1.A.3.a - Transport: Civil Aviation

Air transports differ significantly from land and water transports with respect to emissions production. In air transports, fuels are burned under atmospheric conditions that a) differ markedly from those prevailing at ground level and b) can vary widely.

The main factors that influence the combustion process in this sector include atmospheric pressure, environmental temperature and humidity – all of which are factors that vary considerably with altitude.

In category 1.A.3.a - Civil Aviation the emissions from both national (domestic) and international civil aviation are reported with separate acquisition of flight phases LTO (Landing/Take-off: 0-3,000 feet) and Cruise (above 3,000 feet) where only emissions from LTO from both national and international flights have to be included in the national totals.

Emissions from military aircraft are not included in this category but are reported under military airborne combustion in NFR sub-category 1.A.5.b ii.

Country specifics: The use of aviation gasoline is assumed to take place within the LTO-range of domestic flights only (below 3,000 feet). This assumption is a compromise due to a lack of further information and data.

NOTE: Data available from Eurocontrol via the European Environment Agency (EEA) is not being used for inventory compilation. Nonetheless, depending on its timeliness, it is taken into account for verification purposes.

Estimation of aircraft emissions has been carried out using a tier 3a approach, i.e. under consideration of the annual distances flown by different types of aircraft, deviated into domestic and international flights, also considering the different flight stages L/TO cycle (Landing/Take-off cycle, i.e. aircraft movements below 3,000 feet or about 915 meters of altitude) and cruise.

Essential for emissions reporting is the separation of domestic and international air traffic. This happens using a so-called split factor representing the ratio of fuel consumption for national flights and the over-all consumption.

For determination of this ratio, results from TREMOD AV (TRansport Emissions MODel AViation) have been used, based on the great circle distances flown by the different types of aircraft (Allekotte et al. (2025) ¹⁾. Here, the ratio is calculated on the basis of statistics on numbers of national and international flights departing from German airports provided by the Federal Statistical Office (Statistisches Bundesamt).

For further dividing kerosene consumption onto flight stages LTO and cruise, again results calculated within the TREMOD AV data base based on data provided by the Federal Statistical Office have been used.

Emissions are being estimated by multiplying the kerosene consumption of the flight stage with specific emission factors (EF). Here, emissions of SO₂ are independent from the method used, depending only on the quantity and qualities of the fuel used. In contrast, emissions of NO_x, NMVOC, and CO strongly depend on the types of engines, flight elevations, flight stage, etc. and can be estimated more precisely with higher tiers. The emission factors for NO_x, CO, and NMVOC are therefore computed within TREMOD AV.

The aviation gasoline (avgas) used is not added to the annual kerosene consumptions but reported separately. As proposed in (IPCC, 2006a) ²⁾, emissions caused by the incineration of avgas are calculated using adapted EF and calorific values following a tier1 approach.

For further information on AD (entire time series), EF, key sources, and recalculations see sub-chapters linked above.

Emissions estimation is mainly based on consumption data for jet kerosene and aviation gasoline as provided in the national Energy Balances (AGEB, 2025) ³⁾. For very recent years with no AGEB data available (Normally the last year of the period reported.) data provided by the Federal Office of Economics and Export Control (BAFA) ⁴⁾ is being used.

Table 1: Sources for 1.A.3.a activity data

Table 2: Total inland fuel deliveries to civil aviation, in terajoules

For the present purposes, kerosene-consumption figures from NEB and BAFA statistics have to be broken down by national (= domestic) and international flights: Here, the split has been calculated on the basis of statistics on numbers of national and international flights departing from German airports provided by the Federal Statistical Office (Statistisches Bundesamt) within TREMOD AV ⁶⁾.

Table 3: Ratios for calculating the shares of fuels used in 1.A.3.a ii - Domestic and 1.A.3.a i - International Civil Aviation, in %

Table 4: Resulting annual shares of jet kerosene and avgas used in 1.A.3.a ii - Domestic and 1.A.3.a i - International Civil Aviation, in [TJ]

The deviation of the kerosene consumed onto the two flight stages L/TO and cruise again has been carried based on TREMOD AV estimations allowing the export of kerosene consumption during L/TO for both domestic and international flights.

Table 5: Annual shares of L/TO stage in domestic and international civil aviation, in %

Cruise consumption is then calculated as Total inland deliveries minus consumption druing L/TO.

Emissions have been calculated for each flight phase, based on the respective emission factors. Therefore, the EF used have been taken from a wide range of different sources. In contrast to earlier submissions, the emissions of NO_x, CO und HC are based on aircraft-specific EF deposited within TREMOD AV. With this very detailed estimations average EF are being formed which are than used for emissions reporting.

The EF provided with the current submission represent annual average EF for the entire fleet, calculated as implied EF from the emissions computed within TREMOD AV and therefore differ from the values used in the past.

Sulphur dioxide (SO₂) emissions depend directly on the kerosene's sulphur content which varies regionally as well as seasonally. The EF used by Eurocontrol of 0.84 kg SO₂/t kerosene lies between the values used for German inventory for 1990 to 1994 (1.08 to 1.03 kg SO₂/t) and from 1995 (0.4 kg SO₂/t). In IPCC 2006b ⁹⁾ with 1 kg SO₂/t kerosene value comes very close to the old inventory values provided, based on a sulfur content of 0.05 % of weight. Following current information of the expert committee for the standardization of mineral oil and fuels (Fachausschuss für Mineralöl-und Brennstoffnormung, FAM), the common value for sulphur content of kerosene in Germany is about 0.01% of weight, i.e. one fifth of the IPCC data. In IIR 2009, a sulfur content of 0.021 weight% have been used, based on measurements from 1998 (Döpelheuer (2002)) ¹⁰⁾.

As an EF decreasing due to improved production procedures and stricter critical levels seems plausible, for this report a constant decline between the annual values of 1.08 g SO₂/kg for 1990, 0.4 g for 1998 and 0.2 g for 2009 has been assumed. Thereby, an exhaustive conversion of the sulfur into suflur dioxide is expected. - Due to the EF depending directly on the S content of the kerosene, one annual EF is used for both flight stages.

Nitrogen oxide (NO_x), carbon monoxide (CO) and hydrocarbons (HC) emissions were estimated using IEF calculated within TREMOD AV, based upon more specific (depending on type of aircraft, flight stage) EF mostly taken from the EMEP-EEA data base. For 2009, 40 % of over-all starts (about 70 % of total kilometres flown) had to be linked with adapted EF as it was not possible to directly or even indirectly (via similar types of aircraft) allocate the aircraft used here. Therefore, regression analysis had to be carried out, estimating EF via emission functions that calculate an EF for the respective type of engine depending on the particular take-off weight.

As a basis for these functions the EF of types of aircraft with given EF have been used (see: Allekotte et al. (2024)) ¹¹⁾. From the trend of the emissions calculated within TREMOD AV, annual average EF for the entire fleet have been formed, which have then been used for reporting. Hence, the EF differ widely from those used in earlier submissions.

Ammonia (NH₃) emissions were estimated using an EF of 0.173 g/kg kerosene for both flight stages (UBA, 2009) ¹²⁾.

The EFs for non-methane volatile organic compounds (NMVOC) were calculated as the difference between the EF for over-all hydrocarbons (HC) and the EF for methane (CH₄).

Particulate Matter Within the IPCC EF data base, there are no default data provided for emissions of particulate matter (TSP, PM₁₀, and PM_2.5). Therefore, the EF for dust (Total Suspended Particulate Matter – TSP) are taken over from Corinair (2006) ¹³⁾, giving specific values for an average fleet and for the two flight stages in table 8.2: For national flights 0.7 kg TSP/LTO and 0.2 kg TSP/t kerosene and 0.15 kg TSP/LTO and 0.2 kg TSP/t kerosene for international flights. Following this table, a kerosene consumption per LTO cycle of 825 kg for national and 1,617 kg for international flights have been assumed and the EF for the LTO stage have been estimated.

Regarding Black Carbon, f-BC fractions from EMEP/EEA guidebook 2023, Chapter 1.A.3.a, 1.A.5 - Aviation, Annex 3, Table A3.2 and Conclusion have been applied for both jet kerosene and aviation gasoline. (EMEP/EEA, 2023) ¹⁴⁾

As for polycyclic aromatic hydrocarbons (PAH), tier1 EF from (EMEP/EEA, 2019) ¹⁵⁾ have been apllied here. As the EMEP guidebook does not provide original EF for jet kerosene, values provided for gasoline in road transport have been used here as a proxy and will be replaced by more appropriate data as soon as this is available.

The conversion of EF representing emissions per kilo fuel combusted [kg pollutant/kg kerosene] into energy related EF [kg pollutant/TJ energy] has been carried out using a net calorific value of 43,000 kJ/kg.

For aviation gasoline (avgas) a deviation onto LTO and cruise is assumed to be unnecessary. Therefore, there are no such specific EF used here. As for kerosene, the EF for NO_x, CO and HC have been taken from the calculations carried out within TREMOD AV. Here, for calculating aircraft specific NO_x, CO, and HC emissions corresponding EF from the EMEP-EEA data base have been used that have than been divided by the annual avgas consumption to form annual average EF for emission reporting.

With respect to fuel characteristics, there are no big differences between avgas and gasoline used in passenger cars (PC). Therefore, specific sulphur dioxide (SO₂) emissions from PC gasoline can be carried forward to avgas. - Following the expert committee for the standardization of mineral oil and fuels (FAM), the critical value of sulfur content for gasoline sold at gas stations is 10 mg/kg, i.e. 0,001 % of weight - or one tenth of the kerosene value. Therefore, the EF used for avgas equals the EF used for kerosene reduced by 90 %.

There are different sorts of avgas sold with different lead (Pb) contents. As an exact annual ration of the sorts sold is not available, the most common type of avgas (AvGas 100 LL (Low Lead)) with a lead content of 0.56 g/l is set as an approximation. (see EMEP/EEA (2023), Chapter 1.A.3.a, 1.A.5.b Aviation, Annex 2, page 44, Table A2.1 ¹⁶⁾

The EF(TSP) were calculated from the lead content of AvGas 100 LL by multiplication with a factor 1.6 as used for leaded gasoline in road transport in the TREMOD system.

For NMVOC, an emission factor from the Revised IPCC Guidelines 1996 (pages I 42 and 40) ¹⁷⁾, ¹⁸⁾ is used.

All other emission factors are not available specifically for small aircraft and therefore have been equalized with the EF used for kerosene, national, cruise.

The conversion of the emission factors from [kg emission/kg avgas consumed] into [kg emission/TJ energy converted] has been carried out using a net calorific value of 44,300 kJ/kg.

NOTE: For the country-specific emission factors applied for particulate matter, no clear indication is available, whether or not condensables are included.

For information on the emission factors for heavy-metal and POP exhaust emissions, please refer to Appendix 2.3 - Heavy Metal (HM) exhaust emissions from mobile sources and Appendix 2.4 - Persistent Organic Pollutant (POP) exhaust emissions from mobile sources.

Total jet kerosene inland deliveries remainig unchanged for all years but 2023 within the National Energy Balances. On the other hand, avgas inland deliveries were revised for all years as of 2003 within the same National Energy Balances.

Table 7: Revised total annual inland deliveries of jet kerosene and avgas as provided in NEB line 63, in terajoules [TJ]

Furthermore, the domestic share of total kerosene consumption was revised for 2023 and based on slightly revised background data for this specific year computed within the underlying model, TREMOD Aviation:

Table 8: Revised percental share of kerosene used for domestic flights in 2023, in %

As a result, the amounts of jet kerosene allocated to NFR sub-categories 1.A.3.a i and 1.A.3.a ii and for 2023 had to be revised accordingly. Here, the activity data allocated to NFR 1.A.3.a i was reduced by the same amount by which the activity data allocated to NFR 1.A.3.a ii was increased:

Table 9: Revised amounts of fuel allocated to international (1.A.3.a i) and domestic (1.A.3.a ii) flights, in [TJ]

Besides the routine revision of the underlying model, no specific improvements are planned.

Uncertainty estimates for both activity data and emission factors were newly evaluated during the research project FKZ 3720 51 502 0: “Neubewertung der Unsicherheiten der mit den zurBerechnung der Luftschadstoffemissionen im Verkehrssektor verwendeten Parameter und Methoden” by Allekotte et al. with the final report published in 2023 ¹⁹⁾.

The uncertainty of the activity data is calculated via error propagation taking into accont the uncertainties of “incomplete data collection” (within the provider of the sales staistics, BAFA), “measurement uncertainty” and “attribution accuracy.” Based on information from BAFA, it is assumed that the standard deviation for the data collection is 0.51% (normal distribution)²⁰⁾. Regarding the measurement uncertainty, and using the 99.5% confidence interval to ensure compliance with the measurement tolerance and further assuming a normal distribution, a standard deviation of 0.2% can be obtained²¹⁾. Finally, regarding the accuracy of the distribution, a standard deviation of 0.55% (normal distribution) is derived²²⁾.

Taking into account the three uncertainties mentioned above, as well as the uncertainty regarding the calorific value, the relative uncertainties of sales in civil aviation can be derived using a Monte Carlo simulation (95% confidence interval) ²³⁾:

Due to the relatively low assumed calorific value in TREMOD, a skewed distribution function is obtained, tending towards higher values. For simplicity, a triangular distribution is assumed in the results.

Whereby does the party justify the adding-up of the two amounts provided by BAFA as deliveries 'An die Luftfahrt' and 'An Sonstige' ?

For mineral oils, German National Energy Balances (NEBs) - amongst other sources - are based on BAFA data on the amounts delivered to different sectors. A comparison with consumption data from AGEB and BAFA shows that data from NEB line 76 /63: 'Luftverkehr' equals to the amount added from both columns provided by BAFA ²⁴⁾.

On which basis does the party estimate the reported lead emissions from aviation gasoline?

assumption by party: aviation gasoline = AvGas 100 LL (see EMEP/EEA (2023): Chapter 1.A.3.a, 1.A.5.b Aviation, Annex 2, page 44, Table A2.1) ²⁵⁾ (AvGas 100 LL is the predominant sort of aviation gasoline in Western Europe) ²⁶⁾ lead content of AvGas 100 LL: 0.56 g lead/liter (as tetra ethyl lead) ²⁷⁾

The applied procedure is similar to the one used for calculating lead emissions from leaded gasoline used in road transport. (There, in contrast to aviation gasoline, the lead content constantly declined resulting in a ban of leaded gasoline in 1997.)

On which basis does the party estimate the reported TSP emissions from aviation gasoline?

The TSP emissions calculated depend directly on the reported lead emissions: The emission factor for TSP is 1.6 times the emission factor used for lead: EF(TSP) = 1.6 x EF(Pb). The applied procedure is similar to the one used for calculating TSP emissions from leaded gasoline used in road transport.