Introduction When physical activity is promoted in urban outdoor settings (e.g., walking and cycling), individuals are also exposed to air pollution. It has been reported that short-term lung function increases as a response to physical activity, but this beneficial effect is hampered when elevated air pollution concentrations are observed. Our study assessed the long-term impact of air pollution on the pulmonary health benefit of physical activity. Methods Wearable sensors were used to monitor physical activity levels (SenseWear) and exposure to black carbon (microAeth) of 115 healthy adults during 1 wk in three European cities (Antwerp, Barcelona, London). The experiment was repeated in three different seasons to approximate long-term behavior. Spirometry tests were performed at the beginning and end of each measurement week. All results were averaged on a participant level as a proxy for long-term lung function. Mixed effect regression models were used to analyze the long-term impact of physical activity, black carbon and their interaction on lung function parameters, forced expiratory volume in the first second (FEV₁), forced vital capacity (FVC), FEV₁/FVC, forced expiratory flow (FEF)_25-75, and peak expiratory flow. Interaction plots were used to interpret the significant interaction effects. Results Negative interaction effects of physical activity and black carbon exposure on FEV₁ (P = 0.07), FEV₁/FVC (P = 0.03), and FEF_25-75 (P = 0.03) were observed. For black carbon concentrations up to approximately 1 μg·m^-3, an additional MET·h^-1·wk^-1 resulted in a trend toward lung function increases (FEV_1, FEV₁/FVC, and FEF_25-75 increased 5.6 mL, 0.1% and 14.5 mL·s^-1, respectively). Conclusions We found that lung function improved with physical activity at low black carbon levels. This beneficial effect decreased in higher air pollution concentrations. Our results suggest a greater need to reduce air pollution exposures during physical activity.