Athletes competing at next year's Winter Olympics could be doing so in potentially hazardous, polluted air, a new academic study says.
The report, to be published in the journal Sport and Society and shared with the BBC, looked at air quality data over the past five years for the month of February - when the games will be held - and found poor to hazardous conditions on as many as 15 days, with an average of 9.5 days.
"I am very concerned about the air quality in Beijing," said the report's co-author Dr Madeleine Orr, assistant professor at the State University of New York.
"The challenge for athletes with air quality is that they are at higher risk because they are outdoors and they're exerting themselves. Tiny particles in the air that you can't see lodge themselves in your airways and in your lungs and that can be damaging in the long term. It also can impede performance in the immediate. We're talking carbon, methane, sulphur and so on," she explained.
Similar concerns about air quality were reported before the 2008 summer Games when Chinese authorities introduced measures to reduce pollution - something Orr expects to see again. "The question is will it be enough," she said.
The athlete's view
The biggest impact of any pollution would be felt by competitors in the snow sport endurance events. American biathlete Maddie Phaneuf said: "It's extremely worrying, not only for my own personal health and the effects of breathing that air but also everyone that lives in Beijing and people who will be coming to watch the Olympics, or other athletes competing.
"We're an endurance sport and breathing pretty heavily during our competitions. It's enough where even the slightest change in air pollution is going to affect our lungs and how we feel when we're racing and training so it is challenging and it would be a big concern for me if they didn't clean it up."
What does the International Olympic Committee say?
The IOC, which raised the issue of air pollution when assessing Beijing's bid to host the 2022 Winter Games, says it has been working with local organisers to address it.
"Beijing 2022 Organising Committee has made commitments to curb air pollution to meet World Health Organization standards during Games-time in 2022. Beijing 2022 has already made progress with its efforts to improve air quality. A large number of initiatives have been put in place," it told BBC Sport.
Initiatives include having all venues powered with renewable energy, while the government has invested in a Beijing Clean Air Action Plan.
The IOC also pointed to lower air pollution rates achieved during the 2008 Summer Games in Beijing.
It also said endurance events, such as biathlon and cross country skiing - which are most heavily affected by air pollution - will be taking place in the city of Zhangjiakou, which Chinas says has the best air quality in the region.
The local organising committee has not responded to BBC requests for comment.
Could water use be a problem?
The report also looked at historical data to confirm Beijing's weather is not conducive to winter sports events, with low snow fall meaning the Games will be almost entirely dependent on fake snow - which, as Dr Orr points out, has its own environmental impact with "a severe need for water" to fuel snow guns.
"This is great in terms of providing conditions in order to have the event but is bad from an environmental standpoint."
The IOC says "the snow production capabilities for the Olympic Games Beijing 2022 have been developed according to the highest technical and environmental standards".
The lack of available, real snow, does however raise longer-term concerns about the threat posed to snow sports by climate change, according to Phaneuf, who is an ambassador for an organisation called Protect Our Winters, which wants to raise awareness about this issue.
"That is the scary thing about the viability of the Winter Olympics continuing or our sports continuing as it's going to start getting worse and worse with whether we can even race or what countries can even host the Olympics," she said.
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