METHOD COMPARISONS OF VEHICLE EMISSIONS MEASUREMENTS IN THE FORT MCHENRY AND TUSCARORA MOUNTAIN TUNNELS

Experiments were conducted in the Fort McHenry Tunnel in Baltimore, MD , and in the Tuscarora Mountain Tunnel in Pennsylvania, during the sum mer of 1992 to evaluate real-world automotive emissions. Included in t hese experiments were the first reported measurements of individual ve hicle exhaust in tunnels by a remote sensing device (RSD). Results are compared to integrated emission measurements carried out by analysis of concurrent collections of tunnel air into bags, canisters, and adso rbent traps and by conventional Fourier transform infrared (FTIR) spec troscopy. The vehicles using these highway tunnels proved to be lower emitting than vehicles usually measured by remote sensing in urban are as. At Fort McHenry the RSD-measured CO/CO2 ratios were, on average, h igh compared to either the bag or FTIR measurements (by a factor of 1. 4 +/- 0.2) for the four runs monitored. RSD hydrocarbon data were obta ined only at the uphill location (+ 3.76% grade). RSD HC/CO2 ratios we re lower on average, but statistically indistinguishable when compared with either the FTIR or the integrated uphill measurements. At Tuscar ora, the RSD-measured CO/CO2 ratios were in agreement with the CO/CO2 ratios in the tunnel bag measurements and FTIR measurements (within a factor of 1.00 +/- 0.16 by one method and 0.82 +/- 0.32 by a second, w hen traffic was dominated by light-duty spark-ignition vehicles). The RSD HC/CO2 ratios were, however, higher than the light-duty vehicle es timates from the integrated (bag/canister/Tenax) tunnel measurements b y a Factor of 3, and higher than the FTIR Delta HC/Delta CO2 ratios by an even higher factor, mostly owing to water vapor interferences in t he low average RSD measurements. For the first time RSD measurements w ere collected from a small sample of heavy-duty diesels; comparisons t o the heavy-duty emissions contributions for CO and HC were favorable. Analysis of emissions data For vehicle variability at Fort McHenry re vealed that low CO emitting vehicles tended to be consistently low but that the minority that were high emitters (> 2.5% CO) were more likel y to be high only at the uphill location. Vehicle mileage information was collected al a toll booth in the case of Fort McHenry and at a ser vice plaza in the case of Tuscarora for comparison against the RSD emi ssions measurements. This comparison showed little conventional deteri oration of CO or HC emissions with mileage. The trend consisted of an increased frequency of high emitters with mileage, rather than an incr ease in emissions from all vehicles with increasing mileage. Copyright (C) 1996 Elsevier Science Ltd