Environmental degradation caused by emissions from aircraft is likely to increase in severity with the growth of flying. Until recently, such emissions were considered to be insignificant, but during the last five years, this view has been reversed. The complexity of the effects of pollution in the atmosphere has now been realised, at least qualitatively. The known consequences of some of the main emissions are discussed along with current environmental legislation and pertinent UK Government policy with regard to aviation. Recommendations are given for some future UK transportation-by-aircraft policy objectives that would safeguard the future of our, as yet, relatively pollution-free skies.NOTATIONADS Automatic dependent surveillanceC CarbonCO Carbon monoxideCO 2 Carbon dioxideCOHb CarboxyhaemoglobinDFLVR German Aerospace Research EstablishmentDGLR German Society for Aeronautics and AstronauticsGWP Global warming potentialHC HydrocarbonHNO 2 Nitrous acidH 2 O WaterICAO International Civil Aviation OrganisationIPCC Intergovernmental Panel on Climate ChangeMTOW Maximum take-off weightNASA National Aeronautics and Space AdministrationNm 3 Cubic metre of air at normal atmospheric pressure and 15°CNO Nitric oxideNO x Nitrogen oxidesO 2 OxygenOH Hydroxyl radicalOPR Overall pressure-ratioppm Parts per millionSO 2 Sulphur dioxideSO x Sulphur oxidesUHF Ultra-high frequencyVOC Volatile organic compoundsWHO World Health OrganisationGLOSSARYLoad factor The percentage of an aircraft's passenger- and freight-carrying capacity which is actually used.Long-range cruise speed The speed at which, for reasons connected with aircraft control efficiency, most airliners are usually flown. It exceeds the most cost-effective cruise speed and hence entails 1% increase in the rate of fuel consumption relative to the minimum required consumption.Overall pressure ratio The ratio of the outlet to the inlet pressure for the turbine.Pressure ratio The ratio of the absolute thrust-pressure of the combustor to atmospheric pressure.Radiative heat balance The ratio of solar radiation reflected from the Earth's atmosphere, to that absorbed by the Earth's atmosphere. In the steady state, the amount radiated equals the amount absorbed.Stoichiometric ratio The ratio of air to flammable gas or vapour that achieves complete combustion or chemical combination.