Daniel Short

Determination of Suspended Exhaust PM Mass for Light-Duty Vehicles

This study provides one of the first evaluations of the integrated particle size distribution (IPSD) method in comparison with the current gravimetric method for measuring particulate matter (PM) emissions from light-duty vehicles. The IPSD method combines particle size distributions with size dependent particle effective density to determine mass concentrations of suspended particles. The method allows for simultaneous determination of particle mass, particle surface area, and particle number concentrations. It will provide a greater understanding of PM mass emissions at low levels, and therefore has the potential to complement the current gravimetric method at low PM emission levels. Six vehicles, including three gasoline direct injected (GDI) vehicles, two port fuel injected (PFI) vehicles, and one diesel vehicle, were tested over the Federal Test Procedure (FTP) driving cycle on a light-duty chassis dynamometer. PM mass emissions were determined by the gravimetric (MGravimetric) and IPSD (MIPSD) methods. The results show a systematic bias between methods, with the MIPSD underestimating particle mass relative to MGravimetric (MIPSD = 0.63 × MGravimetric), although there is a relatively strong correlation (R2=0.79) between the methods. The real-time MIPSD showed that more than 55% of the PM mass comes from the first 100 seconds of the FTP for GDI vehicles.

Changes in droplet surface tension affect the observed hygroscopicity of photochemically aged biomass burning aerosol.

This study examines the hygroscopic and surface tension properties as a function of photochemical aging of the aerosol emissions from biomass burning. Experiments were conducted in a chamber setting at the UC-Riverside Center for Environmental Research and Technology (CE-CERT) Atmospheric Processes Lab using two biomass fuel sources, manzanita and chamise. Cloud condensation nuclei (CCN) measurements and off-line filter sample analysis were conducted. The water-soluble organic carbon content and surface tension of the extracted filter samples were measured. Surface tension information was then examined with Köhler theory analysis to calculate the hygroscopicity parameter, κ. Laboratory measurement of biomass burning smoke from two chaparral fuels is shown to depress the surface tension of water by 30% or more at organic matter concentrations relevant at droplet activation. Accounting for surface tension depression can lower the calculated κ by a factor of 2. This work provides evidence for surface tension depression in an important aerosol system and may provide closure for differing sub- and supersaturated κ measurements.

Evaluating the Effects of Aromatics Content in Gasoline on Gaseous and Particulate Matter Emissions from SI-PFI and SIDI Vehicles.

We assessed the emissions response of a fleet of seven light-duty gasoline vehicles for gasoline fuel aromatic content while operating over the LA92 driving cycle. The test fleet consisted of model year 2012 vehicles equipped with spark-ignition (SI) and either port fuel injection (PFI) or direct injection (DI) technology. Three gasoline fuels were blended to meet a range of total aromatics targets (15%, 25%, and 35% by volume) while holding other fuel properties relatively constant within specified ranges, and a fourth fuel was formulated to meet a 35% by volume total aromatics target but with a higher octane number. Our results showed statistically significant increases in carbon monoxide, nonmethane hydrocarbon, particulate matter (PM) mass, particle number, and black carbon emissions with increasing aromatics content for all seven vehicles tested. Only one vehicle showed a statistically significant increase in total hydrocarbon emissions. The monoaromatic hydrocarbon species that were evaluated showed increases with increasing aromatic content in the fuel. Changes in fuel composition had no statistically significant effect on the emissions of nitrogen oxides (NOx), formaldehyde, or acetaldehyde. A good correlation was also found between the PM index and PM mass and number emissions for all vehicle/fuel combinations with the total aromatics group being a significant contributor to the total PM index followed by naphthalenes and indenes.

Assessing the Impacts of Ethanol and Isobutanol on Gaseous and Particulate Emissions from Flexible Fuel Vehicles

This study investigated the effects of higher ethanol blends and an isobutanol blend on the criteria emissions, fuel economy, gaseous toxic pollutants, and particulate emissions from two flexible-fuel vehicles equipped with spark ignition engines, with one wall-guided direct injection and one port fuel injection configuration. Both vehicles were tested over triplicate Federal Test Procedure (FTP) and Unified Cycles (UC) using a chassis dynamometer. Emissions of nonmethane hydrocarbons (NMHC) and carbon monoxide (CO) showed some statistically significant reductions with higher alcohol fuels, while total hydrocarbons (THC) and nitrogen oxides (NOx) did not show strong fuel effects. Acetaldehyde emissions exhibited sharp increases with higher ethanol blends for both vehicles, whereas butyraldehyde emissions showed higher emissions for the butanol blend relative to the ethanol blends at a statistically significant level. Particulate matter (PM) mass, number, and soot mass emissions showed strong reductions with increasing alcohol content in gasoline. Particulate emissions were found to be clearly influenced by certain fuel parameters including oxygen content, hydrogen content, and aromatics content.

Understanding particles emitted from spray and wall-guided gasoline direct injection and flex fuel vehicles operating on ethanol and iso-butanol gasoline blends

ABSTRACT Traffic-related pollutants are an ever-growing concern. However, the composition of particle emissions from new vehicle technologies using relevant current and prospective fuel blends is not known. This study tested four current and up-and-coming vehicle technologies with nine fuel blends with various concentrations of ethanol and iso-butanol. Vehicles were driven on both the federal test procedure (FTP) and the unified cycle (UC). Additional tests were conducted under steady-state speed conditions. The vehicle technologies include spray-guided gasoline direct injection (SG-GDI), wall-guided gasoline direct injection (WG-GDI), port-fuel injection flex fuel vehicle (PFI-FFV), and a wall-guided GDI-FFV. The fuels consisted of 10–83% ethanol and 16–55% iso-butanol in gasoline. The composition of soot, water-insoluble mass (WIM), water-soluble organic mass, and water-insoluble organic mass (WIOM), and OM was measured. The majority of emissions over FTP and UC were water-insoluble (>70%), and WIOM contributes mostly to OM. PFIs have lower soot and particulate matter (PM) emissions in comparison to the WG-GDI technology even while increasing the renewable fuel content. SG-GDI technology, which has not penetrated the market, show promise as soot and PM emissions are comparable to PFI vehicles while preserving the GDI fuel economy benefits. The WIM fraction in GDI-FFV consistently increased with increasing ethanol concentration. Lastly, the impact of the future vehicle emissions and traffic pollutants is discussed. SG-GDI technology is found to be a promising sustainable technology to enhance fuel economy and also reduce PM, soot, and WIM emissions. Copyright

Integrating Cloud Condensation Nuclei Predictions with Fast Time Resolved Aerosol Instrumentation to Determine the Hygroscopic Properties of Emissions Over Transient Drive Cycles

The physical and chemical properties of aerosols emitted from vehicles can vary in composition under different driving conditions. Thus, characterizing ephemeral changes in aerosol cloud condensation nuclei (CCN) activity and apparent hygroscopicity for vehicle-testing procedures conducted over transient drive cycles can be challenging. To evaluate CCN activity of these emitted aerosols, a closure method integrating traditional CCN measurements with fast time resolved aerosol instrumentation typically used to measure engine exhaust was utilized. Calibration of the method predicted activation diameters, Dd, within 10% and 15% of Dd derived from Köhler theory for two stable sources, aerosolized ammonium sulfate and α-pinene secondary organic aerosol, respectively. It was then applied to a transient source to estimate the effect of six different ethanol and iso-butanol gasoline blends on the hygroscopic properties of emissions downstream a gasoline direct injection light duty passenger vehicle over transient drive cycles. To describe the CCN activity, a single hygroscopicity parameter, kappa, was used. Results indicate low CCN activity with kappa ranging between ~0.002 and 0.06. Copyright 2015 American Association for Aerosol Research

A Unique Online Method to Infer Water-Insoluble Particle Contributions

Particle number, size, and composition information is important for constraining aerosol effects on air quality, climate, and health. The composition of particles, especially from vehicular sources, may contain insoluble black carbon (BC) materials that modify particle nucleating properties. In this study, we develop a method to provide quantitative and real-time information on the water-insoluble components found in near-road aerosol sources. A water-based condensation particle counter (W-CPC) and a butanol-based CPC (B-CPC) were used to measure the particle number concentration. Both instruments were coupled with a scanning mobility particle sizer (SMPS) to record the particle number and size data. Real time water-insoluble particle mass was estimated from the difference in particle number concentration between the two CPCs; theoretical water-insoluble mass was calculated from the ideal hygro- scopicity single parameter κ-values. This online method was calibrated with test compounds and then applied to data collected from a field study. Ambient aerosol was sampled from a monitoring station located 15 m from the I-710 freeway in Long Beach, California. The results show that near-roadway emissions contain water-insoluble (BC and non-BC) components. Particle number and BC concentrations increase after changes in wind direction near the freeway on both weekday and weekend measurements. Particles were less hygroscopic (κ ∼ 0.2) before changes in wind direction from downwind to upwind of the freeway (κ > 0.6). Rapid changes in water-solubility can be captured with this technique. By assuming a two-component mixture, the water-insoluble mass fractions were inferred. BC shows a positive correlation with the water-insoluble mass however its presence may not account for the entire water-insoluble mass from the near-roadway source. Copyright 2014 American Association for Aerosol Research

Components of Particle Emissions from Light-Duty Spark-Ignition Vehicles with Varying Aromatic Content and Octane Rating in Gasoline

Typical gasoline consists of varying concentrations of aromatic hydrocarbons and octane ratings. However, their impacts on particulate matter (PM) such as black carbon (BC) and water-soluble and insoluble particle compositions are not well-defined. This study tests seven 2012 model year vehicles, which include one port fuel injection (PFI) configured hybrid vehicle, one PFI vehicle, and six gasoline direct injection (GDI) vehicles. Each vehicle was driven on the Unified transient testing cycle (UC) using four different fuels. Three fuels had a constant octane rating of 87 with varied aromatic concentrations at 15%, 25%, and 35%. A fourth fuel with higher octane rating, 91, contained 35% aromatics. BC, PM mass, surface tension, and water-soluble organic mass (WSOM) fractions were measured. The water-insoluble mass (WIM) fraction of the vehicle emissions was estimated. Increasing fuel aromatic content increases BC emission factors (EFs) of transient cycles. BC concentrations were higher for the GDI vehicles than the PFI and hybrid vehicles, suggesting a potential climate impact for increased GDI vehicle production. Vehicle steady-state testing showed that the hygroscopicity of PM emissions at high speeds (70 mph; κ > 1) are much larger than emissions at low speeds (30 mph; κ < 0.1). Iso-paraffin content in the fuels was correlated to the decrease in WSOM emissions. Both aromatic content and vehicle speed increase the amount of hygroscopic material found in particle emissions.