Air pollution exposure during urban running in Frankfurt, Germany: a randomized crossover comparison of particulate matter levels on park, roadside, and residential routes across morning and early afternoon hours

Background In urban environments, physical activity-induced health effects may be diminished by exposure to air pollution. Typical avoidance strategies, such as running through green spaces or avoiding major roads and rush hours, have not yet been adequately validated. This study quantified particulate matter exposure during running across three adjacent urban microenvironments: a major roadside, a residential area, and an urban park, accounting for diurnal variation. Methods Mobile measurements of particulate matter with aerodynamic diameters ≤ 10 μm (PM 10 ), ≤ 2.5 μm (PM 2.5 ), and ≤ 1 μm (PM 1 ) as well as local urban background concentrations of PM 2.5 and PM 10 were collected during 2 km runs ( n = 60, pace 8:02–4:31 min/km). Runs on major roads ( n = 20), residential streets ( n = 20), or in an urban park ( n = 20), as well as runs in the morning ( n = 30) and in the early afternoon ( n = 30), were equally distributed. Differences between routes, incorporating the effects of daytime and meteorological factors, on particulate matter concentrations were analysed using linear mixed-effects models. Results The lowest concentrations across PM fractions occurred during early-afternoon runs in the park, whereas the highest exposure to PM 10 across all environments was reached during morning runs on the same route. In line with the urban background levels, exposure across all routes was lower during early-afternoon than during morning runs. Humidity, air pressure, wind speed, and temperature were associated with particulate matter exposure during running. A sensitivity analysis using run-level means ( n = 60) did not confirm the route or route×daytime effects as statistically significant, indicating that these patterns require confirmation in larger samples. Conclusion Running in parks in the early afternoon and avoiding busy morning hours may help reduce fine and submicron particle exposure, particularly during calm, humid, and high-pressure conditions when pollutant dispersion is limited. ​However, park routes did not reduce, and at times increased, coarse-particle (PM 10 ) exposure, especially in the morning. These route- and daytime-related differences were not confirmed in a run-level sensitivity analysis and should therefore be regarded as preliminary.