Polluted Air Influences Marathon Finishing Times

A study of 2.7 million marathon finishers found that nitrogen dioxide — not particulate matter — was linked to slower times, with the effect six times larger in recreational runners than elites.

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.

An extensive 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.

Researchers suggest air quality measures deserve a place beside temperature, humidity, and wind in your pre-race weather checks. 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.

Read the full research study “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 ↩︎