THE WORLD BANK South Asia Urban Air Quality Management Briefing Note No. 10 Tackling Diesel Emissions from In-use Vehicles Black smoke belching out of diesel buses and trucks has come to shape the public image of air pollution in many cities. What causes diesel vehicles to be so visibly polluting? Is controlling smoke the best way to address the health impact of diesel emissions? What can we learn from other countries' experience in identifying and repairing gross diesel polluters? W orldwide, diesel vehicles are attracting more to specifications on the return segment. When trucks are and more attention from policymakers. As routinelyoverloaded,thefollowingeffectsaretypicallyseen: concerns about greenhouse emissions from the M The engine has to work harder to produce the power transport sector grow, diesel is increasingly seen as a more needed, resulting in more smoke, especially among efficient fuel alternative to gasoline. As a result, future older engines. worldwide demand growth for motor fuels is anticipated to focus on diesel, while demand growth for gasoline is M Working the vehicle harder tends to increase wear (affecting the engine, tires, brakes, and other vehicle likely to stagnate. components), but the vehicle is often not serviced any At the same time, diesel exhaust contains harmful gases, morefrequently.Asaresult,theengineusuallyoperates liquid droplets and solid particles. The majority of the in a worse state of repair than a vehicle that is not particles are sub-micron in size, the size fraction routinely overloaded. considered most damaging to health, and contain carbon, M Because the vehicle requires more power when organics, sulfates and traces of metallic components. overloaded, there is a tendency to over-fuel the engine. Emerging evidence about the negative health effects of Over-fueling in turn is a significant cause of higher diesel emissions has raised increasing concern, especially black smoke emissions. as chronic inhalation exposure to diesel particles has been shown to pose not only a chronic respiratory hazard, but In industrial countries, the more professional truck fleets also a potential cancer hazard. have learnt that they are financially better off in the long run when they use newer trucks and operate within the In South Asia, as in the rest of the world, emissions from vehicle specifications. This dramatically reduces their in-use vehicles are especially problematic. This note maintenance costs, and virtually eliminates vehicles describes the major causes of high emissions, means of breakingdownontheroad(aparticularlyhigh-costproblem mitigating the emissions, and approaches to improving the for trucks carrying perishable cargo). The underlying monitoring of both new and old diesel vehicles. conditions needed to promote this way of thinking, which Causes of High Smoke Emissions can have a positive impact on both environment and safety, have yet to occur for most truckers in South Asia. Arecentstudyinvestigatingcausesofhighsmokeemissions from diesel vehicles in India [1] identified overloading and Lack of preventive maintenance lack of preventive maintenance as two major causes, with Many automotive repair garages in South Asia are under- the problem being exacerbated by inferior quality engine equipped and in need of mechanic training. The prevalent replacement parts and fuel adulteration (for fuel culture of repairing vehicles when they break down rather adulteration, see Briefing Note No. 7 [2]). than programming preventive maintenance is both the Overloading cause and effect of the lack of qualified technicians using Trucks worldwide have traditionally been loaded to the good diagnostic and repair equipment. Rigorously maximum possibleoften well beyond the designed load enforcing emissions standards is the first step towards of the vehiclein order to increase revenue and profit. In creating demand for upgrading and expanding service and repair facilities. India, the principal long distance goods carrier is a two- axle, 9-ton truck. These are often overloaded to 14­20 Mal-functioning and incorrect adjustment (through tons on outward-bound trips although they operate closer tampering or lack of regular vehicle service) of the 1 engine's air system and fuel systems are important causes Reproducibility is poor when this test procedure is utilized of high smoke emissions. Dirt, clogging, wear and by a large number of testers using different equipment, incorrect pressure settings in diesel fuel injectors, together especially in an environment where financial incentives with inadequate repair and calibration of fuel injection are offered to testers to pass smoking vehicles. Slight pumps and turbochargers, are common causes of high differences in the time taken to accelerate the engine visible exhaust smoke levels. Inadequate and dirty air from low idle to maximum governed speed can lead to filters and restrictive exhaust systems will increase smoke very different exhaust opacity readings. Therefore, the at high loads when the engine is operating at near full rate of acceleration for each engine type needs to be throttle or accelerating quickly. An engine in poor more precisely defined. Each instantaneous reading should mechanical condition can also consume lubricating oil, be corrected for gas temperature, pressure, humidity and thereby emitting higher levels of smoke and hydrocarbons. altitude, as required in the SAE J1667 standard. As In terms of tampering, increasing the fuel delivery of the discussed in Briefing Note No. 9 [3], any dilution of the diesel fuel injection pump and resetting the engine's speed exhaust gases with clean air will lower smoke readings. governor to a higher rpm (revolutions per minute) are This in turn means applying other controls to detect this two common practices, both with the potential to increase practice. Furthermore, it is extremely difficult to get rpm smoke emissions. readings from diesel engines, particularly the older ones, yet accurate rpm readings are essential to add to the Inferior quality of spare parts controls as well. Finally, the ECE R24 procedure, but not Throughout South Asia, there are different grades of SAE J1667, verifies that the engine cylinders' combustion spare parts, starting with genuine original equipment (OE) chambers have reached their normal operating conditions parts with guaranteed quality, followed by varying classes by detecting decreasing opacity readings in consecutive of less expensive parts with lower levels of quality. Most tests and reports results only after these conditions have vehicle owners try, within their financial means, to use been stabilized. "closer to genuine" parts for critical assemblies such as As the above discussion shows, carefully defined test engines and transmissions, and lower cost components protocols need to be followed strictly to have acceptable for "non-critical" areas such as brakes and electrics. reproducibility across different operators and instruments The engine components that most affect emissions are at different test centers. Otherwise, a conscientious probably fuel injection pumps, fuel injectors and vehicle fleet owner regularly checking emissions by turbochargers. Because of the high cost of these conducting in-house smoke tests may find that properly components, a significant fraction of these parts are maintained vehicles routinely fail in the mandatory repaired rather than replaced, using components from emissions tests. This and the resulting driver harassment alternative sources, some with dubious quality. was in fact one of the complaints voiced in the assessment of the emissions program in India [1]. Further procedural Identifying Gross Polluters improvements can be introduced to reduce the opposite Some of the problems outlined above can be better kind of error, by which grossly emitting vehicles are addressed if emission standards are more strongly allowed to pass the test. enforced through an effective vehicle emissions inspection Shortcomings with smoke tests program. Ideally, diesel vehicles that emit Even when prosperly administered, smoke test still have disproportionately high levels of fine particulate matter two distinct problems to be addressed. One set of shouldbeidentifiedandrequiredtoberepaired.Identifying concerns can be addressed in part by using a more those diesel vehicles that are high particulate emitters, reproducible (and more expensive) form of opacity testing, however, is problematic, because the test procedures called a dynamometer test, which can also simulate real- currently used in the emissions inspection test centers do world driving conditions much better than snap not readily identify mass particulate emissions. acceleration. The second problem cannot be, as it Smoke tests underscores the fundamental shortcoming of measuring The most common procedure for testing emissions from smoke (see next section). in-use diesel vehicles is the snap (also called free) (1) The snap acceleration test is not representative of acceleration test defined according to the Society of normal operating conditions. More specifically, it is Automotive Engineers' SAE J1667 (in North America) easier to prepare a vehicle to pass a snap acceleration or ECE R24 (in Europe) standards. The test specifies test than a test under load using a dynamometer, that, with the transmission in neutral, the throttle pedal especially if a transient (as opposed to steady-state) should be pushed rapidly but not abruptly to its full-throttle loaded test is used. In Hong Kong, for example, the position, accelerating the engine from low idle to its environment officials found that diesel vehicle owners maximum governed speed. This is repeated several times temporarily adjusted the fuel injection pump, enabling and the average of the maximum exhaust gas opacity in high smokers to pass the snap acceleration smoke each test is computed. test. When the officials tried to close this loop-hole 2 by introducing the so-called lug-down dynamometer Figure 1. Correlation between Average Smoke test (test conducted at full throttle, with the Opacity in Snap Acceleration and Mass Particulate dynamometer load gradually increased to slow down Emissions in Loaded Transient Tests the engine speed so that the engine is laboring, or "lugging"), they found that the pass rate fell dramatically from 90% to 15% [4]. Further, smoke measurements depend heavily on the drive cycle for a given vehicle-fuel combination. One study[5]showsthatsmokeopacitymeasurementsusing different drive cycles on a loaded dynamometer were poorlycorrelatedwitheachotherforlight-dutyvehicles. Thetwolowestcorrelationcoefficientswere­0.16and 0.0, the highest 0.73. The correlation coefficients for heavy-duty vehicles were higher, with the lowest The above report also compares the results of the so- coefficientbeing0.20andthehighest0.92.Thisimplies called 10-second smoke testused in enforcing thatthesamevehiclemayhavequitelowreadingsunder Australia's national standard for smoke emissionsto one drive cycle and high ones on another, and yet there smoke opacity and mass particulate emissions measured may not be a "typical" drive cycle for all vehicles. in transient dynamometer tests. In a test specifically (2) A smoke test procedure, however well carried out, carried out on an incline, 32% of those that were identified cannot be used for controlling anything other than as smoky vehicles were also found to be high particulate visible smoke. An important question is then whether emitters in the CUEDC, but 68% of smoky vehicles were visible smoke can act as a proxy for particulate matter, found to be low particulate emitters. Overall, the on-road the pollutant with demonstrated health effects. smoke checks classified a higher number of vehicles as Correlation between smoke opacity and fine high emitters than mass particulate measurements. particulate emissions An unfortunate scenario, from the point of view of The diesel engine pollutant of greatest health concern managing a vehicle inspection and maintenance program, is fine and ultra-fine particles. If a diesel-vehicle testing would be one in which vehicle repair lowers particulate program does not lead to the reduction of fine emissions but increases smoke. Such a case was indeed particulate emissions, then it shall have failed in its confirmed in the NEPC's diesel program whereby for two ultimate objective, the reduction of pollutants that vehicle categories (1996-2000 diesel buses heavier than 5 damage the public's health. The question immediately tons and goods vehicles heavier between 12 and 15 tons arises, therefore, as to how closely correlated is for the first, and 1996-2000 goods vehicles heavier than "smoke" with fine particulate matter. 25 tons for the second), particulate emissions decreased by 38% and 14% on average after repair but opacity To answer this and other questions, the National readings increased by 29% and 10%, respectively [8]. Environment Protection Council (NEPC) of Australia commissioned eight projects to collect data on the diesel In light of the above, snap acceleration smoke tests cannot vehicle fleet and emissions characteristics with the be viewed as a means of identifying high particulate objective of developing cost-effective emissions emitters, but rather as diagnostic tests to identify management measures [6]. malfunctioning and defects among older engine vehicles with mechanically controlled fuel systems. For this Figure 1, taken from a project report by Peter Anyon and category of vehicles, these smoke tests may be especially others[7],indicatesaverypoorcorrelationbetweenvisible helpful for identifying tampering to increase power by smoke measured using snap acceleration and mass over-fueling. However, given the poor correlation between particulateemissionsmeasuredinadynamometertestusing smoke and particulate emissions, and the poor correlation a drive cycle for estimating "real-world" emissions from among the results of smoke tests on the same vehicle vehicles in urban areas. The cycle used, called the using different drive cycles, it would make sense to set Composite Urban Emissions Drive Cycle (CUEDC), relatively lenient standards to identify the most serious consists of four segments: congested, minor roads, arterial smoke emitters so as to minimize chances of false failures. roads and highway/freeway driving. The figure illustrates that a number of high particulate emitters have quite low Snap acceleration smoke tests are not at all effective for scores on smoke emissions registered during the free modern, electronically controlled engines or turbo-charged acceleration test, while some of the high "smokers" have engines with boost control. For these vehicle categories, an relatively low particulate emissions compared to the true alternative test procedure has to be identified. Studies to gross polluters. That is to say, snap acceleration smoke datesuggestthatataminimumdynamometer-basedloaded tests run the danger of misclassifying gross polluters as tests are needed, but they are expensive to set up for heavy- relatively clean and low polluters as high emitters. duty diesel vehicles. The series of studies in Australia 3 recommend a short dynamometer-based test with transient monitoring of nitric oxide, and meaningful acceleration segments using a laser light scattering measurements of CO and hydrocarbon emissions. photometertomeasuremassparticulateemissions.However, M Given the high costs of dynamometer testing facilities, this test is still at the pilot stage with no wide application. especially for heavy-duty diesel vehicles, using visual Finally, it is important to view the limitations of smoke smoke checks as a screening toolwhereby those tests in broader perspective. Smoke is a public nuisance, judged to be visible smokers are sent to test centers and more importantly, smoke harms public health. High with dynamometersmay help to reduce the overall smoke emissions, even if particulate emissions prove to cost of the diesel emissions inspection program. While be relatively low, suggest that there is something wrong visual checks are subjective and potentially more prone with the vehicle settings or parts. Given the technical to corruption, using them as a screening tool so that problems associated with measuring particulate emissions those who conduct the checks cannot fine motorists in a garage setting, smoke tests will continue to play an may help to minimize corruption. important role in emissions testing programs for the References foreseeable future. 1. John Rogers. 2002. Assessment of the Pollution Under Conclusions Control Program in India and Recommendations for Identifying gross diesel polluters is significantly more Improvement, prepared for the World Bank, October. difficult than identifying gross gasoline polluters. One Available at . serious problem is the lack of a relatively inexpensive 2. South Asia Urban Air Quality Management Briefing Note and quick method for measuring particulate emissions, No. 7. 2002. "Catching Gasoline and Diesel Adulteration," July. Available at . the pollutant of most concern in South Asia. There is no simple road map, and a multi-prong strategy is needed. 3. South Asia Urban Air Quality Management Briefing Note No. 9. 2002. "Making Vehicle Emissions Inspection M In order to encourage the development of adequately Effective--Learning from Experience in India", November. equipped and staffed service and repair facilities, more Available at . efforts should be directed at improving vehicle 4. W.C. Mok. 2001. "The Experience of Hong Kong SAR, emissions inspection and enforcing standards. China, in Controlling Smoky Vehicles." Available at M There is a need to raise public awareness and create . commercially unattractive. 5. National Environment Protection Council. 2001. Proposed M There needs to be tighter control over the quality of Diesel Vehicle Emissions National Environment Protection Measure Preparatory Work, In-Service Certification spare parts. Correlation Studies. Available at < http://www.ephc.gov.au/ M The most commonly used test for diesel pdf/diesel/Correlation_Studies.pdf>. vehiclessnap acceleration smoke testcan play a 6. Environment Protection and Heritage Council. Diesel limited but useful role, provided that the test procedure Vehicle Emissions Preparatory Projects. Available at is carefully defined to ensure repeatability and the test . protocol is strictly enforced. 7. National Environment Protection Council. 2000. Proposed M The smoke standards for snap acceleration tests should Diesel Vehicle Emissions National Environment Protection be lenient or else there is a serious danger of having a Measure Preparatory Work, In-Service Emissions Performance ­ Phase 2: Vehicle Testing. Available at highfalse-failurerate.Thetestshouldbeseenprimarily . as a means of identifying the grossest of gross polluters 8. National Environment Protection Council. 2001. Proposed among old technology engine vehicles. Diesel Vehicle Emissions National Environment Protection M For modern engine vehicles as well as high annual Measure Preparatory Work, In-Service Emissions Testing mileage commercial vehicles, serious consideration ­ Pilot Study, Fault Identification and Effect of should be given to adopting dynamometer-based tests. Maintenance. Available at . This briefing note was prepared in November 2002 as part of the South Asia program on urban air quality management, funded in part by the joint UNDP/World Bank Energy Sector Management Assistance Program (ESMAP). The objective of the program is to support the region-wide process of developing and adopting cost-effective and viable policies and efficient enforcement mechanisms to reverse the deteriorating trend in urban air. A full set of briefs and other materials are available at . For further information, contact Sameer Akbar (sakbar@worldbank.org) or Masami Kojima (mkojima@worldbank.org) about this program, and John Rogers (jrogers@trafalgar-mexico.com) about this note. 4