Recent increases in the Corporate Average Fuel Economy standards have led to widespread adoption of vehicles equipped with gasoline direct-injection (GDI) engines. Changes in engine technologies can alter emissions. To quantify these effects, we measured gas- and particle-phase emissions from 82 light-duty gasoline vehicles recruited from the California in-use fleet tested on a chassis dynamometer using the cold-start unified cycle. The fleet included 15 GDI vehicles, including 8 GDIs certified to the most-stringent emissions standard, superultra-low-emission vehicles (SULEV). We quantified the effects of engine technology, emission certification standards, and cold-start on emissions. For vehicles certified to the same emissions standard, there is no statistical difference of regulated gas-phase pollutant emissions between PFIs and GDIs. However, GDIs had, on average, a factor of 2 higher particulate matter (PM) mass emissions than PFIs due to higher elemental carbon (EC) emissions. SULEV certified GDIs have a factor of 2 lower PM mass emissions than GDIs certified as ultralow-emission vehicles (3.0 ± 1.1 versus 6.3 ± 1.1 mg/mi), suggesting improvements in engine design and calibration. Comprehensive organic speciation revealed no statistically significant differences in the composition of the volatile organic compounds emissions between PFI and GDIs, including benzene, toluene, ethylbenzene, and xylenes (BTEX). Therefore, the secondary organic aerosol and ozone formation potential of the exhaust does not depend on engine technology. Cold-start contributes a larger fraction of the total unified cycle emissions for vehicles meeting more-stringent emission standards. Organic gas emissions were the most sensitive to cold-start compared to the other pollutants tested here. There were no statistically significant differences in the effects of cold-start on GDIs and PFIs. For our test fleet, the measured 14.5% decrease in CO emissions from GDIs was much greater than the potential climate forcing associated with higher black carbon emissions. Thus, switching from PFI to GDI vehicles will likely lead to a reduction in net global warming.

Particulate matter emissions were measured in two bores of the Caldecott Tunnel in Northern California during August and September 2004. One bore (Bore 1) is open to both heavy- and light-duty vehicles while heavy-duty vehicles are prohibited from entering the second bore (Bore 2). Particulate matter number and mass size distributions, chemical composition, and gaseous copollutants were recorded for four consecutive days near the entrance and exit of each bore. Size-resolved emission factors were determined for particle number, particle mass, elemental carbon, organic carbon (OC), sulfate, nitrate, and selected elements. The size distributions in both the bores showed a single large mode at roughly 15-20 nm in mobility diameter, with occasional smaller modes around 100 nm. The PM10 mass emission factor for heavy-duty vehicles was 14.5 times higher than that of light-duty vehicles. The particles derived from diesel are more abundant in elemental carbon, 70.9% of PM10 emissions, as compared to the light-duty vehicles. Conversely, a greater percentage of OC was found in light-duty emissions than heavy-duty emissions. In comparison to previous studies at the Caldecott Tunnel, less particle mass but more particle numbers are emitted by vehicles than was the case 7 years ago.

[1] For a period of almost 3 years, sampling of size-fractionated ambient particulate matter with diameter below 10 mm (PM 10 ) was performed at urban source sites (Downey and University of Southern California) and inland receptor sites (Claremont and Riverside) in the Los Angeles Basin as part of the Southern California Particle Center and Supersite. Results for size-resolved PM 10 mass, inorganic ions (sulfate and nitrate), metals, elemental carbon, and organic carbon were obtained. Three collocated micro-orifice uniform deposit impactors (MOUDIs) were deployed to collect 24-hour samples roughly once a week. Ultrafine particle concentrations (particle diameter d p < 0.1 mm) were found to be the highest at the source sites resulting from fresh vehicular emissions. Mass concentrations in the accumulation mode (0.1 < d p < 2.5 mm) were lower in winter than in summer, especially at the receptor sites. PM concentrations in the coarse mode (2.5 < d p < 10 mm) were lower in winter and were composed mostly of nitrate and crustal elements (iron, calcium, potassium, silicon, and aluminum). Consistent relative levels of these elements indicate a common source of soil and/or road dust. In the accumulation mode, nitrate and organic carbon were predominant with higher nitrate levels found at the receptor sites. The ultrafine mode PM consisted of mostly organic carbon, with higher wintertime levels at the source sites due to increased organic vapor condensation from vehicles at lower temperatures. Conversely, higher ultrafine organic carbon levels at the receptor areas are due to secondary organic aerosol formation by photochemical reactions as well as increased advection of polluted air masses from upwind.

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Experiments were conducted at the California Air Resources Board Haagen-Smit Laboratory to understand changes in vehicle emissions in response to stricter emissions standards over the past 25 years. Measurements included a wide range of volatile organic compounds (VOCs) for a wide range of spark ignition gasoline vehicles meeting varying levels of emissions standards, including all certifications from Tier 0 up to Partial Zero Emission Vehicle. Standard gas chromatography (GC) and high performance liquid chromatography (HLPC) analyses were employed for drive-cycle phase emissions. A proton-transfer-reaction mass spectrometer measured time-resolved emissions for a wide range of VOCs. Cold-start emissions occur almost entirely in the first 30–60 s for newer vehicles. Cold-start emissions have compositions that are not significantly different across all vehicles tested and are markedly different from neat fuel. Hot-stabilized emissions have varying importance depending on species and may require a driving distance of 200 miles to equal the emissions from a single cold start. Average commute distances in the U.S. suggest the majority of in-use vehicles have emissions dominated by cold starts. The distribution of vehicle ages in the U.S. suggests that within several years only a few percent of vehicles will have significant driving emissions compared to cold-start emissions.