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.     

Effects of Fuel Type,Driving Cycle,and Emission Status on In-Use Vehicle Exhaust Reactivity

ABSTRACT

The introduction of reformulated gasolines significantly reduced exhaust hydrocarbon (HC) mass emissions, but few data are available concerning how these new fuels affect exhaust reactivity. Similarly, while it is well established that high-emitting vehicles contribute a significant portion of total mobile source HC mass emissions, it is also important to evaluate the exhaust reactivity from these vehicles. The objective of this study was to evaluate the relative influence on in-use vehicle exhaust reactivity of three critical factors: fuel, driving cycle, and vehicle emission status. Nineteen in-use vehicles were tested with seven randomly assigned fuel types and two driving cycles: the Federal Test Procedure (FTP) and the Unified Cycle (UC). Total exhaust reactivity was not statistically different between the FTP and UC cycles but was significantly affected by fuel type. On average, the exhaust reactivity for California Phase 2 fuel was the lowest (16 % below the highest fuel type) among the seven fuels tested for cold start emissions. The average exhaust reactivity for high-emitting vehicles was significantly higher for hot stabilized (11%) and hot start (15%) emissions than for low-emitting vehicles. The exhaust reactivities for the FTP and UC cycles for light-end HCs and carbonyls were significantly different for the hot stabilized mode. There was a significant fuel effect on the mean specific reactivity (SR) for the mid-range HCs, but not for light-end HCs or carbonyls, while vehicle emission status affected the mean SR for all three HC compound classes.     

Identification of a potential source of chloroform in urban air: Preliminary Communication

A new potential source of elevated chloroform (CHCl₃) concentrations in urban air is reported. The exhaust gases from gasoline internal combustion engines operated on conventional “leaded” fuel and not equipped with catalytic converters contain parts-per-billion concentrations of chloroform which can, in congested urban areas, contribute significantly to the ambient concentration of chloroform. Exhaust gases from engines burning conventional “leaded” gasoline contain much higher levels of chloroform than do exhaust gases from engines equipped with catalytic converters and operating on “nonleaded” gasoline.     

Airshed Model Evaluation of Reactivity Adjustment Factors Calculated with the Maximum Incremental Reactivity Scale for Transitional-Low Emission Vehicles

Abstract

The California Air Resources Board recently adopted regulations for light- and medium-duty vehicles that require reductions in the ozone-forming potential or “reactivity,” rather than the mass, of nonmethane organic gas (NMOG) emissions. The regulations allow sale of all alternatively fueled vehicles (AFVs) that meet NMOG exhaust emission standards equivalent in reactivity to those set for vehicles fueled with conventional gasoline. Reactivity adjustment factors (RAFs), the ratio of the reactivity (per gram) of the AFV exhaust to that of the conventionally fueled vehicle (CFV), are used to correct the stringent exhaust emission standards. Complete chemical speciation of the exhaust and conversion of each NMOG species to an appropriate mass of ozone using the maximum incremental reactivity (MIR) scale of Carter determines the RAF. The MIR approach defines reactivity where NMOG control is the most effective strategy in reducing ozone concentrations, and assumes it is not important to define reactivity at other conditions, i.e., where NO_x is the limiting precursor.

This study used the Carnegie/California Institute of Technology airshed model to evaluate whether the RAF-adjusted AFV emissions result in ozone impacts equivalent to those of CFV emissions. A matrix of two ozone episodes in the South Coast Air Basin (SoCAB) of California, two base emission inventories, and exhaust emissions from three alternative fuels that meet the first level of the low emission vehicle standards bounds the expected range of conditions. Although very good agreement was found previously for individual NMOG species,² this study noted deviations of up to ±15 percent from the equal ozone impacts for any vehicle/fuel combination required by the California regulations. These deviations appear to be attributable to differences in spatial and temporal patterns of emissions between vehicle fleets, rather than a problem with the MIR approach. The first formally adopted RAF, a value of 0.41 for 85 percent methanol/15 percent gasoline-fueled vehicles, includes a 10 percent increase based on the airshed modeling. The correction to the RAF is different for other fuels and may be different for air basins other than the SoCAB.     

Unleaded Gasoline Shortages and Fuel Switching

The use of leaded gasoline in automobiles equipped with catalytic converters causes deactivation of the converters and leads to significant increases in emissions of reactive hydrocarbons, a precursor of ozone. Such fuel switching may be a contributing factor to the increase in photochemical smog levels recently observed in the South Coast Air Basin (SOCAB).     

Particulate organic compounds emitted from motor vehicle exhaust and in the urban atmosphere

The emission rate of particle-phase petroleum biomarkers in vehicular exhaust compared to the concentrations of these biomarkers in ambient air is used to determine the particulate organic compound concentration due to primary particle emissions from motor vehicles in the southern California atmosphere. A material balance on the organic particulate matter emitted from motor vehicle traffic in a Los Angeles highway tunnel first is constructed to show the proportion which is solvent-extractable and which will elute from a GC column, the ratio of resolved to unresolved compound mass, the portion of the resolved material that can be identified as single organic compounds, and the contribution of different classes of organic compounds to the overall identified fraction. It is shown that the outdoor ambient concentrations of the petroleum biomarkers track primary emissions measured in the highway tunnel, confirming that direct emissions of these compounds from vehicles govern the observed ambient petroleum biomarker concentrations. Using organic chemical tracer techniques, the portion of fine organic particulate matter in the Los Angeles atmosphere which is attributable to direct particle emissions from vehicle exhaust is calculated to vary from 7.5 to 18.3% at different sites throughout the air basin during a summertime severe photochemical smog episode. A similar level of variation in the contribution of primary motor vehicle exhaust to fine particulate organic matter concentrations during different times of day is seen. While peak atmospheric concentrations of fine particulate organic carbon are observed during the 1200–1600 PDT afternoon sampling period, only 6.3% of that material is apportioned to the directly emitted particles from vehicle exhaust. During the morning traffic peak between 0600–1000 PDT, 19.1% of the fine particulate organic material is traced to primary emissions from motor vehicles.     

Comparison of vehicle exhaust emissions from modified diesel fuels

Three diesel fuels, one oil sand-derived (OSD) diesel serving as base fuel, one cetane-enhanced base fuel, and one oxygenate [diethylene glycol dimethyl ether (DEDM)]-blended base fuel, were tested for their emission characterizations in vehicle exhaust on a light-duty diesel truck that reflects the engine technology of the 1994 North American standard. Both the cetane-enhanced and the oxygenate-blended fuels were able to reduce regulated [CO, particulate matter (PM), total hydrocarbon (THC)] and nonregulated [polyaromatic hydrocarbons (PAHs), carbonyls, and other volatile organic chemicals] emissions, except for nitrogen oxides (NO(x)), compared with the base fuel. Although burning a fuel that contains oxygen could conceivably yield more oxygenated compounds in emissions, the oxygenate-blended diesel fuel resulted in reduced emissions of formaldehyde along with hydrocarbons such as benzene, 1,3-butadiene, and PAHs. Reductions in nitro-PAH emissions have been observed in both the cetane-enhanced and oxygenated fuels. This further demonstrates the benefits of using a cetane enhancer and the oxygenated fuel component.     

Speciated hydrocarbon profiles and calculated reactivities of exhaust and evaporative emissions from 82 in-use light-duty Australian vehicles

Mass emissions of non-methane hydrocarbon (NMHC) from 26 pre-1986 and 56 post-1985 catalyst-equipped in-service vehicles were determined from measurements made on a chassis dynamometer using an urban drive cycle. Evaporative emissions were measured on a subset (4 pre-1986 and 8 post-1985) of these vehicles. Average ADR emissions (mg/km) of the individual HCs from the older pre-1986 vehicles were generally 4–7 times the emissions from newer catalyst-equipped vehicles. Evaporative emissions from the older vehicles are also much higher than those of newer vehicles. Exhaust from newer catalyst-equipped vehicles had lower proportions of substituted aromatics and alkenes and higher proportions of lower molecular weight alkanes. The effect of fuel type on the exhaust emissions was also investigated by refuelling 9 of the pre-1986 vehicles with both unleaded and leaded petrol. A 20–40% reduction in HC mass emissions was observed when unleaded petrol was used instead of leaded petrol. Reactivities of the emissions and the contributions from different classes of compounds are also reported. The specific reactivity of the exhaust emissions from newer vehicles was lower than that for older vehicles owing to the smaller proportions of highly reactive alkenes and substituted aromatic species. Moreover, as older vehicles have higher average mass emissions, when considered on a per-km basis, the pre-1986 vehicles have a greater ozone-forming potential than post-1985 vehicles. The specific reactivities of the NMHC (gO₃/gNMHC) of both the heat build and hot soak evaporative emissions were much lower than the exhaust emissions.     

Exhaust Emissions From In-Use Alternative Fuel Vehicles

Abstract

This study examines exhaust emissions from 11 vehicles tested on compressed natural gas, liquefied petroleum gas, methanol, ethanol, and reformulated gasoline fuels (22 vehicle/ fuel combinations). The paper highlights ozone precursor and toxic emissions. Emission rates from some of the presumably well-maintained, low-mileage test vehicles were higher than expected, but fuel effects were consistent with findings of similar studies. Aggregate toxic and non-methane organic emission rates from the variable/flexible fuel vehicles were higher with alcohol fuels than with reformulated gasoline. Lower specific reactivities for emissions with the alcohol fuels offset this negative trait. Specific reactivities of the organic emissions with the alternative fuels were consistently lower than those with the gasoline blends. Compressed natural gas and liquefied petroleum gas fuels had the lowest values. Although specific reactivities were expected to vary from fuel-to-fuel, they also varied considerably from vehicle-to-vehicle.     

Hydrocarbon emissions speciation in diesel and biodiesel exhausts

Diesel engine emissions are composed of a long list of organic compounds, ranging from C₂ to C₁₂₊, and coming from the hydrocarbons partially oxidized in combustion or produced by pyrolisis. Many of these are considered as ozone precursors in the atmosphere, since they can interact with nitrogen oxides to produce ozone under atmospheric conditions in the presence of sunlight. In addition to problematic ozone production, Brookes, P., and Duncan, M. [1971. Carcinogenic hydrocarbons and human cells in culture. Nature.] and Heywood, J. [1988. Internal Combustion Engine Fundamentals.Mc Graw-Hill, ISBN 0-07-1000499-8.] determined that the polycyclic aromatic hydrocarbons present in exhaust gases are dangerous to human health, being highly carcinogenic.The aim of this study was to identify by means of gas chromatography the amount of each hydrocarbon species present in the exhaust gases of diesel engines operating with different biodiesel blends. The levels of reactive and non-reactive hydrocarbons present in diesel engine exhaust gases powered by different biodiesel fuel blends were also analyzed.Detailed speciation revealed a drastic change in the nature and quantity of semi-volatile compounds when biodiesel fuels are employed, the most affected being the aromatic compounds. Both aromatic and oxygenated aromatic compounds were found in biodiesel exhaust. Finally, the conservation of species for off-side analysis and the possible influence of engine operating conditions on the chemical characterization of the semi-volatile compound phase are discussed.The use of oxygenated fuel blends shows a reduction in the Engine-Out emissions of total hydrocarbons. But the potential of the hydrocarbon emissions is more dependent on the compositions of these hydrocarbons in the Engine-Out, to the quantity; a large percent of hydrocarbons existing in the exhaust, when biodiesel blends are used, are partially burned hydrocarbons, and are interesting as they have the maximum reactivity, but with the use of pure biodiesel and diesel, the most hydrocarbons are from unburned fuel and they have a less reactivity. The best composition in the fuel, for the control of the hydrocarbon emissions reactivity, needs to be a fuel with high-saturated fatty acid content.     

Measurement of fine particles in diesel emissions using a real-time aerosol monitor

A real-time monitoring methodology to determine diesel fine particles in diesel emissions has been evaluated. The range of particle size captured by the monitor was approximately 0.1 microm to 1 microm. DustTrak real-time monitors were connected to the dilution tunnel of the vehicle exhaust to measure the emissions during the vehicle tests under both dynamic and steady-state driving conditions, and concentration data were recorded every 5 sec. Test variation of the real-time monitoring among different test days was similar to that measured by traditional filter-based gravimetric method, whereas the repeatability of the monitor data within the same-day tests was better than that of gravimetric method. Correlations between the two methods were established for different fuels tested on a single light duty vehicle. When the emissions from the reference fuel was used to convert the monitor's response to diesel fuels, the levels determined by the real-time monitor were consistent with those measured by gravimetric method among different fuels tested. Use of the real-time monitor could provide information on the levels of fine particles that is more relevant to the public health than the total particles.     

Effect of methyl tertiary butyl ether concentrations on exhaust emissions from gasoline used in the metropolitan area of Mexico City

In this work, the primary objective was to assess the impact of oxygenated fuel on the exhaust emissions from an important fraction of vehicles in the Metropolitan Area of Mexico City (MAMC). The results aim to provide information on the actual effect of MTBE on a fleet that represents more than 60% of the in-use vehicles in the MAMC. Ten vehicles were tested with a low-octane base gasoline, and 10 more with a regular-grade unleaded base gasoline. Three MTBE concentrations, 5, 10, and 15 vol %, were tested following the U.S. Federal Test Procedure (FTP). CO, total HC, and NOx from the exhaust gases were quantitatively evaluated and also characterized for FTP speciated organic emissions. From this data, the O3-forming potential of the fuels was calculated. Results show that for the fleet using low-octane gasoline, the addition of 10% MTBE substantially reduced CO emissions, but total HC concentration in the exhaust showed a modest decrease. For the regular gasoline, the 10% MTBE blend seemed to be the best choice, but there was not a significant decrease in emissions. The specific reactivity of each fuel, expressed in grams of O3 per gram of nonmethane organic gases, increased with MTBE concentration in both cases. This result is important to consider, especially for a region like Mexico City, which has high atmospheric O3 concentrations.     

Germany

ABSTRACT

The 1988 Alternative Motor Fuels Act and the 1990 Clean Air Act Amendments require examination of the potential to favorably influence air quality by changing the composition of motor vehicle fuels. Motor vehicle tailpipe and evaporative emissions were characterized using laboratory simulations of roadway driving conditions and a variety of vehicle-fuel technologies (reformulated gasoline (RFG), methanol (M85), ethanol (E85), and natural gas (CNG)). Speciated organic compound (with Carter MIR ozone potential), CO, and NO_x emission rates and fuel economy were characterized. The Carter MIR ozone potential of combined Federal Test Procedure (FTP) tailpipe and evaporative emissions was reduced more than 90% with CNG relative to RFG, M85, and E85 fuels. FTP toxic compound emissions (benzene, formaldehyde, acetalde-hyde, and 1,3-butadiene) were greater with M85 and E85 fuels than with RFG fuel, and less with CNG fuel than RFG fuel. The most abundant toxic compound was benzene with RFG fuel, formaldehyde with M85 fuel, and acetaldehyde with E85 fuel. FTP MPG fuel economies were reduced with M85 and E85 fuels relative to RFG fuel, consistent with their lower BTU/gal. Energy efficiencies (BTU/mi) were improved with all the alternative fuels relative to RFG. Carter MIR ozone potential was generally reduced with the alternative fuels relative to RFG fuel under REP05 (high speeds and acceleration rates) driving conditions (most significantly with CNG). Toxic aldehyde emissions were reduced under REP05 conditions relative to FTP conditions with all the tested fuels, and toxic benzene emissions were elevated under high acceleration conditions.     

Considerations in Setting Standards for Oxides of Nitrogen

Since 1959 the California Department of Public Health has held responsibility for setting standards for ambient air quality and for motor vehicle emissions. The need for standards for oxides of nitrogen involves consideration both of direct effects and effects resulting from participation in photochemical smog reactions. This paper discusses the various effects of concern and describes the department’s program for establishing air quality standards which will become the basis for vehicle emission standards and serve as guides for control of other sources of oxides of nitrogen.     

Measurement of Fine Particles in Diesel Emissions Using a Real-Time Aerosol Monitor

Abstract

A real-time monitoring methodology to determine diesel fine particles in diesel emissions has been evaluated. The range of particle size captured by the monitor was ～0.1 μm to 1 μm. DustTrak real-time monitors were connected to the dilution tunnel of the vehicle exhaust to measure the emissions during the vehicle tests under both dynamic and steady-state driving conditions, and concentration data were recorded every 5 sec. Test variation of the real-time monitoring among different test days was similar to that measured by traditional filter-based gravi-metric method, whereas the repeatability of the monitor data within the same-day tests was better than that of gravimetric method. Correlations between the two methods were established for different fuels tested on a single light duty vehicle. When the emissions from the reference fuel was used to convert the monitor’s response to diesel fuels, the levels determined by the real-time monitor were consistent with those measured by gravimetric method among different fuels tested. Use of the real-time monitor could provide information on the levels of fine particles that is more relevant to the public health than the total particles.     

Effect of Gasoline Formulation on the Formation of Photosmog: A Box Model Study

Abstract

Based on exhaust gas analyses from the combustion of five different types of gasoline in a passenger car operated on a chassis dynamometer, box model simulations of the irradiation of exhaust/NO_x /air mixtures using an established chemical mechanism for a standardized photo-smog scenario were performed. The fuel matrix used covered wide fractional ranges for paraffinic, olefinic, and aromatic hydrocarbons. Two fuels also contained methyl tertiary butyl ether (MTBE). The different O₃ profiles calculated for each run were compared and interpreted. The O₃ levels obtained were strongly influenced by the exhaust gas concentrations of aromatic and olefinic hydro-carbons. The higher exhaust content of these compounds caused higher O₃ production in the smog system investigated. The conclusion of the present study is that the composition of gasoline cannot be taken directly for the estimation of the emissions’ O₃ creation potential from its combustion. Variation of the dilution in the different calculations showed evidence for an additional influence of transport effects. Accordingly, further detailed exhaust gas analyses followed by more complex modeling studies are necessary for a proper characterization of the relationship between fuel blend and gasoline combustion products.     

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.     

Quantification of personal exposure concentrations to gasoline vehicle emissions in high-end exposure microenvironments: Effects of fuel and season

Mobile-source air toxic (MSAT) levels increase in confining microenvironments (MEs) with numerous emission sources of vehicle exhaust or evaporative emissions or during high-load and cold-start conditions. Reformulated fuels are expected to reduce MSAT and ozone precursor emissions. This study, required under the Clean Air Act Section 211b, evaluated high-end exposures in cities using reformulated (methyl tertiary-butyl ether [MTBE] or ethanol [EtOH]) fuels and conventional gasoline blends. The study investigates 13 high-end MEs, sampling under enhanced exposure conditions expected to result in maximal fuel and exhaust component exposures to carbon monoxide (CO), carbon dioxide (CO₂), BTEX (benzene, toluene, ethylbenzene, xylenes), MTBE, 1,3-butadiene (1,3-BD), EtOH, formaldehyde (HCHO), and acetaldehyde (CH₃CHO). The authors found that day-to-day ME variations in high-end benzene, 1,3-BD, HCHO, and CO concentrations are substantial, but independent of gasoline composition and season, and related to the activity and emission rates of ME sources, which differ from day to day.

Implications: Mobile-source air toxic (MSAT) levels increase in confining microenvironments (MEs) in the presence of vehicular exhaust or evaporative emissions. This study, required under the Clean Air Act Section 211b, evaluated high-end exposures in cities using oxygenated (methyl tertiary-butyl ether or ethanol) and conventional gasoline blends. Personal exposure concentrations were quantified in selected MEs representing the upper end of the frequency distribution of potential population exposures. This work presents the first systematic look at high-end/maximal exposures to multiple contaminants, in multiple microenvironments, in multiple cities, over two seasons, for multiple fuels, making it a very complete evaluation of reformulated fuel impacts on MSAT concentrations in confined microenvironments. The study found that day-to-day ME variations of high-end pollutant concentrations are substantial, but independent of gasoline composition and season, and related to the variable daily activity and emission rates of ME sources. The data collected in this study may be used in bounding exposure modeling estimates that account for time spent in similar confining MEs.     

Seasonal impact of blending oxygenated organics with gasoline on motor vehicle tailpipe and evaporative emissions.

Emissions from a 1988 GM Corsica with adaptive learning closed loop control were measured with 4 fuels at 40, 75, and 90 degrees F. Evaporative and exhaust emissions were examined from each fuel at each test temperature. Test fuels were unleaded summer grade gasoline; a blend of this gasoline containing 8.1 percent ethanol; a refiner's blend stock; and the blend stock containing 16.2 percent methyl tertiary butyl ether. The ethanol and MTBE blends contained 3.0 percent oxygen by weight. Regulated emissions (total hydrocarbons, carbon monoxide, and oxides of nitrogen), detailed aldehydes, detailed hydrocarbons, ethanol, MTBE, benzene, and 1,3-butadiene were determined. The highest levels of regulated emissions were produced at the lower temperature. Blended fuels produced almost twice the evaporative hydrocarbon emissions at high temperatures as did the base fuels. Benzene emissions varied with fuels and operating temperatures, while 1,3-butadiene emissions decreased slightly with increasing temperatures. Formaldehyde emissions were not sensitive to fuel or temperature changes. Ethanol fuel blend total aldehyde emissions increased by 40 percent due to increased acetaldehyde emissions. Fuel blends had approximately a 3 percent economy decrease. The MTBE fuel blend appeared to offer the most reduction in total hydrocarbon, carbon monoxide, and oxides of nitrogen for the fuels and temperatures tested.     

VOC composition and ozone-forming potential of the exhaust gas of in-use motorcycles

The emission profile of volatile organic compounds (VOC) and the ozone-forming potential (OP) of the exhaust gas of six in-use motorcycles (four 4-stroke- and two 2-stroke-engines) were determined. The motorcycles were tested on a chassis dynamometer in a real-world driving cycle. The analysis involved the C2–C12-hydrocarbons as well as the aldehydes and ketones. Additionally, the regulated THC and NO_x emissions were measured according to the test procedure for type approval (ECE 40). Two vehicles did not fulfil the THC emission standard, whereas all vehicles met the requirements for NO_x emission. The aromatic fuel components toluene and xylene, and the combustion products ethene and propene contributed most to the OP of the VOC emission. The highest OP was found with the 2-stroke engines. The VOC profile of the emissions varied with vehicle and driving conditions. The reactivity of the exhaust gas, defined as gram ozone per gram of non-methane organic gases (NMOG), increased with vehicle speed.