Bus, minibus, metro inter-comparison of commuters’ exposure to air pollution in Mexico City

Commuters’ exposure measurements were taken for PM2.5, carbon monoxide (CO) and benzene in minibuses, buses and metro during morning and evening rush hours during January–March 2003 in Mexico City. For PM2.5, the chemical composition was characterized. Total carbon was the most abundant species in fine particles (approximately 50%). Minibuses (49 μg m−3) and buses had similar concentrations of exposure for PM2.5 (53 μg m−3). For CO and benzene the concentrations were higher in minibuses. Morning rush hour was the commuting period with the highest concentrations for minibuses and buses. Metro was the mode of transport with lower concentrations for all pollutants. Carbon monoxide concentrations were similar to those identified in a previous campaign in 2002 and approximately 3.5 times lower than those in a study conducted in 1991. Benzene was characterized systematically in the selected modes of transport. A strong association was observed between wind speed and pollutant concentrations in buses.