 A study by the United States National Library of Medicine concluded that air pollution can decrease marathon performance by 1.4 percent, enough to make the difference in a long race of fine margins. Dr. Philip Osano is from the Stockholm Environment Institute. If you were to run that long period of time in an environment where there's polluted air, you actually cannot be able to sustain it because it really affects your breathing capacity. It affects actually also your blood oxygen levels.