On-Road Particulate Matter (PM_2.5 and PM₁₀) Emissions in the Sepulveda Tunnel, Los Angeles, California

Abstract

Total and speciated particulate matter (PM2.5 and PM10) emission factors from in-use vehicles were measured for a mixed light- (97.4% LD) and heavy-duty fleet (2.6% HD) in the Sepulveda Tunnel, Los Angeles, CA. Seventeen 1-h test runs were performed between July 23, 1996, and July 27, 1996. Emission factors were calculated from mass concentration measurements taken at the tunnel entrance and exit, the volume of airflow through the tunnel, and the number of vehicles passing through the 582 m long tunnel. For the mixed LD and HD fleet, PM2.5 emission factors in the Sepulveda Tunnel ranged from 0.016 (+/-0.007) to 0.115 (+/-0.019) g/vehicle-km traveled with an average of 0.052 (+/-0.027) g/vehicle.km. PM10 emission factors ranged from 0.030 (+/-0.009) to 0.131 (+/-0.024) g/vehicle. km with an average of 0.069 (+/-0.030) g/vehicle.km. The PM2.5 emission factor was approximately 74% of the PM10 factor. Speciated emission rates and chemical profiles for use in receptor modeling were also developed. PM2.5 was dominated by organic carbon (OC) (31.0 +/- 19.5%) and elemental carbon (EC) (48.5 +/- 20.5%) that together account for 79% (+/-24%) of the total emissions. Crustal elements (Fe, Mg, Al, Si, Ca, and Mn) contribute approximately 7.8%, and the ions Cl-, NO3-, NH3+, SO4(2-), and K+ together constitute another 9.8%. In the PM10 size fraction the particulate emissions were also dominated by OC (31 +/- 12%) and EC (35 +/- 13%). The third most prominent species was Fe (18.5 +/- 9.0%), which is greater than would be expected from purely geological sources. Other geological components (Mg, Al, Si, K, Ca, and Mn) accounted for an additional 12.6%. PM10 emission factors showed some dependence on vehicle speed, whereas PM2.5 did not. For test runs in which the average vehicle speed was 42.6 km/h a 1.7 times increase in PM10 emission factor was observed compared to those runs with an average vehicle speed of 72.6 km/h. Speciated emissions were similar. However, there is significantly greater mass attributable to geological material in the PM10, indicative of an increased contribution from resuspended road dust. The PM2.5 shows relatively good correlation with NOx emissions, which indicates that even at the low percent of HD vehicles, which emit significantly more NOx than LD vehicles, they may also have a significant impact on the PM2.5 levels.

Chemical composition of PM 2.5 from two tunnels with different vehicular fleet characteristics

“…OC/EC in WZS tunnel ranged from 0.48 to 1.45 with an average value of 0.86. Emission factors of OC and EC in WZS tunnel were similar to those reported in Sepulveda tunnel (Gillies et al, 2001). Table 2 showed that EFs of water soluble ions including SO ions in WZS and Zhujiang tunnels (He et al, 2008) were in the same order (of magnitude).…”

“…As shown in Table 1, the EFs of PM 2.5 in the WZS tunnel was 70.1 ± 15.9 mg·veh −1 ·km −1 , whereas it was 22.2 ± 6.52 mg·veh −1 ·km −1 in the KXL tunnel. ; It is known that, the PM 2.5 EFs of vehicles could be influenced by many factors, such as vehicle type (Cheng et al, 2010;He et al, 2008), fuel quality (Yue et al, 2015), model year of the vehicles (Liu et al, 2009;Shah et al, 2006), vehicle speed (Gillies et al, 2001), and the features of the road (Pio et al, 2013). EFs of PM 2.5 in this study were compared with those from other tunnel studies in China (Table 1).…”

Source Apportionment of PM2.5 Using a CMB Model for a Centrally Located Indian City

“…Similarly, NO 3 -/EC and NO 3 -/OC ratios were found to be 0.40 ± 0.11, 0.55 ± 0.21, 0.34 ± 0.22 and 0.93 ± 0.23, 1.23 ± 0.32, 1.23 ± 0.43 for R, C and I sites respectively. These ratios of NO 3 -/EC and NO 3 -/OC are higher than those calculated from road tunnel aerosols (0.1 for NO 3 -/EC and 0.09 for NO 3 -/OC) (Gillies et al, 2001) indicating that vehicular as well as biomass burning activities are contributing at all receptor sites.…”

Fine Particulate Matter Emissions Inventories: Comparisons of Emissions Estimates with Observations from Recent Field Programs

“…38,39 The OC/TC fraction of PM 2.5 released by mixed traffic in the Sepulveda Tunnel in Los Angeles was 0.47. 40 This fraction was 0.7 for PM 2.5 released from mixed traffic in a tunnel in Milan, Italy, 41 and 0.28 and 0.6, respectively, for heavy-duty diesel vehicles and light-duty vehicles in the Caldecott Tunnel east of Oakland, CA. 22 Shah et al 42 used a mobile emissions laboratory attached to the tailpipe of heavy-duty diesel trucks to measure OC and EC emissions under varying driving conditions.…”