EMEP/CORINAIR reporting guidelines

One example of a detailed programme for calculating emissions from aircraft is contained in the so-called CORINAIR (Core Inventory of Air Emissions in Europe) that has been developed under EMEP (Co-operative Programme for Monitoring and Evaluation of the Long Range Transmission of Air Pollutants in Europe) to support countries participating in the European-wide emission inventory programme EMEP/CORINAIR.

The CORINAIR methodology is continually being refined and updated and the current version is published in the "third Edition Emission Inventory Guidebook", published electronically via the European Environment Agency Internet web site. A further revision of the Guidebook is anticipated in late 2002 [CORINAIR 2001].

Until recently the CORINAIR methodology for calculating aircraft emissions contained only guidelines for calculating fairly detailed landing and take off (LTO) and more rough cruise emission estimates [Winther 2001]. In the later years the CORINAIR system has been updated. The main improvements are the inclusion of more aircraft types and fuel use and emission data per distance flown for those aircraft (see Table 6 and Figure 16) [CORINAIR 2001]. A recent Danish report exemplifies that the detailed CORINAIR methodology can produce markedly other results than the old methodology. For Denmark, the use of the detailed CORINAIR methodology has, among other things, doubled the national estimate for fuel consumption for domestic aviation [Winther 2001].

Within different countries, there may be large differences in the resources and data availability as well as the relative importance of aircraft emissions. Therefore, within CORINAIR, three methodologies, the Very Simple Methodology, the Simple Methodology and the Detailed Methodology, have been developed for calculating emissions from air traffic. Furthermore, some Member States use national models that may be more detailed than the CORINAIR Detailed Methodology, using additional detailed data such as specific engines and specific LTO operating times.

Table 5:
Overview of CORINAIR methodologies [Corinair 2001]

 

 

LTO

Cruise and climb

Very Simple

Activity
  
  
  
Emission factor

LTO aggregated
Time-in-mode (ICAO)
 
 
Generic aircraft

Fuel residual
 
 
 
Generic aircraft

Simple

Activity
  
 
  
Emission factor

LTO per aircraft type (generic aircraft)
Time-in-mode (ICAO)
  
Per aircraft type

Fuel residual
  
 
 
One generic aircraft

Detailed

Activity
 
 
 
 
 
 
 
Emission factor

LTO per aircraft type (generic aircraft)(option also engine type)
Time-in-mode: Actual if available otherwise ICAO
 
 
 
Per aircraft type (generic aircraft) (option also engine type)

Distances flown
Independent estimate of cruise fuel use
  
  
  
   
 
Per aircraft type (generic aircraft) and distance flown


The difference between the methodologies lies mainly in the aggregation level assumed for the number of aircraft types in the aircraft fleet. In the Very Simple Methodology, estimations are made without considering the actual aircraft types used. The Simple Methodology requires information on the types of aircraft that operate in the country. The Detailed Methodology takes into account cruise emissions for different flight distances.

The three methodologies require different types of data. For the Very Simple Methodology only the total quantity of fuel consumed for domestic and international flights and the total number of aircraft movements for domestic and international flights is needed. The Very Simple Methodology can be used when the number of aircraft movements is known, but the individual aircraft types and their routes are not. The Simple Methodology may be used when additional data on movements by aircraft types used on domestic and international routes are available, but the precise destinations are not available. The Detailed Methodology may be used when data on individual aircraft movements as well as details of departure and arrival airports of individual aircraft on domestic and international flights are known.

When preparing an emission inventory, using one of the three CORINAIR emission calculation methodologies, grouping of the aircraft fleet into representative aircraft categories is used for the calculations in LTO and cruise. In the Very Simple Methodology only a few representative aircraft are included. The Simple methodology is more detailed using 19 representative aircraft categories for calculating LTO emissions while, like it is the case in the Very Simple methodology, only a few representative aircraft categories are used for calculating fuel used and emissions in cruising mode. In the detailed methodology calculations of fuel used and emissions in both LTO and cruise are modelled through using average data on fuel consumption and specific emissions in the LTO phase as well as the cruise phase, including detailed estimates of the specific fuel consumption in cruising modes of different lengths, for around 30 representative categories of aircraft which are meant to represent the world's civil jet fleet. An example of the type of data on fuel consumption and emissions used in the Detailed CORINAIR methodology is shown in Table 6. Recently additional data on a number of turboprop powered regional aircraft has been added, raising the level of detail further.

Table 6:
Example of fuel and emission data for Airbus A330 aircraft used CORINAIR Detailed methodology [Corinair 2001].

Look here!

As illustrated in Table 6, the data used in the Corinair detailed methodology takes into account that the specific amount of emissions of gases from aircraft engines per amount of fuel burnt vary between phases of flight. The methodology also takes into account that the specific fuel burn per kilometre of aircraft depends strongly on the flight distance. As can be seen from Figure 16 the fuel burn per aircraft kilometre is comparably higher on relatively short distances than on longer routes. This is because the aircraft uses a relatively high amount of fuel per kilometre for the landing and take off (LTO) cycle as compared to the cruising phase.

Figure 16:
Examples of data on specific fuel consumption per kilometre for generic/representative aircraft categories used on long-range (upper part of the figure) and on short- and medium range (lower part of the figure) for trips of varying lengths [Falk 1999]

To sum up, countries that participate in the EMEP/CORINAIR inventory programme can choose to use the type of methodology that fits the national data availability and the resources available for the calculations. The advantage of the simple methodology over the very simple methodology is that the emission estimates for the LTO phase become more accurate when using more detailed aircraft data, whereas the estimates for the cruise phase become more accurate when using the detailed CORINAIR methodology or similar country specific models.

8.2 ANCAT/EMCAL reporting guidelines

In 1998 the European Civil Aviation Confence's (ECAC) Group of Experts on the Abatement of Nuisances caused by air transport (ANCAT) decided to establish a sub-group (EMCAL) dealing with emissions calculations. EMCAL circulated a questionnaire on emission matters to 37 ECAC Member States. Because the replies to the questionnaire indicated considerable variations among Member States in methodologies used for emission calculations and reporting ANCAT has produced an "ECAC Recommendation on Methodology for Emissions Calculations" [ECAC 2002a] and accompanying "ECAC/ANCAT/EMCAL Guidance Material" [ECAC 2002b] that was finally approved by ECAC Directors General March 2002.

The ANCAT methodology is basically based upon the EMEP/CORINAIR methodology and consists of three methods, ANCAT 1, ANCAT 2 and ANCAT 3, with different levels of accuracy and complexity, in line with the CORINAIR Very Simple, Simple and Detailed methods. In its "ECAC Recommendation on Methodology for Emissions Calculations" ECAC encourages Member States to calculate the emissions of aviation as accurately as possible using ANCAT method 3 (the most detailed methodology described in the ANCAT Guidance Material). If Member States are not able to use such a detailed methodology or are unable to obtain detailed information on distances flown, they may use the less detailed ANCAT 2 methodology. If Member States are unable to obtain detailed information on aircraft types, they may use the least detailed ANCAT 1 methodology. If a peer reviewed and well-documented national methodology is available, which is more accurate than ANCAT method 3, Member States may use this national methodology when producing emission inventories.

However, probably the most important message of the ECAC Recommendation seems to be that Member States are urged, "to progressively refine and improve the level of accuracy in recording aircraft emission data. States should aim towards calculation of emissions from their aviation activity in accordance with ANCAT method number three or a peer reviewed and well documented national methodology in order to achieve the best practicable level of accuracy [ECAC 2002b, Article 5].

8.3 Eurostat/Eurocontrol/TRENDS emission inventory

The European Commission has started informal discussions with EUROCONTROL, the European Organisation for the Safety of Air Navigation, with a view to possibly concluding an agreement aimed at improving the monitoring of the environmental impacts of civil aviation in Europe. The objective of cooperation would be to enable the European Commission and the EU Member States to monitor better the environmental impact of civil aviation in Europe, in particular as regards GHG emissions, and to provide a basis for better transport statistics in the aviation sector. Eurostat participate in the discussions.

A major element of the envisaged cooperation would be the development of systems to support a regular, sustained supply of consistent and accurate data on emissions from aviation in Europe, including the split on various types of aviation (domestic, intra-EU, international, etc.).

In this context, EUROCONTROL is in a unique position to be able to provide the necessary information due to its role in pan-European air traffic management (ATM). Within EUROCONTROL, the Central Flow Management Unit (CFMU) continuously monitors the airspace and flow management situation throughout Europe. All aircraft operators must notify the CFMU of their intention to operate a civil aviation flight under Instrument Flight Rules (IFR) condition by filing a flight plan. Thus, the EUROCONTROL air traffic movement database constitutes a unique source of consistent, detailed and continuously updated information on every processed IFR flight operation within Europe. It should be noted that Visual Flight Rules (VFR) flights and Military Operational Air Traffic (AOT) generally are not operated as controlled flights and thus are not included in the EUROCONTROL air traffic movement database.

One advantage offered by use of Eurocontrol data is that those Member States who have not been able to make reliable splits between fuel consumption at domestic and international routes will be able to make use of these data in a number of ways: traffic split, fuel consumption split or emissions split. Furthermore the project holds the advantage that international intra-EU flights can be reported separately. As discussed in chapter 7 such data may be needed in the future for the reporting of emissions in the European Union as a whole to the UNFCCC, if international intra-EU flights are to be reported as domestic [Lock 2002].

Recently, Eurostat has produced fuel consumption estimates within a project called TRENDS, which was primarily intended to produce environmental indicators for transport. The TRENDS model is based on the detailed CORINAIR methodology (see section 8.1 for a description of the CORINAIR methodology). IFR (Instrumental Flight Rule) flight data are provided by Eurocontrol and are used to produce estimates of fuel consumption and emissions for each airport/region pair, aircraft type, and time period, split by takeoff, cruise and landing. This is a rather large (350 MB) database in MS Access computing around 75 000 calculations per country per year [Lock 2002].

Table 7:
Comparison between total CO2 emissions from international and domestic aviation in 1999 for selected countries according to Eurostat/TRENDS versus UNFCCC data [Million tonnes of CO2]. Sources: [UNFCCC 2002b] and [Eurostat 2002].

 

Eurostat/TRENDS

UNFCCC

UNFCCC/Eurostat

Austria

1.663.200

1.725.139

96%

Czech Republic

554.400

551.674

100%

Denmark

2.475.900

2.464.143

100%

Spain

12.874.050

12.568.019

102%

Finland

1.552.950

1.523.000

102%

France

19.775.700

19.820.920

100%

Greece

3.937.500

3.945.230

100%

Ireland

1.622.250

1.623.788

100%

Italy

10.902.150

9.865.000

111%

Luxembourg

1.017.450

1.019.120

100%

Netherlands

10.391.850

10.486.430

99%

Norway

2.321.550

2.096.391

111%

Portugal

2.271.150

2.046.555

111%

Sweden

2.879.100

2.898.402

99%

United Kingdom

31.203.900

28.361.328

110%


Preliminary results of the TRENDS model are shown in Table 7 and Figure 17. Table 7 compares the results for total fuel consumption for domestic and international aviation computed in the TRENDS model to the fuel consumption data reported by selected European Annex I countries to the UNFCCC in 1999. For the countries shown in Table 7 the data calculated in TRENDS are fairly close to the data reported to the UNFCCC for most countries. However, for some of the countries that are not included in Table 7 the differences are very great and the variation between years is also large [Eurostat 2002]. The reason for not including the results for those countries is that they have not reported domestic and international fuel consumption data to the UNFCCC [UNFCCC 2002c].

Figure 17 illustrates that for most of the European Annex I countries that have reported fuel consumption for domestic and international aviation to the UNFCCC the share of fuel used for international aviation activities is quite close to what is reported from countries. However, for two of the countries shown here the TRENDS model seem to estimate that a much larger share of the fuel is used for international aviation than what is reported to the UNFCCC.

Figure 17:
Comparison between the split between international and domestic according to Eurostat/Eurocontrol versus UNFCCC data. See Appendix I for further data. Sources: [UNFCCC 2002b] and [Eurostat 2002].

This initiative from the European Commission, Eurostat and EUROCONTROL may improve the data material and may also give the European countries the possibility to crosscheck their data to the data from Eurostat.

8.4 Global emission inventory models

A number of different models have been developed to compute threedimensional (latitude, longitude, altitude) global inventories of civil (and military) aircraft fuel consumption and emissions. For example, such models have been developed by NASA (United States National Aeronautics and Space Administration), by ANCAT/EC (Group of Experts on the Abatement of Nuisances from Civil Air Transport/European Commission), by DLR (the Deutsches Zentrum für Luft- und Raumfahrt) and by the Dutch Ministry of Transport (AERO model). All four studies use models based on methodologies where the aircraft fleet is divided into a number of representative aircraft categories.

IPCC has compared the results of the three first mentioned models for 1992, noting that the inventory calculations are in good agreement, with total fuel used by aviation globally (including military aircraft) ranging between 129- 139 million tonnes and total emissions of NOx (as NO2) ranging between 1.7- 1.8 million tonnes. Of these estimates between 17-26 million tonnes are consumed by military aircraft and around 4 million tonnes are consumed by general aviation. The estimates for the fuel consumed by civil commercial aviation (scheduled plus charter traffic) thus ranges between 110-112 million tonnes [IPCC 1999].

Later published results from the Dutch Ministry of Transport (AERO model) estimate fuel consumption about 17% higher because it uses a more comprehensive flight database. According to the AERO model calculations global aviation fuel consumption for civil scheduled and charter traffic and general aviation equals around 134 million tonnes in 1992, while emissions of NOx are estimated at 1,7 million tonnes [Pulles 2000a]. The 134 million tonnes of fuel is still significantly lower than the 165 million tonnes estimated for the same year by the IEA on the basis of fuel sales statistics (in 2000 the fuel consumption for aviation has grown to around 209 million tonnes [IEA 2002]). A part of the residual 31 million tonnes may have been consumed by military aircraft (estimated at between 17-26 million tonnes by NASA and ANCAT) and the authors of the report describing the AERO results note that a likely further explanation may be that statistical sources on global aviation fuel-use may not take into account that kerosene can be used for other purposes than aviation [Pulles 2000a].

The global inventory models described here are unfortunately only available for the year 1992.

8.5 Discussion on emission inventories

Currently Parties to the UNFCCC can use different methodologies of varying detail in their reporting of aviation emissions to the UNFCCC. A recent ECAC initiative may encourage European countries that participate in ECAC to begin using the Detailed Corinair Methodology for calculating aircraft emissions (see section 8.2). This may increase comparability and accuracy in the reporting from these countries to the UNFCCC.

Another recent initiative from the European Commission, Eurostat and EUROCONTROL, the TRENDS project, may also improve the data material and may also give the European countries the possibility to crosscheck their data to the data from Eurostat. The TRENDS initiative also opens the possibility of calculating fuel use and emissions separately for intra EU flights. As discussed in the previous chapter such data may be needed for the EU emission inventory for the UNFCCC in the future.

In the current situation only Annex I countries report emissions from aviation to the UNFCCC, but around one third of the CO2 emissions from international aviation bunkers in 1999 relate to fuel sold in non-Annex I countries that have not yet agreed to reduction targets under the Climate Convention. Much of the fuel sold in non-Annex I countries may be consumed by airlines registered in Annex I countries or may be consumed by airlines transporting passengers and goods originating from Annex I countries. In case CAEP/ICAO intends to set up an emissions trading scheme the development of a yearly updated global inventory may be useful for calculating the total emissions from aviation, and more exact figures than those available today may also be needed to set up the system. A few global inventories have been conducted, but to the knowledge of the author of this report only for the year 1992, and these inventories are neither as detailed as for example the detailed CORINAIR methodology and neither do they contain accurate data on flights actually performed by all airlines globally.

A working group "Alternative Emissions Methodology Task group" has been set down by CAEP aimed at understanding cruise emissions from aviation. Similarly, the European Commission is currently funding a programme in this area called "NEPAIR". At this time, both projects are seeking to establish methodologies, but not standards, that could be used for certification of aircraft engine cruise emissions, that may be ready by 2003. Currently, the ICAO Emissions Databank only contains certificated data for LTO emissions but these new initiatives may in the future lead to recommendations for the development of standards for engine emissions at cruise [NEPAIR 2002].