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Local air pollution: Localised air pollution results from the combustion process and from the formation of ground level ozone. Combustion products include carbon monoxide (CO), sulphur dioxide (SO₂), nitrogen oxides (NO_x), unburned hydrocarbons and carbon dioxide (CO₂).

Particles are formed through a complex process involving unburned hydrocarbons; sulphur dioxide and NO_x, primary in fuel-rich flames such as those inherent in diesel engines (trucks and ships) and the pulverised coal combustion systems used in power station. Particles under 10 microns (PM₁₀) in diameter can enter deep into the lungs. Exposure to fine particles is associated with increased mortality from cardio-vascular and cardio-pulmonary diseases.
(more information: Health aspects of air pollution with particulate matter, ozone and nitrogen dioxide, WHO, 2003)

Greenhouse gases

Water vapor - Water vapor contributes the most to the greenhouse effect and occurs in the atmosphere as a result of the natural cycle of water  

Carbon dioxide (CO₂) - Carbon dioxide also cycles naturally between the atmosphere and living organisms.  Plants and algae remove CO₂ from the atmosphere via photosynthesis, while all living things release CO₂ via respiration (i.e., breathing).  Carbon dioxide also cycles back and forth between water on the Earth's surface (freshwater and the oceans) and the atmosphere.  In addition to these natural processes, humans release large quantities of CO₂ to the atmosphere by burning fossil fuels, deforestation, and other industrial processes.    

Methane (CH₄) - Methane is a natural byproduct of decomposition, but significant quantities are also produced via agriculture and animal husbandry as well as by fossil fuel production.

Nitrous oxide (N₂O) - Nitrous oxide is released naturally from terrestrial soils and oceans, but substantial quantities are also generated from the use of nitrogen fertilizers in agriculture and through some industrial processes.

Other gases - A number of other natural and man-made gases also contribute to the greenhouse effect, including tropospheric ozone, and industrial gases such as halocarbons.

Aerosols - Aerosols are airborne particles within the atmosphere.  Some aerosols, such as sulfate aerosols and black carbon aerosols are also produced by fossil fuel combustion.  Sulfate aerosols tend to reflect incoming solar radiation, cooling the Earth's surface.  Black carbon aerosols absorb, rather than reflect, solar radiation, which shades the Earth's surface, but warms the atmosphere.

There are six gases listed in the Kyoto Protocol:
carbon dioxide (CO₂); methane (CH₄); nitrous oxide (N₂0); Hydrofluorocarbons (HFCs); perfluorcarbons (PFCs) and sulphur hexafluoride (SF6).

CO₂ equivalent (CO₂-e): The universal unit of measurement to indicate the global warming potential of each of the six greenhouse gases, expressed in terms of the global warming potential of one unit of carbon dioxide. It is used to evaluate releasing different greenhouse gases against a common basis.

CO₂ has the lowest global warming potential rating but is by far the most important because it is emitted in much greater quantity.

Global warming potential rating

Converting between carbon dioxide and Carbon

To convert from C(e) to CO₂ (e), multiply by 44/12.
To convert from CO₂(e) to C(e), multiply by 12/44
The international convention is to report in term of CO₂ equivalents.
(More information: http://www.eea.europa.eu/themes/climate
www.ipcc.ch and www.epa.gov/globalwarming)

Transport

The main contributions of transport to climate change are direct greenhouse gas emissions (CO₂, N₂O, PFCs and HFCs),  precursors of greenhouse gases (NO_x, CO and Volatile Organic Compounds VOCs),  sulphur dioxide, particle emissions, and contrails.

Transport activities has also a large impact on local air quality. 

Shares by sector in EU-15 greenhouse gas emissions in 2004

Source: European Environmental Agency

Transport related emissions for the year 2000

Source: Veronika Eyring et al., Part 1, JGR, 2005,  Institut für Physik der Atmosphäre.

Energy

The basic energy unit is the Joule (J). 1J equals the energy required to do 1N-m (Newton-meter) of work. In many English speaking countries the basic energy unit is the British thermal unit (Btu). The energy required to heat one pound of water by 1 degree Fahrenheit is 1 Btu.

Total energy use is also sometimes quoted in terms of tonnes of oil equivalent (toe)

Energy Efficiency

The efficiency of any energy conversion chain is defined as the ratio of the energy output to the energy input.

Direct Energy Inputs

Direct Energy is the energy used directly by the operation.
The primary definition of direct energy includes the energy contained in the energy carrier (fuel/electricity), plus the energy of extracting, processing, refining and supplying the fuel or electricity, and losses which occur through the process. Due to the distance between energy source (e.g. the Middle East) and the place of energy consumption  the primary energy content is different per region.