### Emissions from energy

#### Indicators:

CO2 emissions from energy use CH4 emissions from energy use N2O emissions from energy use SO2 emissions from energy use | NOx emissions from energy use NMVOC emissions from energy use CO emissions from energy uUse

The energy-related emissions of the major greenhouse gases, ozone precursors and acidifying compounds are presented for the nine energy sectors and five energy carriers distinguished by the Energy Demand and Supply model (TIMER) and the TIMER energy-industry Emissions Model (TEM).

The energy sectors include:

- five energy end-use sectors, i.e. industry, transport, residential (households), services (commercial and public) and other sectors (agriculture and other)
- energy consumption by electric power generation
- other energy transformation
- fossil fuel production (coal production, flaring of gas associated with oil production, gas transmission, etc.)
- marine bunkers (international shipping).

The energy carriers include:

- solid (coal and coal products)
- heavy liquid fuel (HLF) (diesel, residual fuel oil and crude oil)
- light liquid fuels (LLF) (LPG and gasoline)
- gas (natural gas and gasworks gas)
- modern biofuels (such as ethanol).

| #### CO2 emissions from energy use
| unit: Pg C/yr (Petagram of C per year) dimension: region, sector, energy carrier

Most of the energy-related CO2 emissions stem from fossil fuel combustion (energy production and consumption). These emissions are calculated by multiplying energy use with emission factors. With regard to biofuels (both traditional and modern) it is assumed that net carbon emissions to the atmosphere are zero. The energy-related CO2 emissions also include CO2 emissions from gas flaring.

CO2 emissions from energy, together with those from other sources, are used to calculate the CO2 concentration in the atmosphere and the resulting radiative forcing in the atmosphere-ocean system (AOS).

| #### CH4 emissions from energy use
| unit:Tg CH4/yr (Teragram of CH4 per year) dimension: region, sectors, energy carrier

The emissions from energy use stem from a variety of activities: fossil fuel extraction (CH4 emissions from coal mining, CH4 venting from oil extraction and gas production and supply), transport and distribution (e.g., leakages from pipelines), and consumption (incomplete combustion).

The historical emission factors of CH4 for these sources have been taken from the EDGAR database, whereas 1995-2100 period specific scenario assumptions related to changes in the emission factors by technological improvements (see scenario assumptions). The CH4 emissions from coal mining include those from surface and underground coal mining.

The CH4 emissions from energy are used in the atmospheric chemistry model (ACM) of the atmosphere-ocean system (AOS) to derive atmospheric concentrations.

| #### N2O emissions from energy use
| unit:Tg N/yr (Teragram of N per year) dimension: region, sector, energy carrier

Energy-use is a minor anthropogenic source of N2O. Energy-related N2O emissions stem primarily from transportation, energy end-use in the industry sector and power generation. The N2O emission factor from transport sources (energy carrier: LLF, i.e. gasoline) depends on the fraction of catalyst-equipped cars in the vehicle fleet and the age of catalysts, as well as the technological developments of these catalysts. Specific scenario assumptions are made for these emissions factors (see scenario assumptions).

N2O emissions are used in the atmospheric chemistry model (ACM) of the atmosphere-ocean system (AOS) to derive the atmospheric concentration of greenhouse gases.

| #### SO2 emissions from energy use
| unit:Tg S/yr (Teragram of S per year) dimension: region, sector, energy carrier

The most important energy-related source of SO2 in most regions is coal and oil combustion in the electricity generation and industrial sectors. During fuel combustion most of the sulphur contained in the fuel is oxidized to SO2. In the OECD regions, emission controls for SO2 have been implemented in electric utility plants using coal. In other energy sectors different sulphur emission reduction controls are implemented, such as decreasing sulphur standards of fuel for road transport.

Future SO2 emissions under all SRES scenarios are sulphur-control scenarios with changes in fuel mix (substitution of direct use of coal by other fuels, and decreasing sulphur standards of fuel), transition to clean coal technologies (Fuel Gas Desulphurization), and other sulphur emissions reductions. For the period 1995-2010 it is assumed that current national and international emission reduction policies will be fully implemented (UN-ECE Gothenburg protocol 1999 for Europe, the Amendments of the Clean Air Act in the USA), whereas for the long-term various trends of sulphur control policies are implemented (see scenario assumptions).

SO2 emissions are used in the atmospheric chemistry model (ACM) of the atmosphere-ocean system (AOS), where they form sulphate aerosols that reflect sunlight and therefore have a cooling effect on climate. Due to their relative short lifetime, this effect is concentrated in regions where the emissions occur (mainly in the northern Hemisphere).

| #### NOx emissions from energy use
| unit:Tg N/yr (Teragram of N per year) dimension: region, sector, energy carrier

The anthropogenic NOx emissions primarily result from fossil fuel combustion, i.e. from road transportation and power generation. The NOx concentration in the exhaust gases depends on the combustion conditions and is therefore different for the various applications and regions (road vehicles and ships).

The emissions factors in the OECD regions have decreased in the past due to active or gradual improvements in technology or increased diffusion of NOx control technologies. For the near term (2010-2020) the assumptions on the emission factors are based on full implementation of current national and international emission reduction policies (UN-ECE Gothenburg protocol 1999 for Europe, the Amendments of the Clean Air Act in the USA). However, the actual emissions may exceed the formulated targets because it is difficult to abate NOx emissions in a fast-growing transport sector. For the long-term various trends of NOx control policies are implemented (see scenario assumptions).

NOx emissions are used in the atmospheric chemistry model (ACM) of the atmosphere-ocean system (AOS) as input variables to parameterize the impact on OH· and tropospheric ozone concentrations. Both species are important in atmospheric removal processes of carbon monoxide (CO), methane (CH4) and non-methane volatile organic compounds (NMVOC).

| #### NMVOC emissions from energy use
| unit:Tg NMVOC/yr (Teragram of NMVOC per year) dimension: region, sector, energy carrier

The most important energy-related source of NMVOC is fossil fuel combustion, mainly in internal combustion engines in the transportation sector.

For all OECD regions, emissions factors in the transport sector decreased over the past two decades. For the period 2010-2020 the assumptions on the emission factors are based on full implementation of the current national and international emission control policies. In Europe, emissions of NMVOC are controlled by the 5-th Environmental Action Programme of the European Union. However, the actual emissions may exceed the formulated targets because it is difficult to abate NMVOC emissions in a fast-growing transport sector. Specific scenario assumptions were used for transport and energy end-use sectors.

NMVOC emissions from the terrestrial system are used in the atmospheric chemistry model (ACM) of the atmosphere-ocean system (AOS), where they play a role in the atmospheric concentration of carbon monoxide (CO), through which the concentrations of methane and tropospheric ozone are influenced.

| #### CO emissions from energy use
| unit:Tg C/yr (Teragram of C per year) dimension: region, sector, energy carrier

The major source energy-related CO emissions is road transport, and to a lesser extent energy end-use in the residential sector. Assumptions concerning the historical and future trends of the emission factors for transport and energy end-use sectors are similar as those made for NMVOC (see scenario assumptions).

CO emissions are used in the atmospheric chemistry model (ACM) of the atmosphere-ocean system (AOS) to derive atmospheric concentration of greenhouse gases.