Environ. Sci. Technol. 2009 43, 9507–9511
Characteristics of Diesel Truck Emission in China Based on Portable Emissions Measurement Systems H U A N L I U , † K E B I N H E , * ,† JAMES M. LENTS,‡ QIDONG WANG,† AND SEBASTIAN TOLVETT‡ Department of Environmental Science and Engineering, Tsinghua University, Beijing, People’s Republic of China, and International Sustainable Systems Research Center, La Habra, California
Received July 8, 2009. Revised manuscript received September 7, 2009. Accepted October 1, 2009.
Seventy-five diesel vehicles were measured in China using a portableemissionsmeasurementsystem(PEMS).Particularmatter (PM) emission factors and gaseous emission factors for Euro 0 (E0), Euro 1 (E1), Euro 2 (E2), and Euro 3 (E3) trucks were obtained under highway, urban, and rural driving conditions. Vehicle emission regulations in China have successfully reduced carbon monoxide (CO), hydrocarbons (HC) and PM by 62, 56, and 72% on average. Most of the emission reductions were achieved when the control technology went from E0 to E1 in Xi’an, and E2 to E3 in Beijing, which resulted in PM reductions of 79% associated with highway driving and 60% associated with urban or rural driving. Emission levels of oxides of nitrogen (NOX) were not improved from previous emission control steps. Compared with Xi’an, the emission rate is lower in Beijing, which is strong evidence of the effectiveness of the present comprehensive emission control strategy in Beijing. Emissions were grouped into driving bins that corresponded to the energy demand placed on the vehicles. By using this binning approach, it was found that E3 trucks were successfully controlling the high emission rates in aggressive driving bins, which led to the low average emission for E3 trucks.
Introduction Vehicles are important sources of carbon monoxide (CO), hydrocarbons (HC), oxides of nitrogen (NOX), and particular matter (PM) (1, 2). As one of the major vehicle types, diesel trucks are getting more attention due to their contribution to the emissions inventory for NOX and PM (3-6). Since most of the cities in China have restrictions on heavy-duty trucks, the main type of trucks operated in city areas are delivery trucks, known as light-duty trucks (7). China has adopted aggressive truck emission control regulations to address deteriorating air quality. The nation is implementing the European vehicle emission regulation system. In 2000, China adopted the Euro1 (E1) standard, about 8 years after Europe implemented this requirement. China has shortened this gap to 5 years by adopting Euro4 (E4) in 2010. Some cities, such * Corresponding author phone: 86-10-62781889; fax: 86-1062781889; e-mail: hekb@ tsinghua.edu.cn. † Tsinghua University. ‡ International Sustainable Systems Research Center. 10.1021/es902044x CCC: $40.75
Published on Web 11/10/2009
2009 American Chemical Society
as Beijing, have more aggressive adoption schedules to meet local air quality improvement needs (8) (Supporting Information Table SI-S1). Research on truck emissions has been carried out in China in recent years. To investigate the fleet average emissions, tunnel and roadside measurements have been carried out (9-14). In recent years, chassis dynamometer tests and onboard tests with portable emissions measurement systems (PEMS) have become important approaches for vehicle emission research worldwide to obtain emission characteristics directly from the tailpipe (15, 16). However, most of the on-board vehicle emission measurements in China have focused on gaseous pollutants from cars (17, 18). The database on PM emission factors, especially for diesel trucks, is very limited. The goal of this research was to measure emissions from diesel trucks under actual on-road driving conditions using a PEMS. Beijing and Xi’an were chosen as the cities where testing would be conducted. Beijing was chosen for testing since it has the strictest vehicle emission regulations in China. Xi’an was chosen as an example of a more typical city in China. This study aims to (a) set up an emission factor database for both gaseous (EFgaseous) and PM (EFPM) emissions for diesel trucks in China, based on highway, urban, and rural driving conditions in Beijing and Xi’an; (b) Compare the emission factors of this research with other studies carried out in China; (c) evaluate the effects of transitioning from non-Euro Standard (E0) to the Euro3 Standard (E3); and (d) analyze the mechanisms by which truck emissions have been improved by using a bin methodology to look at specific operation/power episodes.
Experimental Details Testing Trucks. On-board vehicle emission tests were carried out in June, 2007 in Beijing and April, 2008 in Xi’an. A total of 75 vehicles were tested, the detailed information concerning the testing is shown in SI Table SI-S2 and Table SI-S3). The vehicles were recruited from transportation companies and from the government. The typical combined load for a truck during testing was its approximate full carrying capacity, including sand bags and instruments. These trucks are classified based on emission standard categories: E0, E1, E2, and E3. Instruments. A SEMTECH-D PEMS was used for this testing. The SEMTECH-D employs a flame ionization detector (FID) to measure THC, a non-dispersive ultraviolet (NDUV) analyzer to measure NOX, a non-dispersive infrared (NDIR) analyzer to measure CO and CO2, and an electrochemical sensor to measure oxygen (O2) (19). The testing error (the difference between PEMS and reference laboratories) was studied by the measurement allowance steering committee (MASC) to ensure PEMS accuracy as it applies to in-use testing (20). These studies demonstrated the system to be both accurate and precise, meeting the Section 40 Code of Federal Regulations (CFR) standards, Part 1065 (21, 22). Calibration gases were used to ensure the accuracy of the system before and after each individual test. A Dekati Mass Monitor (DMM) was used to record second by second PM emissions. The DMM ionizes particulates, collects them by size, and records them in the range from 7 nm to 1.2 µm (23). Based on previous research, the DMM has proved to be an adequate instrument for measuring the mass concentration of engine exhaust, with results comparable to those from the standard gravimetric filter method. In addition, the DMM provides realtime second-by-second data of the mass concentration during transient test cycles (24). Vehicle speed, altitude, VOL. 43, NO. 24, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Summary of emission factors in this study and recent researches (a) OB: on-board; CD: Chassis dynamometer; GZ: Guangzhou; SH: Shanghai; BJ: Beijing; XA: Xi’an; HK: Hong Kong; TW: Taiwan; HT: heavy-duty truck; DT: diesel truck; DB: diesel bus; Hwy: highway driving cycle; Urban: urban driving cycle; Rural: rural driving cycle; (b) The location and average speed for each study are included in the figures, e.g.: Rural, 10. latitude, and longitude were logged continuously using a GPS. A whole-exhaust, mass flow measurement device (4′′ SEMTECH EFM) built by Sensors Incorporated, was used to measure the exhaust flow rate based on pitot tube technology. Two samples of the exhaust were extracted from the mass flow measurement device and routed to the analyzer systems (SI Figure SI-S1). One of the samples was sent directly to the SEMTECH-D gaseous measurement device through a heated line. The second sample was routed through an ejector dilution device that mixed clean air with the sample at a controlled rate range. The exhaust sample in the second train was heated to 110 °C to avoid water and organic condensation. The dilution device was constructed by researchers using a standard flow measurement process. A Dwyer differential pressure transducer, which is accurate to 0.25% of full scale, was used to measure the dilution rate on a second by second basis. The dilution rates in the dilution device varied from “20 to 1” to “30 to 1” depending on the vehicle tested and the exhaust flow rate. A temperature and humidity measure9508
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ment device also provided second by second data on the temperature and humidity of the engine intake air. A schematic plot of the test system (SI Figure SI-S2) and the discussion on system error control (SI Table SI-S4) is included in the SI. On-Road Test Routes. Several papers have discussed the effects of driving cycle on PM emissions and regulated gaseous emissions from diesel vehicles (25, 26). Most of the delivery trucks in China travel from intercity highways to limited access type roadways (called ring roads in China) and then to the surface streets. Thus, typical driving cycles in Beijing include highway and urban driving segments. The highway test route is 19 km, including part of Beijing-Tianjin highway and fourth ring road. Urban routes are defined as arterial roads inside the fourth ring road. The total length of the tested urban route is 4 km. The average speeds on highway and urban roads are 51 and 12 km/h in Beijing. To mimic this type of driving in Xi’an, highway and rural roads were included in the test route. The highway routes in Xi’an include
FIGURE 2. Emission factors based on per fuel consumption. * E0 category has only one truck, so there’s no std. error bars for E0.
FIGURE 3. Driving bin definition by using VSP and stress. part of the airport freeway and the Xi’an-Xian Yang highway, with a total length of 19 km. The rural test routes are selected from arterial roads located in the northeast suburb of Xi’an, while total length is 4 km. Average speeds on highway and rural routes are 48 and 21 km/h The driving patterns observed for the various vehicles in this test were reasonably consistent throughout the day. A total of 1500 km (940 miles) of on-road driving and 43 h of continuous sampling were performed over the tests. An example of a typical test driving cycle can be found in SI (Figure SI-S3).
Results and Discussion On-Road Driving Based Emission Factors and Comparison. The on-road testing results are presented on a g/km basis for the urban, rural, and highway segments in Beijing and Xi’an (Figure 1). The values in the figures represent averages over all tests for a particular vehicle class based on the realworld travel segments in Beijing and Xi’an. The truck emission factors from other studies conducted in China are also provided in the figures, including tunnel (14, 11, 13, 10, 27), roadside (12, 28), on-board (17), and dynamometer tests (14). This data represents all of the presently available emissions measurements for diesel vehicles in China. This study added to the database of instantaneous emissions from on-road vehicles and provides a comprehensive emission factor under all kinds of common driving conditions as a foundation for further research. The EFgaseous measured in Beijing are comparable to the results for the Shanghai diesel trucks (17). These two studies
utilized similar instruments for measuring gaseous pollutants. Most of the tunnel and roadside research programs measured higher EFgaseous than was measured in Beijing. The results from this study are higher than the dynamometer testing placing our results between the dynamometer and other studies. The differences in measurements likely reflect the differences in driving at the point of measurement for the different tests, illustrating the importance of considering driving patterns when interpreting test data. PM emission factors for diesel trucks are of limited availability in China at this time. All the previous researchers make no vehicle classification based on emission standards which makes it difficult to compare emission factors. The emission factors for E1 and newer classes in this research are lower than others. It should be noted that test cycles and sampling methods are not the same across these studies and that the variability in results are as likely to be attributed to these factors as to differences in actual emissions. Emission Factors Based on Fuel Consumption. To better compare the vehicle emission control measures, it is necessary to exclude the influence of engine size. Emissions per unit fuel were calculated to facilitate this comparison. A carbon balance formula (eq 1) was used to convert the emission factors from units of g/km to g/kg of fuel. PM(g/kg) )
PM(g/km) × Wc/diesel (0.866 × HC(g/km) + 0.429 × CO(g/km) + 0.273 × CO2(g/km)) × Fdiesel (1)
Wc/diesel, carbon contain in diesel, g/L. Here use 735 g carbon per liter diesel; Fdiesel, kg/L, generally 0.85 kg/L. Figure 2 includes a fuel based emission factor matrix of four species, four emission standards, and four driving routes. The following three sections are detailed discussion based in Figure 2. Emission Improvements from E1 to E3 Trucks in Beijing. Comparing the fuel based emission factors (Figure 2), the reduction percentage of PM emissions is bigger from VOL. 43, NO. 24, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 4. Comparison of emission rates among truck categories by using bin methodology. E2 to E3 than from E1 to E2 in Beijing. From the E2 to E3 estimate of vehicle revolutions per minute with the average category, the reduction of PM emissions is 79% for the of the VSP in the 0-15 s before the measurement of interest. highway driving cycle and 68% for the urban driving cycles. Stress is an empirically derived parameter to reflect the The HC and CO emissions also improved with more stringent emission influence from vehicle status due to high engine emissions standards from E1 to E3 trucks. With the two stages rpm and load on the catalyst just prior to the event of interest. of improvement, the total reduction of HC is 80% for highway The equations to calculate VSP and stress can be found in driving and 56% for urban driving. For CO, the emissions previous work (7, 35). For this research, bins are classified were cut by 47% for highway and 29% for urban driving by both VSP and stress (Figure 3) to develop the micro comparing E1 to E3 trucks. NOX emission from E3 trucks is emission rates based on second-by-second driving conditions. a lower than E2, but similar to E1 trucks. Average micro emission rates were calculated for each Emission Improvements from E0 to E2 Trucks in Xian. bin by vehicle category (Figure 4). To ensure the credibility The trucks in Xi’an were all certified to E2 or older standards, of the results, bins with logged results of less than 0.5% of so there are no E3 trucks in this database. There was only the total were not calculated. one E0 truck in the randomly selected Xi’an vehicle test fleet. A significant emission reduction from E0 to E3 truck The PM, HC, and CO emissions improved considerably from categories was found for HC, CO, and PM in all bins, especially E0 to E2 trucks (Figure 2). The greatest improvements were for the higher VSP bins (bin 6-10, 16-20, and 26-30). found between the E0 and E1 trucks for CO, HC, and PM. Advanced vehicle technologies in the newer truck categories The EFPM for E1 trucks are 50% of those of E0 trucks. From focused on reducing emissions in high VSP bins caused by E1 to E2, there is a 20-50% further cut in PM, CO, and HC. aggressive driving or high load, which resulted in an overall Comparison between Beijing and Xi’an. Compared with reduction in vehicle emissions. From the data analysis, no Xi’an, the EFPM in Beijing was 20-50% lower for the E1 and reduction has been observed from E1 to E3 for NOX (Figure E2 group (P ) 0.049). NOX was 15-30% lower in Beijing than 4). This result is not consistent with the standards. It should in Xi’an (p ) 0.004) while CO was 50-70% lower (p ) 0.0001). be noted that only one vehicle was tested in E0 group, which The Beijing test truck fleet age is older than that from Xi’an is not enough to reflect the NOX emission level of E0 trucks. in the same category, even though, the emission rate is lower in Beijing. The emissions performance of trucks in Beijing Acknowledgments is strong evidence of the effectiveness of its present comWe express thanks to the sponsors of the Energy Foundation. prehensive emission control strategy. A strict inspection and The work at Tsinghua University was supported by China’s maintenance (I/M) system and low sulfur fuels are key National Basic Research Program (2005CB422201), China’s contributors to the low diesel emission rates in Beijing (29). National High Technology Research and Development The 350 ppm low sulfur diesel standard was implemented Program (2006AA06A305), and the National Natural Science in Beijing in 2005 and an even lower (50 ppm) standard was Foundation of China (20625722). implemented in 2008. The sulfur standard for diesel in the rest of China is recommended to be 500 ppm. The reduction associated with emission controls was more Supporting Information Available effective on highway than on urban or rural segments. No A detailed description of the tested trucks, measurement constant improvement was found for NOX emission from E0 errors, driving cycle, dilution system and the schematic plot to E3 trucks in both Beijing and Xi’an. of the test system are presented. This material is available Analysis of the Emission Reduction Mechanism Based free of charge via the Internet at http://pubs.acs.org. on Driving Bins. vehicle specific power (VSP) is the power demand on the engine per unit vehicle mass, which can be Literature Cited calculated from driving data. Many scholars use VSP to establish emission factor models since VSP shows better (1) Yanowitz, J.; McCormick, R. L.; Graboski, M. S. In-use emissions correlation with pollutant emission rates than other activity from heavy-duty diesel vehicles. Environ. Sci. Technol. 2000, 34 (5), 729–740. parameters (30-34). Engine stress (stress) combines an 9510
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