Analysis of Evaporative and Exhaust-Related On-Board Diagnostic (OBD) Readiness Monitors and DTCs Using I/M and Roadside Data.

Under contract to the EPA, Eastern Research Group analyzed light-duty vehicle OBD monitor readiness and diagnostic trouble codes (DTCs) using inspection and maintenance (I/M) data from four states. Results from roadside pullover emissions and OBD tests were also compared with same-vehicle I/M OBD results from one of the states. Analysis focused on the evaporative emissions control (evap) system, the catalytic converter (catalyst), the exhaust gas recirculation (EGR) system and the oxygen sensor and oxygen sensor heater (O2 system). Evap and catalyst monitors had similar overall readiness rates (90% to 95%), while the EGR and O2 systems had higher readiness rates (95% to 98%). Approximately 0.7% to 2.5% of inspection cycles with a "ready" evap monitor had at least one stored evap DTC, but DTC rates were under 1% for the catalyst and EGR systems, and under 1.1% for the O2 system, in the states with enforced OBD programs. Monitor readiness decreased, and DTC rates increased, as vehicles aged. DTCs were typically limited to a small subset of all possible DTCs for any particular system. For the on-road versus I/M analysis, lower overall readiness rates and higher overall DTC rates occurred during the roadside test than during the I/M test, and the prevalence of roadside DTCs was shown to decrease around the time of the vehicle's I/M test, possibly indicating some positive I/M influence of reducing on-road DTCs. Roadside Acceleration Simulation Mode (ASM) fail rates also decreased around the time of the I/M test, suggesting a positive influence of I/M programs on reducing vehicle emissions.

Real-world exhaust temperature and engine load distributions of on-road heavy-duty diesel vehicles in various vocations.

Real-world vehicle and engine activity data were collected from 90 heavy-duty vehicles in California, United States, most of which have engine model year 2010 or newer and are equipped with selective catalytic reduction (SCR). The 90 vehicles represent 19 different groups defined by a combination of vocational use and geographic region. The data were collected using advanced data loggers that recorded vehicle speed, position (latitude and longitude), and more than 170 engine and aftertreatment parameters (including engine load and exhaust temperature) at the frequency of one Hz. This article presents plots of real-world exhaust temperature and engine load distributions for the 19 vehicle groups. In each plot, both frequency distribution and cumulative frequency distribution are shown. These distributions are generated using the aggregated data from all vehicle samples in each group.

Real-world exhaust temperature profiles of on-road heavy-duty diesel vehicles equipped with selective catalytic reduction.

On-road heavy-duty diesel vehicles are a major contributor of oxides of nitrogen (NOx) emissions. In the US, many heavy-duty diesel vehicles employ selective catalytic reduction (SCR) technology to meet the 2010 emission standard for NOx. Typically, SCR needs to be at least 200°C before a significant level of NOx reduction is achieved. However, this SCR temperature requirement may not be met under some real-world operating conditions, such as during cold starts, long idling, or low speed/low engine load driving activities. The frequency of vehicle operation with low SCR temperature varies partly by the vehicle's vocational use. In this study, detailed vehicle and engine activity data were collected from 90 heavy-duty vehicles involved in a range of vocations, including line haul, drayage, construction, agricultural, food distribution, beverage distribution, refuse, public work, and utility repair. The data were used to create real-world SCR temperature and engine load profiles and identify the fraction of vehicle operating time that SCR may not be as effective for NOx control. It is found that the vehicles participated in this study operate with SCR temperature lower than 200°C for 11-70% of the time depending on their vocation type. This implies that real-world NOx control efficiency could deviate from the control efficiency observed during engine certification.

Measurement and Analysis of the Operations of Drayage Trucks in the Houston Area in Terms of Activities and Exhaust Emissions.

The effects of exhaust emissions on public welfare have prompted the US Environmental Protection Agency to take various actions toward understanding, modeling, and reducing air pollution from vehicles. This study was performed to better understand exhaust emissions of heavy-duty diesel-powered tractor-trailer trucks that operate in drayage service, which involves the moving of shipping containers to or from port terminals. The study involved the use of portable emissions measurement systems (PEMS) to measure both gaseous and particulate matter (PM) mass emission rates and record various vehicle and engine parameters from the test trucks as they performed their normal drayage service. These measurements were supplemented with port terminal gate entry/exit logs for all drayage trucks entering the two Port of Houston Authority container terminals. The datasets were combined to analyze model year characteristics of drayage trucks over time, evaluate port visit frequencies and durations, assess geographic distributions of trucks that perform port service, and estimate the pollutant emissions related to drayage operations. When compared to certification results, measured pollutant emissions generally exceeded certification standards in terms of nitrogen oxides and PM, although this difference may be partly because these vehicles were not tested on certification cycles but rather actual in-use operation. The findings of this work indicate that less than 3.5 percent of gaseous drayage truck emissions are released during operation within port terminals, as drayage trucks operate at higher engine loads during their extensive travels throughout the region around the port.

Evaluation of EDAR vehicle emissions remote sensing technology.

Despite much work in recent years, vehicle emissions remain a significant contributor in many areas where air quality standards are under threat. Policy-makers are actively exploring options for next generation vehicle emission control and local fleet management policies, and new monitoring technologies to aid these activities. Therefore, we report here on findings from two separate but complementary blind evaluation studies of one new-to-market real-world monitoring option, HEAT LLC's Emission Detection And Reporting system or EDAR, an above-road open path instrument that uses Differential Absorption LIDAR to provide a highly sensitive and selective measure of passing vehicle emissions. The first study, by Colorado Department of Public Health and Environment and Eastern Research Group, was a simulated exhaust gas test exercise used to investigate the instrumental accuracy of the EDAR. Here, CO, NO, CH4 and C3H8 measurements were found to exhibit high linearity, low bias, and low drift over a wide range of concentrations and vehicle speeds. Instrument accuracy was high (R2 0.996 for CO, 0.998 for NO; 0.983 for CH4; and 0.976 for C3H8) and detection limits were 50 to 100ppm for CO, 10 to 30ppm for NO, 15 to 35ppmC for CH4, and, depending on vehicle speed, 100 to 400ppmC3 for C3H8. The second study, by the Universities of Birmingham and Leeds and King's College London, used the comparison of EDAR, on-board Portable Emissions Measurement System (PEMS) and car chaser (SNIFFER) system measurements collected under real-world conditions to investigate in situ EDAR performance. Given the analytical challenges associated with aligning these very different measurements, the observed agreements (e.g. EDAR versus PEMS R2 0.92 for CO/CO2; 0.97 for NO/CO2; ca. 0.82 for NO2/CO2; and, 0.94 for PM/CO2) were all highly encouraging and indicate that EDAR also provides a representative measure of vehicle emissions under real-world conditions.

Methods of characterizing the distribution of exhaust emissions from light-duty, gasoline-powered motor vehicles in the U.S. fleet.

Mobile sources significantly contribute to ambient concentrations of airborne particulate matter (PM). Source apportionment studies for PM10 (PM < or = 10 microm in aerodynamic diameter) and PM2.5 (PM < or = 2.5 microm in aerodynamic diameter) indicate that mobile sources can be responsible for over half of the ambient PM measured in an urban area. Recent source apportionment studies attempted to differentiate between contributions from gasoline and diesel motor vehicle combustion. Several source apportionment studies conducted in the United States suggested that gasoline combustion from mobile sources contributed more to ambient PM than diesel combustion. However, existing emission inventories for the United States indicated that diesels contribute more than gasoline vehicles to ambient PM concentrations. A comprehensive testing program was initiated in the Kansas City metropolitan area to measure PM emissions in the light-duty, gasoline-powered, on-road mobile source fleet to provide data for PM inventory and emissions modeling. The vehicle recruitment design produced a sample that could represent the regional fleet, and by extension, the national fleet. All vehicles were recruited from a stratified sample on the basis of vehicle class (car, truck) and model-year group. The pool of available vehicles was drawn primarily from a sample of vehicle owners designed to represent the selected demographic and geographic characteristics of the Kansas City population. Emissions testing utilized a portable, light-duty chassis dynamometer with vehicles tested using the LA-92 driving cycle, on-board emissions measurement systems, and remote sensing devices. Particulate mass emissions were the focus of the study, with continuous and integrated samples collected. In addition, sample analyses included criteria gases (carbon monoxide, carbon dioxide, nitric oxide/nitrogen dioxide, hydrocarbons), air toxics (speciated volatile organic compounds), and PM constituents (elemental/organic carbon, metals, semi-volatile organic compounds). Results indicated that PM emissions from the in-use fleet varied by up to 3 orders of magnitude, with emissions generally increasing for older model-year vehicles. The study also identified a strong influence of ambient temperature on vehicle PM mass emissions, with rates increasing with decreasing temperatures.

Temperature effects on particulate matter emissions from light-duty, gasoline-powered motor vehicles.

The Kansas City Light-Duty Vehicle Emissions Study (KCVES) measured exhaust emissions of regulated and unregulated pollutants from 496 vehicles recruited in the Kansas City metropolitan area in 2004 and 2005. Vehicle emissions testing occurred during the summer and winter, with the vehicles operated at ambient temperatures. One key component of this study was the investigation of the influence of ambient temperature on particulate matter (PM) emissions from gasoline-powered vehicles. A subset of the recruited vehicles were tested in both the summer and winter to further elucidate the effects of temperature on vehicle tailpipe emissions. The study results indicated that PM emissions increased exponentially as temperature decreased. In general, PM emissions doubled for every 20 degrees F drop in ambient temperature, with these increases independent of vehicle model year. The effects of temperature on vehicle emissions was most pronounced during the initial start-up of the vehicle (cold start phase) when the vehicle was still cold, leading to inefficient combustion, inefficient catalyst operation, and the potential for the vehicle to be operating under fuel-rich conditions. The large data set available from this study also allowed for the development of a model to describe temperature effects on PM emission rates due to changing ambient conditions. This study has been used as the foundation to develop PM emissions rates, and to model the impact of ambient temperature on these rates, for gasoline-powered vehicles in the EPA's new regulatory motor vehicle emissions model, MOVES.