Polluted Air Could Cost You Minutes on Marathon Day

Air pollution rarely gets the same attention as heat, humidity, wind, and hills. But if you are racing through a large city, the air you breathe may be another environmental stressor working against you.

A massive cross-sectional study examined 2,756,553 finish times from 75 editions of the six World Marathon Majors between 2010 and 2024. The researchers paired each race with race-day concentrations of nitrogen dioxide (NO₂), a traffic-related pollutant, and fine particulate matter (PM₂.₅). They then estimated how those pollutants were associated with finish time after accounting for heat index, wind, and year.¹Donaldson, J. A., Cai, S., Hey, J. V., Hansell, A. L., Yates, T., Ng, G. A., & O’Driscoll, J. (2026). Air Pollution Impairs Marathon Performance: A Cross-Sectional Analysis of 2.7 Million Finishers Across Six World Marathon Majors. In Sports medicine – open (Vol. 12, Issue 1, p. 128). PubMed. https://doi.org/10.1186/s40798-026-01099-6

• A 5.1-microgram-per-cubic-meter increase in NO₂ was associated with a 7.3-minute slower finish in men and a 7.9-minute slower finish in women. 
• PM₂.₅ was not associated with slower times. 
• The NO₂ association was also larger among recreational runners than elites: 2.12 versus 0.34 additional minutes per 1-microgram-per-cubic-meter increase.

What this means for runners

Air quality deserves a place beside temperature, humidity, and wind in your pre-race check. On high-pollution training days, running earlier, choosing a route away from heavy traffic, or moving a hard workout indoors may reduce exposure. If race-day air is poor, a slightly more conservative start may be sensible (especially for runners with asthma or other respiratory conditions).

But this study does not establish a performance threshold at which every runner should change plans. Treat air quality as one piece of the environmental puzzle, not a prediction about whether or not you’ll automatically run slower.

References

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  Donaldson, J. A., Cai, S., Hey, J. V., Hansell, A. L., Yates, T., Ng, G. A., & O’Driscoll, J. (2026). Air Pollution Impairs Marathon Performance: A Cross-Sectional Analysis of 2.7 Million Finishers Across Six World Marathon Majors. In Sports medicine – open (Vol. 12, Issue 1, p. 128). PubMed. https://doi.org/10.1186/s40798-026-01099-6 ↩︎