Monitoring the impacts of climatic seasons on air quality and VOC concentration trends at Lanseria International Airport in Johannesburg, South Africa.

doi:10.21203/rs.3.rs-4826942/v1

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Monitoring the impacts of climatic seasons on air quality and VOC concentration trends at Lanseria International Airport in Johannesburg, South Africa.

https://doi.org/10.21203/rs.3.rs-4826942/v1

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High emissions of volatile organic compounds (VOC) pose a serious health risk, including cancer. The Environmental Protection Agency (EPA) and the World Health Organization (WHO) list these substances as hazardous air pollutants (HAPs). Air travel and airport operations are major contributors to VOC emissions. Within the VOCs, a group referred to as BTEX (i.e. benzene, toluene, ethyl-benzene and xylenes) pose several health implications on exposure. Therefore, monitoring VOC concentrations at airport settings are imperative. The research was undertaken at Lanseria International Airport for this pilot study. Sampling was conducted in the winters of 2019 and 2020 and the summer of 2020. Monitoring campaigns lasted 14 days, using Radiello Passive Samplers and meteorological data acquired from the South Africa Weather Service (SAWS).

BTEX data indicated that winter 2019 pollutant levels were higher than winter 2020. While summer typically produces lower concentrations than winter, summer 2021 saw greater concentrations than winter 2020. This may be attributed to the changing conditions due to the COVID-19 pandemic lockdown conditions that were experienced. BTEX results for winter 2019, winter 2020, and summer 2021 were 250.8 µg/m³, 133.63 µg/m³, and 232.5 µg/m³, respectively. The kriging interpolation technique was used to construct hotspot spatial distribution maps. Specifically, the paint shop, the fuel farm, and the apron office at the airport had elevated VOC concentrations over the three years. In contrast, the fire training area had some of the lowest concentration levels mapped. In conclusion, seasonal change, environmental conditions, and lockdown regulations significantly influenced BTEX VOC concentrations.

International airport

Seasonal variations

BTEX

VOC

Hotspot Monitoring

Global Burden of Disease (GBD) 2015 found that environmental risk factors contribute to 16% of all-cause mortality, with air pollution being the most significant component (GBD 2015; Ghaffari et al., 2021). VOC-polluted air is a major issue in airport air quality due to its detrimental health effects and impact on concentrations and weather conditions (Moolla et al., 2014; Moolla and Johnson, 2019). They contribute to harmful air pollution by generating secondary pollutants, including tropospheric ozone (Kuyper et al., 2019; Alahabadi et al., 2021). About 16% of benzene and toluene production contributes to tropospheric ozone (Alahabadi et al., 2021).

Ghaffari et al. (2021) found that BTEX chemicals contribute up to 60% of non-methane VOC concentrations in metropolitan settings, with BTEX benzene contributing up to 5%. These monoaromatic hydrocarbons indicate that organic air pollutants originate from several sources, including cars, gas combustion, petrochemical industries, solid waste breakdown, and building materials (Alahabadi et al., 2021). Exposure to BTEX compounds by breathing can cause different health issues in people. Benzene, the most prevalent BTEX species, is classified as a Group 1 human carcinogen by the IARC and Class A by the USEPA (Moolla et al., 2015; Hamid et al., 2020). The TEX components toluene, ethylbenzene, and xylene are hazardous air pollutants (HAPs) (Moolla et al., 2015; Hamid et al., 2020). Other BTEX compounds harm the respiratory and cardiovascular systems (Moolla et al., 2014). Long-term exposure to pollution can harm the nervous system, lungs, and other important organs (Alahabadi et al., 2021). (Alahabadi et al., 2021).

In a recent study, Alahabadi et al. (2021) compared BTEX emissions across different land uses in Iraq, while Ghaffari et al. (2021) investigated ambient BTEX concentrations in urban, rural, and industrial areas with varying traffic densities in Bandar Abbas, Iran. This study compared BTEX's contributions to spatial distribution and emission patterns. The simulation technique evaluated BTEX's exposure risk and identified indoor and outdoor emission sources (Ghaffari et al., 2021). Ghaffari et al. (2021) monitored rural areas, which researchers generally overlook. Industrial and urban areas are prioritised for their rapid contribution, including traffic density, petrol refuelling stations, and building density. In contrast, rural areas have fewer factors (e.g., salon emissions, firewood, forest fire smoke, and plant volatile compounds). Ghaffari et al. (2021) observed that beauty salons in rural locations with low EX component concentrations contribute to BTEX emissions. Most studies in South Africa focus on airports and urban and industrial regions.

According to the South African National Environmental Management: Air Quality Act, 2004, South Africa has a constitutional right to clean air (DEA, 2009; https://www.gov.za/documents/national-environment-management-air-quality-act). This Act safeguards air quality by reducing emissions. High BTEX concentrations in South Africa harm health and the environment, particularly in Highveld Priority Areas (HPA) (Wright et al., 2011). Monitoring air quality standards is crucial for determining dangerous chemical concentrations, such as volatile organic compounds (VOC). The lack of legislation in South Africa regarding VOC levels in ambient air complicates monitoring and emission control efforts. Toluene, ethylbenzene, and xylenes (TEX) harm health, but only benzene is monitored and limited in South African ambient air under government legislation. Benzene exposure was limited to 1.5 ppb in 2016 (Moolla et al., 2015), and standards have not been reviewed, though not in line with WHO standards.

South Africa is a developing nation that relies on industry; Moolla et al. (2014). According to Moolla et al. (2014), inhaling highly toxic BTEX can lead to serious health consequences. South Africans have a constitutional right to good air quality under the 2004 National Environmental Management: Air Quality Act. South Africa has taken steps to reduce fuel emissions, including prohibiting leaded petrol and high-sulphur diesel. South Africa offers LLRP, 95- and 97-unleaded petrol, and 10- and 50-ppm diesel alternatives.

Recent advancements in diesel fuel pose significant threats to fuel attendants, drivers, and the public (Moolla et al., 2014). South Africa lacks laws regulating VOC levels in ambient air, making monitoring and emission control techniques more challenging due to minimal monitoring in most locations. Despite the health risks of toluene, ethylbenzene, and xylenes (TEX), South African government regulation solely monitors and limits benzene in ambient air. Benzene exposure was limited to 1.5 ppb in 2016 (Moolla et al., 2015).

According to Baltrėnas et al. (2011), factors like source strength and atmospheric processes affect BTEX concentration in ambient air. Ambient BTEX concentration levels are influenced by BTEX source emission strength and seasonal atmospheric processes (Baltrėnas et al., 2011; Kuyper et al., 2019). Hydroxyl radical (OH) processes that regulate harmful gas levels primarily eliminate BTEX in the atmosphere. Kuyper et al. (2019) found that benzene and toluene are less reactive BTEX species. BTEX residence lifespan in the atmosphere: 9.4 days for benzene, 1.9 days for toluene, 1.6 days for ethylbenzene, 11.8 h for m-xylene, 19.4 h for p-xylene, and 20.3 h for o-xylene (Baltrėnas et al., 2011). Ethylbenzene and –xylene are highly reactive BTEX species, while benzene and toluene are less reactive (Kuyper et al., 2019). These chemicals are extremely reliant on meteorological conditions.

Winter weather is steady due to low atmospheric OH, high pressure (1,008 hPa), low temperature (10°C) with minimum sunlight, low humidity, and low wind speed (1.20 m s − 1) (Baltrėnas et al., 2011). Inversions trap emissions in the boundary layer and lower troposphere, causing winter brown hazes in low-lying regions like the Cape Flats (Baltrėnas et al., 2011). These conditions have increased BTEX concentrations, especially for less reactive species like benzene and toluene with longer residence times. High atmospheric OH and warm temperatures (approximately 35°C) promote unstable weather, reducing BTEX concentrations and generating secondary pollutants, including tropospheric ozone (O3) through photochemistry (Baltrėnas et al., 2011; Bauri et al., 2016). Additionally, wind direction and velocity can mix and concentrate regional air variances (Kuyper et al., 2019). BTEX levels may impact weather patterns (Moolla & Johnson, 2019).

Over time, studies examined BTEX ambient concentrations, air temperature, ozone production, and health consequences for public, occupational, and safe working environments. Short research in South Africa examines the influence of airport lockdown contributions. Many Asian and European countries, including India, China, France, and Korea, have focused on the impact of COVID-19 and the lockdown (Mokalled et al., 2019; Cai et al., 2021; Kim et al., 2021). A significant gap exists between South African policymakers and research institutes (Kuyper et al., 2019).

Thus, the main aim of this study was to analyse VOC concentrations and air quality trends at Lanseria International Airport, during the winters of 2019 and 2020 and summer of 2020, in a pilot study, during the Covid-19 pandemic lockdown regulations.

Study Area

The pilot study was conducted at Lanseria International Airport South Africa (25° 56' 22.9 "S, 27° 55' 32.1 "E), northwest of the city on the eastern plateau (see Fig. 1). It lies in the Highveld Priority Area (HPA). Flat terrain at 1370 metres above sea level surrounds the airport. (Moolla & Johnson, 2019) (See Fig. 2). Johannesburg has a hot climate with convectional rainfall throughout summer and frigid winters (Roffe et al., 2017).

High-pressure systems continue throughout winter, causing a steady environment into spring with 3–19°C temperatures (Moolla and Johnson, 2019). Summers are warm and wet, with unpredictable weather fostering vertical motion and atmospheric dispersion (Lourens et al., 2011). Summer rain also eliminates pollutants more often; however, winters have surface inversion layers that inhibit vertical movement atmospheric mixing, so primary pollutants are trapped (Lourens et al., 2011). Established in 1974, the airport serves local, regional and international scheduled flights. Landing and take-off (LTO) peaks are usually early in the morning (06:30–10:30), and the airport avionics and aircraft maintenance enterprises exist on the airport's eastern wing (Fig. 2).

Monitoring air quality standards is crucial for analysing and evaluating dangerous pollutants such as VOC concentrations. Hamid et al. (2020) suggest passive sampling approaches are more cost-effective, user-friendly, and dependable than active sampling. Thus, in order to increase exposure, the time weight average (TWA) was evaluated, and concentrations of ambient VOC pollutants were determined. To determine automotive emission sources, the T: B ratio was employed, whereas the m,p-xylene to ethyl benzene (m,p-X: EB) ratio determined air parcel duration. The BTEX interspecies ratios were utilised to assess the source apportionment of BTEX compounds in the ambient air at Lanseria International Airport (Hamid et al., 2020). Gas chromatography was chosen for its reliability in the lab. Hotspots were mapped using Kriging interpolation. In-depth details of the methodological approach are outlined below.

Instrument Description and Sampling Method

Numerous researchers have employed Radiello passive air samplers in sampling methods successfully used this methodology in their research (Khoder, 2007; Zabiegała et al., 2010; Moolla et al., 2015; Roffe, 2017; Moolla and Johnson, 2019; Kim, 2021). The Radiello Passive Samplers have absorbent cartridges in microporous polythene membrane surface (50 mm micro-porous cylinder, 16 mm diameter; 300 mg 40– 60 cardiograph four mesh (Fig. 3) (Moolla and Johnson, 2019). During the sampling, the Radiello Passive Samplers' instruments were secured at a 2-metre height. Chambers protected sample plates and cartridges from potential damage from strong winds or high temperatures which may induce errors (Moolla and Johnson, 2019).

The Passive Samplers were used at several sites to measure the concentration of the airport VOC chemicals and spatial distribution. Previous researchers confirmed the PASs sampling method's dependability (Zabiegała et al., 2010; Moolla et al., 2015; Roffe et al., 2017; Kim et al., 2021; Moolla and Johnson, 2019). 14-day sample campaigns were conducted (viz: in winter 23 June–6 July 2020; and in summer, 6 February − 19 February 2021). Radiello passive samplers were placed per the manufacturer's instructions. Seven winter and eight summer samples were obtained during the sampling campaigns, with one blank sample (n = 15). Collected samples were stored at -4°C for analysis within seven days and submitted to an accredited SANAS lab (i.e. Chemtech Labs, Pty. Ltd.). In 2019, the same sample techniques were used, but campaign monitoring differed. The study lasted ten days and collected 17 samples from the same sampling sites.

T/B Ratios

VOC source apportionment and behaviour were assessed using interspecies ratios. The VOC T/B Ratio was computed using the formula Ratio = toluene: benzene and µg/m³. Dilutions were converted using the quotient rule: D/10 = Q where Q = UD undiluted. For Summer Paint Shop, ten dilutions µg/m³ were converted using the quotient rule calculation.

Meteorological Data

This study analysed temperature, wind speed, wind direction, and humidity VOC spatial fluctuation and dispersion to validate. Weather datasets included temperature, rainfall, wind speed, direction, and humidity (Data sets were available online: https://www.weathersa.co.za/home/equiries_climatedata, accessed on 8 August 2022).

The data was used to create diurnal wind profiles during the sampling period utilising WRPLOT VIEW v8.0.2—Lakes Environmental WR Plot Software (https://www.weblakes.com/software/freeware/wrplot-view/). The wind roses aided in determining concentration patterns and meteorological conditions that contribute to the study site.

Aircraft Statistics

Aviation graphic statistics were obtained from FlightAware (https://flightaware.com/live/airport/FALA#airport-parity-stats-container, accessed September 21, 2022). The FALA international aircraft movement graphic overview is shown in Fig. 3. The daily aircraft arrival and departure numbers are included in this dataset. The graph shows 2020–2022 data statistics, and were extracted using WebPlot Digitizer 2020 (https://automeris.io/WebPlotDigitizer/)

Data was collected to analyse VOC concentration trends, regional distribution, seasonal variations, and primary sources from 2019–2020. Additionally, the impact of BTEX hotspots, meteorological conditions, and lockdown regulations on VOC concentration at the International Airport in Johannesburg, South Africa, was examined. The 2020 winter and 2021 summer results were compared to the 2019 winter to determine VOC concentration trends. Winter pre-lockdown (2019), lockdown (2020), and summer post-lockdown (2021) are shown in Fig. 4. Toluene (13.53 µg/m³), Xylenes (10.49 µg/m³), Benzene (2.51 µg/m³), and Ethylbenzene (1.56 µg/m³) are the target compounds. Overall, the toluene compound had higher mean concentrations than other VOCs in both seasons.

Tables 1 and 2 list the minimum, maximum, mean, toluene/benzene (T/B) ratios and total VOC concentrations for each VOC.

2019–2021 VOC-BTEX Concentrations.

Prior to the COVID-19 pandemic, Moolla and Johnson (2019) conducted a study on VOC-BTEX concentration levels at the airport using Radieollo Passive Samplers. They calculated time-weighted averages, shown in Table 3. Average VOC-BTEX concentrations, from their study, revealed the following key results: VOC concentrations in µg/m³ ranged from 3.07 to 5.78 for benzene, 4.89 to 27.44 for toluene, 0.92 to 16.87 for ethylbenzene, 4.07 to 75.01 for xylenes, and 8.01 to 16.58 for o-xylene. Furthermore, total VOC-BTEX concentrations ranged from 12.95-124.04 µg/m³ during the sample period. In Table 3, the T/B ratio ranges from 1.51 to 5.81 µg/m³. Table 4 displays BTEX values for 2020 and 2021 concentrations. The samplers and sampling sites that correspond with the present study are highlighted in Table 4.

Samples 1,2,6,9,13,14,17 represent fuel farms 1 and 2, the paint shop, the MSC building, the terminal building and the apron office.

With regards to sample 17, the apron office was indoors; however, sample 3 was outdoors. The samples demonstrate the impact of weather conditions compared to winter 2020 outcomes. Additionally, Moolla and Johnson (2019) discovered that meteorology reduced VOC-BTEX levels in indoor and passive outdoor samples.

Seasonal variations, meteorological trends and isoconcentration maps.

The VOC-BTEX total concentrations (µg/m³) ranged from 10.93 to 56.7 and 15.2 to 61.5 throughout winter (23rd June to 6th July 2020) and summer (6–19 February 2021). The average concentrations of VOC-BTEX ranged from 1.6 to 3.5 (µg/m³) for benzene, toluene, ethylbenzene, m, p-xylene, and o-xylene (summer: 5.9 to 30; winter: 3.4 to 21(Tables 1 & 2). In winter 2020, sample 5 at the paint business had the highest VOC-BTEX concentrations (57.7 µg/m³), followed by benzene (2.8 µg/m³) and octane (Table 1). Sample 6, had the lowest VOC-BTEX total values at 9.12 µg m-3. In the summer of 2021, the paint shop had the highest VOC-BTEX total values at 61.5 µg/m³ (Table 2).

The lowest VOC-BTEX content was sample 1 MSP. Build with 15.2 µg/m³ of VOC-BTEX total concentrations, as various chemicals had their lowest concentrations. In summer and winter, Radiello Passive Sampler concentrations (µg/m³) had a T/B ratio of 3.26 to 13.33 and 1.36 to 7.5, respectively (Tables 1 & 2). The T/B ratio identifies mobility sources and solvent usage as the primary air pollution source at the International Airport.

Masiol and Harrison (2014) state that wind speed, relative humidity, and temperature affect air pollution distribution. Thus, low wind speeds, temperature, and relative humidity diminish dispersion and reactivity in low temperatures. In the winter of 2019, the airport had an average wind speed of 1.13 m/s (Moolla and Johnson, 2019). During passive sampling, low wind speed prevented VOC-BTEX from spreading far from their contamination sources. Figure 6 shows the summary of wind speed, temperature, relative humidity, and rainfall throughout the winter 2020 and summer 2021 sampling period. South-easterly winds dominated at an average of 2.49 m/s, with 10.12% calm winds and 17.26% calm winds. Winds varied from all cardinal directions in summer and winter (Fig. 5 a &b). Winter had a mean temperature of 11.1°C, ranging from 1.0°C to 24.0°C (Fig. 6b). The relative humidity ranged from 11–90%, with a mean of 49% (Fig. 6c). Summer temperatures ranged from 15.3°C to 30.3°C, with a mean of 22.3°C (Fig. 6e). Figure 6f shows a mean relative humidity of 66% and a range of 26–94%.

Based on isoconcentration maps, BTEX concentrations are unevenly distributed over the airport, likely due to their principal pollution sources (Fig. 7, 8, & 9). Benzene hotspots display key areas differing from the other three pollutants, in general, throughout all seasons, indicating different impacts and the need for specific management and planning, per pollutant.

Lockdown and post-lockdown aircraft movement.

The aircraft graphic data were sourced from FlightAware (https://flightaware.com/live/airport/FALA#airport-parity-stats-container.com, 2022). This data indicated the average daily number of aircraft LTO year (see Fig. 2). Aircraft movement trends (LTO) were analysed at the airport and are displayed in Fig. 3. Prior to the lockdown (i.e. January 1 to March 25, 2020), flight movements were significantly higher, with 68 daily flights recorded on January 16th .

From March 25th, 2020. South Africa issued a level 5 lockdown alert (https://www.gov.za/Coronavirus.gov.za, 2022), which resulted in a significant decrease in flight movements at the airport. The flight LTO abruptly changed in April, followed by a sudden decrease in levels, resulting in no flights. Lockdown levels are proportionate to flight numbers. A 21-day lockdown alert level 5 began from March 26th to April 30th, 2020. Alert levels 4, 3, and 2 were in place from 1st May to 20th September 2020. Level 1 was in force from September 21st to December 28th, 2020. The airport saw a rise in flights from late October to 1st November 2020, with 38 flights LTO after eight months of nationwide lockdown. From December 2020 to February 2021, the nationwide lockdown was raised to level 3. Therefore, a consistently low number of flights was noted throughout this period. Compared to the previous year, 2021 saw fewer flights due to the lockdown.

The impact of Covid-19 on sampling

High aircraft movements in 2019 relative to 2020 during COVID-19 might be due to lockdown regulations, which stopped most economic activities to avoid widespread COVID-19 infection. The 2019 and 2020 ambient BTEX concentrations trended similarly. The 2019 results for each sample site are higher than the 2020 results (Fig. 4). Thus, the number of aircraft movements during the 2019 sampling period was unquantified. However, the 2020 sample period averaged aircraft movements quantified, with 20 daily flights (Fig. 3). Before the lockdown in 2020, findings show the airport aircraft movements were 60–64 per 14 days, three times more than during lockdown.

The Paint shop and airport Apron had the highest BTEX concentrations in the 2020 sampling campaigns, and were likely affected by paints, inks, vehicles and aeroplane combustion, and nearby operations despite fewer flights being flown. The study by Cavallo et al. (2006) at Leonardo da Vinci Airport in Rome, Italy, found a similar trend. A similar trend was observed for the apron site during the winter season. The study shows that the airport apron had the highest concentrations of BTEX (27.7 µg/m³) compared to other airport sites (building and terminal/office). Moreover, the results for 2020 were lower than those for 2019. The trend of individual BTEX species with higher concentrations in 2019 than in 2020 was observed (see Fig. 4); this pattern shows that all the BTEX individuals for 2019 were higher than in 2020. This is a direct result attributed to the fact that only 281 and 337 flights occurred over the 14-day sample programme in 2020 and 2021, respectively.

Review of 2019 and 2020 winter BTEX concentrations.

During the sample periods, the overall winter BTEX concentrations in 2019 and 2020 were 250.8 µg/m³ and 115.73 µg/m³, respectively (Figs. 8 & 9). Therefore, comparing winter 2019–2020 is crucial. The paint shop displayed higher BTEX levels in winter 2019 (124.04 µg/m³) and winter 2020 (56.7 µg/m³).

The paint shop displayed a BTEX concentration of 124. 04 µg/m³ and 56.7 µg/m³ for winter 2019 and 2020, respectively, with an average of 67.34 µg/m³, indicating considerable difference during the same season. BTEX levels are generally high at paint shops as they contain xylenes and toluene. (Zheng et al., 2018; Moolla and Johnson, 2019; Kim, 2021). Referring to samplers 5 and 6, the results are BTEX-related points sources. Despite being close, samples 5 and 6 differed in 2019 and 2020, with a 56.7 µg/m³ difference. Pre-pandemic, concentrations were better when compared to 2020 values. Various conditions could cause increased ambient BTEX concentrations, including pollution source strengths, airport operations, and weather conditions affect BTEX concentration by promoting pollutant dispersion to lower concentrations or increasing concentrations due to inversion layer/s in specific seasons.

Seasonal concentration of VOC-BTEX

Mean BTEX concentrations for the median summer were higher in 2021; as levels were higher (29.06 µg/m³) as compared to winter concentrations (19.09 µg/m³) in 2020. The overall BTEX concentrations in 2020 and 2021 were 366.13, 133.63, and 232.5 µg/m³. Tables 3 and 4 show the BTEX concentration's mean, lowest, and highest concentrations. Compared to winter, summer BTEX concentrations were higher. Toluene had the highest mean concentration (summer: 11.45 µg/m³; winter: 8.22 µg/m³) for 2020 and 2021, followed by xylenes and ethylbenzene. Toluene and xylene levels were high were solvents were used (painting, coating, printing) and automobile exhaust (Zheng et al., 2018; Kim, 2021). The July mean BTEX concentrations were increased significantly in winter 2020 (from 8.22 1.64 µg/m³ to 11.45 µg/m³) (Tables 3 and 4). According to Cerón-Bretón (2015) and Kim et al. 2021, seasonal variations are often caused by climate and emission source intensity, specifically photochemical reactions.

Mixing layer heights, and great atmospheric stability prevent dilution and dispersion effects of pollutants (Khoder, 2007; Kumar et al., 2018; Kim et al., 2021). Since low mixing heights and very stable conditions are noted across the region in winters, the BTEX levels could be linked to higher winter VOC-BTEX concentrations in earlier research. However, vapours and evaporation of paints, inks, and automobile fuels can occur in hotter weather, BTEX levels can increase in summer (Moolla et al., 2015; Kim et al., 2021).

This study examined seasonal wind patterns and emission intensities throughout the 2020–2021 sampling period, which saw a higher impact from airport operations. Aircraft data showed aircraft movements dominated more in the summer of 2021 than in the winter of 2020 (Fig. 3); consistent with lockdown regulations. The mean benzene concentrations was higher in summer (18 µg/m³) as compared to winter (15.6 µg/m³), contradicting previous findings (Kumar et al., 2018; Kim et al., 2021). This may be due to increased lag time in the atmosphere during this season. However, during monitoring times, benzene levels did not surpass SA AQL (10 µg/m³) and/or the US Environmental Protection Agency’s (EPA) yearly limits, however, exceeded World Health Organization’s (WHO) daily limit.

When concentration levels are compared to international studies; Beirut Rafic Hariri International Airport indicate similar and somewhat higher concentrations (Mokalled et al., 2019); while seasonally BTEX concentrations were found to be higher in summer when compared to a study conducted in India (i.e. during the summer BTEX concentrations were found to be 99.4 µg/m³ (Mokalled et al., 2019). Moolla and Johnson found similar results in 2019. They found that BTEX concentrations at Lanseria International Airport were higher than at Teterboro Airport in the US, which had high vehicle emissions. South Africa's solvent use and airport operations may explain this difference. The differences in concnetrations may be impacted by pollution regulations and gasoline's specific properties used in South Africa versus other nations. Using petrol and other solvents is highly restricted in most Asian and European countries, including India and the US (https://www.epa.gov/gasoline-standards/gasoline-sulfur, 20 October 2022). India's primary diesel grade is ten ppm sulphur diesel. (https://www.transportpolicy.net/standard/india-fuels-diesel-and-gasoline/accessed 18 October 2022). In South Africa, alternative ppm sulphur diesel ranges from 10 to 50. majority grades are 50 ppm (Moolla et al., 2015). Dimitrova (2019) explained that 10 ppm is more environmentally friendly and sulphur-sensitive than 50 ppm. Countries in Europe and Asia have protective devices on petrol, fuel, and paint pumps to reduce vapour emissions; however, South Africa does not have protective devices on identical pumps (Moolla et al., 2015). Moolla et al. (2015) also indicated that South Africa lacks rubber sealers.

BTEX concentrations depend on conditions. Weather conditions show that it caused seasonal shifts; 2021 was higher than 2020. As indicated, weather conditions greatly affect air pollution and spatial distribution (Masiol and Harrison, 2014). In 2021, summer temperatures and humidity were high. However, they did not considerably impact seasonal BTEX levels. Consequently, a prior study conducted at Taichung Airport in Central Taiwan indicated that decreased wind speed may have contributed to the rising correlation coefficients for ambient air particle concentrations (Fang et al., 2015). At the Abidjan Felix Houphouet Boigny Airport, on the other hand, high wind speeds were necessary for controlling air pollution levels (Dominutti et al., 2019).

Furthermore, BTEX pollutant source allocation is crucial. Kuala Lumpur's roadside T: B ratio was 2.2, indicating vehicle emissions (Hamid et al., 2020). However, summer results showed that the paint shop had a 6.98 T: B ratio (Table 2), confirming the source was solvents. The m, p-xylene to ethyl benzene (m, p-X: EB) ratio was employed to measure air parcel ages. Hamid et al. (2020) found that the Kuala Lumpur m, p-X: EB ratio was (1.00), indicating photochemical reaction Ozone-forming processes (Bauri et al., 2016). Thus, this research m, p-X: EB ratio ranges between 2.92–3.62 and 2.9–3.1 in winter 2020 and summer 2021, indicating activity engaged in photochemical reactions (Table 3).

The trend in the spatial distribution

The isoconcentration maps show significantly diverse BTEX concentrations dispersed airport-wide by primary source. This shows that the concentration of ambient BTEX emissions was close to their principal sources across all BTEX species (Figs. 8, 9a, 9b, 10a, 10b). Wind direction is attributed to low concentration during the winter of 2020 because the wind was dispersed in all directions during the sampling campaigns. It appeared that south-easterly winds dominated in 2021 and had little impact because of low wind speed. An earlier Monterrey, Nuevo study in Leon, Mexico, by Cerón-Bretón et al. (2015) observed wind speed and direction affected pollutant movement between sampling sites, affecting seasonal trends. Their findings can be compared to 2020's high wind speed and direction. The isoconcentration plots reveal that increased BTEX concentration was not far from pollution sources (Fig. 7, 8, & 9), affecting concentration more than spatial dispersion.

The isoconcentration maps depict BTEX emissions' spatial distribution trend And indicate that the paint shop is the hotspot since it had significant BTEX levels (Moolla and Johnson 2019). The high amounts of BTEX-containing paints evaporated easily in warm temperatures, causing the paint shop to have high concentrations. A previous study in Seoul, South Korea, found that the high concentrations of the toluene pollutant were due to paints, inks and vehicular exhausts (Kim et al., 2021). Thus, seasonal variation, climatic conditions, and lockdown regulations shaped BTEX's spatial spread VOC-BTEX concentrations, and solvent use dominated BTEX VOC geographical distribution.

This study observed the trends in BTEX concentrations from 2019 to 2021 at Lanseria International Airport throughout the winter of 2019 and 2020, and during the summer of 2021. The study utilised Radiello Passive samplers to analyse the data. The BTEX concentrations during the winter of 2019 were generally higher than those seen during the winter of 2020. Conversely, the readings from summer 2021 were higher than those from 2020. The greatest measured BTEX emission was in the Paint Shop, during both summer and winter, and was impacted by the strength of emissions and the placement of emission sources. Elevated levels of BTEX emissions are observed to originate from using solvents and operating mobile sources. Activities at airports impacted the BTEX levels (benzene, toluene, ethylbenzene, and xylene) in the surrounding environment. Additionally, lockdown measures implemented to minimise the spread of COVID-19 pandemic affected flight movement, and subsequently reduced BTEX concentrations at the airport. Nevertheless, in 2020, the airport to decrease BTEX emissions. Therefore, a direct relationship exists between the quantity of flights, the severity of lockdown measures, climatic conditions and the levels of BTEX concentrations. Therefore, based on the data collected during the sample period, it can be shown that the number of LTO activities for aircraft in 2021 is larger than in 2020. The decrease in emissions in 2020 can be attributed to the limitations placed on aircraft movements and airport-related operations. Generally, a seasonal variation was noted, with increased winter temperatures. In addition, wind velocity in 2020 significantly impacted the concentrations of BTEX compounds compared to 2021.

Acknowldegements

This work was supported by the National Research Foundation (grant number: TTK150709124599). Sincere gratitude goes to Lanseria International Airport, Environmental Division, for supporting sampling strategies and campaigns.

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Monitoring the impacts of climatic seasons on air quality and VOC concentration trends at Lanseria International Airport in Johannesburg, South Africa.

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Abstract

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Introduction

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Discussion

The impact of Covid-19 on sampling

Seasonal concentration of VOC-BTEX

The trend in the spatial distribution

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Supplementary Files

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