Cold Temperature and Biodiesel Fuel Effects on Speciated Emissions of Volatile Organic Compounds from Diesel Trucks

Speciated volatile organic compounds (VOCs) were measured in diesel exhaust from three heavy-duty trucks equipped with modern aftertreatment technologies. Emissions testing was conducted on a chassis dynamometer at two ambient temperatures (−7 and 22 °C) operating on two fuels (ultra low sulfur diesel and 20% soy biodiesel blend) over three driving cycles: cold start, warm start and heavy-duty urban dynamometer driving cycle. VOCs were measured separately for each drive cycle. Carbonyls such as formaldehyde and acetaldehyde dominated VOC emissions, making up ∼72% of the sum of the speciated VOC emissions (∑VOCs) overall. Biodiesel use led to minor reductions in aromatics and variable changes in carbonyls. Cold temperature and cold start conditions caused dramatic enhancements in VOC emissions, mostly carbonyls, compared to the warmer temperature and other drive cycles, respectively. Different 2007+ aftertreatment technologies involving catalyst regeneration led to significant modifications of VOC emissions that were compound-specific and highly dependent on test conditions. A comparison of this work with emission rates from different diesel engines under various test conditions showed that these newer technologies resulted in lower emission rates of aromatic compounds. However, emissions of other toxic partial combustion products such as carbonyls were not reduced in the modern diesel vehicles tested

Carbonaceous Aerosols Emitted from Light-Duty Vehicles Operating on Gasoline and Ethanol Fuel Blends

This study examines the chemical properties of carbonaceous aerosols emitted from three light-duty gasoline vehicles (LDVs) operating on gasoline (e0) and ethanol-gasoline fuel blends (e10 and e85). Vehicle road load simulations were performed on a chassis dynamometer using the three-phase LA-92 unified driving cycle (UDC). Effects of LDV operating conditions and ambient temperature (−7 and 24 °C) on particle-phase semivolatile organic compounds (SVOCs) and organic and elemental carbon (OC and EC) emissions were investigated. SVOC concentrations and OC and EC fractions were determined with thermal extraction-gas chromatography–mass spectrometry (TE-GC-MS) and thermal-optical analysis (TOA), respectively. LDV aerosol emissions were predominantly carbonaceous, and EC/PM (w/w) decreased linearly with increasing fuel ethanol content. TE-GC-MS analysis accounted for up to 4% of the fine particle (PM_2.5) mass, showing the UDC phase-integrated sum of identified SVOC emissions ranging from 0.703 μg km^–1 to 18.8 μg km^–1. Generally, higher SVOC emissions were associated with low temperature (−7 °C) and engine ignition; mixed regression models suggest these emissions rate differences are significant. Use of e85 significantly reduced the emissions of lower molecular weight PAH. However, a reduction in higher molecular weight PAH entities in PM was not observed. Individual SVOC emissions from the Tier 2 LDVs and fuel technologies tested are substantially lower and distributed differently than those values populating the United States emissions inventories currently. Hence, this study is likely to influence future apportionment, climate, and air quality model predictions that rely on source combustion measurements of SVOCs in PM

Temperature and Driving Cycle Significantly Affect Carbonaceous Gas and Particle Matter Emissions from Diesel Trucks

The present study examines the effects of fuel [an ultralow 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 sampling media are analyzed using advanced gas chromatograpy/mass spectrometry methods. Study-wide OC and EC emissions are 0.735 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 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 multistudy 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 8 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

Effects of Cold Temperature and Ethanol Content on VOC Emissions from Light-Duty Gasoline Vehicles

Emissions of speciated volatile organic compounds (VOCs), including mobile source air toxics (MSATs), were measured in vehicle exhaust from three light-duty spark ignition vehicles operating on summer and winter grade gasoline (E0) and ethanol blended (E10 and E85) fuels. Vehicle testing was conducted using a three-phase LA92 driving cycle in a temperature-controlled chassis dynamometer at two ambient temperatures (−7 and 24 °C). The cold start driving phase and cold ambient temperature increased VOC and MSAT emissions up to several orders of magnitude compared to emissions during other vehicle operation phases and warm ambient temperature testing, respectively. As a result, calculated ozone formation potentials (OFPs) were 7 to 21 times greater for the cold starts during cold temperature tests than comparable warm temperature tests. The use of E85 fuel generally led to substantial reductions in hydrocarbons and increases in oxygenates such as ethanol and acetaldehyde compared to E0 and E10 fuels. However, at the same ambient temperature, the VOC emissions from the E0 and E10 fuels and OFPs from all fuels were not significantly different. Cold temperature effects on cold start MSAT emissions varied by individual MSAT compound, but were consistent over a range of modern spark ignition vehicles