Aviation Noise and Air Pollution: Results of a Study at Entebbe International Airport, Uganda ()
1. Introduction
Pollution is a pressing multi-sectoral challenge implicated in the progression of the decadal climate change [1]. Particularly, air and noise pollution present health, economic and social threats to countries globally [1]. There are now growing concerns by global aviation authorities and environmentalists that airports have substantial contributions to environmental pollution [2] [3] [4] [5]. They have been implicated for various ecological issues relating to acid rain, climate change, tropospheric ozone and potential risks linked to regional, ecological, environmental and public health [6]. For example, aircraft emissions of pollutants such as carbon dioxide, sulphur dioxide and volatile organic compounds are known to contribute to the atmospheric pool of greenhouse gases [3]. Aircraft air pollutant emissions are grossly categorized into 1) emissions during the landing and take-off (LTO) cycle and 2) those during the non-LTO flight cycle [3]. The former produce emissions with prominent impacts compared with the latter [7] [8] [9]. Increase in air transport volumes and expansion of airports to meet future capacity needs have made aircraft emissions during the LTO more prominent and of general research interest [4] [10] [11] [12].
Previous advances to establish air quality in Uganda and East Africa at large have been impeded by inadequate regulatory grade equipment required to record long term data and track vacillations in air pollution both temporally and spatially, as well as assess their influences on public health [1] [13] [14]. This is primarily due to the prohibitive cost of air quality monitoring equipment, and the difficulty in obtaining appropriate calibration and certification services [15] [16] [17]. Despite the paucity of air quality data, previous studies indicate that air pollution is an environmental concern that has undermined the development of safe, inclusive, resilient and sustainable cities [13]. A Systems Approach to Air Pollution (ASAP)-East Africa team has supplemented available long-term air quality monitoring with spot measurement campaigns at selected sites including outdoor and indoor locations in Uganda [14].
On the other hand, aircrafts contribute to noise pollution particularly during take-off and landing [18]. Ideally, airports should be away from human habitation so that people are not affected by the noise caused by the air traffic [19]. However, this is not the case in many countries, where human habitation is in close proximity to airports [20]. People who live away from airports but under the flight path may also get disturbed by high noise levels [21]. Noise arising from aviation activities has been implicated in the etiology and aggravation of cardiovascular diseases, hypertension, psychological ill-health, lowering of cognitive ability in children, annoyance and sleep disturbances [22] [23]. In the current study, we report on the concentration of some priority air pollutants and noise pollution levels at Entebbe International Airport (EBB), Uganda.
2. Methods
2.1. Study Area
Entebbe Airport is the principal and only Ugandan international airport. It is situated approximately six kilometers Southwest of Entebbe town at coordinates 00˚02'33"N 32˚26'37"E [24]. Located on the Northern shores of Lake Victoria (Figure 1), the airport is more than 30 kilometers away and South West of the central business district and capital city of Uganda (Kampala) [25]. The airport is straddled by equator at latitude 00.020 North and longitude 320 East, for which reason it is described as the “Airport on the Equator” [26]. At about 3782 feet above sea level, the airport is part of a peninsular bordering Africa’s biggest fresh water-Lake Victoria.
2.2. Determination of Noise Levels
Noise levels were determined using a Castle GA112 octave band sound level meter (Castle Advanced Solutions, UK). Noise levels were measured thrice daily by giving a time range of 4 hours from the initial test (i.e. at 8:00 am, 12:00 pm and 4:00 pm). This is because noise intensity is dispersed very easily and therefore it cannot be taken at close intervals [27].
2.3. Measurement of Air Pollutant Levels
Particulate matter with diameters less than 2.5 and 10 microns (PM2.5 and PM10, respectively) in air were measured using a BR-SMART-126 Particle Counter
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Figure 1. Map of Uganda showing the location of Entebbe International Airport. Inset is the location of Uganda on the African continent.
(Blatn Science & Technology Co. Ltd., Beijing, China) [28]. Aeroqual S500L portable air quality monitor (Aeroqual Limited, Auckland, New Zealand) was used for measuring carbon dioxide, carbon monoxide, hydrogen sulphide, sulphur dioxide, ozone and volatile organic compounds (VOCs) concentration. The free Series 500 6.4 PC Software was used for data extraction from the monitor. Testing for all the air pollutant parameters was done after every 1 hour for 8 hours (8:00 am to 4:00 pm, East African Standard Time). All handheld devices employed in this study were pre-calibrated before usage for effectiveness and quality assurance purposes.
2.4. Risk Assessment
Mean values of PM2.5 and PM10 were compared with the World Health Organization guidelines i.e. annual mean for PM2.5 is 10 μg/m3, 24-hour mean = 25 μg/m3 while PM10 = 20 μg/m3 and 24-hour mean = 50 μg/m3 [29]. The mean values were harnessed to compute the air quality index (AQI). The indices for each pollutant (average of the total sum from each sampling location) were calculated using Equation (1) [30] [31] [32].
(1)
The AQI according to United State Environmental Protection Agency (US EPA) is an index for reporting daily air quality as it indicates how clean or unhealthy the air is, the level of concern and the health effects [30] [31] [32]. The AQI focuses on “health effects an individual may experience within a few hours or days after breathing unhealthy air”. Table 1 shows the air quality index rating [33] [34] and the AQI pollutant concentration specific range for PM2.5 and PM10. Generally, lower AQI values indicate better air quality [30] [31] [32].
2.5. Data Analysis
Quantitative data were presented as means ± standard deviation of replicates. The analyses were done using GraphPad Prism statistical software (version 9.1.0, GraphPad Software, USA). Results obtained were compared with international compliance guidelines.
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Table 1. Air quality index (AQI), PM2.5 and PM10 concentration color codes and the air pollutant level of health concern.
3. Results and Discussion
3.1. Noise Pollution Levels
Aviation activities have become one of the causes of acoustic degradation of the environment [35] [36] [37]. Figure 2 shows that Entebbe International Airport experiences irregular noise frequencies with the midday having the highest noise intensities. The international standards for aviation noise levels are estimated at 60 decibels (dB) for daytime (6:00 am - 10:00 pm). Therefore, the levels did not match with the International Aviation Standards for sometimes of the day. This causes discomposure at the airport especially at the terminal which is a public area all the times. However, the noise levels were also increased due to surface traffic and construction works following the current expansion of the airport. A study in Turkey reported that the rush hour for Van Ferit Melen airport is between 10:00 and 14:00 hours. The measured noise level average was 96.0 ± 8.4 dB in the apron and 86.0 ± 8.7 dB in the terminal area [27].
Previous studies linked aviation noise to sleep disturbances, hypertension, heart diseases, cognitive and learning deficits in children [38]. According to ISO standards, 0 - 26 dB hearing value is the normal hearing range, 27 - 40 dB can cause very mild hearing loss, 41 - 55 dB to mild hearing loss, 56 - 70 dB causes moderate hearing loss, 71 - 90 dB causes advanced hearing loss while 90 dB and above may cause more advanced hearing loss [39].
3.2. Air Pollutants Concentration
The levels of air pollutants determined are shown in Table 2. Particulate matter (PM2.5 and PM10) ranged from 3.0 to 17.0 μg/m3 and 3.0 to 21.0 μg/m3, respectively. This implies that the particulate matter levels at EBB were all below the World Health Organization recommended levels of PM2.5 and PM10 (i.e. daily mass concentrations of 25 μg/m3 and 50 μg/m3) [40]. Particulate matter is a common proxy indicator for air pollution as it has effects on people more than
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Figure 2. Noise levels at different times of the day at Entebbe International Airport, Uganda.
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Table 2. Average concentration of air pollutants at Entebbe International Airport, Uganda.
aND: Not detected.
any other pollutant. Particulate matter is a complex mixture of solid and liquid particles of organic and inorganic substances (sulphates, nitrates, ammonia, sodium chloride, black carbon, mineral dust and water) suspended in the air. PM10 have the potential to penetrate and lodge deep inside the lungs. Fine particulate matter (PM2.5) is a concerning air pollutant, particularly if it exceeds the WHO limit of 25 μg/m3 24-hour mean [40] because they can penetrate the lung barrier and enter the blood system. Chronic exposure to PM contributes to the risk of developing cardiovascular and respiratory diseases as well as of lung cancer [41].
Toxic volatile organic compounds (VOCs) like benzene, toluene, ethyl benzene and xylenes (BTEX) are atmospheric pollutants that present serious threats to human health [42] [43] [44]. Their emissions related to aircraft are not only during combustions but also result from resting losses from aircraft fuel tanks and during refuelling of the aircraft [45]. In this study, the concentration of VOCs was lower than the limit of 500 μg/m3 [46]. VOCs such as 1,3-butadiene, benzene and vinyl chloride were classified by the International Agency for Research on Cancer in Group 1 as carcinogenic for humans [47]. They also cause eye and respiratory irritations, headache, dizziness, visual disorders as well as memory impairment [48]. At least 14 single or complex compounds are listed as hazardous by the Federal Aviation Administration, which in addition to polyaromatic hydrocarbons comprise acetaldehyde, 1,3-butadiene, n-hexane, acrolein, benzene, styrene, xylene, toluene, propionaldehyde, ethylbenzene, formaldehyde and lead compounds [49]. A recent study assessed 46 VOCs in the indoor air of the control tower maintenance room, potentially affecting employees, where a correlation was found between aircraft number and concentrations of light aldehydes/ketones [44].
Carbon monoxide and hydrogen sulphide concentrations were low (undetected in some cases) as compared to carbon dioxide concentrations. While the global trend is aiming at zero carbon dioxide emissions, the current study indicated that EBB produces substantial amounts of carbon dioxide which is a greenhouse gas. On the other hand, the current Occupational Safety and Health Administration permissible exposure limit for carbon monoxide is 50 ppm as an 8-hour time-weighted average concentration [50]. Carbon monoxide with its ability to combine with iron in haemoglobin may lead to carbon monoxide poisoning, a condition typified by headache, dizziness and drowsiness. Excessive exposure may cause loss of consciousness (coma) and ultimately death at high concentrations [51]. The 8-hour limit for hydrogen sulphide is 10 ppm and was not exceeded in this study. Exposure to this gas may cause eye, throat and nose irritations, bronchial constriction in asthmatic patients, spontaneous abortion, increased blood lactate concentration, decreased skeletal muscle citrate synthase activity, headache, dizziness, nausea, vomiting, coughing, difficulty in breathing, olfactory paralysis, convulsions and death in severe cases [52] [53].
Serious health risks also arise from exposure to ozone and sulphur dioxide. The WHO set 100 μg/m3 8-hour mean as the guideline for ozone [41], which was not exceeded at EBB in this study (Table 2). Ground level ozone is one of the
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Table 3. Average PM concentrations and AQI for the different locations studied at EEB.
reactants in the formation of photochemical smog, along with nitrogen oxides (NOx) from vehicle and industry emissions and volatile organic compounds (VOCs) emitted by automobiles [54]. It is one of the six criteria air pollutants prescribed by the United States Environmental Protection Agency. At high concentrations in the air, ozone can trigger asthma, bronchitis and emphysema, cause breathing problems, reduce lung function or cause lung diseases [41] [55]. The WHO guideline for SO2 is 200 μg/m3 1-hour mean or 40 µg/m3 (annual mean). This pollutant has effects on the respiratory system (the lungs) and causes eye irritation. Its ability to trigger inflammation of the respiratory tract causes coughing, mucus secretion, aggravation of asthma and chronic bronchitis if inhaled at higher concentrations [41].
3.3. Health Risk Assessment Results
As indicated in Table 3, the results of risk assessment based on particulate matter indicated that the air quality indices were all less than 50, which corresponds to good air quality. A recent report indicated that the air quality index of EBB is 60, with the dominant air pollutant being PM2.5 [56]. In the neighboring Kampala, monitored PM2.5 data indicated that air quality of the city is typically at levels considered “unhealthy for sensitive groups” to “unhealthy” according to the United States Environment Protection Agencies Air Quality Index (AQI) [14].
4. Conclusion
Airports form part of an interconnected world but also have many accrued environmental footprints. This study established that Entebbe International Airport experiences irregular noise frequencies with the midday having the highest noise intensities. Though some of the air pollutants are below recommended threshold, carbon dioxide was recorded at higher concentrations. Therefore, the aviation authorities need to ensure that these air pollutants are monitored and controlled continuously. The expansion of EBB concurrent with the development of residential areas might increase the noise and air pollution if cleaner technologies are not embraced. Further studies should perform audiogram assessments (acoustic estimation of noise-induced hearing loss) at the airport.
Acknowledgements
The authors are grateful to the World Bank, the Inter-University Council of East Africa (IUCEA) for the scholarship awarded to Waganesh Admase and Timothy Omara through the Africa Center of Excellence II in Phytochemicals, Textiles and Renewable Energy (ACE II PTRE) at Moi University (Kenya) which made this study possible. Elly Olomo and Jasper Okino are grateful to the Mobility for Innovative Renewable Energy Technologies (MIRET) scheme (under the Intra-Africa Academic Mobility Scheme of the European Union Funding) hosted at Moi University for the scholarships awarded to them that made this collaboration possible.