AERONOx EU project to study impact of NOx emissions from aircraft at altitudes between 8 to 15 km.

Aerosols Airborne suspension of small particles.

Aerosol Precursors Gases or chemi-ions that may undergo gas to particle conversion.

Aerosol Size Distribution Particle concentration per unit size interval.

AEROTRACE Project funded by the EU to measure trace species in the exhaust of aero engines.

Albedo The ratio between reflected and incident solar flux.

Anthropogenic Caused or produced by humans.

Background Atmosphere The atmosphere remote from anthropogenic or volcanic influences.

Binary Nucleation Nucleation from two gas phase species.

Black Carbon Graphitic carbon, sometimes referred to as elemental or free carbon.

Block Time The time elapsed from start of taxi out at origin to the end of taxi in at destination.

Bunker Fuels (International) Fuels consumed for international marine and air transportation.

Catalytic Cycle A cycle of chemical reactions, involving several chemical compounds, that depends on the presence of a specific compound which remains unchanged during these reactions.

Charged Particles Particles carrying a positive or negative electric charge.

Chemi-ion Charged cluster of a few molecules.

Cirrus High, thin clouds composed of mainly ice particles.

Climate Model A numerical representation of the climate system. Climate models are of two basic types: (1) static, in which atmospheric motions are neglected or are represented with a simple parameterization scheme such as diffusion; and (2) dynamic, in which atmospheric motions are explicitly represented with equations. The latter category includes general circulation models (GCMs).

Cluster A set of molecules forming an entity.

Coagulation Collision between two (or more) particles resulting in one larger particle.

Combustion Efficiency Ratio of the heat released in combustion to the heat available from the fuel.

Condensation The process of phase transition from gas to liquid.

Condensation Nucleus A particle that can be activated to continual growth through the condensation of water by exposure to a high supersaturation with respect to water.

Contrail Condensation trail (i.e., white line-cloud often visible behind aircraft).

Differential Mobility Analysis A technique for measuring a particle's size by putting an electric charge on it, and measuring its electric mobility in an electric field.

Direct Radiative Impact Radiative forcing of aerosols or gases by scattering and absorption of solar and terrestrial radiation.

Dp/F00 The ICAO regulatory parameter for gaseous emissions, expressed as the mass of the pollutant emitted during the landing/take-off (LTO) cycle divided by the rated thrust (maximum take-off power) of the engine.

Economies in Transition National economies that are moving from a period of heavy government control toward lessened intervention, increased privatization, and greater use of competition.

Emission Index The mass of material or number of particles emitted per burnt mass of fuel (for NOx in g of equivalent NO2 per kg of fuel; for hydrocarbons in g of CH4 per kg of fuel).

Energy Efficiency Ratio of energy output of a conversion process or of a system to its energy input; also known as first-law efficiency.

Engine Pressure Ratio The ratio of the mean total pressure at the last compressor discharge plane of the compressor to the mean total pressure at the compressor entry plane, when the engine is developing its take-off thrust rating (in ISA sea-level static conditions).

Equivalence Ratio Ratio of actual fuel-air ratio to stoichiometric fuel-air ratio.

Feedback When one variable in a system triggers changes in a second variable that in turn ultimately affects the original; a positive feedback intensifies the effect, and a negative reduces the effect.

Freezing The process of phase transition from liquid to solid state.

Freezing Nucleus Any particle that, when present within a mass of supercooled water, will initiate growth of an ice crystal about itself.

Greenhouse Gas A gas that absorbs radiation at specific wavelengths within the spectrum of radiation (infrared) emitted by the Earth's surface and by clouds. The gas in turn emits infrared radiation from a level where the temperature is colder than the surface. The net effect is a local trapping of part of the absorbed energy and a tendency to warm the planetary surface. Water vapor (H2O), carbon dioxide CO2), nitrous oxide (N2O), methane (CH4), and ozone (O3) are the primary greenhouse gases in the Earth's atmosphere.

Heterogeneous Chemistry Chemical reactions that involve both gaseous and liquid/solid ingredients.

Heterogeneous Nucleation Formation of liquid or solid particles on the surface of other material.

Homogeneous Chemistry Chemistry in the gas phase.

Homogeneous Nucleation Formation of particles from gas-phase species.

Indirect Radiative Impact Radiative forcing induced not directly but by changing other scattering or absorbing components of the atmosphere (clouds or gases).

Jet The continuous strong stream of exhaust gases leaving the engine exit.

Kerosene Hydrocarbon fuel for jet aircraft.

Landing/Take-Off (LTO) Cycle A reference cycle for the calculation and reporting of emissions, composed of four power settings and related operating times for subsonic aircraft engines [Take-Off - 100% power, 0.7 minutes; Climb - 85%, 2.2 minutes; Approach - 30%, 4.0 minutes; Taxi/Ground Idle - 7%, 26.0 minutes].

Lean Blow Out The fuel-air ratio of a combustion chamber at 'flame out.'

Lean Pre-Mixed Pre-Vaporized Description of principal combustor features.

Life-Cycle Cost The cost of a good or service over its entire lifetime.

Log Normal Function of the form y(x) = (C1/x)*exp(-(lnx-lnx0)**2/C2), where C1, C2, and x0 are constants.

Long-Wave Range The terrestrial spectral radiation range at wavelengths larger about 4 mm.

Low Emissivity A property of materials that hinders or blocks the transmission of a particular band of radiation (e.g., that in the infrared).

Mach Number Speed divided by the local speed of sound.

Mitigation An anthropogenic intervention to reduce the effects of emissions or enhance the sinks of greenhouse gases.

NOx Oxides of nitrogen, defined as the sum of the amounts of nitric oxide (NO) and nitrogen dioxide (NO2) with mass calculated as if the NO were in the form of NO2.

Nucleation Phase change of a substance to a more condensed state initiated at a certain loci within a less condensed state.

Optical Depth or Optical Thickness The parameter of a transparent layer of gases or particles defined as the logarithm of the ratio between incident and transmitted radiative flux.

Organic Carbon The carbonaceous fraction of ambient particulate matter consisting of a variety of organic compounds.

Overall Efficiency (h) The ratio between mechanical work delivered by an engine relative to the chemical energy provided from burning a fuel [h = (thrust x speed)/(specific combustion heat x fuel consumption rate)].

Ozone A gas that is formed naturally in the stratosphere by the action of ultraviolet radiation on oxygen molecules. A molecule of ozone is made of up three atoms of oxygen.

Ozone Hole A substantial reduction below the naturally occurring concentration of ozone, mainly over Antarctica.

Ozone Layer A layer of ozone gas in the stratosphere that shields the Earth from most of the harmful ultraviolet radiation coming from the Sun.

Particulate Mass Emission Index The number of grams of particulate matter generated in the exhaust per kg of fuel burned.

Particulate Number Emission Index The number of particles generated in the exhaust per kg of fuel burned.

Plume The region behind an aircraft containing the engine exhaust.

Polar Stratospheric Clouds Large, diffuse, ice-particle clouds that form in the stratosphere usually over polar regions.

Polar Vortex In the stratosphere, a strong belt of winds that encircles the South Pole at mean latitudes of approximately 60°S to 70°S. A weaker and considerably more variable belt of stratospheric winds also encircles the North Pole at high latitudes during the colder months of the year.

Pressure Ratio The ratio of the mean total pressure exiting the compressor to the mean total pressure of the inlet when the engine is developing take-off thrust rating in ISA sea level static conditions.

Primary Energy The energy that is embodied in resources as they exist in nature (e.g., coal, crude oil, natural gas, uranium, or sunlight); the energy that has not undergone any sort of conversion.

Radiative Forcing A change in average net radiation (in W m^-2) at the top of the troposphere resulting from a change in either solar or infrared radiation due to a change in atmospheric greenhouse gases concentrations; perturbance in the balance between incoming solar radiation and outgoing infrared radiation.

Rated Output The maximum thrust available for take-off under normal operating conditions, as approved by the certificating authority.

Relative Humidity The ratio of the partial pressure of water vapor in an air parcel to the saturation pressure (usually over a liquid unless specified otherwise).

Reservoir Molecules Molecules in the atmosphere that bind with atoms or other molecules and prevent them from participating in chemical reactions.

Scavenging The process of removal of gases or small particles in the atmosphere by uptake (condensation, nucleation, impaction, or coagulation) into larger (cloud or precipitation) particles.

Short-Wave Range The solar spectral range from about 0.3 to 4 mm.

Soot Carbon-containing particles produced as a result of incomplete combustion processes.

Specific Fuel Consumption The fuel flow rate (mass per time) per thrust (force) developed by an engine.

Stakeholders Person or entity holding grants, concessions, or any other type of value which would be affected by a particular action or policy.

Stoichiometric Ratio The fuel-air ratio at which all oxygen is consumed (approximately 0.068).

Stratosphere The stably stratified atmosphere above the troposphere and below the mesosphere, at about 10- to 50-km altitude, containing the main ozone layer.

Surface Area Density Surface area of aerosol per unit volume of atmosphere.

Susceptibility Probability for an individual or population of being affected by an external factor.

Sustainable A term used to characterize human action that can be undertaken in such a manner as to not adversely affect environmental conditions (e.g., soil, water quality, climate) that are necessary to support those same activities in the future.

Tropopause The boundary between the troposphere and the stratosphere, usually characterized by an abrupt change in lapse rate (vertical temperature gradient).

Troposphere The layer of the atmosphere between the Earth's surface and the tropopause below the stratosphere (i.e., the lowest 10 to 18 km of the atmosphere) where weather processes occur.

Ultraviolet Radiation Energy waves with wavelengths ranging from about 0.005 to 0.4 µm on the electromagnetic spectrum. Most ultraviolet rays coming from the Sun have wavelengths between 0.2 and 0.4 µm. Much of this high-energy radiation is absorbed by the ozone layer in the stratosphere.

Volatiles Particles that evaporate at temperatures less than about 100°C.

Vulnerability The extent to which climate change may damage or harm a system; it depends not only on a system's sensitivity, but also on its ability to adapt to new climatic conditions.

Wake The turbulent region behind a body or aircraft.

Windmilling Inoperative engine with ram airflow through it.

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