On-road emission factors from light-duty vehicles measured in Hsuehshan Tunnel (12.9 km), the longest tunnel in Asia

This study is based on 82 days of continuous air-quality monitoring using two mobile monitoring vans provided by the Taiwan Environmental Protection Administration (TEPA). The purpose of the study is to reveal variations of air quality without forced ventilation from on-road emissions of light-duty vehicles (LDV) inside the Hsuehshan Tunnel. Since it was opened to traffic in June 2006, only LDV have been allowed to pass the Hsuehshan Tunnel, the longest tunnel in Taiwan and in Asia. The hourly concentrations of air pollutants at four monitoring sites inside the tunnel (pollutant: downslope entrance, downslope exit, upslope entrance, upslope exit) are as follows: (CO: 6.9 +/- 5.4, 13.6 +/- 8.7, 4.6 +/- 3.2, 14.6 +/- 8.0 ppm), (NO (X) : 534 +/- 311, 1198 +/- 640, 460 +/- 242, 1704 +/- 692 ppb), (SO2: 7 +/- 5, 18 +/- 10, 9 +/- 4, 26 +/- 10 ppb), (NMHC: 1.9 +/- 2.5, 3.5 +/- 3.0, 0.8 +/- 0.9, 2.7 +/- 1.9 ppm), (PM10: 50 +/- 28, 62 +/- 29, 59 +/- 25, 85 +/- 30 mu g m(-3)), and (PM2.5: 31 +/- 18, 45 +/- 22, 35 +/- 18, 62 +/- 23 mu g m(-3)). The emission factors (EFs) from LDV in this study (pollutant: downslope EF, upslope EF in mg veh(-1) km(-1)) is estimated respectively as follows: (CO: 909 +/- 469, 1468 +/- 631), (NO (X) : 145 +/- 67, 331 +/- 166), (SO2: 3 +/- 2, 6 +/- 3), (NMHC: 96 +/- 65, 121 +/- 63), (PM10: 2 +/- 2, 5 +/- 4), and (PM2.5: 2 +/- 2, 4 +/- 3). It shows that the upslope pollutant EFs are twice as big as those of the downslope. However, among these EFs, the NMHC EF is less affected by the road gradient. Likewise, its upslope EF is only 1.3 times as big as that of the downslope. In summary, the results are useful for examining the emissions from the local fleet of vehicles under the driving conditions present during the study and for observing the changes in fleet emission rates upon future replication of the study.