Thermally derived carbon fractions including organic carbon (OC) and elemental carbon (EC) have been reported for the U.S. Interagency Monitoring of PROtected Visual Environments (IMPROVE) network since 1987 and have been found useful in source apportionment studies and to evaluate quartz-fiber filter adsorption of organic vapors. The IMPROVE_A temperature protocol defines temperature plateaus for thermally derived carbon fractions of 140°C for OC1, 280°C for OC2, 480°C for OC3, and 580°C for OC4 in a helium (He) carrier gas and 580°C for EC1, 740°C for EC2, and 840°C for EC3 in a 98% He/2% oxygen (O 2 ) carrier gas. These temperatures differ from those used previously because new hardware used for the IMPROVE thermal/optical reflectance (IMPROVE_TOR) protocol better represents the sample temperature than did the old hardware. A newly developed temperature calibration method demonstrates that these temperatures better represent sample temperatures in the older units used to quantify IMPROVE carbon fractions from 1987 through 2004. Only the thermal fractions are affected by changes in temperature. The OC and EC by TOR are insensitive to the change in temperature protocol, and therefore the long-term consistency of the IMPROVE database is conserved. A method to detect small quantities of O 2 in the pure He carrier gas shows that O 2 levels above 100 ppmv also affect the comparability of thermal carbon fractions but have little effect on the IMPROVE_TOR split between OC and EC.

Four heavy-duty and medium-duty diesel vehicles were tested in six different aftertreament configurations using a chassis dynamometer to characterize the occurrence of nucleation (the conversion of exhaust gases to particles upon dilution). The aftertreatment included four different diesel particulate filters and two selective catalytic reduction (SCR) devices. All DPFs reduced the emissions of solid particles by several orders of magnitude, but in certain cases the occurrence of a volatile nucleation mode could increase total particle number emissions. The occurrence of a nucleation mode could be predicted based on the level of catalyst in the aftertreatment, the prevailing temperature in the aftertreatment, and the age of the aftertreatment. The particles measured during nucleation had a high fraction of sulfate, up to 62% of reconstructed mass. Additionally the catalyst reduced the toxicity measured in chemical and cellular assays suggesting a pathway for an inverse correlation between particle number and toxicity. The results have implications for exposure to and toxicity of diesel PM.

Abstract. Thermal/optical methods have been widely used for quantifying total carbon (TC), organic carbon (OC), and elemental carbon (EC) in ambient and source particulate samples. Thermally defined carbon fractions have been used for source identification. Temperature precision in thermal carbon analysis is critical to the allocation of carbon fractions. The sample temperature is determined by a thermocouple, which is usually located in the oven near the sample. Sample and thermocouple temperature may differ owing to different thermal properties between the sample filter punch and the thermocouple, or inhomogeneities in the heating zone. Quick-drying temperature-indicating liquids (Tempil Inc., South Plainfield, NJ) of different liquefying points are used as temperature calibration standards. These consist of chemicals that change their appearance at specific temperatures and can be optically monitored to determine the sample temperature. Temperature measures were evaluated for three different models of carbon analyzers. Sample temperatures were found to differ from sensor temperatures by 10 to 50 • C. Temperature biases of 14 to 22 • C during thermal analysis were found to change carbon fraction measurements. The temperature indicators allow calibration curves to be constructed that relate the sample temperature to the temperature measured by a thermocouple.

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.

Over the past two decades vehicle emission standards in the United States have been dramatically tightened with the goal of reducing urban air pollution. Secondary organic aerosol (SOA) is the dominant contributor to urban organic aerosol. Experiments were conducted at the California Air Resources Board Haagen-Smit Laboratory to characterize exhaust organics from 20 gasoline vehicles recruited from the California in-use fleet. The vehicles spanned a wide range of emission certification standards. We comprehensively characterized intermediate volatility and semivolatile organic compound emissions using thermal desorption two-dimensional gas-chromatography− mass-spectrometry with electron impact (GC × GC-EI-MS) and vacuumultraviolet (GC × GC-VUV-MS) ionization. Single-ring aromatic compounds with unsaturated C4 and C5 substituents contribute a large fraction of the intermediate volatility organic compound (IVOC) emissions in gasoline vehicle exhaust. The analyses of quartz filters used in GC × GC-VUV-MS show that primary organic aerosol emissions were dominated by motor oil. We combined our new emissions data with published SOA yield parametrizations to estimate SOA formation potential. After 24 h of oxidation, IVOC emissions contributed 45% of SOA formation; BTEX compounds (benzene, toluene, xylenes, and ethylbenzene), 40%; other VOC aromatics, 15%. The composition of IVOC emissions was consistent across the test fleet, suggesting that future reductions in vehicular emissions will continue to reduce SOA formation and ambient particulate mass levels.