Tollbooth workers and mobile source-related hazardous air pollutants: how protective is the indoor environment?

Tollbooth workers are potentially exposed to high levels of mobile source-related air pollutants due to the proximity and intensity of the source. To evaluate this worker hazard, we measured the concentration of air toxins including volatile organic compounds (VOCs) and particle-bound polycyclic aromatic hydrocarbons (PAHs) inside and outside a Baltimore Harbor Tunnel tollbooth during the summer of 2001. Mean outdoor benzene and 1,3-butadiene concentrations varied by shift with the morning (10.7 and 19.8 microg/m3) exceeding afternoon (7.2 and 14.9 microg/m3) and the lowest levels observed during the night (3.7 and 4.9 microg/m3, respectively) when traffic volume was the lowest. In comparison, considerable protection was provided to workers bythe indoor environment where lower concentrations of 1,3-butadiene and benzene were observed for all three shifts (2.9 and 6.7, 0.9 and 3.2, and 0.9 and 2.4 microg/m3, respectively). The greatest protection offered by the tollbooth was observed during the afternoon shift (5-8-fold reduction in indoor concentration), whereas the morning and night shifts experienced similar protection (2-4-fold reduction). Chlorinated hydrocarbons were observed at higher concentrations within the tollbooth, indicating the presence of indoor sources and the opportunity for exposure mitigation. Levels of PAHs were similarly reduced from outdoors (50 ng/m3) to indoors (15.4 ng/m3). The protective nature of the tollbooth highlighted in this study is likely due to the positive pressure control ventilation system that was present at this specific facility, which represents 55% of tollbooths in Maryland. This study provides an estimate of tollbooth workers potential exposures to various mobile source-related pollutants and highlights the protective nature of tollbooths equipped with positive pressure control ventilation systems.