United Nations Environment Programme

UNEP Toolkit



Acidification. This occurs when excessive amounts of sulphuric and nitric acid – which are formed from sulphur and NOx emissions into the atmosphere – are deposited in the environment.

Biofuel. Vehicle fuel derived from biomass, i. e grain, sugar cane, corn, wood.

Bioethanol. Ethanol derived from biomass, usually sugar cane, corn or grain.

Biodiesel. Diesel derived from biomass, usually rapeseed or other vegetable oils.

CO = carbon monoxide. Carbon monoxide is a colourless, odourless and tasteless – but toxic – gas formed in incomplete combustion. CO is extremely dangerous if inhaled at high concentrations because it has a greater affinity than oxygen for red blood cells (haemoglobin), reducing its ability to transport oxygen to vital organs.

CO2 = carbon dioxide. Carbon dioxide is a colourless gas formed during the combustion of any material containing carbon and is an important greenhouse gas.

Cardiovascular diseases.  Diseases that affect the heart and circulatory system.

Climate change. This is the process whereby human activities resulting in the emission of greenhouse gases (mostly CO2 and methane) change the climate in the long term. This is also referred to as “global warming”

CNG = Compressed Natural Gas. Clean vehicle fuel used in adapted normal combustion engines.

Dispersion model. Model that describes the dispersion of vehicle emission into the surrounding environment

Dose-response model.  Model that describes the relationship between a concentration of a certain pollutant and the health effects in people

DOC = Diesel Oxidation Catalyst. Reduces PM and HC emissions from diesel vehicles. Requires low sulphur diesel (500 parts per million or below).

DPF = Diesel Particulate Filter. Reduces PM and HC emissions from diesel vehicles. Requires low or ultra low sulphur diesel, (50 parts per million or below).

Drive train. The drive train includes the energy conversion and the power distribution system in the vehicle, or put more simply, the engine and the transmission on a normal vehicle (a mechanical drive train). An electric drive train used in a hybrid vehicle, fuel cell vehicle, or in an electric vehicle consists of an electric motor, power electronics, power battery, and a transmission.

FCEV = Fuel Cell Electric Vehicle. Future efficient vehicle technology that uses a fuel cell instead of a combustion engine, see below.

Fuel cell. Chemical engine that converts hydrogen (H2) to electricity and water with high efficiency.

HEV = Hybrid Electric Vehicle. Efficient new vehicle technology that combines an electric motor with a combustion motor. See also PHEV (Plug in hybrids).

Eco driving. Education in softer driving behaviour that saves both the environment and lives.

EGR = Exhaust Gas Recirculation. Exhaust system that reduces the emissions of NOX from diesel vehicles

Electric vehicle. Vehicle with an electric drive train, see below. Can be either a battery powered electric vehicle, a hybrid electric vehicle, or a fuel cell electric vehicle.

Emission factors. The emission per km driven under normal conditions for vehicles, usually measured in g/km.

Engine tune-up. Optimising the engine’s performance by calibrating the ignition system, air supply system, and fuel supply system.

Euro standards. European Union emission standards (in g/km). Started with Euro 1 in the early 1990s up to recently adopted and more stringent Euro 5 and Euro 6.

Eutrophication . This is also called “nutrient pollution” and is caused partly by NOx emissions.

Greenhouse gas. Gas that contributes to global warming and thus climate change.

HC=Hydrocarbons. Pollutant formed under combustion. Together with NOx and under the influence of sunlight, HC can form ground level ozone, see below

Hydrogen. Possible future vehicle fuel. Gaseous at normal temperatures and pressure. Can be derived from anything that contains hydrogen.

ICEV = Internal combustion engine vehicle. Today’s conventional vehicle with a combustion engine.

Low sulphur diesel. Diesel with less sulphur, usually less than 500 parts per million (ppm)

NOx=Nitrogen Oxides. NOx is the common name for nitrogen oxide (NO) and nitrogen dioxide (NO2).

O3=Ozone. Ozone is found in the lower atmosphere (ground-level ozone is also a main component of photochemical smog) and higher up in the stratosphere (stratospheric ozone). Ground-level ozone can also be called photochemical smog and damages human health

Pb = Lead. Lead is a bluish or silver-grey soft metal. Two of its most important forms in terms of air pollution are tetraethyl lead and tetra methyl lead. These two forms of lead are used as "anti-knock" additives in petrol.

Plug in hybrids (PHEV) = Hybrid electric vehicle that can also be charged with electricity from the electric grid. Not commercially available today but expected to become available commercially in the future

PM = Particulate matter or small particles emitted from the exhaust.

PM 10. Particles smaller than 10 microns.

PM 2.5. Particles smaller than 2.5 microns.

Unleaded petrol. Petrol with no added lead. Standard in most countries today

Ultra low sulphur diesel (ULSD). Diesel with very low sulphur levels (less than 50 ppm). Standard in the EU and in the US today.

Respiratory diseases. Diseases that affect the lung system.

Retrofit. Fitting an exhaust emission control technology on an existing vehicle.

Solar hydrogen. Hydrogen derived from solar energy via electrolysis of water (solar electricity +water= hydrogen + oxygen).

SO2  = Sulphur dioxide. Sulphur dioxide is a colourless heavy gas with a pungent smell, also known to be an irritant. SO2 causes acidification (see glossary)

Suspended particulate matter (SPM). This refers to particles in the air of all sizes. SPM is a complex mixture of organic substances, present in the atmosphere both as solid particles and liquid droplets. They include fumes, smoke, dust and aerosols.

3-way catalyst. Catalyst that reduces hydrocarbons, Nitrogen oxides and carbon monoxide (3) from petrol fuelled vehicles. Requires lead free petrol.

2-stroke engine. Older type of engine still used in smaller engine applications such as small mopeds, lawn mover, and motorcycles. Most engines today are 4-strokes.  “2-stroke” refers to the number of linear movements of the piston between every ignition.

Wheel alignment. Correcting wheels that are not aligned (parallel).

VOC = Volatile Organic Compounds. Volatile organic compounds are comprised of a wide range of individual substances including hydrocarbons (alkenes, alkenes, and aromatics), halocarbons (e.g. trichloroethylene), and oxygenates (alcohols, aldehydes, and hetons). They are all organic compounds and are volatile enough to exist as vapour in the atmosphere under normal conditions.