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Temperature and Driving Cycle Significantly Affect Carbonaceous Gas and Particle Matter Emissions from Diesel Trucks
Citation:
Hays, M., W. Preston, BJ George, I. George, R. Snow, J. Faircloth, T. Long, R. Baldauf, AND J. McDonald. Temperature and Driving Cycle Significantly Affect Carbonaceous Gas and Particle Matter Emissions from Diesel Trucks. ENERGY AND FUELS. American Chemical Society, Washington, DC, 31(10):11034-11042, (2017). https://doi.org/10.1021/acs.energyfuels.7b01446
Impact/Purpose:
Despite the potential benefits of biofuel use, there is public health concern about the possible direct and indirect environmental and air quality impacts. Replacement of petroleum diesel with biodiesel in vehicles can reduce pollutant emissions, including particulate matter (PM), CO, elemental carbon (EC), polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs), and total hydrocarbons (THC). However, reductions are not always realized and vary by pollutant. Although few studies investigate the health effects of biodiesel PM emitted from vehicles, there is evidence suggesting that biodiesel can be more mutagenic and cytotoxic than petroleum diesel and also evidence showing reduced mutagenicity. Knowledge of compositional differences is indeed important for understanding the toxicological effects of aerosol particles and is also required for proper accounting within the global emissions inventories that support dispersion, air quality, forecasting, and chemical mass balance models. The present dynamometer study aims to examine the effects on SVOC emissions following a switch from ultra-low-sulfur diesel fuel (ULSD) to a soy-methyl-ester based B20 fuel in three heavy-duty diesel vehicles. This study observes conditions under which PAH compounds with MW ≥ 252 amu appear in diesel particles downstream of the CDPF and can even reach low-end concentrations reported earlier for much larger HDDVs with poorly controlled exhaust streams. This rare observation suggests that analysis of PAHs in particles emitted from modern L/MHDDVs may be more complex than recognized previously. In the final analysis, this study provides information that EPA can use to meet its statutory reporting requirements related to RFS impacts (http://www.epa.gov/oig).
Description:
The present study examines the effects of fuel (an ultra-low sulfur diesel [ULSD] versus a 20% v/v soy-based biodiesel—80% v/v petroleum blend [B20]), temperature, load, vehicle, driving cycle, and active regeneration technology on gas- and particle-phase carbon emissions from light and medium heavy-duty diesel vehicles (L/MHDDV). The study is performed using chassis dynamometer facilities that support low temperature operation (-6.7 °C versus 21.7 °C) and heavy loads up to 12,000 kg. Organic and elemental carbon (OC-EC) composition of aerosol particles is determined using a thermal-optical technique. Gas- and particle-phase semivolatile organic compound (SVOC) emissions collected using traditional filter and polyurethane foam (PUF) sampling media are analyzed using advanced gas chromatograpy/mass spectrometry (GC/MS) methods. Study-wide OC and EC emissions are 0.735 mg/km and 0.733 mg/km, on average. The emissions factors for diesel vehicles vary widely, and use of a catalyzed diesel particle filter (CDPF) device generally mutes the carbon particle emissions in the exhaust, which contains ~90% w/w gas-phase matter. Interestingly, replacing ULSD with B20 did not significantly influence SVOC emissions, for which sums range from 0.030 mg/km to 9.4 mg/km for the L/MHDDVs. However, both low temperature and vehicle cold-starts significantly increase SVOCs in the exhaust. Real-time particle measurements indicate vehicle regeneration technology did influence emissions, although regeneration effects went unresolved using bulk chemistry techniques. A multi-study comparison of the toxic particle-phase polycyclic aromatic hydrocarbons (PAHs; molecular weight (MW) ≥ 252 amu) in diesel exhaust indicates emission factors that span up to eight orders of magnitude over the past several decades. This study observes conditions under which PAH compounds with MW ≥ 252 amu appear in diesel particles downstream of the CDPF and can even reach low-end concentrations reported earlier for much larger HDDVs with poorly controlled exhaust streams. This rare observation suggests that analysis of PAHs in particles emitted from modern L/MHDDVs may be more complex than recognized previously.
URLs/Downloads:
DOI: Temperature and Driving Cycle Significantly Affect Carbonaceous Gas and Particle Matter Emissions from Diesel Trucks
https://pubs.acs.org/doi/abs/10.1021/acs.energyfuels.7b01446
Free access through PubMed Central