Characterization of Particulate Matter in Different Bores of a Tunnel with Distinct Vehicle Composition and Concentrated Emissions

Abstract

P-075 Introduction: Exposure to ambient particulate matter (PM) has been associated to multiple adverse health effects. In urban environments motor vehicles are one major source contributing to ambient PM concentrations. The vehicle fleet is a mixture of vehicle types which make unequal contributions to the ambient PM burden. To explore the differential contribution by vehicle type, we used a real-world laboratory provided by Baltimore's Fort McHenry Tunnel. Sampling stations were set up in the exhaust plenums of 2 different bores of the tunnel. One bore (Bore 4) carries predominately diesel traffic and Bore 3 carries predominately passenger cars with other mixed traffic. Comparisons of the size, concentration, physical and chemical characteristics of particulate matter in both bores were conducted. Methods: Particulate matter samples were collected in each bore using PM10 and PM2.5 impactors. Particle size was determined using an Aerodynamic Particle Sizer (APS) and a multi-staged DRUM sampler. Continuous monitoring was also conducted in each Bore using a ThermoMIE pDR. In addition, bulk airborne dust was collected using a high volume cyclone collector. Once characterized, this bulk dust will be used for in vivo and in vitro testing to assess PM toxicity. Results: Measurements within each tunnel with the MIE pDR show a 1.7 fold difference between bores. PM concentration in Bore 4 was 242% and 250% higher than Bore 3 for PM10 and PM2.5, respectively. Mean PM10 concentration levels for Bore 4 and Bore 3 were 121 ug/m3 (sd 66 ug/m3,) and 50 ug/m3 (sd 13 ug/m3) respectively. PM2.5 mean concentrations were 87 ug/m3 (sd 43 ug/m3) and 34 ug/m3 (sd 11ug/m3) for Bore 4 and Bore 3, respectively. Paired t-test analysis of PM10 and PM2.5 samples indicate a significant difference (P < 0.001). PM concentration in the different tunnel bores was found to be dependent on the overall numbers of vehicles, as well as the number of diesel-powered vehicles. Metal content of the airborne PM also varied significantly between bores and was dependent on vehicle traffic composition. Discussion and Conclusions: The differences in fleet composition between the two bores of the Ft. McHenry Tunnel provide a unique opportunity to evaluate vehicular emissions in a highly concentrated real-world environment. The results of this study provide data on an important source signature, i.e. diesel-powered vehicles. Finally, bulk PM collected inside the tunnel will be used to assess the relative toxicity of PM collected from each of the tunnel bores.