Environmental issues for aviation
Like any other form of public mass transport that relies on finite planetary resources, aviation cannot (in its present form) be considered sustainable in the very long term.Because of the finite nature of the resources upon which aviation relies, it is more realistic in the medium term to think how best to improve the sustainability of air transport rather than it achieving sustainable development.
Demand for air transport is continually growing and, if this demand is to be met with all the attendant benefits, society must also accept the costs (noise, pollution, climate change, risk, resource use etc). Whilst it is not possible to make aviation sustainable (in its present form) in the very long term, much can be and is being done to improve aviation’s sustainability including:
- ensuring safety and security;
- efficiently optimising available capacity;
- collaborating to achieve a shared vision for more sustainable aviation;
- making decisions based on optimising the balance between social, economic and environmental imperatives;
- serving the need for mobility in a manner where the greatest overall benefit will arise, meeting the needs of stakeholders;
- taking every opportunity to minimise adverse impacts and resource use by creating and operating more efficient ATM systems, equipment and technology;
- targeting efforts where they will produce the greatest improvement in our citizen’s quality of life;
- investing in adequate research, training, education and awareness;
- being transparent and honest about both the good and bad aspects of air transport;
- avoid conflicting policy and regulations.
- Aircraft noise
- Local air quality
- Climate change
- Third party risk
- Environmental economics
- Aviation emissions
Noise has historically been the principal environmental issue for aviation. It remains high on the agenda of public concern.
Noise disturbance is a difficult issue to evaluate as it is open to subjective reactions. Its impact is not a lasting one on the actual environment, but it can have significant adverse effects on people living close to an airport, including: interference with communication, sleep disturbance, annoyance responses, learning acquisition, performance effects and cardiovascular and psycho-physiological effects.
Unless there are very many aircraft following a route, it is widely recognised that aircraft flying at a height of at least 10,000ft above the ground do not usually produce “significant” noise impact. But because of the subjective nature of disturbance and the wide variance of local factors, this is not an absolute rule. It is normal for aircraft noise to be associated with airports, because of the low height involved.
To reach an understanding of average noise levels, noise is usually modelled using computer programmes that simulate aircraft “virtually” following an airports operating procedures, but with suitable variability such as track dispersion to make it more realistic. These models, such as the widely used “International Noise Model”, produce aircraft noise footprints for the number of and type of aircraft using an airport in order to calculate the extent of particular noise levels around the airport. This will assume average weather conditions. These noise “contours” can then be placed on a map to see which communities are subjected to different degrees of average noise levels. But it should be remembered that, as average conditions rarely occur, the noise contours are only indicative of typical noise impact.
The most widely used unit for measuring noise levels is dB(A) - the A-weighted scale in decibels. This unit attempts to reflect human reaction to "loudness".
Other dB based measurement units are uniquely related to aircraft.
The perceived noise (PNdB) and effective perceived noise (EPNdB) scales incorporate the different frequencies and duration of noise patterns, resulting from various speeds and modes of operation of aircraft. There is no agreement, even amongst the experts, on which measurement is the most representative, or the most relevant in a particular situation. However, the International Civil Aviation Organisation (ICAO) uses EPNdB for expressing its noise certification standards.
The European Community proposes “Lden” as the common unit for measuring transport noise. Day-evening-night level (Lden) is based on Leq over a whole day with a penalty of 10 dB(A) for night time noise (22.00-7.00) and an additional penalty of 5 dB(A) for evening noise (i.e. 19.00-23.00).
A guide to noise level
- normal conversation 50 - 60 dB(A)
- a loud radio 65 - 75 dB(A)
- a busy street 78 - 85 dB(A)
- a heavy lorry about 7 metres away 95 - 100 dB(A)
- a pighouse at feeding time 110 dB(A)
- a chain saw 115 - 120 dB(A)
- a jet aircraft taking off 25 metres away 140 dB(A) (unlikely to impact the general public!)
Aircraft noise management
All commercial aircraft must meet the International Civil Aviation Organization's (ICAO's) noise certification standards. These apply to aircraft designs and types when they are first approved for operational use, and they have been progressively tightened since the initial standard was adopted in 1971.
The 33rd ICAO Assembly adopted Resolution A33/7 introducing the concept of a ‘balanced approach’ to noise management, thereby establishing a policy approach to address aircraft noise. The ‘balanced approach’ concept of aircraft noise management comprises four principal elements and requires careful assessment of all different options to mitigate noise, including:
- reduction of aircraft noise at source;
- land-use planning and management measures;
- noise abatement operational procedures; and,
- operating restrictions.
The Balanced Approach has since been incorporated into European Community legislation as Directive EC/2002/30).
Other commonly applied noise management measures include:
- depicting preferred noise routes on a map that avoid residential areas as far as possible;
- avoiding over-flying sensitive sites such as hospitals and schools;
- ensuring that the optimum runway(s) and routes are used as far as conditions allow;
- using continuous descent approaches and departure noise abatement techniques;
- avoiding unnecessary use of auxiliary power units by aircraft on-stand;
- building barriers and engine test-pens to contain and deflect noise;
- towing aircraft instead of using jet engines to taxi;
- limiting night operations;
- limiting the number of operations or the extent of a critical noise contour;
- providing noise insulation for the most severely affected houses;
- applying different operational charges based on the noisiness of the aircraft;
- monitoring individual noise levels and penalising any breach.
Local air quality
Local air quality at airports
Aviation air quality concerns are principally related to the areas on and around airports. Further, for most airports the most significant air quality related emissions presently come from ground transport (cars, buses, trains etc). However, because of factors such as growth in demand, more public transport access to airports, and the long service life of aircraft, it is widely expected that aircraft will eventually become the dominant air quality related pollution source for many airports.
Aircraft engines produce emissions that are similar to other emissions resulting from any oil based fuel combustion. These, like any exhaust emissions, can effect local air quality at ground level. It is emissions from aircraft below 1,000 ft above the ground (typically around 3 kilometres from departure or, for arrivals, around 6 kilometres from touchdown) that are chiefly involved in influencing local air quality. These emissions disperse with the wind and blend with emissions from other sources such as domestic heating emissions, factory emissions and transport pollution.
The chief local air quality relevant emissions attributed to aircraft operations at airports are as follows :
- Oxides of Nitrogen (NOx);
- Carbon Monoxide (CO);
- Unburnt hydrocarbons (CH4 and VOCs);
- Sulphur Dioxide (SO2);
- Fine Particulate Matter (PM10 and PM2.5);
These are produced by aircraft engines, auxiliary power units, apron vehicles, de-icing, and apron spillages of fuel and chemicals. Often NOx is by far the most abundant and is often considered the most significant pollutant from an air quality standpoint.
Air quality qualification methods
Emissions to air disperse and mix with emissions from other sources. Presently there are no international standards for air quality quantification methods.
This involves sampling the local air and analysing for NOx, particulates and other important pollution species. The sampling is often done on a 24 hour continuous basis. Locating the measurement equipment is important because of prevailing weather patterns, the position of emission sources linked to the airport and the proximity of residential areas. Various analysis equipment exists including mechanical-chemical sampling equipment and real-time spectrum analysis monitors. Sometimes, mobile monitoring stations or a combination of different methods are used to allow greatest flexibility.
This involves creating an inventory for all significant emitters linked to the airport such as aircraft, ground vehicles (airside and landside), fixed plant such as boilers and fugitive emission sources such as maintenance facilities. The characteristics of the emitters are also determined (operating patterns and emission levels). This data is combined with typical weather patterns in a sophisticated model to predict with reasonable accuracy, the degree of contribution of the airport to local pollution levels and what the dispersion patterns are.
The following measures are commonly used at airports to address emission below 1000 ft:
- low fuel/emission aircraft departure procedures;
- Continuous Descent Approach and Low Power - Low Drag techniques;
- avoiding aircraft queuing on the ground;
- avoiding unnecessary use of aircraft Auxiliary Power Units;
- taxiing management (e.g. towing and single engine taxi);
- increasing the use of public transport, cycling and pedestrian access to an airport (probably the major potential source of benefit);
- supporting and encouraging staff to “car share” or to use more sustainable transport access;
- the use of electric vehicles or less polluting fuels (liquid and natural gas);
- use less polluting fuels in airport buildings;
- ensure adequate vehicle maintenance;
- avoiding combustion equipment running when not required;
- energy management in buildings and for airfield systems (very often the most cost effective opportunity);
- fugitive emission controls.
All of these can contribute to reducing air quality related emissions, whilst at the same time delivering other economy and climate change benefits. For operational measures however, there may also be trade-offs with capacity and noise, and a full assessment should be made before adoption.
Climate change is a change in the "average weather" that a given region experiences, including such factors as storm frequency, temperature, wind patterns and precipitation. Since society becomes increasingly reliant on energy consumption in work at home and for mobility, the heat-trapping nature of the atmosphere has increased. As our scientific understanding of this situation increases, so does public concern and the requirement for a policy response.
Aviation contributes a small but growing proportion to this problem (less than 4% of man-made atmospheric emissions). A key factor however, is that some of aviation's emissions are emitted in the upper atmosphere and may have a more direct effect.
Many countries have ratified The Kyoto Protocol which is an amendment to the United Nations Framework Convention on Climate Change (UNFCCC). These countries commit to reduce carbon dioxide and five other greenhouse gases, or engage in emissions trading if they maintain or increase emissions of these gases. A total of 141 countries have ratified the agreement. Notable exceptions include the United States and Australia.
Affect of aviation on climate change
Aircraft perturb the atmosphere by changing background levels of trace gases and particles and through condensation trails (contrails). Aircraft emissions include greenhouse gases such as CO2 and water vapour that trap terrestrial radiation and chemically active gases that alter natural greenhouse gases, such as O3 and CH4. Particles may directly interact with the Earth’s radiation balance or influence the formation and radiative properties of clouds.
Aircraft “Contrails” are lines of ice crystals that are formed by the aircraft disturbing the air in certain conditions (e.g. moisture content, temperature etc) with some contribution from combustion exhaust. It is now widely believed that these contrails can trigger the formation of cirrus clouds which thus affect climate. In 1992, aircraft contrails were estimated to cover about 0.1% of the Earth’s surface on an annually averaged basis with larger regional values. Contrails tend to warm the Earth’s surface, similar to thin high clouds. The contrail cover is projected to grow to 0.5% by 2050 at a rate which is faster than the rate of growth in aviation fuel consumption.
Closer to the ground, airport related operations also contribute to climate change, though emitters such as aircraft, passenger transport trips, airfield ground transport, airport buildings and airfield systems. Below 1,000ft aviation related emissions also affect air quality which is covered elsewhere. Measures to improve climate change impact at heights of less than 1,000ft above the ground, may also have an air quality benefit.
Managing the effect of aviation on climate change
There are a number of policy options being considered at governmental level and, instruments such as ICAO engine emission standards are helping to reduce aircraft fuel use and greenhouse gas emissions. However, other than general efficiency aims and, because the science on the relative climate effects of altitude, contrails and NOx is not yet fully understood the evaluation of potential policy solutions with the certainty of a positive result is incomplete.
Nevertheless there is a lot that can be done to conserve fuel which in-turn reduces climate change forcing effects:
- Making routes more direct;
- Aiming for a fuel optimised flight profile;
- Increasing load factor and the capacity (and use) of more fuel optimised routes;
- Operating more fuel efficient aircraft;
- Avoid holding and queuing aircraft with engines running (in the air and on the ground);
- Avoiding noise restrictions and procedures that do not achieve sufficient benefit compared to the other environmental disbenefits;
- Using effective fuel optimised speeds when circumstances change;
- Using the other potential management options in the air quality section.
Affect of climate change on aviation
Climate change itself may also have direct and indirect effects on aviation; for example:
- More severe weather patterns (winds, storms and visibility) affecting capacity or efficiency;
- Shifting route-demand patterns due to changes in preferred destination;
- Water shortage constraining airport development;
- Sea level rises affecting low lying airports;
- Changing wind directions affecting runway configuration;
- Changes to winterisation requirements;
- The suppression of demand phenomenon cause by major catastrophe;
- Economic burden caused by climate change may reduce potential disposable income and hence propensity to travel.
Measuring climate change
In terms of global climate change itself, this is measured using a term "radiative [climate change] forcing" effect which tries to describe the net effect of both the positive and negative climate change effects of an emission, i.e. to account for the fact that some emissions may have both global warming and global cooling effects. Quantifying these complex climate effects requires a combination of chemical science to work out how different pollutants inter-react and complex atmospheric models to see how changes might happen.
Third party risk
Third party risk
Although the probability of an accident per flight is very small, local risk levels around airports are higher than one might expect. This is caused by the fact that, while the probability of an accident per take-off or landing is very small, the number of landings and take-offs is often very large (typically several hundred thousand at a major international hub airport). The resulting annual probability of an accident at a large airport therefore, is usually much greater than the small probability of being involved in an aircraft accident as a passenger.
Affect of aviation on third party risk
The closer air routes are to an airport, the greater the concentration of over-flight and hence of risk. Similarly the continuous growth in demand for air transport is also increasing over-flight of residential areas. These facts coupled with difficulties in enforcing land-use planning restrictions, mean that for some airports the number of people in risk areas is increasing as is the number of over-flights.
Affect of third party risk on aviation
Third party risk is sometimes covered in the formal “Environmental Impact Assessment” undertaken to evaluate an airport’s ‘major’ proposals for growth. The EC EIA Directive 85/337/EEC does not specifically require a “third party risk” assessment, however as it requires the assessment of the direct and indirect effects of a project on human beings, it can be taken as implicit if 85/337/EEC is applied.
Although at present of less significance than noise and air-quality, it is widely believed that third party risk is moving rapidly up the policy agenda. The results of this could be increased constraints and obligations.
Quantifying third party risk
At present, no Pan-European legislation exists to give guidance on what level of individual risk is acceptable. The two main examples of national guidelines that exist in this area are those in the UK and The Netherlands.
In the UK, the Health and Safety Executive has recommended that individual risks higher than 10-4 per annum be regarded as intolerable for the public and those below 10-6 per annum be regarded as broadly acceptable. In addition, it has been recommended that the UK base Public Safety Zones (PSZ) around airports on the 10-5 per annum contour. New housing development should not be permitted within the PSZ and dwellings within the 10-4 per annum contour should be purchased by the airport operator and the occupants moved away.
In the Netherlands, in addition to criteria based on individual risk, criteria also exist for use of F-N curves (a way of presenting Group Risk) although these have not been applied in practice to Dutch airports.
It is advisable to seek guidance on the tolerability of risk arising from aircraft impacts from State bodies.
Managing third party risk
Third party risk depends on primary risk factors such as runway incursion management, bird hazard management and land-use planning support, which could reduce third party risk. These in turn are affected by a range of other influences such as airfield equipment provision, safety management skills and community relations. Good guidance on these issues is given by ICAO and by EUROCONTROL.
Thus the following measures may be adopted. Some are a part of good safety practice others are specific to third party risk and should only be undertaken if the risk demands it:
- Adequately assess the range of factors that may contribute to third party risk and the third party risk itself using best practice methods. This is especially required when major airport or Terminal Control Area changes or development are planned.
- Employ an adequate safety management system, especially covering runway incursions or any operational safety issue (e.g. Foreign Object Damage) that may cause an accident involving third parties (e.g. impacting on terminal buildings or residential areas).
- Control bird hazard through a mixture of passive (ecological) and active (bird scaring) means, and by land-use planning support such as restricting the development of rubbish tips close to an airport.
- Seek adequately enforced land-use planning protection that prevents inappropriate development in risk zones.
- Where such development already exists, seek to relocated third parties, preventing the re-habitation of the buildings cleared.
- Operate a well tested major incident recovery plan.
- Operate a vortex strike repair scheme to respond to minor third party risk incident caused by vortices impacting on roofs.
Environmental issues are being seriously addressed by industry, research institutes and European and International organisations.
There is now general consensus that economic instruments offer great potentials for governments to improve environmental performance in a cost-effective manner. This potential could be fully exploited with the integration of environmental, economic and also social concerns in policy making. This is particularly urgent with the reduction of greenhouse gas emissions where policies capable of meeting objectives (at the least cost) become increasingly urgent for most countries. The integration of socio-enviro-economic factors is also vital to ensure we fully understand the trade-offs relating to our decision making.
We must improve our understanding of socio-enviro-economic interrelationships and of the indirect economic costs and benefits arising from ATM. This will help us to develop a policy and approach that acknowledges the synergies and trade-offs between these different imperatives, and ensures that the optimum balance is achieved where possible.
- Understand ATM’s externalities (+/-) and their economic values.
- Include enviro-social-economic issues in our business case assessments.
Within the framework of the better regulation package, the European Commission is proposing several concrete actions to improve the way it designs policy. One of these is the introduction of a new integrated impact assessment method. The Göteborg and the Laeken Councils introduced two important political considerations:
- to consider the effects of policy proposals in their economic, social and environmental dimensions; and
- to simplify and improve the regulatory environment.
EUROCONTROL is committed to follow the highest standards of good governance and better regulation Principles. The use of existing material should facilitate EUROCONTROL decision-making in full consistency with EC requirements and sustainable development Principles.
The aim is to identify critical factors to be reviewed for establishing “Impact Assessments” for EUROCONTROL purposes. The objective is also to try and strengthen the credibility of the Agency proposals for instance through increased transparency, readability and shared ownership of the basic assumptions and methodologies followed.
The natural cycle of water in the atmosphere is complex, involving a suite of closely coupled physical processes. This is particularly true in the troposphere, where there is continual cycling between water vapour, clouds, precipitation, and ground water. Water vapour and clouds have large radiative effects on climate and directly influence tropospheric chemistry. The stratosphere is much drier than the troposphere.
Nevertheless, water vapour is important in determining radiative balance and chemical composition, most dramatically in polar ozone loss through the formation of polar stratospheric clouds. Emissions of water vapour by the global aircraft fleet into the troposphere are small compared with fluxes within the natural hydrological cycle; however, the effects of contrails and enhanced cirrus formation must be considered. Water vapour resides in the troposphere for about 9 days. In the stratosphere, the time scale for removal of any aircraft water emissions is longer (months to years) than in the troposphere, and there is a greater chance for aircraft emissions to increase the ambient concentration. Any such increase could have two effects: a direct radiative effect with a consequent influence on climate, and a chemical perturbation of stratospheric ozone both directly and through the potentially increased occurrence of polar stratospheric clouds at high latitudes.
The behaviour of CO2 within the atmosphere is simple and well understood. There are no important formation or destruction processes that take place in the atmosphere itself. Atmospheric sources and sinks occur principally at the Earth’s surface and involve exchanges with the biosphere and the oceans. The effect of CO2 on climate change is direct and depends simply on its atmospheric concentration. CO2 molecules absorb outgoing infrared radiation emitted by the Earth’s surface and lower atmosphere. The observed 25–30% increase in atmospheric CO2 concentrations over the past 200 years has caused a warming of the troposphere and a cooling of the stratosphere. There has been much discussion about how stabilization of CO2 concentrations might be achieved in the future. One of the most important factors is the accumulated emission between now and the time at which stabilization is reached.
The amount of CO2 formed from the combustion of aircraft fuel is determined by the total amount of carbon in the fuel because CO2 is an unavoidable end product of the combustion process (as is water). The subsequent transport and processing of this CO2 in the atmosphere follows the same pathways as those of other CO2 molecules emitted into the atmosphere from whatever source. Thus, CO2 emitted from aircraft becomes well mixed and indistinguishable from CO2 from other fossil fuel sources, and the effects on climate are the same. The rate of growth in aviation CO2 emission is faster than the underlying global rate of economic growth, so aviation’s contribution, along with those of other forms of transportation, to total emissions resulting from human activities is likely to grow in coming years.
Nitrogen oxides (NO and NO2 are jointly referred to as NOx) are present throughout the atmosphere. They are very influential in the chemistry of the troposphere and the stratosphere, and they are important in ozone production and destruction processes. There are a number of sources (oxidation of N2O, lightning, fossil fuel combustion) whose contribution to NOx concentrations in the upper troposphere are not well quantified.
In all regions, the chemistry of the atmosphere is complex; aircraft NOx emissions are best viewed as perturbing a web of chemical reactions with a resultant impact on ozone concentrations that differs with location, season, and so forth. In the upper troposphere and lower stratosphere, aircraft NOx emissions tend to cause increased ozone amounts, so increased ozone and its greenhouse effects are the main issues for NOx emissions from subsonic aircraft. The pathways of other atmospheric constituents are also affected. Principal among these effects for NOx emissions is the reduction in the atmospheric lifetime and concentration of methane, another greenhouse gas. On the other hand, NOx emissions at the higher altitudes (18 km or above) of supersonic aircraft tend to deplete ozone.
Although this covers a wide range of substances contained within aircraft exhaust emissions, the compounds of concern include sulphate aerosols and soot. These particles are heavily involved in the formation of contrails and cirrus clouds.
Sulphate aerosols play a critically important part in the stratosphere where they determine the NOx budget, and changes in sulphate levels would therefore have an effect on ozone levels.
In 1992, aircraft line-shaped contrails were estimated to cover about 0.1% of the Earth’s surface on an annually averaged basis with larger regional values. Contrails tend to warm the Earth’s surface, similar to thin high clouds. The contrail cover is projected to grow to 0.5% by 2050 at a rate which is faster than the rate of growth in aviation fuel consumption.
This faster growth in contrail cover is expected because air traffic will increase mainly in the upper troposphere where contrails form preferentially, and may also occur as a result of improvements in aircraft fuel efficiency. Contrails are triggered from the water vapour emitted by aircraft and their optical properties depend on the particles emitted or formed in the aircraft plume and on the ambient atmospheric conditions. The radiative effect of contrails depends on their optical properties and global cover, both of which are uncertain.
Extensive cirrus clouds have been observed to develop after the formation of persistent contrails. Increases in cirrus cloud cover (beyond those identified as line-shaped contrails) are found to be positively correlated with aircraft emissions in a limited number of studies. About 30% of the Earth is covered with cirrus cloud. On average an increase in cirrus cloud cover tends to warm the surface of the Earth. An estimate for aircraft-induced cirrus cover for the late 1990s ranges from 0 to 0.2% of the surface of the Earth.