Analazying The Impact Of Aviation Noise Pollution
When the Wright Brothers first flew their aircraft above Kitty Hawk, North Carolina, airplanes were still just a dream. From that dream, the aviation industry boomed and aircraft in the skies became more popular, though not a means of transportation for an everyday citizen. Over the decades the population has boomed and now there are airlines capable of carrying several hundred individuals across the world and is affordable for most people. This affordability led to nearly one billion passengers flying throughout the year and to meet this demand, airports are scheduling flights from sunrise till far past sundown. With the increase in flights every day to meet the economic demands of the industry, noise pollution is on the rise. More so than ever, the aviation industry and the communities surround the airports are faced with challenges to reduce this noise pollution through technological advancements and legislation to ensure the damage to individuals in these communities is minimal. If unable to reduce noise pollution, the aviation industry faces increasingly stronger legislation which can drive up the cost of commercial travel by air. Another impact of noise pollution and the inability to reduce noise at airports is the total closure of airports as some cities look to completely erase airfields from their cities.
Analyzing the Impact of Aviation Noise Pollution on the Population and How Technology Can Help
At the time of the Wright brother’s first flight in winter of 1903 the total world population hovered around two billion individuals across all seven continents and Henry Ford incorporates Ford Motor Company. Since the beginning of the 20th century the population has nearly quadrupled and the aviation industry has grown in leaps and bounds with flight progressing from mere minutes off the ground to aircraft capable of flying non-stop thanks to aerial refueling. Both the expansion of the population and the aviation industry has led to a clash between the two as aircraft became louder, airports larger and as cities continue to grow, edging closer to airports across the world. Often airports, which were long ago developed in less developed areas, such as the case for San Diego International Airport, are now surrounded with no room for expansion.
The expansion of both airports and the general population has led to increased noise pollution complaints. Noise pollution has become such as important matter, that it now tops the list of concerns when discussing an airport expansion. Michael McCabe states, “an estimated that more than ten million Americans suffer from noise-induced hearing loss and twenty million are exposed to potentially damaging noise levels” (as cited in Falzone, 1999, p. 773). To mitigate the damages from noise pollution the aviation industry has looked at new technology to reduce noise pollution for aircraft operations while also facing stricter noise pollution legislation over the last few decades.
Typically, the concept of pollution is generalized as man-made pollutants that are damaging to the environment such as plastic bags that make it the ocean or car emissions which affect the ozone layer and therefore noise pollution doesn’t garner much attention. However, the United States Environmental Protection Agency (EPA) describes noise pollution as “unwanted or disturbing sound . . .[which] interferes with normal activities such as sleeping, conversation or disrupts or diminishes one’s quality of life” (Clean Air Act Overview, n.d.). As cites and airports expand, airports often end up surrounded by residential neighborhoods or commercial buildings. This mixture of environments creates issues of noise pollution from airport operations such as aircraft movement and maintenance operations. As of 2011, only two percent of the population in Europe was exposed to aircraft noise, which is relatively small compared to 45 percent of the population exposed to noise from road traffic, but the International Civil Aviation Organization analysis (ICAO) expects an increase of 42 percent by 2020 (Attenborough, Tokarev & Zaporozhets, 2011, p. 3). In industrialized countries across the world, aircraft traffic noise contributes to urban populations being exposed to day-night average sound levels of over 50 decibels (dB), while urban locations are exposed to day-night average sound levels of less than 50 decibels due to outdoor traffic (Passchier-Vermeer & Passchier, 2000, p. 124).
Noise pollution effects are determined by the duration of the level, which are measured in decibels and the duration of the noise, as well as the sound’s frequency. When assessing the impact of noise pollution around an airport, measurement of the noise is typically conducted using the Day-Night Average Sound Level (DNL) formula which averages the sound energy over given periods of time. The day-night average sound level formula is used to account for noise level differences at different parts of the day, generally one period is during daylight hours, while the second period is during the night, while some countries break this further down into three period to include the evening. This formula considers that during the nighttime background noise and household activity decreases during the night therefore the impact of noise pollution is greater than during daytime and therefore adds a penalty for each aircraft operation during these times to the formula. The Environmental Protection Agency (1974) points out that while there is no standard weighted penalty across the world, the typical penalty is 10 decibels for a two-period day, and 5 decibels for a three-period day (p. 20).
To better understand the impacts of noise pollution surrounding airports, the Federal Aviation Administration (FAA) uses the Integrated Noise Model (INM), which takes the day-night average sound level noise contours and then creates noise exposure maps. The integrated noise model retrieves information from a database which has information on different industry aircraft to include military aircraft, whether they are powered by turbofan, turbojet or propeller-driven engines. The Federal Aviation Administration (2005) notes that this database covers information on departure profiles for different trip lengths, aircraft approach parameters and the Sound Exposure Level (SEL) versus distance curves for a multitude of thrust settings for each aircraft in the database (p. F-16). The contours expressed on the noise exposure map illustrate the noise exposure surrounding the airports in terms of day-night average sound levels across a topographic map extending outwards from the airport’s runways (Figure 1.1). Any areas represented on the noise exposure map with a day-night average sound level of over 75 is considered severe noise exposure, while a day-night average sound level of 65 represents significant noise exposure levels.
The three main sources of noise pollution generated at any airfield come from the aircraft engine, which could either be a turbojet or turbofan, the airframe of the aircraft or generated from propellers on rotorcraft. While there are still some aircraft that still operate with turbojet aircraft, over the past three decades most aircraft manufacture and engine manufacturers have turned to the turbofan engine for better reliability, economy and reduced noise pollution. The noise created by the aircraft engine is based upon several different aspects of the engine; (1) the variation in velocity and temperature of the gasses that bypass the both the duct and engine nozzles; (2) the difference in the pressure ratio between the fan and compressor; and (3) how the turbine pressure ratio decreases (Attenborough, Tokarev & Zaporozhets, 2011, p. 65). The most obvious noise pollution created by an aircraft engine is the combustion chamber noise, but the compressor, fan and turbine components of the engine also contribute to the overall noise pollution created by the aircraft. With an aircraft engine that is a high-bypass engine, the mixing of the hot air that travels through the core of the engine and the cold air that is bypassed around the core through the fan must also be taken into considerations when they meet within the atmosphere behind the aircraft engine.
Noise generated from the airframe of an aircraft is the result of the different aerodynamic fixtures on the aircraft which include horizontal and vertical tails, the aircraft landing gear wheel wells, as well as primary and secondary flight controls on the wings. If the aircraft is also a short takeoff and landing aircraft, such as the Lockheed Martin F-35B, Short-Takeoff and Vertical Lift variation, there are additional noise sources to consider, including the under-wing doors and propulsion directing devices. Once powerplant noise is reduced upon an aircraft’s approach, the noise generated by the airframe is the largest source of noise generated by the aircraft at that time. During the approach sequence of an aircraft, one reason the airframe becomes the largest source of noise pollution is due to the landing gear system of the aircraft. Once the landing gear is extended on approach, the main landing gear struts, wheels and tires generate low frequency noise, while the hoses and lines installed on the gear generate noise at a higher frequency, creating a broad frequency spectrum that is important to overall noise levels generated by the aircraft (Yong, Xunnian, & Dejiu, 2012, p. 250). Second to the noise generated by the landing gear would be the high lift devices located on the aircraft wings which can include flaps, leading edge flaps, slats and spoilers depending on the approach angle of the aircraft which is more noticeable on aircraft equipped with high-bypass turbofan aircraft. The noise created by these lift devices is believed to be caused by vortices interacting with the sides of the lift devices and with how the air travels across the flap surfaces.
Turboprop aircraft are popular among air carriers to transport passengers on shorter flights between nearby cities and the main hub thanks to their great fuel efficiency at slower speeds, but it comes at a cost. On average, turboprop engines are 10 to 30 decibels louder than commercial jet airliners, but mostly at lower frequency tones (Kincaid, Laba, Padula, 1997, p. 229). On turboprop aircraft, the primary noise source is the propeller. Fluctuations in pressure that are caused by lift and draft disturbances give the propeller a loading noise, while the thickness of the noise is produced by the periodic displacement of air due to the volume of the spinning propeller blades (Attenborough, Tokarev & Zaporozhets, 2011, p. 85). The amount of noise generated by a turboprop engine will be determined by the number of blades and the rotational speed of the blades.
While most helicopters generate less noise than required by noise certification standards, noise complaints stemming from helicopters have become popular in large cities as more heliports open. The main contributors to noise pollution on helicopters come from the main rotor, the tail rotor and the turbine engine, though most of the noise generated by the turbine engine is directed upwards, making it less noisy than typical turbojet and turboprop engines. The noise generated by the mechanical systems of the turbine engine emit at higher frequencies and since they are generated upward, dissipate quicker into the atmosphere. Helicopters have a wide acoustic spectrum with one noise spectrums created the main and tail rotor, and then a sperate spectrum created by the rotor blades as they interact with the atmosphere and are influenced by thrust, the number of blades and diameter of the rotor blades.
While noise pollution doesn’t present a visual impact on the surrounding environment, studies have shown that noise pollution has significant impacts on individuals to include hearing impairment, cardiovascular issues and sleep disturbances. Typically noise in considered just an annoyance, something that disrupts communications and activities, but Stansfeld and Matheson (2003) emphasized that continuous exposure to noise levels of 85-90 decibels can lead to progressive hearing loss and an increase in hearing sensitivity because of how the sound energy impacts the inner ear. A hearing handicap as described by International Organization for Standardization (ISO) (as cited in Passchier-Vermeer & Passchier, 2000), is defined as “the disadvantage imposed by hearing impairment sufficiently severe to affect one’s personal efficiency in the activities of daily living” (p. 125).
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