Carbon Monoxide Species Research Articles

Conversion of wet ethanol to syngas via filtration combustion: An experimental and computational investigation

Ethanol is often promoted as the biofuel of the future, yet its acceptance as a fuel for combustion devices is limited by the cost of production. Since most combustion engines cannot tolerate high concentrations of water, the ethanol must be distilled and dehydrated, requiring large amounts of energy. Ethanol also has great potential as a feedstock for syngas consisting of hydrogen, carbon monoxide, and other species. The conversion, called reforming, of ethanol to syngas does not necessarily require dehydration or distillation, thus eliminating or reducing the costs associated with those processes. In addition, there is potential for obtaining additional hydrogen from the water in the mixture. In this paper, we investigate the conversion of wet ethanol, or ethanol that has not been fully distilled or dehydrated, to syngas in an inert porous reactor. Experimental and computational results over a range of equivalence ratios, inlet velocities, and water fractions are presented. The results indicate that wet ethanol is a promising biological source for hydrogen.

High-Temperature Reaction in the Freeboard Region above a Bubbling Fluidized Bed

A plug flow model is presented for the oxidation of hazardous carbon monoxide into inert carbon dioxide taking place in the freeboard region above a freely bubbling fluidized reactor. The extent of the reaction in oxygen- and water vapor-bearing flue gas is described as a function of the fraction of solids ejected into the freeboard from the bed surface, the relative throughput, the gas density, and the global rate of reaction. Experimental measurements were conducted to determine the axial concentration profiles of carbon monoxide and other species throughout the freeboard. Steady-state measurements were carried out in an electrically heated reactor with an inner diameter of 9.36 cm above a gently fluidized bed of heat-resistant ceramsite particles in which a precursive liguid fuel (isopropanol) was burned. The global burnout reaction is assumed to be first order in carbon monoxide and one-half order with respect to oxygen and water vapor. The rate parameters for CO and O2 reacting in the freeboard were ...

Coadsorption of CO and NO on the Cu2O(111) surface: A periodic density functional theory study

Coadsorption of carbon monoxide (CO) and nitric oxide (NO) on the Cu(2)O(111) surface was studied using periodic density functional theory calculations. It is interesting to find that CO+NO on Cu(2)O(111) could react to form adsorbed NCO surface species. Coadsorption of CO and NO could give rise to the formation of a O-C...N-O complex well bound to the Cu(2)O(111) surface, in which both the C-O and N-O bonds are greatly activated and the C-N bond is formed. Consequently, the reaction of CO with NO to form adsorbed NCO and CNO species may occur, for which it is disclosed that NCO formation is more possible than CNO formation both thermodynamically and kinetically. In addition, our calculations of searching transition states reveal that it is facile for NCO formation both kinetically and thermodynamically when CO+NO reaction takes place at Cu(CUS) site, and is impossible when this reaction takes places at O(vac) site. Moreover, CO(2) species cannot form when CO+NO reaction occurs at O(vac) site. Therefore, oxygen vacancy on Cu(2)O(111) does not play a positive role on CO+NO reaction to forming NCO, CNO, or CO(2) species.

Primary and secondary organic carbon downwind of Mexico City

Abstract. In order to study particulate matter transport and transformation in the Megacity environment, fine particulate carbon was measured simultaneously at two supersites, suburban T1 and rural T2, downwind of Mexico City during the MILAGRO field campaign in March 2006. Organic carbon (OC), element carbon (EC), and total carbon (TC=OC+EC) were determined in near real-time using a Sunset semi-continuous OCEC field analyzer. The semi-empirical EC tracer method was used to derive primary organic carbon (POC) and secondary organic carbon (SOC). Diurnal variations of primary and secondary carbon were observed at T1 and T2, which resulted from boundary layer inversion and impacted by local traffic patterns. The majority of organic carbon particles at T1 and T2 were secondary. The SOCTC% (SOC%=SOC/TC×100%) at T1 ranged from 0.5–93.8% with an average of 63.5±17.2%. The SOCTC% at T2 ranged from 9.3–98.1% with an average of 67.4±12.4%. The average EC to PM2.5 percentage (ECPM%=EC/PM2.5×100%) and OCPM% were 6.0% and 20.0% over the whole sampling time at T1. The POC to PM percentage (POCPM%) and SOCPM% were 3.7% and 16.3%, respectively at the same site. The maximum ECPM% was 21.2%, and the maximum OCPM% was 57.2% at T1. The maximum POCPM% was 12.9%, and the maximum SOCPM% was 49.7% at T1. Comparison of SOC and POC at T1 and T2 showed similar characteristics under favorable meteorological conditions, which indicated that transport from T1 towards T2 took place. Strong correlations between EC and carbon monoxide (CO) and odd nitrogen species (NO and NOx) were observed at T1. This indicated that EC had nearby sources, such as local traffic emissions. The EC/CO ratio derived by linear regression analysis, with units of μg C/m3 and μg/m3, respectively, was 0.004 at T1. Correlations were also seen between OC and SOC vs. the sum of oxidants, such as O3 and NO2, suggesting the secondary nature of carbons observed at T1.

Quantifying desorption and rearrangement rates of carbon monoxide on a PEM fuel cell electrode

A simple procedure to quantify the rates of carbon monoxide (CO) desorption from, and simultaneous rearrangement on, supported platinum fuel cell electrode (Pt on Vulcan XC-72R) is reported. The surface coverage of CO on Pt electrode in equilibrium with bulk CO was measured from the anodic peaks in the CO stripping voltammogram. The decline in these surface coverages due to desorption and rearrangement, once CO was replaced by N 2 in the gas phase was recorded and used in conjunction with a kinetic model to quantify the respective rates. Two distinct CO oxidation peaks observed in the voltammogram due to the oxidation of two distinct ad-species, namely weakly and strongly adsorbed CO ( C O ad I and C O ad II ), were baseline corrected and deconvoluted using a bimodal Gaussian distribution. Saturation surface coverage of C O ad I decreased with increasing temperature, while the opposite was true for C O ad II . Rearrangement from C O ad II to C O ad I was faster than the desorption rate of either CO species. The desorption rate of C O ad II was at least an order of magnitude lower than that of C O ad I molecules at all temperatures studied. The activation energies for desorption of C O ad I and C O ad II were estimated to be 24.08 and 27.99 kJ/mol, respectively. The activation energy for rearrangement from C O ad I to C O ad II was 35.23 kJ/mol and that from C O ad II to C O ad I was 27.55 kJ/mol.

Reactivity of 3-hexyne on oxygen modified Ru(0 0 1) surfaces: Observation of oxametallacycles by RAIRS

The chemical behaviour of 3-hexyne on oxygen modified Ru(0 0 1) surfaces has been analysed under ultrahigh-vacuum, using reflection–absorption infrared spectroscopy (RAIRS). The effects of oxygen coverage, 3-hexyne exposure and adsorption temperature were studied. Two modified Ru(0 0 1) surfaces were prepared: Ru(0 0 1)-(2 × 2)-O and Ru(0 0 1)-(2 × 1)-O that correspond to oxygen coverages ( θ O) of 0.25 and 0.5 ML, respectively. The striking result is the direct bonding to an O atom when the modified surfaces are exposed to a very low dose (0.2 L) of 3-hexyne at low temperature (100 K). For θ O = 0.25 ML, an unsaturated oxametallacycle [Ru–O–C(C 2H 5) C(C 2H 5)–Ru] is proposed, identified by RAIRS for the first time, through the νC C and νCO modes. Further decomposition at 110 K yields smaller oxygenated intermediates, such as acetyl [μ 3-η 2(C,O)-CH 3CO], co-adsorbed with a small amount of carbon monoxide and non-dissociated species. The temperature at which a fraction of molecules undergoes complete C–C and C–H bond breaking is thus much lower than on clean Ru(0 0 1). The ultimate decomposition product observed by RAIRS at 220 K is methylidyne [ CH]. Another key observation was that the adsorption temperature is not determinant of the reaction route, contrarily to what occurs on clean Ru(0 0 1): even when 3- hexyne strikes the surface at a rather high temperature (220 K), the multiple bond does not break completely. For θ O = 0.5 ML, a saturated oxametallacycle [Ru–O–CH(C 2H 5)–CH(C 2H 5)–Ru] is also proposed at 100 K, identified by the ν asO–C–C (at 1043 cm −1) and ν sO–C–C (at 897 cm −1) modes, showing that some decomposition with C–H bond breaking occurs. For this oxygen coverage, the reaction temperatures are lower, and the intermediate surface species are less stable.

Experimental and numerical conversion of liquid heptane to syngas through combustion in porous media

The conversion of liquid heptane to syngas in a porous medium reactor consisting of a packed bed of alumina pellets is investigated numerically and experimentally. In experiments, the exhaust gas was analyzed for hydrogen, carbon monoxide, carbon dioxide, methane, and hydrocarbon species over equivalence ratios from 1.4 to 3.8 and a range of mixture inlet velocities. The efficiency of the noncatalytic fuel reformer regarding hydrogen production, carbon monoxide production and energy conversion is assessed. At constant inlet velocity, hydrogen production increases with increasing equivalence ratio, whereas hydrogen conversion efficiency reaches its peak value around an equivalence ratio of 3.0. Tests at a constant equivalence ratio of 2.5 show that conversion efficiency increases with mixture inlet velocity, and experimental values in excess of 80% are obtained for the highest tested velocity of 80 cm/s. Similar trends are observed for carbon monoxide conversion and energy efficiencies, where peak values exceed 90% and 80%, respectively. Some discrepancies are noted between the experimental and numerical results in the ultrarich regime. Overall, the results indicate favorable conditions for fuel reforming between equivalence ratios of 2.5 and 3.5 and show that the inlet velocity has a significant effect on the performance of noncatalytic fuel reforming. Substantial efficiency gains are observed for increased inlet velocities, which are attributed to increases in the reactor temperature.

Confinement of fire-induced smoke and carbon monoxide transportation by air curtain in channels

Experimental and numerical studies were performed in this paper to study the possibility of utilizing air curtain for confinement of fire-induced smoke and carbon monoxide transportation along channels. Bench scale experiments were preliminarily performed in a 3.6 m long model channel. Complementary computational fluid dynamics (CFD) simulation was carried out by Fire Dynamics Simulator (FDS) for an 88 m long full scale channel, in order to see the longitudinal carbon monoxide concentration distribution along the real channel with air curtain discharged. Results showed that both the smoke and CO gases released by the fire were well confined to almost remain in the near fire region of the channel at one side of the air curtain. The gas temperature and CO concentration in the protection zone at the other side reduced significantly by an exponential trend with the increase of discharge velocity of the air curtain. These indicated that the air curtain can be an effective measure for confining the transportation of smoke and carbon monoxide species in long channel fires.

Measurements of nonmethane hydrocarbons in 28 United States cities

Between 1999 and 2005 a sampling campaign was conducted to identify and quantify the major species of atmospheric nonmethane hydrocarbons (NMHCs) in United States cities. Whole air canister samples were collected in 28 cities and analyzed for methane, carbon monoxide (CO) and NMHCs. Ambient mixing ratios exhibited high inter- and intra-city variability, often having standard deviations in excess of 50% of the mean value. For this reason, ratios of individual NMHC to CO, a combustion tracer, were examined to facilitate comparison between cities. Ratios were taken from correlation plots between the species of interest and CO, and most NMHCs were found to have correlation coefficients ( r 2) greater than 0.6, particularly ethene, ethyne and benzene, highlighting the influence of vehicular emissions on NMHC mixing ratios. Notable exceptions were the short-chain alkanes, which generally had poor correlations with CO. Ratios of NMHC vs. CO were also used to identify those cities with unique NMHC sources.

Airborne Measurements of Trace Organic Species in the Upper Troposphere Over Europe: the Impact of Deep Convection

Environmental Context. In the upper troposphere, sources of HOx such as acetone, peroxides, and aldehydes can play an important role in governing the production and destruction of ozone. Convection (over both land and sea) carries gases that can contribute to increased levels of HOx to the upper troposphere. The chemical impact of convection on the continental upper troposphere over Europe is studied by sampling the upper troposphere. Mass spectrometry techniques are used to analyze the collected samples. Such a study should aid in understanding the impact meteorological events have on atmospheric chemistry. Abstract. The volume mixing ratios of several organic trace gases and ozone (O3) were measured in the upper troposphere over Europe during the UTOPIHAN-ACT aircraft campaign in July 2003. The organic trace gases included alkanes, isoprene, aromatics, iodomethane, and trichloroethylene, oxygenates such as acetone, methanol, formaldehyde, carbon monoxide, and longer-lived tracer species such as chlorofluorocarbons and halochloroflurocarbons. The aim of the UTOPIHAN-ACT project was to study the chemical impact of deep convection on the continental upper troposphere. A Lear Jet aircraft, based in Germany, was flown at heights between 6 and 13 km in the region 59°N–42°N to 7°W–13°E during July 2003. Overall, the convectively influenced measurements presented here show a weaker variability lifetime dependence of trace gases than similar measurements collected over the Mediterranean region under more stable high-pressure conditions. Several cases of convective outflow are identified by the elevated mixing ratios of organic species relative to quiescent background conditions, with both biogenic and anthropogenic influences detectable in the upper troposphere. Enhancement at higher altitudes, notably of species with relatively short chemical lifetimes such as benzene, toluene, and even isoprene indicates deep convection over short timescales during summertime. The impact of deep convection on the local upper tropospheric formaldehyde and HOx budgets is assessed.

A matrix isolation study of the photochemically induced reactions of nitrogen dioxide with 1,2-dibromoethene and 1,2-dichloroethene using Fourier transform infrared spectroscopy

Photolyses of matrices of either BrCH CHBr/NO 2/Ar or ClCH CHCl/NO 2/Ar using quartz-filtered radiation ( λ > 240 nm) led to the appearance of infrared bands attributable to carbonyl, carbon monoxide, and ketene species; no bands belonging to a precursor complex NO 2⋯XCH CHX (where X = Br or Cl) were observed upon matrix deposition. The possible reaction pathway is discussed.

Chemical composition of air masses transported from Asia to the U.S. West Coast during ITCT 2K2: Fossil fuel combustion versus biomass‐burning signatures

As part of the Intercontinental Transport and Chemical Transformation experiment in 2002 (ITCT 2K2), a National Oceanic and Atmospheric Administration (NOAA) WP‐3D research aircraft was used to study the long‐range transport of Asian air masses toward the west coast of North America. During research flights on 5 and 17 May, strong enhancements of carbon monoxide (CO) and other species were observed in air masses that had been transported from Asia. The hydrocarbon composition of the air masses indicated that the highest CO levels were related to fossil fuel use. During the flights on 5 and 17 May and other days, the levels of several biomass‐burning indicators increased with altitude. This was true for acetonitrile (CH3CN), methyl chloride (CH3Cl), the ratio of acetylene (C2H2) to propane (C3H8), and, on May 5, the percentage of particles measured by the particle analysis by laser mass spectrometry (PALMS) instrument that were attributed to biomass burning based on their carbon and potassium content. An ensemble of back‐trajectories, calculated from the U.S. west coast over a range of latitudes and altitudes for the entire ITCT 2K2 period, showed that air masses from Southeast Asia and China were generally observed at higher altitudes than air from Japan and Korea. Emission inventories estimate the contribution of biomass burning to the total emissions to be low for Japan and Korea, higher for China, and the highest for Southeast Asia. Combined with the origin of the air masses versus altitude, this qualitatively explains the increase with altitude, averaged over the whole ITCT 2K2 period, of the different biomass‐burning indicators.

CO interaction with Ni3Al alloy: XPS, LEIS and TPD study

Polycrystalline Ni3Al alloy surface was investigated during CO adsorption–desorption experiments by means of X-ray photoelectron spectroscopy (XPS), low energy ion scattering (LEIS) and temperature programmed desorption (TPD). It was shown that CO partially dissociates giving nickel bonded carbon and carbon monoxide species and aluminum bonded oxygen. Thermal desorption was characterized by both low temperature CO desorption peaks typical for Ni–Al alloy, and high temperature one of highly reactive sites with lower CO dissociative barrier.

Infrared studies of carbon monoxide binding to carbon monoxide dehydrogenase/acetyl-CoA synthase from Moorella thermoacetica.

Carbon monoxide dehydrogenase/acetyl-CoA synthase (CODH/ACS) is a bifunctional enzyme that catalyzes the reversible reduction of carbon dioxide into carbon monoxide and the coupled synthesis of acetyl-CoA from the carbon monoxide produced. Exposure of CODH/ACS from Moorella thermoacetica to carbon monoxide gives rise to several infrared bands in the 2100-1900 cm(-1) spectral region that are attributed to the formation of metal-coordinated carbon monoxide species. Infrared bands attributable to M-CO are not detected in the as-isolated enzyme, suggesting that the enzyme does not contain intrinsic metal-coordinated CO ligands. A band detected at 1996 cm(-1) in the CO-flushed enzyme is assigned as arising from CO binding to a metal center in cluster A of the ACS subunit. The frequency of this band is most consistent with it arising from a terminally coordinated Ni(I) carbonyl. Multiple infrared bands at 2078, 2044, 1970, 1959, and 1901 cm(-1) are attributed to CO binding at cluster C of the CODH subunit. All infrared bands attributed to metal carbonyls decay in a time-dependent fashion as CO(2) appears in the solution. These observations are consistent with the enzyme-catalyzed oxidation of carbon monoxide until it is completely depleted from solution during the course of the experiments.

Laboratory Precision Measurements of the Rotational Spectrum of12C17O and13C17O

High-precision millimeter and submillimeter wave measurements were performed on two 17O isotopically substituted carbon monoxide species, i.e., 12C17O and 13C17O. Covering the frequency region from 100 GHz to 1 THz, the accuracy achievable is estimated to be ±5 kHz in the Doppler-limited mode and ±1 kHz for sub-Doppler-resolution measurements. From a weighted least-squares fit, the following molecular rotational parameters for 12C17O and 13C17O were obtained: for 12C17O, and for 13C17O, in both instances, the H0 values were kept fixed to IR data. The oxygen 17O nucleus exhibits a sizeable electric nuclear quadrupole moment, which has been measured for both isotopomers, i.e., eQq(12C17O) = 4.298(44) MHz and eQq(13C17O) = 4.355(182) MHz. The high precision of the Lamb dip measurements allowed us to observe additional small hyperfine effects caused by the magnetic moment of the 17O nucleus. These precision measurements allowed the determination of the nuclear spin-rotation constant CI(17O) = -31.60(72) Hz for 12C17O, solely from the Cologne data set. The highly precise transition frequencies reported here should warrant deep interstellar searches for the two molecules 12C17O and 13C17O. The latter has not been detected in space until very recently. On the basis of our laboratory data, we were able to report the discovery of 13C17O (by Bensch and coworkers) along with the observations of two additionalrare CO isotopomers including 12C17O and 12C18O toward core C of the ρ Ophiucus molecular cloud.

The Evolution of the Circumstellar Environment of Embedded Young Stars from Observations of Rare Species of Carbon Monoxide

Studies of the properties of the circumstellar material around young embedded sources can provide important insights into the relative importance of infall and outflow in clearing the circumstellar environment. In this paper we report one such study of 20 of the most deeply embedded young stars in the Taurus molecular cloud using the J = 1 → 0, J = 2 → 1, and J = 3 → 2 transitions of C18O and C17O. The profiles comprise a narrow component, with a line width of ~0.7 km s-1 plus in many cases a second broader component that contains a similar mass of material. The broad-component line width decreases with increasing source age as measured by the source bolometric temperature, consistent with what would be expected if the broad component traces the interaction between a stellar wind and ambient material. The momentum flux of the broad-component emission in the immediate vicinity of the forming star is comparable to that in the spatially extended outflows from these sources and also decreases with increasing source age. Comparison with models of this interaction provide a reasonable match to the behavior of the broad component with source age. The derived total column density toward the sources shows a systematic decrease with increasing bolometric temperature and implies a circumstellar mass-loss rate that varies from ~10-4 M☉ yr-1 for the youngest sources to ~10-8 M☉ yr-1 for sources in the late Class I phase. The broad components are sufficiently massive and energetic to clear the circumstellar environment on timescales of ~105 yr, and we argue that the broad component of the C18O line profiles is the dense, low-velocity inner part of the outflow from the sources and may be the material being directly swept up by the stellar wind. The widths of the broad and narrow components are correlated, indicating that the narrow-component material is already being stirred by the stellar wind, even in the youngest sources.

Adsorption of Carbon Monoxide on Platinum in Hot Aqueous Acidic Solution from 423 to 533 K.

In order to evaluate adsorption of CO species onto precious metal electrodes during electrochemical oxidation of methanol under hot aqueous conditions, adsorption of carbon monoxide (CO) on a Pt electrode was studied in hot aqueous solution of 0.005 M H2SO4–0.2 M Na2SO4 by a fast potential sweep method at temperatures ranging from 423 to 533 K under the corresponding vapor pressure. An electrochemical half cell fabricated in a pressure vessel was employed to realize electrochemical measurement under this high temperature and pressure. Adsorption characteristics of CO were determined at CO partial pressure up to 0.39 MPa. Increasing temperature resulted in a decrease in the adsorption amount of CO on Pt electrodes. Under 0.1 MPa of the CO partial pressure, CO almost covers the electrode at 423 K, while a negligible amount is adsorbed at 533 K. At 473 K, CO surface coverage on a Pt electrode in aqueous solution increased with the CO partial pressure.

Photochemically Induced Reactions of Ozone with 1,2-Dibromoethene and 1,2-Dichloroethene: An FT-IR Matrix Isolation Study

The co-deposition of ozone with the halogenated ethenes, 1,2-dibromoethene and 1,2-dichloroethene, in argon matrices and the subsequent photolysis cycles using radiation of different wavelengths (λ > 350 nm, λ > 290 nm, and λ > 240 nm) have been examined using FT-IR spectroscopy. Ozonolysis occurs after irradiation at relatively long wavelengths, (λ > 350 nm), due to the formation of an ozone···XCHCHX (X = Br or Cl) π complex upon deposition and is believed to follow the Criegee pathway because the expected HC(O)X (X = Br or Cl) intermediates are detected. The carbonyl species HC(O)X dissociate to form the carbon monoxide species, OC···HX and OC···(HX)2 (X = Br or Cl). However, the identification of a novel ketene species XHCCO suggests that a further mechanism to the Criegee one is followed in the case of halogenated ethenes. Moreover the photochemically induced reaction of XCHCHX deposited in oxygen matrices produced the similar photoproducts HC(O)X and OC···HX as well as the ketene type species XHCCO, ...

Oxidation and reduction effects of propane–oxygen on Pd–chlorine/alumina catalysts

Pd–chloride precursor salt was used to prepare Pd/Al2O3 catalysts. TPSR measurements showed three distinct reactions for the oxidation of propane on palladium surface under excess of hydrocarbon: complete oxidation, steam reforming and propane hydrogenolysis. Propane oxidation on palladium catalysts was related to the Pd2+ sites observed on Pd/Al2O3 through infrared of adsorbed carbon monoxide. In fresh catalysts reduced by H2, the IR spectra showed the linear and bridge adsorbed CO species on the Pd0 surface. After propane reaction, a new band at 2130 cm-1 related to CO adsorption on Pd2+ species was noted. Carbon monoxide species adsorbed on Pd0 were also observed in all samples after reaction. Our results suggest surface ratios of Pd0/PdO during the propane oxidation. On the other hand, time on stream conversions of the complete oxidation of propane were affected by either the water generated during the reaction or added as a reactant at 10 vol%. The water generated by the reaction helped to eliminate chlorine residues in the form of oxychloride species leading to an increasing of the activity. However, the presence of water into the reaction mixture caused a strong decreasing of the activity. The inhibition mechanism of propane oxidation in the presence of water consisted in the dissociative adsorption of water on palladium sites with the possible formation of palladium hydroxide (Pd–OH) at the surface, diminishing the number of active surface sites. Dynamic fluctuations into the reaction conditions supported the idea that a pseudo‐equilibrium adsorption–desorption of water was reached. After water removal or increasing in the reaction temperature the equilibrium was shifted to the direction of OH–Pd decomposition. This behavior suggests that the inhibitory effect of water is a reversible phenomenon, being a function of the amount of water and the reaction temperature.

The Impact of California Phase 2 Reformulated Gasoline on Real-World Vehicle Emissions

ABSTRACT In mid-1996, California implemented Phase 2 Reformulated Gasoline (RFG). The new fuel was designed to further decrease emissions of hydrocarbons (HCs), oxides of nitrogen (NOx), carbon monoxide (CO), sulfur dioxide (SO2), and other toxic species. In addition, it was formulated to reduce the ozone-forming potential of the HCs emitted by vehicles. Previous studies have observed that emissions from on-road vehicles can differ significantly from those predicted by mobile source emissions models, and so it is important to quantify the change in emissions in a real-world setting. In October 1995, prior to the introduction of California Phase 2 RFG, the Desert Research Institute (DRI) performed a study of vehicle emissions in Los Angeles' Sepulveda Tunnel. This study provided a baseline against which the results of a second experiment, conducted in July 1996, could be compared to evaluate the impact of California Phase 2 RFG on emissions from real-world vehicles. Compared with the 1995 experiment, CO and NOx emissions exhibited statistically significant decreases, while the decrease in non-methane hydrocarbon emissions was not statistically significant. Changes in the speciated HC emissions were evaluated. The benzene emission rate decreased by 27% and the overall emission rate of aromatic compounds decreased by 22% comparing the runs with similar speeds. Emissions of alkenes were virtually unchanged; however, emissions of combustion related unsaturates (e.g., acetylene, ethene) increased, while heavier alkenes decreased. The emission rate of methyl tertiary butyl ether (MTBE) exhibited a larger increase. Overall changes in the ozone-forming potential of the emissions were not significantly different, with the increased contributions to reactivity from paraffins, ole-fins, and MTBE being offset by a large decrease in reactivity due to aromatics.