As the issue of air pollution continues to grow, athletes are turning to science to give them a clearer picture of how to avoid the smog.

Air quality sensors have been installed in sports facilities in six countries across Africa, with the data being used by coaches drawing up training schedules and event organisers looking to keep competitors safe.

“If you run in a polluted city you can decrease your performance,” two-time Olympic marathon champion Eliud Kipchoge told BBC Sport Africa.

“When you go to a polluted city, you really feel that your lungs are really compressed.”

Air pollution causes more than 1.2 million deaths annually in Africa, according to the United Nations and the Clean Air Fund, making it the second-largest cause of death across the continent.

The situation is particularly worrying for those who train regularly, because someone exercising can take in as much as 20 times more air than a person at rest – meaning they also breath in 20 times more pollutants.

Badly polluted environments can therefore make all the difference for elite athletes looking for crucial marginal gains.

For example, one study by the United States National Library of Medicine found that air pollution can decrease marathon performance by 1.4%.

“If you were to run that long period of time in an environment where there’s polluted air, you cannot sustain it,” said Dr Philip Osano of the Stockholm Environment Institute (SEI), the organisation which has installed the sensors in conjunction with United Nation’s Environment Programme (UNEP).

“It really affects your breathing capacity and your blood oxygen levels.”