Measuring vehicle volumes and monitoring and modeling of PM_2.5 concentrations in a travel center associated with a major urban interstate and interchange

The Watt Road interchange that crosses over I-40 interstate in West Knox County, TN is associated with three travel centers which have overnight parking spaces for approximately 700 vehicles, primarily occupied by heavy heavy-duty diesel vehicles (HHDDV). Field studies were conducted to characterize the traffic patterns by vehicle type within the I-40 and Watt Road corridors and travel centers, and to monitor and model PM_2.5 concentrations resulting from the various vehicle activities within the corridors and at the PETRO travel center. Traffic volumes and the associated vehicle mixes were measured for each hour of day. Monitoring PM2.5 concentrations was conducted using a forward light scattering aerosol monitoring system (DataRAM, MIE, Inc.). Modeling of the concentrations was also conducted using the CAL3QHC highway air pollutant prediction model to predict concentrations resulting from the vehicle activities.

Total vehicle volumes measured on I-40 were about 3 times heavier during the daytime than during the night, while HHDDV volumes were less deviate and rather consistent throughout the day. On Watt Road, total vehicle and HHDDV volumes were about 3 times heavier during the daytime than during the night. In the travel centers, 46.2 % of HHDDV were idling during the night while 40.7 % of them were idling during the daytime. The ambient contributions of real-time PM_2.5 concentrations attributed to vehicle traffic measured within the corridors were 0.3, 2.6, 6.8 and 8.9 µg/m³ from a local highway (US-381), I-40/I-75, Watt Road and travel centers, respectively. Ten minute average PM_2.5 concentrations were monitored at the PETRO travel center under four different conditions: stable and unstable atmospheric conditions during dry meteorological periods, and stable and unstable atmospheric conditions immediately after a heavy rain. PM_2.5 concentrations contributed from the travel center were from 18 to 27 % of the downwind concentrations. A comparison of the predicted and monitored concentrations suggests that PM_2.5 concentrations monitored in the micro-scale of the travel center (downwind 10 to 20 meters from the emission source) may be more affected by an induced mechanical turbulence around HHDDV than by macro-scale atmospheric stabilities. During dry meteorological periods, monitored PM_2.5 concentrations may also have been influenced by re-entrainment of gray-black road dust associated with the HHDDV activities.