William Crews

Variations in Speciated Emissions from Spark-Ignition and Compression-Ignition Motor Vehicles in California's South Coast Air Basin

Abstract The U.S. Department of Energy Gasoline/Diesel PM Split Study examined the sources of uncertainties in using an organic compound-based chemical mass balance receptor model to quantify the contributions of spark-ignition (SI) and compression-ignition (CI) engine exhaust to ambient fine particulate matter (PM2.5). This paper presents the chemical composition profiles of SI and CI engine exhaust from the vehicle-testing portion of the study. Chemical analysis of source samples consisted of gravimetric mass, elements, ions, organic carbon (OC), and elemental carbon (EC) by the Interagency Monitoring of Protected Visual Environments (IMPROVE) and Speciation Trends Network (STN) thermal/optical methods, polycyclic aromatic hydrocarbons (PAHs), hopanes, steranes, alkanes, and polar organic compounds. More than half of the mass of carbonaceous particles emitted by heavy-duty diesel trucks was EC (IMPROVE) and emissions from SI vehicles contained predominantly OC. Although total carbon (TC) by the IMPROVE and STN protocols agreed well for all of the samples, the STN/IMPROVE ratios for EC from SI exhaust decreased with decreasing sample loading. SI vehicles, whether low or high emitters, emitted greater amounts of high-molecular-weight particulate PAHs (benzo[ghi]perylene, indeno[1,2,3-cd]pyrene, and coronene) than did CI vehicles. Diesel emissions contained higher abundances of two- to four-ring semivolatile PAHs. Diacids were emitted by CI vehicles but are also prevalent in secondary organic aerosols, so they cannot be considered unique tracers. Hopanes and steranes were present in lubricating oil with similar composition for both gasoline and diesel vehicles and were negligible in gasoline or diesel fuels. CI vehicles emitted greater total amounts of hopanes and steranes on a mass per mile basis, but abundances were comparable to SI exhaust normalized to TC emissions within measurement uncertainty. The combustion-produced high-molecular-weight PAHs were found in used gasoline motor oil but not in fresh oil and are negligible in used diesel engine oil. The contributions of lubrication oils to abundances of these PAHs in the exhaust were large in some cases and were variable with the age and consumption rate of the oil. These factors contributed to the observed variations in their abundances to total carbon or PM2.5 among the SI composition profiles.

THE INFLUENCE OF AMBIENT TEMPERATURE ON TAILPIPE EMISSIONS FROM 1984-1987 MODEL YEAR LIGHT DUTY GASOLINE MOTOR VEHICLES

Motor-vehicle emissions are sensitive to a number of variables including ambient temperature, driving schedule (speed versus time), and fuel composition. Hydrocarbon, aldehyde, carbon monoxide, and oxides of nitrogen emissions were examined with nine recent technology 4-cylinder gasoline motor vehicles at 70F, 40F, and 20F. About 200 hydrocarbon and 12 aldehyde compounds were included in the organic emissions characterization. Two fuels and two driving schedules were used. Typically, hydrocarbon and carbon monoxide emissions were significantly increased by reduced ambient temperature. Oxides of nitrogen emissions also increased, but to a lesser extent. There were no predictable formaldehyde emissions trends with temperature. Paraffinic and aromatic hydrocarbon emission fractions were sensitive to fuel composition, but the olefinic emission fraction (dominated by ethylene and propylene) was not. With low temperature cold start tests, preceding transient driving with a 5 minute engine idle resulted in reduced carbon monoxide emission rates and elevated oxides of nitrogen emission rates. Hydrocarbon emission rates were not predictable sensitive to the preliminary idle.

Methods of Characterizing the Distribution of Exhaust Emissions from Light-Duty, Gasoline-Powered Motor Vehicles in the U.S. Fleet

Abstract Mobile sources significantly contribute to ambient concentrations of airborne particulate matter (PM). Source apportionment studies for PM10 (PM ≤ 10 µm in aerodynamic diameter) and PM2.5 (PM ≤ 2.5 µm in aerodynamic diameter) indicate that mobile sources can be responsible for over half of the ambient PM measured in an urban area. Recent source apportionment studies attempted to differentiate between contributions from gasoline and diesel motor vehicle combustion. Several source apportionment studies conducted in the United States suggested that gasoline combustion from mobile sources contributed more to ambient PM than diesel combustion. However, existing emission inventories for the United States indicated that diesels contribute more than gasoline vehicles to ambient PM concentrations. A comprehensive testing program was initiated in the Kansas City metropolitan area to measure PM emissions in the light-duty, gasoline-powered, on-road mobile source fleet to provide data for PM inventory and emissions modeling. The vehicle recruitment design produced a sample that could represent the regional fleet, and by extension, the national fleet. All vehicles were recruited from a stratified sample on the basis of vehicle class (car, truck) and model-year group. The pool of available vehicles was drawn primarily from a sample of vehicle owners designed to represent the selected demographic and geographic characteristics of the Kansas City population. Emissions testing utilized a portable, light-duty chassis dynamometer with vehicles tested using the LA-92 driving cycle, on-board emissions measurement systems, and remote sensing devices. Particulate mass emissions were the focus of the study, with continuous and integrated samples collected. In addition, sample analyses included criteria gases (carbon monoxide, carbon dioxide, nitric oxide/nitrogen dioxide, hydrocarbons), air toxics (speciated volatile organic compounds), and PM constituents (elemental/ organic carbon, metals, semi-volatile organic compounds). Results indicated that PM emissions from the in-use fleet varied by up to 3 orders of magnitude, with emissions generally increasing for older model-year vehicles. The study also identified a strong influence of ambient temperature on vehicle PM mass emissions, with rates increasing with decreasing temperatures.

Criteria and Air-Toxic Emissions from In-Use Automobiles in the National Low-Emission Vehicle Program

Abstract The U.S. Environmental Protection Agency (EPA) implemented a program to identify tailpipe emissions of criteria and air-toxic contaminants from in-use, light-duty low-emission vehicles (LEVs). EPA recruited 25 LEVs in 2002 and measured emissions on a chassis dynamometer using the cold-start urban dynamometer driving schedule of the Federal Test Procedure. The emissions measured included regulated pollutants, particulate matter, speciated hydrocarbon compounds, and carbonyl compounds. The results provided a comparison of emissions from real-world LEVs with emission standards for criteria and air-toxic compounds. Emission measurements indicated that a portion of the in-use fleet tested exceeded standards for the criteria gases. Real-time regulated and speciated hydrocarbon measurements demonstrated that the majority of emissions occurred during the initial phases of the cold-start portion of the urban dynamometer driving schedule. Overall, the study provided updated emission factor data for real-world, in-use operation of LEVs for improved emissions modeling and mobile source inventory development.

CHARACTERIZATION OF EMISSIONS FROM A METHANOL FUELED MOTOR VEHICLE

Exhaust, evaporative, and refueling emissions were examined from a methanol fueled Ford Escort operated with M85 (85 percent methanol-15 percent gasoline) and M100 (100 percent methanol) fuels. Exhaust and evaporative emissions were examined for vehicle operation at summer and winter ambient temperatures, while refueling emissions were examined at typical summer temperatures. Regulated emissions (total hydrocarbons, carbon monoxide, nitrogen oxides) as well as formaldehyde, methanol, and detailed hydrocarbon emissions were examined. Results indicated that carbon monoxide, methanol, hydrocarbon, and formaldehyde exhaust emissions increased substantially when the vehicle was operated at reduced temperatures. Formaldehyde emissions were more fuel sensitive than hydrocarbon, carbon monoxide and methanol emissions. A significant portion of the total organic evaporative and refueling emissions with M85 fuel was comprised of hydrocarbons. Both hydrocarbon and methanol evaporative emissions were dependent on test...

EMISSION FROM IN-USE HEAVY-DUTY GASOLINE TRUCKS

Apportionment of air pollution to sources requires knowledge of source emission strengths and/or chemical and physical characteristics. The literature is deficient in data useful for this purpose for heavy-duty motor vehicles, which can be important sources of air pollution in certain microenvironments. Emissions factors are developed in this study for heavy-duty gasoline trucks using chassis dynamometer simulations of urban driving conditions. The sensitivity of the emissions to such considerations as the characteristics of the speed-time driving schedule, vehicle payload, and chassis configuration are examined. Emissions characterization includes total and individual hydrocarbons, aldehydes, carbon monoxide, oxides of nitrogen, total particulate matter, particulate organics, lead, bromine, chlorine, and the fraction of total particulate less than 2 ..mu..m. Preliminary comparisons of emissions obtained using transient engine and transient chassis test procedures are also reported.

Absence of 14C in PM2.5 Emissions from Gasohol Combustion in Small Engines

PM2.5 combustion emissions from small engines (string trimmer and chainsaw) using gasoline containing biogenic ethanol were collected and analyzed for their 14 C content. The sampling methodology was designed to minimize potential bias from organic artifact effects. The 14 C in the PM2.5 emissions was found to be drastically smaller (approximately a factor of 40) than the 14 C amounts measured in the fuels. This suggests that the current method of using 14 C measurements on ambient aerosol to estimate the contribution from fossil fuel combustion will be little affected by increased use of ethanol-containing gasoline.

AMBIENT TEMPERATURE AND DRIVING CYCLE EFFECTS ON CNG MOTOR VEHICLE EMISSION

This paper describes an emissions study of two vans powered by compressed natural gas (CNG). One van was relatively new, while the other had been driven more than 120,000 mi. The purpose of the study was to obtain emissions information which could be used to predict the impact of CNG use on ambient air quality and air toxic concentrations, and to develop a better understanding of the effect of ambient temperature variations on CNG emissions. Using four different driving cycles, emission tests were carried out at 20{degree}F, 75{degree}F, and 105{degree}F. Test results agree with previous findings that document low emissions of nonmethane hydrocarbons from CNG vehicles. Results also confirm the expectation that CNG emissions are not significantly affected by ambient temperature variations, although an increase in formaldehyde emission was noted for the 20{degree}F cold-start tests.