Emission intensity


An emission intensity is the emission rate of a given pollutant relative to the intensity of a specific activity, or an industrial production process; for example grams of carbon dioxide released per megajoule of energy produced, or the ratio of greenhouse gas emissions produced to gross domestic product. Emission intensities are used to derive estimates of air pollutant or greenhouse gas emissions based on the amount of fuel combusted, the number of animals in animal husbandry, on industrial production levels, distances traveled or similar activity data. Emission intensities may also be used to compare the environmental impact of different fuels or activities. In some case the related terms emission factor and carbon intensity are used interchangeably. The jargon used can be different, for different fields/industrial sectors; normally the term "carbon" excludes other pollutants, such as particulate emissions. One commonly used figure is carbon intensity per kilowatt-hour, which is used to compare emissions from different sources of electrical power.

Methodologies

Different methodologies can be used to assess the carbon intensity of a process. Among the most used methodologies there are:
Different calculation methods can lead to different results. The results can largely vary also for different geographic regions and timeframes considered for the calculations. For example, Chinese oil fields emit between 1.5 to more than 40 g of CO2eq per MJ with about 90% of all fields emitting 1.5–13.5 g CO2eq. Such highly skewed carbon intensity patterns necessitate disaggregation of seemingly homogenous emission activities and proper consideration of many factors for understanding.

Estimating emissions

Emission factors assume a linear relation between the intensity of the activity and the emission resulting from this activity:
Emissionpollutant = Activity * Emission Factorpollutant
Intensities are also used in projecting possible future scenarios such as those used in the IPCC assessments, along with projected future changes in population, economic activity and energy technologies. The interrelations of these variables is treated under the so-called Kaya identity.
The level of uncertainty of the resulting estimates depends significantly on the source category and the pollutant. Some examples:
A literature review of numerous total life cycle energy sources emissions per unit of electricity generated, conducted by the Intergovernmental Panel on Climate Change in 2011, found that the emission value, that fell within the 50th percentile of all total life cycle emissions studies were as follows.
TechnologyDescription50th percentile
Hydroelectricreservoir4
Windonshore12
Nuclearvarious generation II reactor types16
Biomassvarious230
Solar thermalparabolic trough22
Geothermalhot dry rock45
Solar PVPolycrystalline silicon46
Natural gasvarious combined cycle turbines without scrubbing469
Coalvarious generator types without scrubbing1001

Fuel/
Resource		Thermal
g/MJth		Energy Intensity
W·hth/W·he		Electric
g/kW·he
wood
Peat
CoalB:91.50–91.72
Br:94.33
88		B:2.62–2.85
Br:3.46
3.01		B:863–941
Br:1,175
955
Oil
Natural gascc:68.20
oc:68.40
51		cc:2.35
oc:3.05 		cc:577
oc:751
599
Geothermal
Power		~TL0–1
TH91–122
Uranium
Nuclear power		WL0.18
WH0.20 		WL60
WH65
Hydroelectricity
Conc. Solar Pwr±15#
Photovoltaics
Wind power
Note: 3.6 MJ = megajoule 1 kW·h = kilowatt-hour, thus 1 g/MJ = 3.6 g/kW·h.
Legend: B = Black coal –, Br = Brown coal , cc = combined cycle, oc = open cycle, TL = low-temperature/closed-circuit , TH = high-temperature/open-circuit, WL = Light Water Reactors, WH = Heavy Water Reactors, #Educated estimate.

Carbon intensity of regions

The following tables show carbon intensity of GDP in market exchange rates and purchasing power parities. Units are metric tons of carbon dioxide per thousand year 2005 US dollars. Data are taken from the US Energy Information Administration. Annual data between 1980 and 2009 are averaged over three decades: 1980-89, 1990–99, and 2000–09.
1980-891990-992000-09
Africa1.131491.207021.03995
Asia & Oceania0.862560.830150.91721
Central & South America0.558400.572780.56015
EurasiaNA3.317862.36849
Europe0.368400.372450.30975
Middle East0.987791.214751.22310
North America0.693810.586810.48160
World0.621700.661200.60725

1980-891990-992000-09
Africa0.488440.502150.43067
Asia & Oceania0.661870.592490.57356
Central & South America0.300950.307400.30185
EurasiaNA1.431611.02797
Europe0.404130.388970.32077
Middle East0.516410.656900.65723
North America0.667430.566340.46509
World0.544950.548680.48058

In 2009 CO2 intensity of GDP in the OECD countries reduced by 2.9% and amounted to 0.33 kCO2/$05p in the OECD countries.. The USA posted a higher ratio of 0.41 kCO2/$05p while Europe showed the largest drop in CO2 intensity compared to the previous year. CO2 intensity continued to be roughly higher in non-OECD countries. Despite a slight improvement, China continued to post a high CO2 intensity. CO2 intensity in Asia rose by 2% during 2009 since energy consumption continued to develop at a strong pace. Important ratios were also observed in countries in CIS and the Middle East.

Carbon intensity in Europe

Total CO2 emissions from energy use were 5% below their 1990 level in 2007. Over the period 1990–2007, CO2 emissions from energy use have decreased on average by 0.3%/year although the economic activity increased by 2.3%/year. After dropping until 1994, the CO2 emissions have increased steadily until 2003 and decreased slowly again since. Total CO2 emissions per capita decreased from 8.7 t in 1990 to 7.8 t in 2007, that is to say a decrease by 10%.
Almost 40% of the reduction in CO2 intensity is due to increased use of energy carriers with lower emission factors.
Total CO2 emissions per unit of GDP, the “CO2 intensity”, decreased more rapidly than energy intensity: by 2.3%/year and 1.4%/year, respectively, on average between 1990 and 2007.
The Commodity Exchange Bratislava has calculated carbon intensity for Voluntary Emissions Reduction projects carbon intensity in 2012 to be 0.343 tn/MWh.

Emission factors for greenhouse gas inventory reporting

One of the most important uses of emission factors is for the reporting of national greenhouse gas inventories under the United Nations Framework Convention on Climate Change. The so-called Annex I Parties to the UNFCCC have to annually report their national total emissions of greenhouse gases in a formalized reporting format, defining the source categories and fuels that must be included.
The UNFCCC has accepted the Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories, developed and published by the Intergovernmental Panel on Climate Change as the emission estimation methods that must be used by the parties to the convention to ensure transparency, completeness, consistency, comparability and accuracy of the national greenhouse gas inventories. These IPCC Guidelines are the primary source for default emission factors. Recently IPCC has published the 2006 IPCC Guidelines for National Greenhouse Gas Inventories. These and many more greenhouse gas emission factors can be found on IPCC's Emission Factor Database. Commercially applicable organisational greenhouse gas emission factors can be found on the search engine, EmissionFactors.com.
Particularly for non-CO2 emissions, there is often a high degree of uncertainty associated with these emission factors when applied to individual countries. In general, the use of country-specific emission factors would provide more accurate estimates of emissions than the use of the default emission factors. According to the IPCC, if an activity is a major source of emissions for a country, it is 'good practice' to develop a country-specific emission factor for that activity.

Emission factors for air pollutant inventory reporting

The United Nations Economic Commission for Europe and the EU National Emission Ceilings Directive require countries to produce annual National Air Pollution Emission Inventories under the provisions of the Convention on Long-Range Transboundary Air Pollution.
The European Monitoring and Evaluation Programme Task Force of the European Environment Agency has developed methods to estimate emissions and the associated emission factors for air pollutants, which have been published in the EMEP/CORINAIR Emission Inventory Guidebook on Emission Inventories and Projections TFEIP.

Intensity targets

Coal, being mostly carbon, emits a lot of CO2 when burnt: it has a high CO2 emission intensity. Natural gas, being methane, has 4 hydrogen atoms to burn for each one of carbon and thus has medium CO2 emission intensity.

Greenhouse gases

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In an August 31, 2018 article by Masnadi et al which was published by Science, the authors used "open-source oil-sector CI modeling tools" to "model well-to-refinery CI of all major active oil fields globally—and to identify major drivers of these emissions." They compared 90 countries with the highest crude oil footprint. The Science study, which was conducted by Stanford University found that Canadian crude oil is the "fourth-most greenhouse gas intensive in the world" behind Algeria, Venezuela and Cameroon.