Nature of Odor Components in Diesel Exhaust

Offensive exhaust odors are characteristic of diesel engines. One problem in control and reduction of odor is lack of understanding of odorant sources and mode of formation. The solution of this problem depends on identification of the odorants so that study of their formation and control can be undertaken. A human panel performed odor assessments in studying raw and modified diesel exhaust and synthetic blends representing portions of diesel exhaust. Their assessments were used in determining odorant identity and quantitative contribution to exhaust odor. Low molecular weight aldehydes appear to contribute little to diesel odors. The sulfur and nitrogen oxides have been examined as odorants but of these apparently only nitrogen dioxide is a potential odor contributor.     

Composition,Size and Control of Automotive Exhaust Particulates

This paper on automobile exhaust particulates describes total particulate composition, size of exhausted lead particulates, and the effects of traps on total lead emitted. This study was conducted using cars manufactured during 1966-1970. Work in suspended particulate emission from several vehicles operated on a chassis dynamometer under Federal 7-mode cycle conditions has shown: (1 ) cars vary widely in the amounts and composition of their particulate emissions; (2) cold-cycle operation gives 2-8 times more particulate than hot engine operation; (3) lead compounds represent less than one-third of total particulates, the remainder being carbon compounds along with ammonium and nitrate ions and unknown materials; (4) carbon emission for stabilized cars using leaded gasoline varies widely but averages about 35% of the total; (5) suspended particulate emissions are nearly equal with new cars whether or not lead is present; (6) exhausted lead varies with the condition of the exhaust system and ranges between 7 and 30% of the lead consumed by the engine; (7) fuel additives affect the amount of emitted particulates; (8) probe sampling techniques underestimate by a large factor the amount of particulates emitted by vehicles; and (9) trapping systems offer potential for greatly reducing the emission of suspended total particulates.     

Review of Federally Sponsored Research on Diesel Exhaust Odors

The information presented in this paper is directed to persons concerned with control of exhaust odors from diesel-engine-powered vehicles. This paper summarizes projects sponsored by the Environmental Protection Agency (EPA) over the past years in the field of diesel-exhaust odor. These investigations have concentrated on developing measurement methods for quantifying different odor levels, evaluating various odor control methods, and evaluating public opinions of such odors.

A human panel method using odor reference standards has been found suitable to measure these odor levels. In addition to this technique, chemical characterization work has been sponsored under a project jointly sponsored by the Coordinating Research Council and the EPA to isolate and identify those species responsible for the odor.

Knowledge of these odorous compounds and the techniques necessary to isolate them should lead to development of a chemical method to measure this type of odor, in place of human panelists. Such basic information would also lead to developing control techniques to minimize this odor.

Several control techniques were evaluated for diesel exhaust odor. To date, the most effective method is an improved needle injector for use in the Detroit Diesel type E 6V-71 engine commonly used in buses.

Finally, public reaction to diesel-engine-exhaust odor has been measured. It has been found that a systematic relationship exists between increasing public objections and increasing diesel odor intensity.     

Composition of Exhaust from a Regenerative Turbine System

Particulate and hydrocarbon content of gases in a regenerative gas turbine was analyzed at several points. Particle samples were measured with a condensation nuclei counter, a light scattering single particle counter and an impactor. Hydrocarbon analyses were made using gas chromatography. The effects of operation with JP-4 and No. 2 fuel oil were noted. It was concluded that a regenerative gas turbine will not add appreciably to the burden of air pollution. In fact, particulate contamination levels in the exhaust less than those in the inlet air indicates that the high rotation rate may result in some air cleaning. Low hyd rocarbon contents in the exhaust gas were ascribed to efficient combustion under the operating conditions used in this work. In general, it was concluded that hydrocarbon levels significantly lower than those seen from gasoline or diesel engines could be expected from a well maintained and operated regenerative gas turbine.     

Particulate Matter in New Technology Diesel Exhaust (NTDE) is Quantitatively and Qualitatively Very Different from that Found in Traditional Diesel Exhaust (TDE)

ABSTRACT

Diesel exhaust (DE) characteristic of pre-1988 engines is classified as a “probable” human carcinogen (Group 2A) by the International Agency for Research on Cancer (IARC), and the U.S. Environmental Protection Agency has classified DE as “likely to be carcinogenic to humans.” These classifications were based on the large body of health effect studies conducted on DE over the past 30 or so years. However, increasingly stringent U.S. emissions standards (1988–2010) for particulate matter (PM) and nitrogen oxides (NO_x) in diesel exhaust have helped stimulate major technological advances in diesel engine technology and diesel fuel/lubricant composition, resulting in the emergence of what has been termed New Technology Diesel Exhaust, or NTDE. NTDE is defined as DE from post-2006 and older retrofit diesel engines that incorporate a variety of technological advancements, including electronic controls, ultra-low-sulfur diesel fuel, oxidation catalysts, and wall-flow diesel particulate filters (DPFs). As discussed in a prior review (T. W. Hesterberg et al.; Environ. Sci. Technol. 2008, 42, 6437-6445), numerous emissions characterization studies have demonstrated marked differences in regulated and unregulated emissions between NTDE and “traditional diesel exhaust” (TDE) from pre-1988 diesel engines. Now there exist even more data demonstrating significant chemical and physical distinctions between the diesel exhaust particulate (DEP) in NTDE versus DEP from pre-2007 diesel technology, and its greater resemblance to particulate emissions from compressed natural gas (CNG) or gasoline engines. Furthermore, preliminary toxicological data suggest that the changes to the physical and chemical composition of NTDE lead to differences in biological responses between NTDE versus TDE exposure. Ongoing studies are expected to address some of the remaining data gaps in the understanding of possible NTDE health effects, but there is now sufficient evidence to conclude that health effects studies of pre-2007 DE likely have little relevance in assessing the potential health risks of NTDE exposures.

IMPLICATIONS Based on the distinct physical and chemical properties of New Technology Diesel Exhaust (NTDE), it has become clear that findings from the health effects studies conducted on traditional DE (TDE) over the last 30 years have little relevance to NTDE, which is more similar to the exhaust from compressed natural gas (CNG) or gasoline engine emissions than to traditional TDE. Once sufficient health effects data are available for NTDE, it will thus be necessary to conduct new hazard and risk assessments for NTDE that are independent of the DE toxicological database acquired on emissions from pre–2007 diesel technology.     

Generation and Characterization of Diesel Exhaust in a Facility for Controlled Human Exposures

Abstract

An idling medium-duty diesel truck operated on ultralow sulfur diesel fuel was used as an emission source to generate diesel exhaust for controlled human exposure. Repeat tests were conducted on the Federal Test Procedure using a chassis dynamometer to demonstrate the reproducibility of this vehicle as a source of diesel emissions. Exhaust was supplied to a specially constructed exposure chamber at a target concentration of 100 µg · m^-3 diesel particulate matter (DPM). Spatial variability within the chamber was negligible, whereas emission concentrations were stable, reproducible, and similar to concentrations observed on the dynamometer. Measurements of nitric oxide, nitrogen dioxide, carbon monoxide, particulate matter (PM), elemental and organic carbon, carbonyls, trace elements, and polycyclic aromatic hydrocarbons were made during exposures of both healthy and asthmatic volunteers to DPM and control conditions. The effect of the so-called “personal cloud” on total PM mass concentrations was also observed and accounted for. Conventional lung function tests in 11 volunteer subjects (7 stable asthmatic) did not demonstrate a significant change after 2-hr exposures to diesel exhaust. In summary, we demonstrated that this facility can be effectively and safely used to evaluate acute responses to diesel exhaust exposure in human volunteers.     

Measurement of Exhaust Emissions in Piston And Diesel Engines by Dispersive Spectroscopy

A versatile but simple, reliable, rugged, and compact vehicle exhaust monitoring system has been developed, allowing detection of carbon monoxide (CO), carbon dioxide (COo), high and low hydrocarbons (HHC and LHC), and nitric oxide (NO). The analysis is performed by dispersive absorption spectroscopy with instrumentation designed and fabricated for this demanding industrial environment. The operation of the instrumentation is described here, as well as results for both diesel and piston engine emission testing. This equipment has been used for California 7 mode-7 cycle hot start and cold start tests, the California heavy-duty engine test cycles, EPA CVS tests reading bag samples and also continuous dilute, and finally it has been used for idle checks. Testing has been performed on production automobiles, as well as those equipped with thermal reactors or catalytic mufflers, and also both heavy-duty gasoline and diesel. engines. The instrumentation has shown very good correlation with other established techniques, and because of its sensitivity, selectivity, ruggedness, and simplicity, has been shown to be suitable for vehicle emission analysis. Applications include assembly-line testing, engine testing, certification testing, quality audit testing, emission lab testing, and research.     

The Effect of Fuel Composition on Atmospheric Aerosol Due to Auto Exhaust

Aerosols attributable to automobile exhaust can be classified as two types—primary aerosol (initially present in the exhaust) and secondary aerosol (generated photochemically from hydrocarbons and nitrogen oxides in the exhaust). In this study, investigation was made of possible effects of motor-fuel composition on the formation of these aerosols. Secondary aerosol, of principal interest in this work, was produced by irradiating auto exhaust in Battelle-Columbus’ 610 ft³ environmental chamber. A limited number of determinations of primary aerosol in diluted auto exhaust was made at the exit of a 36 ft dilution runnel. Determination of both primary and secondary aerosol was based on light-scattering measurements.

Exhaust was generated with seven full-boiling motor gasolines, both leaded and nonleaded, in a 1967 Chevrolet which was not equipped with exhaust-emission control devices. Changes in fuel composition produced a maximum factor of three difference in light scattering due to primary aerosol. Aerosol yields, for consecutive driving cycles on the same fuel, vary considerably; as a result, ranking the fuels on the basis of average primary aerosol yield was not very meaningful. In addition to fuel composition, the more important independent variables are initial SO₂ concentration, relative humidity and initial hydrocarbon concentration. Statistical analysis of the data indicates that the seven test fuels can be divided into two arbitrary groups with regard to secondary aerosol-forming potential. The fuels in the lower light-scattering group had aromatic contents of 15 and 21%, while those in the higher light-scattering group had aromatic contents of 25, 48, and 55%. Although the fuels can be grouped on the basis of a compositional factor, the grouping of fuels with aromatic content ranging from 25 to 55% indicates that this compositional factor cannot be equated simply with aromatic content. In an associated study of the aerosol-forming potential of individual hydrocarbons prominent in auto exhaust, it was observed that aromatics produce substantially more photochemical aerosol than olefins and paraffins. However, experiments with binar/hydrocarbon mixtures containing aromatjcs, as well as in these exhaust experiments, a strong dependence of aerosol yield on the aromatic components is is not observed. Thus, the data indicate that the dependence of secondary aerosol formation on fuel factors is a complex one and cannot be predicted solely on the basis of a sirigle hydrocarbon component reactivity scale.

The two types of automobile aerosol did not have the same dependence on fuel, composition. The variation in total light scattering attributable to primary plus secondary aerosol was less than that due to either component alone. It therefore was concluded that the light scattering due to automobile exhaust emissions in these experiments was not significantly affected by changing fuel composition.     

Methylcyclopentadienyl Manganese Tricarbonyl as an Antiknock: Composition and Fate of Manganese Exhaust Products

Methylcyclopentadienyl manganese tricarbonyl (MMT) has been marketed as a combustion improver for fuel oil and turbine fuel. Use concentrations for this purpose are about 0.025 g manganese/gal in fuel oil and 0.08 to 0.5 g/gal in turbine fuels. In addition, it has been used to a small extent in gasoline.     

Effect of Fuel Properties on Mutagenic Activity in Extracts of Heavy-duty Diesel Exhaust Particulate

The effect of varying fuel properties on the emission of mutagenic materials was studied in diesel exhaust particles from a heavy duty engine run under transient speed and load conditions while using nine fuels varying in aromatics, sulfur and boiling point. Mutagenic activity of the soluble organic fraction (SOF) of the particulate was determined using the Ames Salmonella test system with strain TA98 with and without S9 activation. Increasing mutagenic activity relative to fuel consumed (mutants/lb fuel) or to engine work output (mutants/hp-h) was correlated with increasing fuel aromatics (p < 0.05), but not with fuel sulfur. Increased fuel sulfur levels were correlated with increased amounts of SOF but with decreasing mutagenic activity of the SOF (mutants/microgram SOF) (p < 0.05). As a result, mutants/hp-h were essentially the same for high- and low-sulfur fuels with high aromatics. No association was found between the fuels’ boiling points and the mutagenic activity of the SOF. Mutagenic activity with S9 was generally lower than without, but the correlations were not changed.     

Selected Ion Chromatograms and Tandem Mass Spectrometry for Detection of Trace Polycyclic Aromatic Hydrocarbons in Diesel Exhaust

Abstract

Polycyclic aromatic hydrocarbon (PAH) measurements are essential for scientists and engineers who investigate these anthropogenic compounds. Diesel engines contribute to the problem, so analysts are measuring PAHs from these sources. However, diesel exhaust presents special problems for precise analytical measurements. The exhaust matrix is very complex; consequently, PAH detection sensitivity deteriorates, especially for trace PAHs in the exhaust. Yet, these are conditions and amounts that exist in real samples. Nonetheless, selected ion chromatogram (SIC) and tandem mass spectrometry (MS/MS) techniques improve trace PAH detection; ion trap technology makes both mass techniques possible. The purpose of this investigation was to evaluate SIC and MS/MS for applications to measure PAHs in diesel exhaust samples. The signal-to-noise ratio for accurate quantitation improves, relative to traditional mass techniques, because these techniques ignore or eliminate interfering components. On a VF-5MS chromatographic column, these techniques improve sensitivity and reproducibility. They produce a superior limit of detection in the useful range for PAH samples extracted from actual engine exhaust, 10–30 pg for the smaller PAHs and 1–6 ng for the larger PAHs. The results with SIC and MS/MS are reproducible, so analysts can report PAH amounts with defined statistical confidence intervals. SIC and MS/MS improve detection for trace PAHs in convoluted diesel exhaust samples.     

Field Measurements of Particulate Matter Emissions,Carbon Monoxide,and Exhaust Opacity from Heavy-Duty Diesel Vehicles

ABSTRACT

Diesel particulate matter (PM) is a significant contributor to ambient air PM₁₀ and PM_2.5 particulate levels. In addition, recent literature argues that submicron diesel PM is a pulmonary health hazard. There is difficulty in attributing PM emissions to specific operating modes of a diesel engine, although it is acknowledged that PM production rises dramatically with load and that high PM emissions occur during rapid load increases on turbocharged engines. Snap-acceleration tests generally identify PM associated with rapid transient operating conditions, but not with high load. To quantify the origin of PM during transient engine operation, continuous opacity measurements have been made using a Wager 650CP full flow exhaust opacity meter. Opacity measurements were taken while the vehicles were operated over transient driving cycles on a chassis dynamometer using the West Virginia University (WVU) Transportable Heavy Duty Vehicle Emissions Testing Laboratories. Data were gathered from Detroit Diesel, Cummins, Caterpillar, and Navistar heavy-duty (HD) diesel engines. Driving cycles used were the Central Business District (CBD) cycle, the WVU 5-Peak Truck cycle, the WVU 5-Mile route, and the New York City Bus (NYCB) cycle. Continuous opacity measurements, integrated over the entire driving cycle, were compared to total integrated PM mass. In addition, the truck was subjected to repeat snap-acceleration tests, and PM was collected for a composite of these snap-acceleration tests. Additional data were obtained from a fleet of 1996 New Flyer buses in Flint, MI, equipped with electronically controlled Detroit Diesel Series 50 engines. Again, continuous opacity, regulated gaseous emissions, and PM were measured. The relationship between continuous carbon monoxide (CO) emissions and continuous opacity was noted. In identifying the level of PM emissions in transient diesel engine operation, it is suggested that CO emissions may prove to be a useful indicator and may be used to apportion total PM on a continuous basis over a transient cycle. The projected continuous PM data will prove valuable in future mobile source inventory prediction.     

Effect of Methanol on Exhaust Composition of a Fuel Containing Toluene,n-Heptane,and Isooctane

This study describes the variations in the chemical composition of the exhaust from a single cylinder engine when up to 25% methanol is added to a fuel blend of toluene, isooctane, and n-heptane. Under fuel-rich conditions, and with increasing methanol concentration, it is observed that unburned fuel and benzene emissions increase, exhaust acetylene remains constant, and propylene, isobutylene, methane, ethylbenzene, and styrene concentrations decrease. As oxygen becomes more available, the effects of methanol are reduced, and at an equivalence ratio of 1.25—excess oxygen now is present—methanol no longer affects the concentration of exhaust hydrocarbons. These observations are explained by the reactions of formaldehyde—an incomplete combustion product of methanol— with alkyl radicals derived from the fuel. The photochemical reactivity of the exhaust is unchanged when up to 15% of methanol is present in the fuel at an equivalence ratio of 0.85, but increases at higher methanol contents because of the increase in unburned toluene in the exhaust.     

Effects of Air-Fuel Ratio on Composition of Hydrocarbon Exhaust from Toluene,Toluene-n Heptane Mixture and Isooctane

This study describes the variations in the chemical composition of the exhaust at various air-fuel ratios when toluene, toluene-n-heptane mixture, and isooctane are used as fuels in a Labeco single cylinder engine. The exhaust products from toluene are divided into three groups: those which decrease as the equivalence ratio is increased: toluene, benzene, methane, and dimethylacetylene; those which increase with increasing equivalence ratio: benzaldehyde, and products which exhibit a maximum at an equivalence ratio of 1, then decrease: acetylene, ethyl acetylene, ethyl benzene, and styrene. Combustion of the mixture of 25 volume percent n-heptane in toluene reveals interesting information, compared to emissions from pure toluene: concentrations of ethyl benzene, styrene, and dimethylacetylene surprisingly are increased by factors of 1.9, 1.9, and 2.1 respectively, probably because reactive radicals derived from heptane interact with toluene to form unsaturated molecules. Ethyl acetylene, benzene, and benzaldehyde remained unchanged but the fractional mole concentration of unreacted toluene decreased. These results show that fuels rich in aromatics may produce less unsaturates than when diluted with aliphatic fuels. For isooctane fuel, methane, and isooctane in the exhaust decrease as the equivalence ratio is increased, while isobutylene, propylene, ethylene, and propadiene concentrations exhibit maxima at an equivalence ratio of 1.     

Development of an Odor Panel for Evaluation of Odor Control Equipment

The odor panel using the syringe dilution technique has been successfully used to judge the effectiveness of control equipment in eliminating industrial odor problems by monitoring stack emissions. Data is presented using this odor panel method for efficiency tests of direct-flame fume incinerators performed in a large variety of industrial process applications, including pulp and paper mills, rubber processing plants, food processing plants, wire enameling plants, glass fiber manufacturing plants, paint bake ovens, brake manufacturing plants, caster manufacturing plants, rendering plants, and chemical plants. Test data shows that this method of measuring odor using the syringe dilution technique is a useful and practical tool in analyzing odor problems and determining the effectiveness of control equipment by monitoring stack emissions.