Chemical mass balance receptor model applied to ambient C2–C9 VOC concentration in Seoul,Korea: Effect of chemical reaction losses

A chemical mass balance (CMB) receptor model was used for estimating the diurnal contributions of VOC emission sources to the ambient C₂–C₉ VOC concentration in Seoul, Korea. For this purpose, the VOC concentrations were measured in the morning, the afternoon, and the evening. The samples were collected using a 2-h integrated SUMMA canister. The source profiles were developed for the CMB calculation in the Seoul area. To investigate the effect of the chemical reaction loss of VOCs on the CMB calculation, the modified model employing a decay factor and the standard model that considers no loss were compared. The modified model estimated that the vehicle exhaust (52%) was the largest leading source of VOCs in the Seoul atmosphere, followed by the use of solvents (26%), gasoline evaporation (15%), the use of liquefied petroleum gas (LPG) (5%), and the use of liquefied natural gas (LNG) (2%). Relative source contribution for vehicle exhaust showed a clear diurnal variation with a high in the morning and evening and a low in the afternoon, while the contribution of evaporative emissions (gasoline evaporation and solvent usage) showed a different diurnal pattern from that of the vehicle exhaust, exhibiting a high in the afternoon and evening and a low in the morning. It was found that the difference between the total source contribution (μg m⁻³) estimated from these two models was not statistically significant. However, when the paired-sample t-test is applied to the individual sources, a significant difference was found for the vehicle exhaust and the solvent use. In addition, the modified model brought forth a better performance with high R² and low χ² as compared to those obtained from the standard model in the CMB calculation. The vehicle exhaust and solvent use were estimated to be the largest and the second largest contributors to ambient benzene as well as ozone formation potential (OFP), respectively. Based on above results we believe that incorporating the reaction loss in the CMB calculations helps to better fit the source profile to the ambient VOC concentrations. However, the reaction loss does not significantly affect the estimation of source contributions.     

A Characterization of Emissions from an Early Model Flexible-Fuel Vehicle

An emission study was conducted on a 1987 Ford Crown Victoria flexible-fuel vehicle, an early prototype which had been driven about 25,000 miles. The vehicle was run on both gasoline and a blend of 85 percent methanol and 15 percent gasoline. Emission rates of regulated pollutants (hydrocarbons, carbon monoxide, nitrogen oxides, formaldehyde, and methanol) and nonregulated pollutants (speciated organic materials) were determined for both exhaust and evaporative emissions. Tests were run varying the driving cycle, ambient temperature and catalytic converter. In general, hydrocarbon composition of exhaust emissions was significantly affected by catalyst replacement and cold starts, slightly affected by driving schedule, and unaffected by ambient temperature and test fuel. Hydrocarbon composition of evaporative emissions was only sensitive to the type of evaporative test being performed: diurnal tests typically had larger fractions of lower molecular weight paraffins than hot soak tests.     

Sensitivity of source apportionment of urban particulate matter to uncertainty in motor vehicle emissions profiles

A sensitivity analysis was conducted to characterize sources of uncertainty in results of a molecular marker source apportionment model of ambient particulate matter using mobile source emissions profiles obtained as part of the Gasoline/Diesel PM Split Study. A chemical mass balance (CMB) model was used to determine source contributions to samples of fine particulate matter (PM2.5) collected over 3 weeks at two sites in the Los Angeles area in July 2001. The ambient samples were composited for organic compound analysis by the day of the week to investigate weekly trends in source contributions. The sensitivity analysis specifically examined the impact of the uncertainty in mobile source emissions profiles on the CMB model results. The key parameter impacting model sensitivity was the source profile for gasoline smoker vehicles. High-emitting gasoline smoker vehicles with visible plumes were seen to be a significant source of PM in the area, but use of different measured profiles for smoker vehicles in the model gave very different results for apportionment of gasoline, diesel, and smoker vehicle tailpipe emissions. In addition, the contributions of gasoline and diesel emissions to total ambient PM varied as a function of the site and the day of the week.     

Diurnal and weekday variations in the source contributions of ozone precursors in California's South Coast Air Basin

For at least 30 years, ozone (O3) levels on weekends in parts of California's South Coast (Los Angeles) Air Basin (SoCAB) have been as high as or higher than on weekdays, even though ambient levels of O3 precursors are lower on weekends than on weekdays. A field study was conducted in the Los Angeles area during fall 2000 to test whether proposed relationships between emission sources and ambient nonmethane hydrocarbon (NMHC) and oxides of nitrogen (NOx) levels can account for observed diurnal and day-of-week variations in the concentration and proportions of precursor pollutants that may affect the efficiency and rate of O3 formation. The contributions to ambient NMHC by motor vehicle exhaust and evaporative emissions, estimated using chemical mass balance (CMB) receptor modeling, ranged from 65 to 85% with minimal day-of-week variation. Ratios of ambient NOx associated with black carbon (BC) to NOx associated with carbon monoxide (CO) were approximately 1.25 +/- 0.22 during weekdays and 0.76 +/- 0.07 and 0.52 +/- 0.07 on Saturday and Sunday, respectively. These results demonstrate that lower NOx emissions from diesel exhaust can be a major factor causing lower NOx mixing ratios and higher NMHC/NOx ratios on weekends. Nonmobile sources showed no significant day-of-week variations in their contributions to NMHC. Greater amounts of gasoline emissions are carried over on Friday and Saturday evenings but are, at most, a minor factor contributing to higher NMHC/NOx ratios on weekend mornings.     

Sensitivity of Source Apportionment of Urban Particulate Matter to Uncertainty in Motor Vehicle Emissions Profiles

Abstract

A sensitivity analysis was conducted to characterize sources of uncertainty in results of a molecular marker source apportionment model of ambient particulate matter using mobile source emissions profiles obtained as part of the Gasoline/Diesel PM Split Study. A chemical mass balance (CMB) model was used to determine source contributions to samples of fine particulate matter (PM_2.5) collected over 3 weeks at two sites in the Los Angeles area in July 2001. The ambient samples were composited for organic compound analysis by the day of the week to investigate weekly trends in source contributions. The sensitivity analysis specifically examined the impact of the uncertainty in mobile source emissions profiles on the CMB model results. The key parameter impacting model sensitivity was the source profile for gasoline smoker vehicles. High-emitting gasoline smoker vehicles with visible plumes were seen to be a significant source of PM in the area, but use of different measured profiles for smoker vehicles in the model gave very different results for apportionment of gasoline, diesel, and smoker vehicle tailpipe emissions. In addition, the contributions of gasoline and diesel emissions to total ambient PM varied as a function of the site and the day of the week.     

Source apportionment of daily fine particulate matter at Jefferson Street, Atlanta, GA, during summer and winter

The primary emission source contributions to fine organic carbon (OC) and fine particulate matter (PM2.5) mass concentrations on a daily basis in Atlanta, GA, are quantified for a summer (July 3 to August 4, 2001) and a winter (January 2-31, 2002) month. Thirty-one organic compounds in PM2.5 were identified and quantified by gas chromatography/mass spectrometry. These organic tracers, along with elemental carbon, aluminum, and silicon, were used in a chemical mass balance (CMB) receptor model. CMB source apportionment results revealed that major contributors to identified fine OC concentrations include meat cooking (7-68%; average: 36%), gasoline exhaust (7-45%; average: 21%), and diesel exhaust (6-41%; average: 20%) for the summer month, and wood combustion (0-77%; average: 50%); gasoline exhaust (14-69%; average: 33%), meat cooking (1-14%; average: 5%), and diesel exhaust (0-13%; average: 4%) for the winter month. Primary sources, as well as secondary ions, including sulfate, nitrate, and ammonium, accounted for 86 +/- 13% and 112 +/- 15% of the measured PM2.5 mass in summer and winter, respectively.     

VOC composition of current motor vehicle fuels and vapors, and collinearity analyses for receptor modeling

The formulation of motor vehicle fuels can alter the magnitude and composition of evaporative and exhaust emissions occurring throughout the fuel cycle. Information regarding the volatile organic compound (VOC) composition of motor fuels other than gasoline is scarce, especially for bioethanol and biodiesel blends. This study examines the liquid and vapor (headspace) composition of four contemporary and commercially available fuels: gasoline (<10% ethanol), E85 (85% ethanol and 15% gasoline), ultra-low sulfur diesel (ULSD), and B20 (20% soy-biodiesel and 80% ULSD). The composition of gasoline and E85 in both neat fuel and headspace vapor was dominated by aromatics and n-heptane. Despite its low gasoline content, E85 vapor contained higher concentrations of several VOCs than those in gasoline vapor, likely due to adjustments in its formulation. Temperature changes produced greater changes in the partial pressures of 17 VOCs in E85 than in gasoline, and large shifts in the VOC composition. B20 and ULSD were dominated by C₉ to C₁₆n-alkanes and low levels of the aromatics, and the two fuels had similar headspace vapor composition and concentrations. While the headspace composition predicted using vapor-liquid equilibrium theory was closely correlated to measurements, E85 vapor concentrations were underpredicted. Based on variance decomposition analyses, gasoline and diesel fuels and their vapors VOC were distinct, but B20 and ULSD fuels and vapors were highly collinear. These results can be used to estimate fuel related emissions and exposures, particularly in receptor models that apportion emission sources, and the collinearity analysis suggests that gasoline- and diesel-related emissions can be distinguished.     

Formaldehyde,Melhanol and Hydrocarbon Emissions from Methanol-fueled Cars

Exhaust and evaporative emissions tests were conducted on several methanol- and gasoline-fueled vehicles. Separate samples for chromatographlc analysis of formaldehyde, methanol, and Individual hydrocarbons were collected in each of the three phases of the driving cycle and in each of the two portions of the evaporative emissions test. One vehicle, equipped with an experimental variable-fuel engine, was tested using methanol/gasoline fuel mixtures of 100, 85, 50,15, and 0 percent methanol. Combustion-generated hydrocarbons were lowest using methanol fuel, and increased several-fold as the gasoline fraction was increased. Gasoline components In the exhaust Increased from zero as the gasoline fraction of the fuel was Increased. On the other hand, formaldehyde emissions were several times higher using methanol fuel than they were using gasoline. A dedicated methanol car and the variable-fuel car gave similar emissions patterns when they both were tested using methanol fuel. The organic-carbon composition of the exhaust was 85-90 percent methanol, 5-7 percent formaldehyde, and 3-9 percent hydrocarbons. Several cars that were tested using gasoline emitted similar distributions of hydrocarbons, even through the vehicles represented a broad range of current and developmental engine families and emissions control systems. These vehicles continue the trend of the past twenty years toward less photochemically reactive exhaust, with higher percentages of methane and total alkanes, and correspondingly lower percentages of oleflns and aromatlcs.     

Spatial gradients and source apportionment of volatile organic compounds near roadways

Concentrations of 55 volatile organic compounds (VOCs) (C₂–C₁₂) are reported near a highway in Raleigh, NC. Thirty-minute samples were collected at eight locations, ranging from approximately 10–100 m perpendicular from the roadway. The highest concentrations of VOCs were generally measured closest to the roadway, and concentrations decreased exponentially with increasing distance from the roadway. The highest mean concentration for individual VOCs were for ethylene (3.10 ppbv) (mean concentration at x = 13 m), propane (2.27 ppbv), ethane (1.91 ppbv), isopentane (1.54 ppbv), toluene (0.95 ppbv), and n-butane (0.89 ppbv). Concentrations at the nearest roadway location (x = 13 m) were generally between 2.0 and 1.5 times those from the farthest roadway location (x = 92 m). The data were apportioned into four source categories using the EPA Chemical Mass Balance Model (CMB8.2): motor vehicle exhaust, compressed natural gas, propane gas, and evaporative gasoline. The majority of the VOCs resulted from motor vehicle exhaust (67 ± 12%) (% of total VOC at x = 13 m ± S.D.). Compressed natural gas, propane gas, and evaporative gasoline accounted for approximately 15%, 7% and 1% of the total VOC emissions, respectively, at x = 13 m.     

Chemical composition of major VOC emission sources in the Seoul atmosphere

This paper describes a chemical analysis of volatile organic compounds (VOCs) for five emission sources in Seoul. The source categories included motor vehicle exhaust, gasoline evaporation, paint solvents, natural gas and liquefied petroleum gas (LPG). These sources were selected because they have been known to emit significant quantities of VOCs in the Seoul area (more than 5% of the total emission inventory). Chemical compositions of the five emission sources are presented for a group of 45 C2-C9 VOCs. Motor vehicle exhaust profiles were developed by conducting an urban tunnel study. These emissions profiles were distinguished from the other emission profiles by a high weight percentage of butanes over seasons and propane in the wintertime. It was found that this is due to the wide use of butane-fueled vehicles. To obtain gasoline vapor profiles, gasoline samples from five major brands for each season were selected. The brands were blended on the basis of the marketshare of these brands in Seoul area. Raoult's law was used to calculate gasoline evaporative compositions based on the liquid gasoline compositions. The measured and estimated gasoline vapor compositions were found to be in good agreement. Vehicle and gasoline evaporation profiles were made over seasons because of the seasonal change in their compositions. Paint solvent emissions profiles were produced based on a product-use survey and sales figures. These profiles are a composite of four major oil-based paints and thinning solvent. The source profile of natural gas was made on a methane-free basis. It was found that Ethane and propane were the most abundant compounds accounting for 95% of the natural gas composition. LPG was largely composed of propane and ethane and the remaining components were minor contributors.     

Source apportionment of PM2.5 at two Seattle chemical speciation sites

ABSTRACT

Positive Matrix Factorization analysis of PM_2.5 chemical speciation data collected from 2015–2017 at Washington State Department of Ecology’s urban NCore (Beacon Hill) and near-road (10th and Weller) sites found similar PM_2.5 sources at both sites. Identified factors were associated with gasoline exhaust, diesel exhaust, aged and fresh sea salt, crustal, nitrate-rich, sulfur-rich, unidentified urban, zinc-rich, residual fuel oil, and wood smoke. Factors associated with vehicle emissions were the highest contributing sources at both sites. Gasoline exhaust emissions comprised 26% and 21% of identified sources at Beacon Hill and 10th and Weller, respectively. Diesel exhaust emissions comprised 29% of identified sources at 10th and Weller but only 3% of identified sources at Beacon Hill. Correlation of the diesel exhaust factor with measured concentrations of black carbon and nitrogen oxides at 10th and Weller suggests a method to predict PM_2.5 from diesel exhaust without a full chemical speciation analysis. While most PM_2.5 sources exhibit minimal change over time, primary PM_2.5 from gasoline emissions is increasing on average 0.18 µg m^?3 per year in Seattle.     

Source apportionment of fine particulate matter in Phoenix, AZ, using positive matrix factorization

Speciated particulate matter (PM)2.5 data collected as part of the Interagency Monitoring of Protected Visual Environments (IMPROVE) program in Phoenix, AZ, from April 2001 through October 2003 were analyzed using the multivariate receptor model, positive matrix factorization (PMF). Over 250 samples and 24 species were used, including the organic carbon and elemental carbon analytical temperature fractions from the thermal optical reflectance method. A two-step approach was used. First, the species excluding the carbon fractions were used, and initially eight factors were identified; non-soil potassium was calculated and included to better refine the burning factor. Next, the mass associated with the burning factor was removed, and the data set rerun with the carbon fractions. Results were very similar (i.e., within a few percent), but this step enabled a separation of the mobile factor into gasoline and diesel vehicle emissions. The identified factors were burning (on average 2% of the mass), secondary transport (7%), regional power generation (13%), dust (25%), nitrate (9%), industrial As/Pb/Se (2%), Cu/Ni/V (7%), diesel (9%), and general mobile (26%). The overall contribution from mobile sources also increased, as some mass (OC and nitrate) from the nitrate and regional power generation factors were apportioned with the mobile factors. This approach allowed better apportionment of carbon as well as total mass. Additionally, the use of multiple supporting analyses, including air mass trajectories, activity trends, and emission inventory information, helped increase confidence in factor identification.     

Receptor Model Evaluation of the Southeast Michigan Ozone Study Ambient NMOC Measurements

Abstract

Large-scale studies like the Southeast Michigan Ozone Study (SEMOS) have focused attention on quantifying and spedating inventories for volatile organic compounds (VOCs). One approach for evaluating the accuracy of a VOC emission inventory is the development of a chemical mass balance (CMB) receptor model for ambient non-methane organic compound (NMOC) measurements. CMB evaluations of ambient hydrocarbon data provide a sample-specific allocation of emissions to individual source categories. This study summarizes the results of an application of the CMB model to the NMOC data from the SEMOS study. Comparison of CMB results with emission inventory values for the Detroit area show that vehicle emissions are well represented by the inventory, as are architectural coatings and coke ovens. Estimated emissions from petroleum refineries and graphic arts industries are much lower in the inventory than determined from the receptor allocation. Under-reporting of fugitive VOC emissions from petroleum refineries is an ongoing problem. Emissions from graphic arts industries are underestimated in the inventory partly because of the broad characterization of the emission factor (i.e., mass emitted/capita), which may be less useful when specific locations and days are under consideration. This study also demonstrates the effectiveness of the CMB approach when used prospectively to track the implementation of emission control strategies. While vehicle emission concentrations were unchanged from 1988 to 1993, measurement-based CMB results suggest a decrease in evaporative emissions during this time period resulting from Reid vapor pressure (RVP) reductions (from 11.0 psi in 1988 to 8.6 psi in 1993) and fleet turnover. Changes in emissions from coke plants and petroleum refineries were also seen in the CMB allocations for these sources.     

Diurnal and Weekday Variations in the Source Contributions of Ozone Precursors in California’s South Coast Air Basin

Abstract

For at least 30 years, ozone (O₃) levels on weekends in parts of California’s South Coast (Los Angeles) Air Basin (SoCAB) have been as high as or higher than on weekdays, even though ambient levels of O₃ precursors are lower on weekends than on weekdays. A field study was conducted in the Los Angeles area during fall 2000 to test whether proposed relationships between emission sources and ambient nonmethane hydrocarbon (NMHC) and oxides of nitrogen (NO_x) levels can account for observed diurnal and day-of-week variations in the concentration and proportions of precursor pollutants that may affect the efficiency and rate of O₃ formation. The contributions to ambient NMHC by motor vehicle exhaust and evaporative emissions, estimated using chemical mass balance (CMB) receptor modeling, ranged from 65 to 85% with minimal day-of-week variation. Ratios of ambient NO_x associated with black carbon (BC) to NO_x associated with carbon monoxide (CO) were approximately 1.25 ± 0.22 during weekdays and 0.76 ± 0.07 and 0.52 ± 0.07 on Saturday and Sunday, respectively. These results demonstrate that lower NO_x emissions from diesel exhaust can be a major factor causing lower NO_x mixing ratios and higher NMHC/NO_x ratios on weekends. Nonmobile sources showed no significant day-of-week variations in their contributions to NMHC. Greater amounts of gasoline emissions are carried over on Friday and Saturday evenings but are, at most, a minor factor contributing to higher NMHC/NO_x ratios on weekend mornings.     

Contribution of the gasoline distribution cycle to volatile organic compound emissions in the metropolitan area of Mexico City

Gasoline distribution in the metropolitan area of Mexico City (MAMC) represents an area of opportunity for the abatement of volatile organic compound (VOC) emissions. The gasoline distribution in this huge urban center encompasses several operations: (1) storage in bulk and distribution plants, (2) transportation to gasoline service stations, (3) unloading at service stations' underground tanks, and (4) gasoline dispensing. In this study, hydrocarbon (HC) emissions resulting from breathing losses in closed reservoirs, leakage, and spillage from the operations just listed were calculated using both field measurements and reported emission factors. The results show that the contribution of volatile HC emissions due to storage, distribution, and sales of gasoline is 6651 t/year, approximately 13 times higher than previously reported values. Tank truck transportation results in 53.9% of the gasoline emissions, and 31.5% of emissions are generated when loading the tank trucks. The high concentration of emissions in the gasoline transportation and loading operations by tank trucks has been ascribed to (1) highly frequent trips from distribution plant to gasoline stations, and vice versa, to cope with excessive gasoline sales per gasoline station; (2) low leakproofness of tank trucks; and (3) poor training of employees. In addition, the contribution to HC evaporative and exhaust emissions from the vehicles of the MAMC was also evaluated.     

Regulated and unregulated emissions from an internal combustion engine operating on ethanol-containing fuels

In the present work, the effect of ethanol addition to gasoline on regulated and unregulated emissions is studied. A 4-cylinder OPEL 1.6 L internal combustion engine equipped with a hydraulic brake dynamometer was used in all the experiments. For exhaust emissions treatment a typical three-way catalyst was used. Among the various compounds detected in exhaust emissions, the following ones were monitored at engine and catalyst outlet: methane, hexane, ethylene, acetaldehyde, acetone, benzene, 1,3-butadiene, toluene, acetic acid and ethanol. Addition of ethanol in the fuel up to 10% w/w had as a result an increase in the Reid vapour pressure of the fuel, which indicates indirectly increased evaporative emissions, while carbon monoxide tailpipe emissions were decreased. For ethanol-containing fuels, acetaldehyde emissions were appreciably increased (up to 100%), especially for fuel containing 3% w/w ethanol. In contrast, aromatics emissions were decreased by ethanol addition to gasoline. Methane and ethanol were the most resistant compounds to oxidation while ethylene was the most degradable compound over the catalyst. Ethylene, methane and acetaldehyde were the main compounds present at engine exhaust while methane, acetaldehyde and ethanol were the main compounds in tailpipe emissions for ethanol fuels after the catalyst operation.     

Characterization of emissions from a variable gasoline/methanol fueled car.

In response to the occurrence of the increasingly severe ambient ozone exceedances, regional environmental managers are examining the possibility of a cleaner fuel for automobiles. At this time the leading candidate appears to be methanol. In anticipation of a shift to methanol, flexible-fueled automobiles capable of operating on gasoline and/or methanol are being developed. This study examines both the exhaust and evaporative emissions from a prototype General Motors Variable Fuel Corsica. Results are reported for tests conducted at temperatures of 40 degrees, 75 degrees, and 90 degrees F, and for fuels M0 M25, M50, M85, and M100. In addition to regulated emissions and fuel economy, emission rates for methanol, aldehydes, and a large number of hydrocarbon compounds were measured. The data indicate that increasing the fuel's methanol content does not affect the exhaust organic emission rate (calculated in accordance with the regulation) from flexible-fueled cars, but formaldehyde and methanol comprise increasingly greater portions of the organic material while hydrocarbons comprise less. Increasing fuel methanol content has no significant effect on exhaust regulated emission rates (organic material, carbon monoxide, and nitrogen oxides) nor on the composition of total hydrocarbons, except for methane, which increases substantially. The effect of ambient temperature on both exhaust and evaporative emissions is similar to its effect on gasoline cars: organic and carbon monoxide exhaust emissions increase substantially at the lower temperatures, and evaporative emissions increase steadily with increases in temperature.     

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.     

Characterization of Emissions from a Variable Gasoline/Methanol Fueled Car

In response to the occurrence of the increasingly severe ambient ozone exceedances, regional environmental managers are examining the possibility of a cleaner fuel for automobiles. At this time the leading candidate appears to be methanol. In anticipation of a shift to methanol, flexible-fueled automobiles capable of operating on gasoline and/or methanol are being developed. This study examines both the exhaust and evaporative emissions from a prototype General Motors Variable Fuel Corsica. Results are reported for tests conducted at temperatures of 40°, 75°, and 90° F, and for fuels MO M25, M50, M85, and M100. In addition to regulated emissions and fuel economy, emission rates for methanol, aldehydes, and a large number of hydrocarbon compounds were measured. The data indicate that increasing the fuel's methanol content does not affect the exhaust organic emission rate (calculated in accordance with the regulation) from flexible-fueled cars, but formaldehyde and methanol comprise increasingly greater portions of the organic material while hydrocarbons comprise less. Increasing fuel methanol content has no significant effect on exhaust regulated emission rates (organic material, carbon monoxide, and nitrogen oxides) nor on the composition of total hydrocarbons, except for methane, which increases substantially. The effect of ambient temperature on both exhaust and evaporative emissions is similar to its effect on gasoline cars: organic and carbon monoxide exhaust emissions increase substantially at the lower temperatures, and evaporative emissions increase steadily with increases in temperature.     

A Fuel-Based Motor Vehicle Emission Inventory

Abstract

A fuel-based methodology for calculating motor vehicle emission inventories is presented. In the fuel-based method, emission factors are normalized to fuel consumption and expressed as grams of pollutant emitted per gallon of gasoline burned. Fleet-average emission factors are calculated from the measured on-road emissions of a large, random sample of vehicles. Gasoline use is known at the state level from sales tax data, and may be disaggregated to individual air basins. A fuel-based motor vehicle CO inventory was calculated for the South Coast Air Basin in California for summer 1991. Emission factors were calculated from remote sensing measurements of more than 70,000 in-use vehicles. Stabilized exhaust emissions of CO were estimated to be 4400 tons/day for cars and 1500 tons/day for light-duty and medium- duty trucks, with an estimated uncertainty of ±20% for cars and ±30% for trucks. Total motor vehicle CO emissions, including incremental start emissions and emissions from heavy-duty vehicles were estimated to be 7900 tons/day. Fuelbased inventory estimates were greater than those of California's MVEI 7F model by factors of 2.2 for cars and 2.6 for trucks. A draft version of California's MVEI 7G model, which includes increased contributions from high-emitting vehicles and off-cycle emissions, predicted CO emissions which closely matched the fuel-based inventory. An analysis of CO mass emissions as a function of vehicle age revealed that cars and trucks which were ten or more years old were responsible for 58% of stabilized exhaust CO emissions from all cars and trucks.