impact of aviation industry to environment

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Indian Institute of Space Science

and Technology

CH-311 Environmental Science andEngineering

Assignment-2

Impact of aviation industry onenvironment

Author:

Shubham MauryaSupervisor:

Dr. KG Sreejalekshmi

September 28, 2015


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1 Introduction

Flight through air requires sufficient thrust to overcome drag and gravityand hence the role of propulsion comes into play. Since the first flight ofmankind by Wright brothers at Kitty Hawk in 1903, aviation has progressedat an astonishing rate to become a key contributor of growth in developedcountries. Because of the success of aviation industries, flight operationsconsume increasing amounts of fuel and produce more emissions and noise.Nowadays, fossil fuel emissions and noise generated by aircraft are majorsource of environmental pollution. The estimated growth in the aviationsector in near future would further increase global emissions and the effectof emissions at high altitudes would also be more pronounced.

2 Environmental issues

The following are the environmental impacts contributed by aviation industrywhich need to be tackled before its too late.

takeoff and approach noise (Jet engines in aircraft produce very highintensity sound. Supersonic planes produces shock waves and produceunbearable noise to nearby habitation.)

flyover noise resulting from aircraft cruising at high altitudes.

sonic booms and hyperbooms (i.e., the thermospherically refracted andvery low intensity remains of sonic booms)

noise by taxiing and engine run-ups.

fuel dumping

emission of Carbon monoxide, hydrocarbons, and oxides of nitrogen inthe airport area (typically below 3,000 feet)

contrail formation

emissions of CO2

emissions in the upper troposphere and stratosphere (from both sub-sonic and supersonic aircraft) of water vapor, NOx, sulphur particles,

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Figure 1: Contrail formation by exhaust gases of jet engine over Antarctica

and carbon particles. Ozone depletion is also attributed to NOx emis-sions.

potential for greenhouse effects and depletion of stratospheric ozone

2.1 Climate change

Emissions from flight vehicles are quantified by estimating radiative forcingand global warming potential of pollutants.

Radiative forcing is defined as The change in average radiation (inWatts per square metre: W/m2) at the top of the tropopause resulting froma change in either solar or infrared radiation due to a change in atmosphericgreenhouse gases concentrations; perturbance in the balance between incom-ing solar radiation and outgoing infrared radiation.[1]

GWP (Global Warming Potential) is defined as the cumulative ra-diative forcing effects of a gas over a specified time horizon resulting fromthe emission of a unit mass of gas relative to a reference gas.[1]

Aviation climate impacts are due to both carbon dioxide and non-carbondioxide emissions (see Figure 2). The non-CO2 emissions include water va-por (H2O), nitrogen oxides (NOx), sulpfur oxides (SOx), hydrocarbons (HC),and black carbon (or soot) particles. Climate impacts of CO2 emissions are

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Figure 2: Schematic representation of aircraft emissions and their causal link-

ages with potential climate and social welfare impacts. Note that both thelevel of scientific uncertainties and policy relevance increase from characteri-zation of emissions to social damage attributions. (Adapted from Wuebbleset al., 2007 )

well characterized and are independent of source location due to its relativelylong atmospheric lifetime. On the other hand, non-CO2 climate impacts ofaviation emissions are quite variable in space and time. The primary factorfor non-CO2 emissions from aircraft is that the largest portion of these emis-sions are emitted in the flight corridors throughout the upper troposphere

and lower stratosphere at altitudes of 8 km to 13 km ( 26,000-40,000 ft ).The lifetime of the associated atmospheric changes ranges from minutes forcontrails, to years for changes in methane.[1]

The only greenhouse gas emissions from aviation are CO2 and watervapours: other emissions, e.g. NOx and particles cause changes in radiative

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Figure 3: Radiative forcings from aviation emissions (gases and aerosols) in1992 as estimated by the IPCC

forcing (RF) but are not contributors to global warming effect. Emissionsof water vapour from current subsonic aviation are small and contribute (di-rectly) albeit in a negligibly small manner to global warming. Total CO2 avi-ation emissions is approximately 2% of the Global Greenhouse Emissions.[2]

From Fig.3, we observe that CO2, contrails and ozone formation (due toNOx emissions in tropopause) contribute to positive radiative forcing i.e.,they heat up the atmosphere.

2.2 Noise pollution

A moving aircraft including its jet engine or propeller causes compressionand rarefaction of the air, producing motion of air molecules. These pressuredisturbances are propagated as sound. If these pressure waves lie withinthe audible range of humans, a sensation of hearing is produced. Differentaircrafts have noise levels with different intensity and frequencies. The noise

originates from two main sources:

Aerodynamic noise -Aerodynamic noise results from flow of air aroundfuselage and control surfaces. It is same as fluttering sound heard whena rod or stick is swung through air at high speeds. This type of noise

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increases with aircraft speed and altitude. The noise is more at lower

altitudes because of higher density of air. Engine and mechanical noises- the majority of engine noise is due to

jet noise. The high velocity air jet leaving through the engine exhausthas significant shear layer instability that rolls up into ring vortices.The eventual breaking of these vortices causes turbulence and sound ispropagated.

There are several health consequences of elevated sound levels. It cancause hearing impairment, hypertension, ischemic heart disease, annoyance,sleep disturbance, and decreased school performance. Although some hearingloss occurs naturally with age, in many developed nations the impact ofnoise is sufficient to impair hearing over the course of a lifetime. Elevatednoise levels can create stress, increase workplace accident rates, and stimulateaggression and other anti-social behaviors.[3].

3 Solving environmental issues

3.1 Dealing with emissions

Biofuels extracted from sustainable oil crops such as jatropha, camelinaand algae or from wood and waste biomass can reduce the overall carbon

footprint by around 80% over their full lifecycle. Test flights using biofuelshave been carried out by dozens of airlines and have proven that biofuelswork and can be mixed with existing jet fuel. [4]

Once economically viable and commercially available at scale, biofuelscould improve local air quality and reduce aviation-related life-cycle green-house gas (GHG) emissions, advancing aviations longstanding commitmentto minimize environmental impact

Varying height and speed of aircraft reduces emissions and savesfuel. A recent study has revealed that aircraft crossing the Atlantic cansave between one and two per cent of the fuel costs per flight by varying

their speeds and heights they fly, according to the latest results of a trialconducting by air navigation service providers in Canada and the UK andfive partner airlines. This translates to a reduction of 200 to 400 litres of fuelcorresponding to 525 to 1,050 kilograms of GHG emissions. With close to

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Figure 4: Noise-reducing chevrons on a Rolls-Royce Trent 1000 turbofanengine

400,000 flights each year, the potential economic and environmental benefitsare substantial. [5]

Drag reduction by winglets can reduce induced drag which consumesmajority of the fuel.

3.2 Countering noise pollution

High bypass ratio enginesreduce noise significantly. Modern high-bypassturbofan engines, for example, are quieter than the turbojets.

Acoustic damping by sound absorption materials including foams, fibers,membranes, perforated panels, etc. These materials have good noise reduc-tion abilities at the high frequency range, but exhibit few sound absorptionproperties in the low- and medium-frequency range (250-2000 Hz) in whichhuman sensitivity to noise is fairly high. The aviation industry is currentlyusing traditional materials such as perforated panel, fibers, and foam fornoise reduction with limited results. Compared to these traditional materi-als, electrospun nanofibers exhibit high absorption coefficients in almost all

frequency ranges.Contours on land near runway if properly designed can reduce the

noise levels by destructive interference of sound. The settlement near airportswould be highly benefited by this method.

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References

[1] Aviations Contribution to Climate Change, ICAO Environment report(2010)

[2] IPCC Fourth Assessment report(AR4):Climate Change (2007), Geneva,Switzerland

[3] Kryter, Karl D. (1994). The handbook of hearing and the effects of noise:physiology, psychology, and public health. Boston: Academic Press ISBN0-12-427455-2

[4] IATA Sustainable Alternative FuelAdvocacy, 1st edition, 2015

[5] AIRE: Delivering Green results through partnershipWebsite:http://www.sesarju.eu/innovation-solution/demonstrating-sesar/aire

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impact of aviation industry to environment

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