Lubricating oil and fuel contributions to particulate matter emissions from light-duty gasoline and heavy-duty diesel vehicles

Size-resolved particulate matter emissions from heavy-duty diesel vehicles (HDDVs) and light-duty gasoline vehicles (LDGVs) operated under realistic driving cycles were analyzed for elemental carbon (EC), organic carbon (OC), hopanes, steranes, and polycyclic aromatic hydrocarbons. Measured hopane and sterane size distributions did not match the total carbon size distribution in most cases, suggesting that lubricating oil was not the dominant source of particulate carbon in the vehicle exhaust. A regression analysis using 17alpha(H)-21beta(H)-29-norhopane as a tracer for lubricating oil and benzo[ghi/perylene as a tracer for gasoline showed that gasoline fuel and lubricating oil both make significant contributions to particulate EC and OC emissions from LDGVs. A similar regression analysis performed using 17alpha(H)-21beta(H)-29-norhopane as a tracer for lubricating oil and flouranthene as a tracerfor diesel fuel was able to explain the size distribution of particulate EC and OC emissions from HDDVs. The analysis showed that EC emitted from all HDDVs operated under relatively high load conditions was dominated by diesel fuel contributions with little EC attributed to lubricating oil. Particulate OC emitted from HDDVs was more evenly apportioned between fuel and oil contributions. EC emitted from LDGVs operated underfuel-rich conditions was dominated by gasoline fuel contributions. OC emitted from visibly smoking LDGVs was mostly associated with lubricating oil, but OC emitted from all other categories of LDGVs was dominated by gasoline fuel. The current study clearly illustrates that fuel and lubricating oil make separate and distinct contributions to particulate matter emissions from motor vehicles. These particles should be tracked separately during ambient source apportionment studies since the atmospheric evolution and ultimate health effects of these particles may be different. The source profiles for fuel and lubricating oil contributions to EC and OC emissions derived in this study provide a foundation for future source apportionment calculations.     

Size-resolved emissions of organic tracers from light- and heavy-duty vehicles measured in a California roadway tunnel

Individual organic compounds found in particulate emissions from vehicles have proven useful in source apportionment of ambient particulate matter. Species of interest include the hopanes, originating in lube oil, and selected PAHs generated via combustion. Most efforts to date have focused on emissions and apportionment PM10 or PM2.5 However, examining how these compounds are segregated by particle size in both emissions and ambient samples will help efforts to apportion size-resolved PM, especially ultrafine particles which have been shown to be more potent toxicologically. To this end, high volume size-resolved (coarse, accumulation, and ultrafine) PM samples were collected inside the Caldecott tunnel in Orinda, California to determine the relative emission factors for these compounds in different size ranges. Sampling occurred in two bores, one off-limits to heavy-duty diesel vehicles, which allows determination of the different emissions profiles for diesel and gasoline vehicles. Although tunnel measurements do not measure emissions over a full engine duty cycle, they do provide an average emissions profile over thousands of vehicles that can be considered characteristic of "freeway" emissions. Results include size-fractionated emission rates for hopanes, PAHs, elemental carbon, and other potential organic markers apportioned to diesel and gasoline vehicles. The results are compared to previously conducted PM2.5 emissions testing using dynamometer facilities and othertunnel environments.     

Effects of reformulated gasoline and motor vehicle fleet turnover on emissions and ambient concentrations of benzene

Gasoline-powered motor vehicles are a major source of toxic air contaminants such as benzene. Emissions from light-duty vehicles were measured in a San Francisco area highway tunnel during summers 1991, 1994-1997, 1999, 2001, and 2004. Benzene emission rates decreased over this time period, with a large (54 +/- 5%) decrease observed between 1995 and 1996 when California phase 2 reformulated gasoline (RFG) was introduced. We attribute this one-year change in benzene mainly to RFG effects: 36% from lower aromatics in gasoline that led to a lower benzene mass fraction in vehicle emissions, 14% due to RFG effects on total nonmethane organic compound mass emissions, and the remaining 4% due to fleet turnover. Fleet turnover effects accumulate over longer time periods: between 1995 and 2004, fleet turnover led to a 32% reduction in the benzene emission rate. A approximately 4 microg m(-3) decrease in benzene concentrations was observed at a network of ambient air sampling sites in the San Francisco Bay area between the late 1980s and 2004. The largest decrease in annual average ambient benzene concentrations (1.5 +/- 0.7 microg m(-3) or 42 +/- 19%) was observed between 1995 and 1996. The reduction in ambient benzene between spring/summer months of 1995 and 1996 due to phase 2 RFG was larger (60 +/- 20%). Effects of fuel changes on benzene during fall/winter months are difficult to quantify because some wintertime fuel changes had already occurred prior to 1995.     

On-road particulate matter (PM2.5 and PM10) emissions in the Sepulveda Tunnel, Los Angeles, California

Total and speciated particulate matter (PM2.5 and PM10) emission factors from in-use vehicles were measured for a mixed light- (97.4% LD) and heavy-duty fleet (2.6% HD) in the Sepulveda Tunnel, Los Angeles, CA. Seventeen 1-h test runs were performed between July 23, 1996, and July 27, 1996. Emission factors were calculated from mass concentration measurements taken at the tunnel entrance and exit, the volume of airflow through the tunnel, and the number of vehicles passing through the 582 m long tunnel. For the mixed LD and HD fleet, PM2.5 emission factors in the Sepulveda Tunnel ranged from 0.016 (+/-0.007) to 0.115 (+/-0.019) g/vehicle-km traveled with an average of 0.052 (+/-0.027) g/vehicle.km. PM10 emission factors ranged from 0.030 (+/-0.009) to 0.131 (+/-0.024) g/vehicle. km with an average of 0.069 (+/-0.030) g/vehicle.km. The PM2.5 emission factor was approximately 74% of the PM10 factor. Speciated emission rates and chemical profiles for use in receptor modeling were also developed. PM2.5 was dominated by organic carbon (OC) (31.0 +/- 19.5%) and elemental carbon (EC) (48.5 +/- 20.5%) that together account for 79% (+/-24%) of the total emissions. Crustal elements (Fe, Mg, Al, Si, Ca, and Mn) contribute approximately 7.8%, and the ions Cl-, NO3-, NH3+, SO4(2-), and K+ together constitute another 9.8%. In the PM10 size fraction the particulate emissions were also dominated by OC (31 +/- 12%) and EC (35 +/- 13%). The third most prominent species was Fe (18.5 +/- 9.0%), which is greater than would be expected from purely geological sources. Other geological components (Mg, Al, Si, K, Ca, and Mn) accounted for an additional 12.6%. PM10 emission factors showed some dependence on vehicle speed, whereas PM2.5 did not. For test runs in which the average vehicle speed was 42.6 km/h a 1.7 times increase in PM10 emission factor was observed compared to those runs with an average vehicle speed of 72.6 km/h. Speciated emissions were similar. However, there is significantly greater mass attributable to geological material in the PM10, indicative of an increased contribution from resuspended road dust. The PM2.5 shows relatively good correlation with NOx emissions, which indicates that even at the low percent of HD vehicles, which emit significantly more NOx than LD vehicles, they may also have a significant impact on the PM2.5 levels.     

Environmental implications on the oxygenation of gasoline with ethanol in the metropolitan area of Mexico City

Motor vehicle emission tests were performed on 12 in-use light duty vehicles, made up of the most representative emission control technologies in Mexico City: no catalyst, oxidative catalyst, and three way catalyst. Exhaust regulated (CO, NOx, and hydrocarbons) and toxic (benzene, formaldehyde, acetaldehyde, and 1,3-butadiene) emissions were evaluated for MTBE (5 vol %)- and ethanol (3, 6, and 10 vol %)-gasoline blends. The most significant overall emissions variations derived from the use of 6 vol % ethanol (relative to a 5% MTBE base gasoline) were 16% decrease in CO, 28% reduction in formaldehyde, and 80% increase in acetaldehyde emissions. A 26% reduction in CO emissions from the oldest fleet (< MY 1991, without catalytic converter), which represents about 44% of the in-use light duty vehicles in Mexico city, can be attained when using 6 vol% ethanol-gasoline, without significant variation in hydrocarbons and NOx emissions, when compared with a 5% vol MTBE-gasoline. On the basis of the emissions results, an estimation of the change in the motor vehicle emissions of the metropolitan area of Mexico city was calculated for the year 2010 if ethanol were to be used instead of MTBE, and the outcome was a considerable decrease in all regulated and toxic emissions, despite the growing motor vehicle population.     

Fine particle emissions from on-road vehicles in the Zhujiang Tunnel, China

Little is known about the characteristics of particulate matter emissions from vehicles in China, although such information is critical in source apportionment modeling, emission inventories, and health effect studies. In this paper, we report a comprehensive characterization of PM2.5 emissions in the Zhujiang Tunnel in the Pearl River Delta region of China. The chemical speciation included elemental carbon, organic carbon, inorganic ions, trace elements, and organic compounds. The emission factors of individual species and their relative distributions were obtained for a mixed fleet of heavy-duty vehicles (19.8%) and light-duty vehicles (80.2%). In addition, separate emission factors of PM2.5 mass, elemental carbon, and organic matter for heavy-duty vehicles and light-duty vehicles also were derived. As compared to the results of other tunnel studies previously conducted, we found that the abundances and distributions of the trace elements in PM2.5 emissions were more varied. In contrast, the characteristics of the trace organic compounds in the PM2.5 emissions in our study were consistent with characteristics found in other tunnel studies and dynamometer tests. Our results suggested that vehicular PM2.5 emissions of organic compounds are less influenced by the geographic area and fleet composition and thereby are more suitable for use in aerosol source apportionment modeling implemented across extensive regions.     

Size-resolved source apportionment of airborne particle mass in a roadside environment

Airborne particulate hopanes, steranes, and polycyclic aromatic hydrocarbons (PAHs) were measured in six size fractions < 1.8 microm particle diameter at one site upwind and two sites downwind of the Interstate 5 freeway in San Diego, CA. The smallest size fraction collected was exclusively in the ultrafine size range (D(p) < 0.1 microm; PM0.1). Size distributions of hopanes, steranes, and PAHs peaked between 0.10-0.18 microm particle aerodynamic diameter with a tail extending into the PM0.1 size range. This pattern is similar to previous dynamometer studies of hopane, sterane, and PAH size distributions emitted from gasoline- and diesel-powered vehicles. Size-resolved source profiles were combined to form an "on-road" profile for motor oil, diesel, and gasoline contributions to EC and OC. The resulting equations were used to predict source contributions to the size distributions of EC and OC in the roadside environment. The method successfully accounted for the majority of the carbonaceous material in particles with diameter < 0.18 microm, with significant residual material in larger size fractions. The peak in both the measured and predicted EC size distribution occurred between 0.1-0.18 microm particle aerodynamic diameter. The predicted OC size distribution peaked between 0.1-0.18 microm particle diameter, butthe measured OC size distribution peaked between 0.56-1.0 microm particle diameter, possibly because of secondary organic aerosol formation. Predicted OC concentrations in particles with diameter < 0.18 microm were greater than measured values 18 m downwind of the roadway but showed good agreement 37 m downwind. The largest source contributions to the PM0.1 and PM0.18 size fractions were different. PM0.18 was dominated by diesel fuel and motor oil combustion products while PM0.1 was dominated by diesel fuel and gasoline fuel combustion products. Total source contributions to ultrafine (PM0.1) EC concentrations 37 m downwind of the roadway were 44 +/- 6% diesel fuel, 21 +/- 1% gasoline, 5 +/- 6% motor oil, and 30% unknown. Total source contributions to ultrafine (PM0.1) OC concentrations 37 m downwind of the roadway were 46 +/- 5% diesel fuel, 44 +/- 5% gasoline, 20 +/- 15% motor oil with a slight overprediction (11%). Diesel fuel appears to make the single largest contribution to ultrafine (PM0.1) particle mass given the fleet distribution during the current experiment.     

Measurement of emissions from air pollution sources. 5. C1-C32 organic compounds from gasoline-powered motor vehicles

Gas- and particle-phase organic compounds present in the tailpipe emissions from an in-use fleet of gasoline-powered automobiles and light-duty trucks were quantified using a two-stage dilution source sampling system. The vehicles were driven through the cold-start Federal Test Procedure (FTP) urban driving cycle on a transient dynamometer. Emission rates of 66 volatile hydrocarbons, 96 semi-volatile and particle-phase organic compounds, 27 carbonyls, and fine particle mass and chemical composition were quantified. Six isoprenoids and two tricyclic terpanes, which are quantified using new source sampling techniques for semi-volatile organic compounds, have been identified as potential tracers for gasoline-powered motor vehicle emissions. A composite of the commercially distributed California Phase II Reformulated Gasoline used in these tests was analyzed by several analytical methods to quantify the gasoline composition, including some organic compounds that are found in the atmosphere as semi-volatile and particle-phase organic compounds. These results allow a direct comparison of the semi-volatile and particle-phase organic compound emissions from gasoline-powered motor vehicles to the gasoline burned by these vehicles. The distribution of n-alkanes and isoprenoids emitted from the catalyst-equipped gasoline-powered vehicles is the same as the distribution of these compounds found in the gasoline used, whereas the distribution of these compounds in the emissions from the noncatalyst vehicles is very different from the distribution in the fuel. In contrast, the distribution of the polycyclic aromatic hydrocarbons and their methylated homologues in the gasoline is significantly different from the distribution of the PAH in the tailpipe emissions from both types of vehicles.     

Remote sensing of ammonia and sulfur dioxide from on-road light duty vehicles

This study reports the largest data set of on-road, fuel-based mass emissions of ammonia and sulfur dioxide from vehicles of known make, model year, and fuel type. Ammonia is the first pollutant observed for which the emissions decrease with increasing fleet age from 10 to 20 years. The fixed nitrogen emission ratio is 15.0% by mass and 24.7% by mole, larger than current models predict. Diesel fueled vehicles emit more SO2 than gasoline, and unexpectedly, gasoline SO2 emissions decrease continuously with newer model year vehicles.     

Optimization-based source apportionment of PM2.5 incorporating gas-to-particle ratios

A modified approach to PM2.5 source apportionment is developed, using source indicative SO2/PM2.5, CO/PM2.5, and NOx/PM2.5 ratios as constraints, in addition to the commonly used particulate-phase source profiles. Additional information from using gas-to-particle ratios assists in reducing collinearity between source profiles, a problem that often limits the source-identification capabilities and accuracy of traditional receptor models. This is especially true in the absence of speciated organic carbon measurements. In the approach presented here, the solution is based on a global optimization mechanism, minimizing the weighted error between apportioned and ambient levels of PM2.5 components, while introducing constraints on calculated source contributions that ensure that the ambient gas-phase pollutants (SO2, CO, and NOy) are reasonable. This technique was applied to a 25-month dataset of daily PM2.5 measurements (total mass and composition) at the Atlanta Jefferson Street SEARCH site. Results indicate that this technique was able to split the contributions of mobile sources (gasoline and diesel vehicles) more accurately than particulate-phase source apportionment methods. Furthermore, this technique was able to better quantify the direct contribution (primary PM2.5) of coal-fired power plants to ambient PM2.5 levels.     

Hydrogen cyanide exhaust emissions from in-use motor vehicles

Motor vehicle exhaust emissions are known to contain hydrogen cyanide (HCN), but emission rate data are scarce and, in the case of idling vehicles, date back over 20 years. For the first time, vehicular HCN exhaust emissions from a modern, in-use fleet at idle have been measured. The 14 tested light duty motor vehicles were operating at idle as these conditions are associated with the highest risk exposure scenarios (i.e., enclosed spaces). Vehicular HCN was detected in 89% of the sampled exhaust streams and did not correlate with instantaneous air-fuel-ratio or with any single, coemitted pollutant. However, a moderate correlation between HCN emissions and the product of carbon monoxide and nitric oxide emissions was observed under cold-start conditions. Fleet average, cold-start, undiluted HCN emissions were 105 +/- 97 ppbV (maximum: 278 ppbV), whereas corresponding emissions from vehicles operating under stabilized conditions were 79 +/- 71 ppbV (maximum: 245 ppbV); mean idle fleet HCN emission rates were 39 +/- 35 and 21 +/- 18 microg-min(-1) for cold-start and stabilized vehicles, respectively. The significance of these results is discussed in terms of HCN emissions inventories in the South Coast Air Basin of California and of health risks due to exposure to vehicular HCN.     

Quantifying the emission benefits of opacity testing and repair of heavy-duty diesel vehicles

The objective of this study was to begin to quantify the benefits of a smoke opacity-based (SAE J1667 test) inspection and maintenance program. Twenty-six vehicles exhibiting visible smoke emissions were recruited: 14 pre-1991 vehicles and 12 1991 and later model year vehicles. Smoke opacity and regulated pollutant emissions via chassis dynamometer were measured, with testing conducted at 1609 m above sea level. Twenty of the vehicles were then repaired with the goal of lowering visible smoke emission, and the smoke opacity testing and pollutant emissions measurements were repeated. For the pre-1991 vehicles actually repaired, pre-repair smoke opacity averaged 39% and PM averaged 5.6 g/mi. NOx emissions averaged 22.1 g/mi. After repair, the average smoke opacity had declined to 26% and PM declined to 3.3 g/mi, while NOx emissions increased to 30.9 g/mi. For the 1991 and newer vehicles repaired, pre-repair smoke opacity averaged 59% and PM averaged 2.2 g/mi. NOx emissions averaged 12.1 g/mi. After repair, the average opacity had declined to 30% and PM declined to 1.3 g/mi, while NOx increased slightly to 14.4 g/mi. For vehicles failing the California opacity test at >55% for pre-1991 and >40% for 1991 and later model years, the changes in emissions exhibited a high degree of statistical significance. The average cost of repairs was 1088 dollars, and the average is very similar for both the pre-1991 and 1991+ model year groups. Smoke opacity was shown to be a relatively poor predictor of driving cycle PM emissions. Peak CO or peak CO and THC as measured during a snap-acceleration were much better predictors of driving cycle PM emissions.     

Emission factors for gas-powered vehicles traveling through road tunnels in São Paulo, Brazil

The objective of this study was to improve the vehicular emissions inventory for the light- and heavy-duty fleet in the metropolitan area of S?o Paulo (MASP), Brazil. To that end, we measured vehicle emissions in road tunnels located in the MASP. On March 22-26, 2004 and May 04-07, 2004, respectively, CO, CO2, NOx, SO2, and volatile organic compounds (VOCs) emissions were measured in two tunnels: the Janio Quadros, which carries light-dutyvehicles; and the Maria Maluf, which carries light-duty vehicles and heavy-duty diesel trucks. Pollutant concentrations were measured inside the tunnels, and background pollutant concentrations were measured outside of the tunnels. The mean CO and NOx emission factors (in g km(-1)) were, respectively, 14.6 +/- 2.3 and 1.6 +/- 0.3 for light-duty vehicles, compared with 20.6 +/- 4.7 and 22.3 +/- 9.8 for heavy-duty vehicles. The total VOCs emission factor for the Maria Maluf tunnel was 1.4 +/- 1.3 g km(-1). The main VOCs classes identified were aromatic, alkane, and aldehyde compounds. For the heavy-duty fleet, NOx emission factors were approximately 14 times higher than those found for the light-duty fleet. This was attributed to the high levels of NOx emissions from diesel vehicles.     

Measurements of OVOCs and NMHCs in a Swiss highway tunnel for estimation of road transport emissions

Eighteen oxygenated volatile organic compounds (OVOCs) and eight nonmethane hydrocarbons (NMHCs) were measured continuously during a two-week campaign in 2004 in the Gubrist highway tunnel (Switzerland). The study aimed to estimate selected OVOC and NMHC emissions of the current vehicle fleet under highway conditions. For the measured OVOCs the highest EFs were found for ethanol (9.7 mg/km), isopropanol (3.2 mg/km), and acetaldehyde (2.5 mg/km), followed by acetone, benzaldehyde, and acrolein. Formaldehyde, the most abundant OVOC measured in other studies, was not measured by the method applied. Relative emissions of the measured OVOCs were estimated to contribute approximately 6 and 4% to the total road traffic VOC emissions from Switzerland and Europe, respectively. Results are compared with those from previous studies from the same tunnel performed in 1993 and 2002, and from campaigns in other tunnels. A continuous reduction in the emission factors (EFs) was determined for all measured compounds from 1993 until 2004. The relative contributions of light-duty vehicles (LDV) and heavy-duty vehicles (HDV) to the total emissions indicated that OVOCs were mainly produced by the HDVs, whereas LDVs dominated the production of the NMHCs.     

Climate and health relevant emissions from in-use Indian three-wheelers fueled by natural gas and gasoline

Auto-rickshaws in India use different fuels and engine technologies, with varying emissions and implications for air quality and climate change. Chassis dynamometer emission testing was conducted on 30 in-use auto-rickshaws to quantify the impact of switching from gasoline to compressed natural gas (CNG) in spark-ignition engines. Thirteen test vehicles had two-stroke CNG engines (CNG-2S) and 17 had four-stroke CNG engines (CNG-4S), of which 11 were dual-fuel and operable on a back-up gasoline (petrol) system (PET-4S). Fuel-based emission factors were determined for gaseous pollutants (CO(2), CH(4), NO(X), THC, and CO) and fine particulate matter (PM(2.5)). Intervehicle variability was high, and for most pollutants there was no significant difference (95% confidence level) between "old" (1998-2001) and "new" (2007-2009) age-groups within a given fuel-technology class. Mean fuel-based PM(2.5) emission factor (mean (95% confidence interval)) for CNG-2S (14.2 g kg(-1) (6.2-26.7)) was almost 30 times higher than for CNG-4S (0.5 g kg(-1) (0.3-0.9)) and 12 times higher than for PET-4S (1.2 g kg(-1) (0.8-1.7)). Global warming commitment associated with emissions from CNG-2S was more than twice that from CNG-4S or PET-4S, due mostly to CH(4) emissions. Comprehensive measurements and data should drive policy interventions rather than assumptions about the impacts of clean fuels.     

Evaluation of the vehicle inspection/maintenance program in the Metropolitan Area of Mexico City

The Inspection/Maintenance Program in the Metropolitan Area of Mexico City (MAMC) mandates a test every 6 months for all gasoline motor vehicles as one of the strategies to decrease emissions of vehicular pollutants. FTP-75 and ASM procedures were performed in our facilities to a fleet of 108 in-use motor vehicles before and after the approval of the I/M mandatory test When our laboratory-simulated ASM data were compared with those of the official certificate, a large difference was observed between them. On the other hand, audits at the test-only centers indicate poor maintenance of the analytical instruments and dynamometers. On the basis of our FTP results, an estimation of the emissions change for the MAMC fleet shows a net 4% decrease in CO emissions, while total hydrocarbons and NOx increased 9 and 8%, respectively. Our results indicate that the I/M system in the MAMC lacks the technical capability and investment to ensure that software and hardware are properly maintained, calibrated, and upgraded. Sometimes limited attention is paid to ensure adequate training of inspectors, auditors, and quality control staff.     

Real-time gaseous, PM and ultrafine particle emissions from a modern marine engine operating on biodiesel

Emissions from harbor-craft significantly affect air quality in populated regions near ports and inland waterways. This research measured regulated and unregulated emissions from an in-use EPA Tier 2 marine propulsion engine on a ferry operating in a bay following standard methods. A special effort was made to monitor continuously both the total Particulate Mass (PM) mass emissions and the real-time Particle Size Distribution (PSD). The engine was operated following the loads in ISO 8178-4 E3 cycle for comparison with the certification standards and across biodiesel blends. Real-time measurements were also made during a typical cruise in the bay. Results showed the in-use nitrogen oxide (NOx) and PM(2.5) emission factors were within the not to exceed standard for Tier 2 marine engines. Comparing across fuels we observed the following: a) no statistically significant change in NO(x) emissions with biodiesel blends (B20, B50); b) ～ 16% and ～ 25% reduction of PM(2.5) mass emissions with B20 and B50 respectively; c) a larger organic carbon (OC) to elemental carbon (EC) ratio and organic mass (OM) to OC ratio with B50 compared to B20 and B0; d) a significant number of ultrafine nuclei and a smaller mass mean diameter with increasing blend-levels of biodiesel. The real-time monitoring of gaseous and particulate emissions during a typical cruise in the San Francisco Bay (in-use cycle) revealed important effects of ocean/bay currents on emissions: NO(x) and CO(2) increased 3-fold; PM(2.5) mass increased 6-fold; and ultrafine particles disappeared due to the effect of bay currents. This finding has implications on the use of certification values instead of actual in-use emission values when developing inventories. Emission factors for some volatile organic compounds (VOCs), carbonyls, and poly aromatic hydrocarbons (PAHs) are reported as supplemental data.     

A systems evaluation on the effectiveness of a catalyst retrofit program in China

A low-cost, rare-earth oxide (REO) catalyst has been recommended as part of China's retrofit program for Chinese carbureted vehicles. This study evaluated: (1) the emission reduction efficiency of the REO catalyst during chassis dynamometer testing on the FTP cycle; (2) the effect that fuel properties had on tailpipe emissions and catalyst efficiency; (3) the importance of vehicle premaintenance as part of a retrofit protocol; and (4) the emission reductions obtained following implementation of the program. Results also show that current in-use Chinese noncatalyst, carbureted vehicles operate excessively rich, resulting in extremely high emissions of CO, gaseous toxic compounds, and other non-methane hydrocarbon species (NMHC). Preretrofit maintenance alone has the potential to reduce these emissions by approximately 50%. Dynamometer emission tests showed emissions reductions of >95% for hydrocarbons, CO, and gaseous toxics after retrofit of the REO catalyst. In particular, the relative unit health risk associated with the decrease in emissions of airborne toxic compounds using unleaded Chinese fuel was reduced from 6.33 to 0.30. (Use of low-sulfur California Phase II gasoline rather than current in-use Chinese fuel reduced emissions further.) Following implementation of the program, a follow-up study showed that in-use emissions benefits were considerably less than anticipated, primarily because of poor quality control at the retrofit service centers, a less aggressive preretrofit maintenance procedure, and unauthorized modification to the recommended retrofit control system. Overall results indicate that a carefully controlled retrofit program using REO catalyst technology can reduce emissions significantly. However, well-defined implementation guidelines, and strict adherence to these guidelines are needed to achieve maximum benefits.     

Carbonyl and nitrogen dioxide emissions from gasoline- and diesel-powered motor vehicles

Carbonyls can be toxic and highly reactive in the atmosphere. To quantify trends in carbonyl emissions from light-duty (LD) vehicles, measurements were made in a San Francisco Bay area highwaytunnel bore containing essentially all LD vehicles during the summers of 1999, 2001, and 2006. The LD vehicle emission factor for formaldehyde, the most abundant carbonyl, did not change between 1999 and 2001, then decreased by 61 +/- 7% between 2001 and 2006. This reduction was due to fleet turnover and the removal of MTBE from gasoline. Acetaldehyde emissions decreased by 19 +/- 2% between 1999 and 2001 and by the same amount between 2001 and 2006. Absent the increased use of ethanol in gasoline after 2003, acetaldehyde emissions would have further decreased by 2006. Carbonyl emission factors for medium- (MD) and heavy-duty (HD) diesel trucks were measured in 2006 in a separate mixed-traffic bore of the tunnel. Emission factors for diesel trucks were higher than those for LD vehicles for all reported carbonyls. Diesel engine exhaust dominates over gasoline engines as a direct source of carbonyl emissions in California. Carbonyl concentrations were also measured in liquid-gasoline samples and were found to be low (< 20 ppm). The gasoline brands that contained ethanol showed higher concentrations of acetaldehyde in unburned fuel versus gasoline that was formulated without ethanol. Measurements of NO2 showed a yearly rate of decrease for LD vehicle emissions similar to that of total NOx in this study. The observed NO2/NOx ratio was 1.2 +/- 0.3% and 3.7 +/- 0.3% for LD vehicles and diesel trucks, respectively.     

The effects of the catalytic converter and fuel sulfur level on motor vehicle particulate matter emissions: gasoline vehicles

Scanning mobility and electrical low-pressure impactor particle size measurements conducted during chassis dynamometer testing reveal that neither the catalytic converter nor the fuel sulfur content has a significant effect on gasoline vehicle tailpipe particulate matter (PM) emissions. For current technology, port fuel injection, gasoline engines, particle number emissions are < or = 2 times higher from vehicles equipped with blank monoliths as compared to active catalysts, insignificant in contrast to the 90+% removal of hydrocarbons. PM mass emission rates derived from the size distributions are equal within the experimental uncertainty of 50-100%. Gravimetric measurements exhibit a 3-10-fold PM mass increase when the active catalyst is omitted, which is attributed to gaseous hydrocarbons adsorbing onto the filter medium. Both particle number and gravimetric measurements show that gasoline vehicle tailpipe PM emissions are independent (within 2 mg/mi) of fuel sulfur content over the 30-990 ppm concentration range. Nuclei mode sulfate aerosol is not observed in either test cell measurements or during wind tunnel testing. For three-way catalyst equipped vehicles, the principal sulfur emission is SO2; however a sulfur balance is not obtained over the drive cycle. Instead, sulfur is stored on the catalyst during moderate driving and then partially removed during high speed/load operation.