A Critical Comparison of Exposure Estimators for Airborne Particulate Matter in Urban Cyclists

Urban cyclists experience elevated traffic-related air pollutant (TRAP) exposures due to proximity to emissions and increased breathing rates during exercise. Conventional assessments rely on concentration summaries, which may misrepresent actual inhaled doses and misclassify individuals in health studies. Street-level concentrations exhibit high temporal variability, producing non-normal distributions that challenge conventional averaging approaches. This study compares concentration- and dose-based methods to characterize cyclist exposure during urban commuting. Fifty-seven healthy adults completed cycling trips on two 9-km routes (high- and low-traffic) using conventional or electrically assisted bicycles. Real-time monitoring measured black carbon, ultrafine particles, PM_2.5, and PM₁₀. Heart rate-derived breathing rates enabled individualized inhaled dose calculations using three temporal integration methods. Mean concentrations correlated strongly with time-integrated concentrations (r = 0.988-0.998). Simplified dose calculations closely approximated full temporal integration (r > 0.999), with median dose ratios of 0.99-1.01. However, correlations between mean concentrations and inhaled doses were weaker (r = 0.72-0.78). Between 29% and 50% of participants changed exposure quartiles when comparing concentration- and dose-based classifications, with the highest reclassification for ultrafine particles (46-50%). These findings demonstrate that physiological variability substantially influences exposure classification during active commuting, supporting the integration of inhaled dose metrics in cyclist exposure assessment and epidemiological studies.