WAS HI NGTON STATE 

D E P ARTM E NT OF 

E C 0 L 0 G Y 

Assessment of Potential Strategies 

to Reduce Emissions from Diesel Engines 

in Washington State 

December 31,2003 

Prepared for: 

Washington State Department of Ecology 

Prepared by: 

Kim Lyons 

Washington State University 

Cooperative Extension - Energy Program 

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Publication Number 05-02-005 
Table of Contents 

Introduction - Diesel Particulate Matter Emission Reduction Measures 

1 Fuels 

1.1 Ultra-Low Sulfur Diesel 

1.2 Biodiesel 

1.3 Fuel/Water Emulsions (PuriNox) 

2 Engines and Exhaust After-treatment (Retrofit) Technologies 

2.1 New Engine Technologies 

2.2 Diesel Oxidation Catalysts 

2.3 Diesel Particulate Filters 

3 Programs 

3.1 Smoke Testing or Emission Inspection Programs 

3.2 Idling Restrictions 

3.3 Diesel Emission Reduction Programs (Other States) 

4 Source Categories 

4.1 School Buses 

4.2 Marine Engines 

4.3 Locomotives 

4.4 Construction Equipment 

4.5 Agricultural Equipment 

4.6 Logging Equipment 

4. 7 Commercial/Industrial Equipment 

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8 

13 

15 

20 

24 

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46 

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56 

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Diesel Particulate Matter Emission Reduction Measures 

Introduction 

Diesel is the dominant fuel used by the commercial transportation sector. Because diesel 

engines offer important fuel economy, power and durability advantages, they are often 

the engine of choice for heavy-duty applications. In the United States, approximately 94 

percent of all freight is moved by diesel power. Diesel engines also power most non-road 

equipment including construction and agricultural equipment, marine vessels and 

locomotives. 

While the operational advantages of diesel engines are clear, diesel fuel is a major 

contributor to particulate matter (PM) emissions. Diesel particulate emissions are of 

increasing concern as they are small (often less than 2.5 microns in size), and consist of a 

complex mix of engines oils, sulfates and inorganic materials. These particles have been 

identified by health experts as contributing to a variety of lung related illnesses including 

asthma, emphysema and bronchitis. There is also growing evidence that exposure to 

diesel particulates may increase the risk of cancer in humans. In 1998, the California Air 

Resources Board declared diesel particulate emissions a toxic air contaminant and a 

potential cancer risk. In 2000, the U.S. Environmental Protection Agency (EPA) 

identified diesel PM as a " likely human carcinogen," and followed this with new 

stringent standards aimed at reducing emissions from on-road vehicles by as much as 90 

percent. 

Although the new EPA standards will go a long way to improve diesel emissions in the 

future, these standards remain a few years off and will primarily impact new engines. 

However, because of their durability and long life, older uncontrolled diesel engines will 

continue to make up a significant portion of the heavy duty vehicle fleet for years to 

come. As a result, efforts are underway to improve emissions from diesel engines 

already in operation and include a variety of strategies from fuel reformulations to engine 

retrofits. 

The purpose of this report is to identify technologies and actions which can reduce PM 

emissions in existing diesel engines. Information was gathered through an extensive 

web-based search, followed up, in some cases, by direct contact with industry 

representatives and project managers involved in specific diesel reduction programs. 

To date, most of the diesel PM reduction efforts have focused on either new engine 

replacements or retrofitting existing engines with post-combustion emission control 

equipment. Of primary interest are diesel oxidation catalysts and diesel particulate filters. 

Diesel oxidation catalysts (DOCs) have been in use for over 20 years in more than 

270,000 retrofit applications. They are relatively inexpensive and are robust enough to 

be used in many non-road applications such as construction and mining equipment. They 

are not overly sensitive to fuel sulfur content and can achieve PM reductions of25 

percent or more. 
Diesel particulate filters (DPFs) also offer retrofit opportunities. However, because these 

devices require specific engine conditions to operate effectively, they cannot be used in 

some applications. DPFs work best with newer engines that achieve higher, sustained 

engine exhaust temperatures. DPFs also require the use of ultra-low sulfur diesel. 

Although DPFs cost two to three times more than oxidation catalysts, they can achieve 

PM removal efficiencies in excess of 90 percent. 

Low sulfur diesel fuels or alternative fuels can also provide PM control. Reducing the 

sulfur content of diesel fuels provides a direct fuel-related reduction in particulate matter 

emissions. More importantly, low sulfur fuel allows the use of emission control 

technologies which have been proven effective in providing significant PM control. As a 

result, most diesel PM control programs also include a low sulfur diesel component. 

Currently, ultra-low sulfur diesel is available in western Washington at a cost premium of 

1 0 to 11 cents per gallon. 

Other fuels and fuel technologies that can provide PM benefits include biodiesel, natural 

gas, diesel/water emulsions and diesel/electric hybrids. Natural gas, biodiesel and 

diesel/electric hybrid technology are all currently being used in heavy-duty engine 

applications in Washington. However, natural gas and diesel/electric hybrid applications 

would typically fall under a new vehicle purchase, although natural gas retrofits or 

repowering opportunities do exist. While significant emission benefits can be achieved 

through the use of these technologies when compared to baseline diesel equipment; a 

more meaningful comparison should include advanced diesel technology engines fueled 

with ultra-low sulfur diesel. Here, emission benefits may still favor the diesel 

alternatives, but the degree of benefits is smaller. 

In contrast, biodiesel and water/diesel emulsions are direct fuel substitutes that can be 

used with little or no modifications to an existing diesel engine. For most biodiesel 

applications, a 820 blend is used, which consists of 80 percent diesel and 20 percent 

biodiesel. The fuel is available in Washington at a price premium of around $0.20-$0.30 

per gallon. PM emission reductions are estimated at about I 0 percent or more for 820. 

Water/diesel emulsion fuels blend about 20 percent water with diesel. A surfactant and 

additives make up about one percent of the mix and maintain the emulsion. For the most 

part, this is a proprietary fuel marketed under the name PuriNOx. While there are no 

current users of PuriNOx in Washington, it is being used successfully in other parts of the 

country where PM reductions of 40 percent or more have been reported. 

Smoke testing and idling restrictions may also provide PM control. A smoke test 

program uses opacity measurements to identify trucks which emit high levels of smoke. 

Failing trucks are then targeted for improvements, typically at the owners' expense. 

Idling restrictions are intended to reduce the idle time of a diesel engine, which in turn 

reduces diesel engine emissions. This control measurement is being applied in a couple 

of ways. One is to establish operational guidelines which direct a vehicle driver, such as 

a school bus or construction equipment operator, to turn their engine off during queuing 

or other idle periods. This approach is being used extensively in New England states. 

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Another approach is to employ auxiliary power technologies which allow drivers to turn 

off their main engines during extended idle periods. In some cases, the power technology 

is provided independent of the truck through a plug system, often referred to as truck stop 

electrification. Some of these technologies can reduce engine idle emissions by 90 

percent. 

While other PM control strategies are available, those discussed appear to be the primary 

control measures currently being employed around the U.S. Because PM control 

measures may differ for different applications, this report also looked at some end use 

applications, including marine engines, buses, agricultural equipment and construction 

equipment. For the most part, PM control actions are being investigated and applied 

across sectors. However, small market sectors, such as agricultural equipment, are only 

just beginning to receive attention, with little to no demonstrated use of specific PM 

control measures. 

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3.1 Smoke Testing or Emission Inspection Programs 

The 1990 Clean Air Act required EPA to develop light duty vehicle inspection and 

maintenance standards (liM) to help control vehicle emissions. Program implementation 

of these standards was relegated to the states. A growing concern over health related PM 

effects motivated some states to extend l/M programs to include heavy duty diesel 

vehicles (HDDV). Currently, 17 states, including Washington, have some type of diesel 

I/M program (Colorado 2002). 

HDDV 1/M programs may employ a roadside measurement ofthe amount of visible 

smoke being emitted from a vehicle's exhaust system under some specified test 

conditions. In addition, some jurisdictions require annual or semi-annual inspections of 

HDDVs which are performed at fleet maintenance facilities or centralized inspection 

sites. 

The roadside smoke opacity test is often carried out at weigh stations, custom inspection 

facilities or any other suitable site which allows easy access to and from the highway. 

Tests are random in that they are unannounced and are held at varying inspection sites. 

Vehicles are selected for opacity testing based on visual observation of the vehicles as 

they approach the test site. High smoke emitters are flagged for inspection, with selection 

based on inspector experience. The roadside test usually applies to all HDDVs, 

regardless of origin, and is free of charge. Failing the test may result in a fine, which is 

often waived or reduced ifthe owner furnishes proof that the reason for failure has been 

corrected. 

Annual or periodic programs operate similar to the light duty liM test. Here, HDDV 

operators are required to complete a smoke test within a jurisdiction, are charged for the 

testing, and can be fined or denied registration renewals until the reason for failure is 

fixed or at least attempted to be fixed . Unlike roadside testing, periodic testing does not 

single out high emitters for testing. Instead, all vehicles (with the possible exception of 

newer vehicles up to the latest three or four model years) need to show that they can pass 

inspection. 

Proponents of periodic inspections argue that this approach captures all registered 

vehicles within a given jurisdiction and encourages vehicle owners to consistently 

maintain their vehicles with respect to smoke emissions. Proponents of roadside 

inspections argue that roadside testing targets only the gross emitters and can be moved 

around to areas where dirty vehicles are observed to operate. Further, roadside testing 

treats all smoking vehicles the same and does not discriminate between vehicles 

registered in and out of state. 

Because HDDVs often move between jurisdictions and states, a push was made to 

develop a standardized protocol for smoke testing. In 1997, the EPA Office of Mobile 

Sources issued a "Guidance to States on In-Use Smoke Test Procedure for Highway 

Heavy-Duty Diesel Vehicles." This document provides guidance on how to conduct 

smoke tests using the SAE Recommended Practice J 1667, Snap-Acceleration Smoke Test 

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Procedure. 11667 was developed in 1996 with the help ofthe engine manufacturers, 

trucking industry, smoke testing equipment manufacturers and state and federal 

regulators (http://www.arb.ca.gov/msprog/hdvip/saej 1667.pdf). 

The test is performed on a vehicle when it is standing still and in neutral. The engine is 

accelerated without any external load to the maximum governed speed. A smoke meter 

is placed at the end of the exhaust pipe and the opacity of the smoke is measured. The 

opacity is expressed in percent of light reduction, and is the degree to which the exhaust 

obscures a beam of light shining through it. 

EPA recommends that states employ 11667 opacity failure points (the point at which the 

vehicle fails a smoke test) of 55 percent for pre-1991 vehicles and 40 percent for 1991 

and later model year vehicles. 

Emissions 

Actual emission benefits resulting from smoke testing programs have not been well 

documented. The goal of smoke testing is to reduce visible, black exhaust smoke. While 

it is commonly accepted that less smoke means lower particulates, a reduction in the 

opacity of the particulate matter does not necessarily result in a reduction in its total mass 

(Canada EPS 2000). The Colorado Diesel Stakeholder Group noted that the continued 

use of opacity as a surrogate measurement tool to identify high-emitting vehicles should 

be reevaluated. At best, opacity levels identify some but not all high-emitting engines 

(Colorado 2002). 

Recently, Energy and Environment Analysis, Inc (EEA) was contracted by the state of 

Colorado to quantify the emissions benefits of smoke testing of heavy duty vehicles 

(EEA, 2001). Although their research sample was small (only 26 vehicles total), EEA 

did come up with some interesting observations. Their primary conclusion was that the 

standard opacity cut-points of 55 percent for pre-1991 vehicles and 40 percent for later 

vehicle models may not be appropriate, at least for the state of Colorado. EEA argued 

that the cut-points, initially developed by the state of California, are too high, and were 

originally set conservatively because of California's requirement of zero errors of a 

vehicle being failed incorrectly. 

EEA found that, for pre-1991 vehicles failing at a 45 percent opacity cutpoint (instead of 

the standard 55 percent), repair reduced PM emissions by 45 to 50 percent. For 1991 and 

newer vehicles (all of which failed the 40 percent opacity cutpoint), repairs produced a 

greater than 40 percent reduction in opacity and a 25 to 30 percent reduction in emissions 

of PM (EEA.) EEA also found that NOx levels went up but still remained within the 

established standards, and that aldehyde and PAH emissions were reduced dramatically 

following repair. The average cost of repair was $1,088. 

Early work by various researchers suggests that there is some correlation between smoke 

opacity and PM emissions. Based on their study results, however, EEA indicated that 

smoke opacity is at best a poor predictor of PM emissions. They suggested that driving 

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cycle CO and THC emissions are correlated much more strongly with PM and that an 

improved liM test procedure based on tailpipe measurement of CO and THC be 

developed (EEA). 

Smoke testing costs are difficult to assess as it depends on what is counted as cost. Costs 

could include: 

• program administration costs; 

• administrative costs to fleets, including annual labor costs to complete the 

inspections; and 

• costs to fleet or vehicle owners which could include vehicle down time, vehicle 

repair costs, testing fees, testing fines, and annual increased maintenance costs 

due to voluntary repairs done in order to avoid failing the test. 

California's Heavy Duty Vehicle Roadside Inspection Program has an estimated total 

program cost of about $5.6 million per year, or $280 per vehicle inspected (Colorado 

2002). Ofthis amount, vehicle owners pay about $1.9 million for increased maintenance 

and lost opportunity costs, and the state pays about $3.7 million to annually inspect the 

vehicles (not counting Highway Patrol costs). Between June 1998 and September 2001 , 

64,648 visual inspections were performed. During this time frame, the fail rate was 4,538 

vehicles, or about seven percent. Program managers indicate that they inspect about 

20,000 vehicles annually, which equates to about 1,400 vehicle failures per year at a 

seven percent fail rate (Colorado 2002). 

California also conducts a periodic inspection program. Here, all fleets of two or more 

California-registered HDDYs (about 291 ,600) are subject to an annual self-inspection 

using the snap acceleration test. A four model year exemption is allowed, which is 

estimated at 26 percent of the fleet. The state audits the fleets for compliance, with less 

than one percent of the fleets requiring formal action (Colorado 2002). State costs for 

auditing are $0.5 million annually. The cost of self testing is estimated at $18.1 million 

per year. The annual program cost is estimated at $84 per vehicle inspected. In addition, 

vehicle repairs resulting from inspection programs are estimated to improve fuel 

economy and effectively offset the costs of repair to the operator. 

In 1997, CARB estimated that the cost-effectiveness of the HDDV smoke test program in 

reducing criteria pollutants was superior to other emission control programs. In fact, the 

HDDV smoke test program was estimated to be between 2.4 and 4.7 times more costeffective than other control method (Canada 2000). Current estimates by CARB suggest 

that the programs cost about $1.05 per pound of emission reduction (tri-national HDDV 

smoke test workshop-3/2002). 

Other issues 

In a recent workshop sponsored by the Northeast States for Coordinated Air Use 

Management and CARB, participants raised some common themes concerning heavy 

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duty vehicle emission testing (tri-nat workshop). These issues included a need to better 

correlate opacity and PM (and NOx); a need to revisit current opacity cut-points; and a 

need to develop new, advanced emission testing methods ( loaded test, chassis test, onboard diagnostics) for use with new engine technologies. 

Representatives from a number of organizations had concerns with the current opacity 

cut-points. Some felt that the current levels may be allowing too many potentially 

polluting vehicles to pass the smoke test. The state of Colorado has lowered their cutpoints to below the accepted EPA standard and California is investigating the need for 

more restrictive cut-points as well. While the current snap-idle test appeared to be 

acceptable to the majority of participants, a need for advanced testing methods was raised 

in response to newer engines. Some participants argued that with newer engines, visible 

smoke was not necessarily a good indicator of particulate emissions, and as a result, spot 

or road-side inspections were going to lose their effectiveness. 

Smoke testing is primarily a tool to reduce visible smoke emissions from heavy duty 

diesel vehicles. The relationship between opacity and PM is not fully understood; 

however, it appears that lowering opacity should provide PM emission reductions. The 

Colorado Diesel Stakeholder Work Group observed that, although high opacity readings 

indicate high PM emissions, low opacity does not necessarily indicate low PM emissions. 

They further acknowledged that the lack of quantitative emissions data makes it difficult 

to judge the effectiveness of their HDDV Inspection and Maintenance program in 

reducing diesel emissions. However, they concluded that the program provides 

undeniable benefits as an incentive for good maintenance and as a deterrent to vehicle 

tampering (Colorado 2002). 

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