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.

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].

Particulate matter with diameters less than 2.5 and 10 microns (PM_2.5 and PM₁₀, respectively) in air were measured using a BR-SMART-126 Particle Counter

(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.

Mean values of PM_2.5 and PM₁₀ were compared with the World Health Organization guidelines i.e. annual mean for PM_2.5 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].

AQI pollutant = Air pollutant concentration WHO standard × 100 % (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 PM_2.5 and PM₁₀. Generally, lower AQI values indicate better air quality [30] [31] [32].

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.

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].

The levels of air pollutants determined are shown in Table 2. Particulate matter (PM_2.5 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 PM_2.5 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

^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 (PM_2.5) 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

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].

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 PM_2.5 [56]. In the neighboring Kampala, monitored PM_2.5 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].