Size-Resolved Emissions of Organic Tracers from Light- and Heavy-Duty Vehicles Measured in a California Roadway Tunnel

Abstract

Individual organic compounds found in particulate emissions from vehicles have proven useful in source apportionment of ambient particulate matter. Species of interest include the hopanes, originating in lube oil, and selected PAHs generated via combustion. Most efforts to date have focused on emissions and apportionment PM10 or PM2.5 However, examining how these compounds are segregated by particle size in both emissions and ambient samples will help efforts to apportion size-resolved PM, especially ultrafine particles which have been shown to be more potent toxicologically. To this end, high volume size-resolved (coarse, accumulation, and ultrafine) PM samples were collected inside the Caldecott tunnel in Orinda, California to determine the relative emission factors for these compounds in different size ranges. Sampling occurred in two bores, one off-limits to heavy-duty diesel vehicles, which allows determination of the different emissions profiles for diesel and gasoline vehicles. Although tunnel measurements do not measure emissions over a full engine duty cycle, they do provide an average emissions profile over thousands of vehicles that can be considered characteristic of "freeway" emissions. Results include size-fractionated emission rates for hopanes, PAHs, elemental carbon, and other potential organic markers apportioned to diesel and gasoline vehicles. The results are compared to previously conducted PM2.5 emissions testing using dynamometer facilities and othertunnel environments.

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

“…For DV, the PAHs, hopane and sterane accounted for approximately 0.9%, and 0.7% of OC, while BghiP (0.002 mg·veh −1 ·km −1 ) had the highest value in the PAHs, followed by Pyr (0.215 mg·veh −1 ·km −1 ), Fluo (0.113 mg·veh −1 ·km −1 ) and Chry (0.102 mg·veh −1 ·km −1 ). The result obtained from the roadway tunnel (Phuleria et al, 2006) for LDV was similar to that of the diesel vehicles, that is, that BghiP was the most abundant of the PAHs, followed by BaP, and Chry. It is known that the LMW PAHs are mostly associated with diesel engines, while the HMW PAHs are associated with gasoline engine (Chen et al, 2013).…”

Calculated respiratory exposure to indoor size-fractioned polycyclic aromatic hydrocarbons in an urban environment

“…Source diagnostics based on several PAH isomeric ratios (Supplementary material) indicated that indoor particulate PAHs were mainly derived from fossil fuel combustion such as automobile exhaust. However, other studies indicated that particulate PAHs newly discharged from automobiles were mainly distributed in the ultrafine fraction (Miguel et al, 1998;Phuleria et al, 2006). A similar inconsistency was also observed in Saitama City of Japan, which was ascribed to coagulation of fine particles (Kawanaka et al, 2009).…”

Current Understanding of Ultrafine Particulate Matter Emitted from Mobile Sources

“…These results were consistent for hopanes, steranes, BC, and high-molecular-weight PAHs with those obtained in a highway tunnel near San Francisco. 80 Biswas et al 81 investigated the volatility of ambient UFPM collected near I-710 highway in Los Angeles using a TDMA. Sampling was conducted at 10-and 150-m downwind from the highway and the analysis was conducted for particles of 20, 40, 80, and 120 nm in diameter.…”