Health experts are keeping a close eye on the air quality in London as the Summer Games get closer.
"I haven't noticed it at all," said Emily Thomas of Texas. "So far it hasn't bothered me and probably won't."
Doctors are warning Olympic athletes the pollution around London could cause breathing issues during strenuous exercise. The pollution could trigger coughing, wheezing and shortness of breath in athletes with asthma or exercised-induced asthma.
"If you are an athlete and you're really breathing hard, you're going to be breathing in a lot air, which isn't of the cleanest quality," said Dr. Jacqueline Eghrari-Sabet, a fellow at the American Academy of Allergy, Asthma & Immunology.
Environmental groups are monitoring pollution closely and say recent sunshine and low winds are creating the perfect storm for smog.
"It is worrying, having this smog episode so close to the games," said Simon Birkett, the founder of Clean Air in London. "We don't know what will happen over the next two weeks as the games progress."
Allergy and asthma experts say exercise triggers asthma in about one in six Olympic athletes. And it's not just the athletes who are at risk. Richard Martinez of Colorado has asthma. He knows pollution can make his symptoms worse.
"It probably will by the end of the trip it will probably have a little bit of impact," Martinez said.
One clean air group has set up more than 100 stations across London to keep track of pollution levels.
Environmental experts expect pollution levels to be moderate this week in London, which they say can still cause problems for anyone with breathing problems.
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