causes – Quit Playing Games (With Our Earth)

April 4, 2022Jo Ee Kwek No Comments

Skyglow or skyfall? Shining a light on light pollution impacts at the Olympic Games (1)

When we talk about the types of pollution affecting the Olympic Games, most of us might think of air and water pollution, and for good reason. After all, pollutants are most commonly transported through air and water mediums, resulting in their impacts being easily observed when contaminated air and water are consumed. Similarly, the United States Environmental Protection Agency (EPA, 2021) seemingly hints toward air and water pollution when defining pollutants as substances that “adversely affect the usefulness of a resource or the health of humans, animals or ecosystems”.

However, such perceptions of pollution are restrictive, and overlook the impact that intangible but pervasive entities — such as light — have on biota. In recent years, light pollution has been increasingly identified as one of the most harmful types of pollution, as it not only worsens sleep patterns, but also disrupts wildlife behaviour (Chepesiuk, 2009). It has also become increasingly common amidst the general rise in affluence levels and construction of brightly-lit cityscapes worldwide (Chepesiuk, 2009).

Light pollution has become increasingly pervasive, amidst the excessive use of artificial lighting to light up urban centres and homes (Coetzee, 2019)

It is thus of little wonder that the Olympic Games — being an internationally-recognised mega-event that seeks to impress through the use of grand infrastructure and spectacular displays — is a major producer of light pollution. From the launching of fireworks to end the Olympic Games on a high, to the liberal use of electric lights to illuminate venues and optimise spectator experience, artificial light is found almost everywhere. This is unfortunately to the point that it overwhelms the visual senses and eventually, the human brain.

A case in point would be the 2012 London Olympic Games, which was hailed as one of the most “thoughtfully planned” but light-intensive Olympic Games in history. As reported by LEDs Magazine (2012), nearly 70000 LED modules were positioned beside spectator seats, 14000 lamps were located within the Olympic Stadium. This was not inclusive of the additional 25000 LED modules used for nighttime lighting at the Olympic Park (LEDs Magazine, 2012). While the use of such light was arguably necessary as it made holding competitions at night possible, their excessive use had brought about sleep disorders amongst the general population. 67% of adults reported disrupted sleep while 31% suffered from insomnia, as their overexposure to artificial light had led to decreasing pineal melatonin production and control over circadian rhythms (Falchi et al., 2011). In other words, the retina was increasingly hit by light photons, causing the mind to be overstimulated (Chepesiuk, 2009).

The massive numbers of LED modules and lamps used at the 2012 London Olympic Games was associated with increasing sleep disorder rates amongst British adults (Peralta, 2012)

Hence, it is clear that light pollution has adverse long-term impacts on human health that — rather interestingly — do not discriminate on the basis of socioeconomic status and race. Rather, light pollution is most commonly experienced in developed countries (Gallaway, Olsen and Mitchell, 2010), where the use of artificial light for urban landscapes is regarded as a hallmark of economic progress. Unfortunately, the same does not apply for wildlife, with both sea and land species being equally vulnerable to light pollution impacts. With that, do look out for my next post on this dark issue!

References

Chepesiuk, R. (2009). Missing the dark: health effects of light pollution. Environmental Health Perspectives, 117(1). https://doi.org/10.1289/ehp.117-a20

Coetzee, B. (2019). Light pollution: the dark side of keeping the lights on [Online image]. The Conversation. https://theconversation.com/light-pollution-the-dark-side-of-keeping-the-lights-on-113489

Falchi, F., Cinzano, P., Elvidge, C. D., Keith, D. M., & Haim, A. (2011). Limiting the impact of light pollution on human health, environment and stellar visibility. Journal of environmental management, 92(10), 2714-2722. https://doi.org/10.1016/j.jenvman.2011.06.029

Gallaway, T., Olsen, R. N., & Mitchell, D. M. (2010). The economics of global light pollution. Ecological economics, 69(3), 658-665. https://doi.org/10.1016/j.ecolecon.2009.10.003

LEDs Magazine. (2012, August). LED lighting plays prominent role in Olympic Games. LEDs Magazine. https://www.ledsmagazine.com/leds-ssl-design/driver-ics/article/16698368/led-lighting-plays-prominent-role-in-olympic-games

Peralta, E. (2012). As It Happened: The London Olympics’ Opening Ceremony [Online image]. NPR. https://www.npr.org/sections/thetorch/2012/07/27/157501561/live-blog-the-opening-ceremony

United States Environmental Protection Agency (2021, July 15). Report on the Environment Glossary. https://www.epa.gov/report-environment/roe-glossary#:~:text=into%20a%20waterway.-,pollutant%3A,substances%20introduced%20by%20human%20activities.

March 7, 2022Jo Ee Kwek No Comments

In deep water — The making of a water pollution crisis at the 2016 Rio Olympic Games (2)

In our previous post, we explored the anthropogenic causes of water pollution at the 2016 Rio Olympic Games and highlighted the pressing need to control these point sources. In this post, however, we will analyse Rio de Janeiro’s water pollution crisis using a different lens — residence time. Through investigating the persistence of pollutants in Rio de Janeiro’s Guanabara Bay, we can gain insight on the physical factors that contributed to the crisis.

You might recall from our second post that residence time refers to the duration that pollutants stay in a medium before being removed. Indeed, in the context of water pollution, residence time is calculated by dividing the amount of pollutant in the water body by the inflow or outflow rate of the pollutant. This means that we not only have to consider the total amount of pollutants, but also the duration needed to flush out pollutants by renewing water bodies.

We can thus deduce that pollutants found in Rio de Janeiro’s untreated waste have a long residence time, as waste is continuously accumulated in water bodies while water renewal rates remain low. As outlined by Fistarol et al. (2015), it takes approximately 11 days to renew 50% of water in Guanabara Bay, meaning that it requires at least 22 days for pollutants to be completely flushed out. While this residence time appears short considering that a massive 25 cubic metres of waste is discharged every second (Cotovicz Jr et al., 2016), it remains problematic as pollutants cannot be removed in time for consecutively-held Olympic water sports events. This is especially so for sailing and open-water swimming events, which often take place in Guanabara Bay and require athletes to cover long distances in the water (Keith, 2016). Furthermore, water renewal rates vary across Guanabara Bay, with these rates being the lowest in inner regions where tidal circulation is low (Fistarol et al., 2015). This suggests that pollutant residence time is particularly long in these regions, as pollutants are seldom flushed out.

Given long residence time of pollutants at Guanabara Bay, Olympic sailors and open-water swimmers are highly susceptible to gastrointestinal illnesses (Wharton, 2014)

In analysing residence time, it is also crucial to consider the breakdown of pollutants, as different pollutants have different residence times. One of the most persistent pollutants in Guanabara Bay is methane, which is released from untreated sewage and degrades water quality by causing acidification (Cotovicz Jr et al., 2016). According to Junge (1974), methane has a residence time of 4 years, suggesting that even after pollutants are flushed out through water renewal every 22 days, traces of methane still exist. This is supported by Cotovicz Jr et al. (2016)’s findings that methane concentrations in central Guanabara Bay are perpetually high, not only because of low tidal circulation but also the degasification of dissolved methane into the atmosphere. Thus, this reinforces that pollutant types also influence the severity of Rio’s water pollution crisis, as they affect residence time and the extent of water quality degradation.

The release of long-lasting pollutants from untreated waste, such as methane, has exacerbated water pollution in Rio de Janeiro (Davis and Manfred, 2015)

In hindsight, while Rio’s water pollution crisis stemmed from poor waste management policy, it was made worse by long pollutant residence times. While there is little that water governing bodies can do to reduce pollutant residence times, which depend on uncontrollable factors like tidal circulation, this awareness can hopefully galvanise them into ramping up waste management efforts. Only then can the extent of long-term waste accumulation be minimised, and Olympic athletes safely compete in the waters.

References

Cotovicz Jr, L. C., Knoppers, B. A., Brandini, N., Poirier, D., Costa Santos, S. J., & Abril, G. (2016). Spatio‐temporal variability of methane (CH4) concentrations and diffusive fluxes from a tropical coastal embayment surrounded by a large urban area (Guanabara Bay, Rio de Janeiro, Brazil). Limnology and Oceanography, 61(S1), S238-S252. https://doi.org/10.1002/lno.10298

Davis, S. & Manfred, T. (2015). A 2016 Rio Olympics waterway has levels of viruses akin to raw sewage — here’s what it looks like [Online image]. Business Insider. https://www.businessinsider.com/rio-olympics-water-pollution-sewage-photos-2015-7

Fistarol, G. O., Coutinho, F. H., Moreira, A. P. B., Venas, T., Cánovas, A., de Paula Jr, S. E., … & Thompson, F. L. (2015). Environmental and sanitary conditions of Guanabara Bay, Rio de Janeiro. Frontiers in microbiology, 6, 1232. https://doi.org/10.3389/fmicb.2015.01232

Junge, C. E. (1974). Residence time and variability of tropospheric trace gases. Tellus, 26(4), 477-488. https://doi.org/10.1111/j.2153-3490.1974.tb01625.x

Keith, E. F. (2016). Treating Rio’s Wastewater Beyond the Olympics. Natural Resources & Environment, 31(4), 48-50. http://www.jstor.org/stable/44213918

Wharton, D. (2014). Sailors test polluted waters at 2016 Rio de Janeiro Olympic site [Online image]. Los Angeles Times. https://www.latimes.com/sports/sportsnow/la-sp-sn-sailors-2016-rio-de-janeiro-olympics-20140811-story.html

March 4, 2022Jo Ee Kwek No Comments

In deep water — The making of a water pollution crisis at the 2016 Rio Olympic Games

2 October 2009 signified a turning point for Rio de Janeiro’s environmental scene. Following decades of grappling with ill-managed waste disposal and severe water contamination (Trendafilova, Graham and Bemiller, 2017), the Brazilian city was declared as host of the 21st Olympic Games. This moment was historic not only because it marked an achievement once unthinkable, but also because it provided Rio de Janeiro the golden opportunity to clean its polluted waterways and improve its urban image.

Yet, these feelings of pride and optimism quickly dissolved into anger and disappointment, as targets of achieving 80% sewage treatment remained unmet. More alarmingly, Rio de Janeiro’s iconic Guanabara Bay remained nearly as polluted as before, making it less than ready to host upcoming Olympic water sports events. This raised a big question among the general public and international community: why was water pollution unresolved despite the increased construction of sewage systems?

Just days before the Olympics, reports revealed that Rio’s Guanabara Bay remained clogged with untreated waste, raising health concerns amongst athletes (Biller and Smith, 2016)

The answer lay in the high rates of improper waste disposal, especially in favelas. As we might recall from the previous post, favelas mostly lack access to sewage facilities, resulting in domestic waste being discharged directly into adjacent water bodies. This lack of access does not only refer to the measly number of facilities, which officials have addressed by ramping up construction works in neighbourhoods surrounding Guanabara Bay (Keith, 2016), but also their poor proximity to favelas. As noted by Fistarol et al. (2015), favelas occupy large areas of non-inhabited forest land, making it challenging to identify centrally-accessible areas where facilities can be built. Furthermore, favelas are unevenly distributed around Rio de Janeiro (Figure 1), with some located in hilly areas above 50 metres in elevation. Therefore, favela dwellers who live far from sewage facilities have little choice but to dispose of their waste in smaller tributaries (Keith, 2016).

Figure 1: Distribution of favelas in Rio de Janeiro (O’Hare and Barke, 2002)

However, these tributaries often merge into larger channels connected to Guanabara Bay, which receives liquid effluents produced from 16 municipalities (Fistarol et al., 2015). This results in the significant accumulation of domestic waste in Guanabara Bay, which surpasses the rate of wastewater treatment. According to Figure 2, the number of secondary and tertiary channels flowing into Guanabara Bay far exceeds the number of wastewater treatment plants, with there only being two plants within Guanabara Bay’s drainage basin. It is hence unsurprising that water pollution has not abated despite the higher uptake of sewage treatment facilities, as waste disposal rates in favelas outpace that of treatment.

Figure 2: Map of tributaries connected to Guanabara Bay (Comitê de Bacia da Baía de Guanabara, 2013)

Ultimately, it is regrettable that state efforts to clean up Guanabara Bay — and Rio de Janeiro’s notorious reputation as “an open sewer” — have failed. Only 78% of households are connected to sewer systems (Keith, 2016), with this percentage not accounting for favelas, and water quality remains poor based on World Health Organisation guidelines. It is hence evident that water pollution is a complex issue, and can only be addressed when its point sources are accurately identified and controlled to prevent large-scale pollutant transport. Furthermore, in linking back to our second post on the complexity of collecting Olympic pollution data, we should recognise that data collection is not always an objective exercise, with marginalised groups often being excluded from the process.

References

Biller, D. & Smith, M. (2016). Rio Promised to Clean Up Guanabara Bay Before the Olympics [Online image]. Bloomberg. https://www.bloomberg.com/features/2016-unsolved-murder-in-rio/

Comitê de Bacia da Baía de Guanabara. (2013). Location of Wastewater Treatment Plants around Guanabara Bay [Online image]. Comitê de Bacia da Baía de Guanabara. http://www.comitebaiadeguanabara.org.br/sig-rhbg/

Keith, E. F. (2016). Treating Rio’s Wastewater Beyond the Olympics. Natural Resources & Environment, 31(4), 48-50. http://www.jstor.org/stable/44213918

O’Hare, G., & Barke, M. (2002). The favelas of Rio de Janeiro: A temporal and spatial analysis [Online image]. GeoJournal. https://doi.org/10.1023/A:1025134625932

Trendafilova, S., Graham, J., & Bemiller, J. (2017). Sustainability and the olympics: the case of the 2016 Rio summer games. Journal of Sustainability Education, 16(3), 1-22. http://www.susted.com/wordpress/wp-content/uploads/2018/01/Trendafilova-Graham-Bemiller-JSE-Fall-2017-General-PDF.pdf

February 25, 2022Jo Ee Kwek No Comments

Swimming in sewage: How improper waste disposal has clouded the Olympic Games

Welcome back to Quit Playing Games (With Our Earth)! Earlier, we have discovered how air pollution is generated at the Olympic Games, resulting in profound health and socioeconomic impacts that play out across different geographical scales. In the next few posts, however, we will be exploring a different type of pollution — one that is arguably more visible, but equally far-reaching in effect.

That is none other than water pollution, which has emerged as a rising concern for Olympic water sports events in recent years. As defined by Owa (2013), water pollution arises when pollutant amounts are so large that the water is no longer suitable for specific uses, such as drinking and bathing. This has precisely been the case at several Olympic Games, with the most notorious example being the 2016 Rio Olympic Games where waters were found to contain viruses 1.7 million times more hazardous than that in America.

The issue of water pollution first came into the spotlight during the 2016 Olympic Games, when dangerous pollutant levels were detected in Rio’s waters (New York Times, 2015).

So, what leads to water pollution at the Olympic Games? While determining its exact cause is challenging as water pollution can be nonpoint source with “many possible points of origin” (Hill, 2012, p. 239), improper waste disposal remains a key contributor. This is especially so for domestic and industrial waste (Owa, 2013), which often go mismanaged as waste treatment infrastructure are unable to keep pace with rapid urban population growth and industrial expansion (Trendafilova, Graham and Bemiller, 2017). In Rio, for example, population growth has spiked alongside the number of slums or favelas without access to sewage systems, resulting in nearly half of Rio’s waste being dumped into the sea untreated (Vidal, 2016). Similarly, the lack of separate drainage systems for rainfall and sewage in Tokyo has led to the flushing of untreated sewage into Tokyo Bay during rainy seasons, so as to avoid overwhelming the central treatment system (Yokoyama, 2021).

The excessive presence of pollutants in Olympic swimming pools has led to an alarming phenomenon: these pools have turned a murky shade of green (Forbes, 2016)

Needless to say, such long-term dumping of waste into central water bodies has given rise to operational problems for host cities. Not only is water in Olympic pools and sailing venues murky as it is obtained from these water bodies, it also contains excessive viral loads that make it unsafe for athletes to compete. More significantly, the presence of these health hazards has led numerous athletes to pull out of events, concomitantly pushing host cities to undertake cleaning measures to assuage athletes’ fears while maintaining their image. On that note, the next post will investigate how unregulated anthropogenic activity and waste disposal led to disastrous water pollution at the 2016 Rio Olympic Games, so stay tuned!

References

Forbes. (2016). Why Are Rio’s Olympic Pools Green And Smelly? Ryan Lochte’s Hair Holds The Answer [Online image]. Forbes. https://www.forbes.com/sites/grrlscientist/2016/08/15/chemistry-its-why-the-rio2016-pool-water-is-green/?sh=39506b082d6c

Hill, M. K. (2012). Water Pollution. In M. K. Hill (Ed.), Understanding Environmental Pollution (pp. 236-285). Cambridge University Press. https://doi.org/10.1017/cbo9780511840654

New York Times. (2015). Filthy Rio de Janeiro Water a Threat at 2016 Olympics [Online image]. New York Times. https://www.nytimes.com/2015/07/31/sports/olympics/filthy-rio-de-janeiro-water-a-threat-at-2016-olympics.html

Owa, F. D. (2013). Water pollution: sources, effects, control and management. Mediterranean journal of social sciences, 4(8), 65-68. https://doi.org/10.5901/mjss.2013.v4n8p65

Vidal, J. (2016, August 3). Why is Rio de Janeiro finding it so hard to clear up its waste? The Guardian. https://www.theguardian.com/global-development/2016/aug/03/why-is-rio-de-janeiro-finding-it-so-hard-to-clear-up-its-waste-olympic-games

Yokoyama, E. (2021, July 14). Just Days Before Olympics, Tokyo’s Outdoor Swimming Venue Stinks. Bloomberg. https://www.bloomberg.com/news/articles/2021-07-13/two-weeks-before-tokyo-olympic-swimming-event-the-water-stinks

February 1, 2022Jo Ee Kwek No Comments

Blaze of glory, or guilt? Illuminating the pollutive impact of the Olympic Torch

Welcome back to Quit Playing Games (With Our Earth)! Last week, we explored how transport contributes to air pollution at the Olympic Games. Today, we will be looking at yet another aspect of the Olympic Games that significantly generates air pollution but often goes overlooked — the Olympic Torch.

The Olympic Torch is arguably the most symbolic element of the Olympic Games, though it often gets neglected by spectators in favour of sports matches and medal ceremonies. Its bright, fizzling flame that burns ever so fiercely not only epitomises the light of life, but also the spirit of resilience displayed by Olympic athletes. It is thus unsurprising that the Olympic Torch remains lit throughout the Olympic Games, given its cultural significance.

The Olympic Torch is traditionally regarded as a symbol of victory and resilience, earning it the honourable title of the ‘blaze of glory’ (Times Of India, 2021)

This (literal) blaze of glory to kickstart the Olympic Games, however, belies the sheer amount of pollutants released into the atmosphere. Such pollution occurs in several stages, with the first being transportation (linking back to what I mentioned in my previous post!). In this stage, the Olympic Torch is transported by air to different cities as part of the customary torch relay, producing carbon emissions. For example, at the 2008 Beijing Olympic Games, the Olympic Torch was carried around 23 cities (Demerjian, 2008). This expansive journey spanning over 85000 miles saw 462400 gallons of fuel being burnt, emitting an estimated 5500 tons of carbon dioxide (Demerjian, 2008).

The Olympic Torch being transported by plane to the UK for the 2012 Olympic Games (Meikle, 2012)

The second stage of lighting the Olympic Torch adds to these emissions. As reported by Madlin (2008), the Olympic Torch is fuelled by propane, with 12.6 pounds of carbon dioxide being emitted for every gallon of propane burnt. With the torch being perpetually lit, one can only imagine the amount of propane being burnt to prevent the flame from dying out, and the amount of carbon emissions produced. The Olympic Torch is thus symbolic of more than just athletes’ glory, but also the widespread air pollution that we are guilty of generating.

Therein lies the controversial question of whether the Olympic Torch should be cancelled, and if we should adopt environmentally-friendly alternatives (Zhou, 2015). Arriving at a consensus will undoubtedly be challenging given diverse stakeholder opinions — for example, host cities and the International Olympic Committee may prioritise the cultural symbolism of the Olympic Torch. Nonetheless, we should still raise awareness on the impacts of air pollution, so that stakeholders can obtain a clearer understanding of the trade-offs involved and make a more informed decision. In fact, some impacts at the city level will be covered in my next post, so do look forward to that!

References

Demerjian, D. (2008, April 8). Olympic Torch Emits 5,500 Tons of CO2. Wired. https://www.wired.com/2008/04/olympic-torch-e/

Madlin, C. (2008, April 29). The Carbon Olympics. Slate. http://www.slate.com/articles/health_and_science/green_room/2008/04/the_carbon_olympics.html

Meikle, J. (2012, May 18). Olympic torch takes its seat for flight to UK. [Online image]. The Guardian. https://www.theguardian.com/sport/2012/may/18/olympic-torch-flight-uk

Times Of India (2021). One year late, virus-delayed Tokyo Olympics torch relay begins. [Online image]. Times Of India. https://timesofindia.indiatimes.com/sports/tokyo-olympics/one-year-late-virus-delayed-tokyo-olympics-torch-relay-begins/articleshow/81681359.cms

Zhou, D. (2015). The IOC’s Social Responsibilities in Constructing Global Low Carbon Economy. International Journal of Simulation–Systems, Science & Technology, 16. https://doi.org/10.5013/ijssst.a.16.3a.10

January 28, 2022Jo Ee Kwek No Comments

Steering towards environmental disaster: Transport-induced air pollution at the Olympic Games

“It is the things you cannot see coming that are strong enough to kill you,” award-winning author Jodi Picoult had once said. This could not be further from the truth for air pollution, which is one of the least visible but most harmful types of pollution. Not only are key pollutants such as nitrogen dioxide and particulate matter highly toxic (Bonsu et al., 2020), they are also widely embedded in modern life.

Air pollution is omnipresent in various aspects of urban lifestyles, particularly transport (Organisation for Economic Co-operation and Development, 2014)

It is thus unsurprising that the Olympic Games — being a mega event involving the large-scale consolidation of urban activity from transportation to construction — significantly generates air pollution. While exact statistics remain uncertain as mentioned previously, the presence of smoggy skies and high respiratory infection rates suggest that air pollution at the Olympic Games is a clear cause for concern. It is hence instrumental to identify the biggest underlying triggers, so that authorities can work towards mitigating their impacts.

One of such triggers is transport, which facilitates the movement of those involved in the Olympic Games at different spatial scales. At the global scale, air transport is used to transport athletes and spectators from their home countries to the host city. While this transport mode is efficient given its relatively high speed and load capacity, enabling the large-scale transnational movement of people, it is also highly pollutive. Commercial aircraft emit significant amounts of nitrogen dioxide when flying in the free troposphere, forming the greenhouse gas ozone which traps outgoing solar radiation at the ground level (Colvile et al., 2001). Carbon dioxide, a pollutant which is produced during fuel combustion for aircraft engines, exacerbates such warming by absorbing outgoing infrared radiation (Colvile et al., 2001). While air travel at the Olympic Games only generates 65000 tons of carbon dioxide, constituting barely one month’s worth of emissions from a coal plant (Jacobo, 2021), its environmental and health-related impacts remain worrying as these pollutants have long residence times.

The emission of nitrogen dioxide by aeroplanes in the free troposphere exacerbates the greenhouse effect (Hotten, 2019)

Land transport at the city scale is equally, if not more, pollutive. During the Olympic Games, road traffic is remarkably high, not only because of the need for vehicles to transport athletes and staff to Olympic venues, but also the surge in tourists travelling there. This produces substantial vehicle emissions which not only contain radiation-trapping ozone, but also particulate matter that jeopardises air quality and causes respiratory illnesses when overly inhaled (He, Fan and Zhou, 2016).

It is hence crucial to be mindful of the significant role that transport plays in causing air pollution at the Olympic Games — only then can we foresee air pollution and its associated impacts, and take mitigation measures. Otherwise, we will be literally and figuratively steering towards environmental disaster.

References

Bonsu, N. O., Pope, F., Ababio, M. O., Appoh, E., Ashinyo, M. E., Essuman, S. N., Donkor, L. CS., & Thomson, I. (2020). How Coronavirus (COVID-19) has made the invisible silent killer of air pollution visible: lessons for building resilient communities. Biomedical Journal of Scientific & Technical Research, 28(1), 21219-21220. https://doi.org/10.26717/bjstr.2020.28.004587

Colvile, R. N., Hutchinson, E. J., Mindell, J. S., & Warren, R. F. (2001). The transport sector as a source of air pollution. Atmospheric environment, 35(9), 1537-1565. https://doi.org/10.1016/s1352-2310(00)00551-3

He, G., Fan, M., & Zhou, M. (2016). The effect of air pollution on mortality in China: Evidence from the 2008 Beijing Olympic Games. HKUST Institute for Emerging Market Studies Working Paper No. 2015-03. Available at: https://iems.ust.hk/publications/iems-working-papers/guojun-he-effect-air-pollution-mortality-china-olympic

Hotten, R. (2019). Could aviation ever be less polluting? [Online image]. BBC. https://www.bbc.com/news/business-48185337

Jacobo, J. (2021, August 2). How the Tokyo Olympics could affect climate change. ABC News. https://abcnews.go.com/International/tokyo-olympics-ban-spectators-affect-environment/story?id=78151177

Organisation for Economic Co-operation and Development (2014). The Cost of Air Pollution [Online image]. Organisation for Economic Co-operation and Development. https://www.oecd.org/env/the-cost-of-air-pollution-9789264210448-en.htm