The impact of a Bus Rapid Transit system on commutersʹ exposure to Benzene, CO, PM2.5 and PM10 in Mexico City

Carbon monoxide (CO), benzene and other volatile organic compounds (VOCs) and suspended particles PM2.5 and PM10 were measured inside public transportation vehicles, before and after a new Bus Rapid Transit (BRT) system was implemented in Mexico City in June 2005. The objective was to evaluate the BRT systemʹs impact on commutersʹ exposure to these air pollutants. The BRT system replaced conventional transport modes along 20 km of Insurgentes Avenue, and features confined corridors and new articulated diesel buses. We assessed the impact of the transportation mode on commutersʹ exposure using least squares regression models. We also analyzed the chemical composition of VOCs to evaluate the possible origin of these species. The implementation of the BRT system resulted in reductions in commutersʹ exposure to CO, benzene and PM2.5 ranging between 20% and 70%. No significant reductions in PM10 exposure were observed. Lower commuting times further reduced total commutersʹ exposure. Major sources affecting VOCs inside all transport modes are likely to be related to traffic and to emissions from the use of Liquefied Petroleum Gas. The results suggest that BRT systems could in general be an effective means of reducing human exposure to traffic related air pollutants and associated health impacts.