Diesel truck idling emissions measurements at PM_2.5 hot spot

The University of Tennessee and Oak Ridge National Laboratory conducted a 5-month-long air monitoring study at the Watt Road interchange on 1-40 in Knoxville, Tennessee, where 20,000 heavy-duty trucks travel the Interstate each day. In addition, three large truck stops are situated at this interchange, where as many as 400 trucks idle engines at night. As a result, high levels of PM_2.5 have been measured near the interchange, often exceeding National Ambient Air Quality Standards. This paper presents the results of the air monitoring study, illustrating average hourly patterns of PM_2.5 resulting from diesel truck emissions on the Interstate and at the truck stops. Most of the PM_2.5 concentrations detected occurred during the night, when the largest contribution of emissions was from idling trucks rather than trucks on the Interstate. A nearby background air monitoring site was used to identify the contribution of regional PM_2.5 emissions, which were also a significant factor in the concentrations measured at the site. The relative contributions of regional background, local truck idling, and trucks on the Interstate to local PM_2.5 concentrations are presented and discussed in the paper. The results indicate the potential significance of diesel truck idling emissions to the occurrence of hot spots of high PM _2.5 concentrations near large truck stops, ports, or border crossings. The significance of truck idling emissions is similar to the findings of other studies.