A first-of-its-kind study examining the efficacy of post-2007 diesel emissions control technologies meeting federal regulations has found zero incidence of cancerous lung tumors in rats subjected to diesel exhaust.
The implications of the Advanced Collaborative Emissions Study (ACES) by the Health Effects Institute (HEI) are that humans have much less to worry about with new or retrofitted diesel engines. The study also documents other positive ramifications for human health compared to what would be expected with pre-2007 tech diesel engines.
HEI’s multi-year peer-reviewed study tested the potentially worst offenders – Class 8 semi tractor trailer engines. Large truck engines consume the most fuel and make the most power thus the HEI’s findings cast a positive light on all in-compliance diesel engines down to those in today’s new passenger cars.
Based in Boston, the HEI is co-sponsored by the U.S. Environmental Protection Agency (EPA), U.S. Federal Highway Administration, California Air Resources Board (CARB), and the vehicle industry.
Tested were off-the-shelf truck engines of post-2007 specification, randomly selected to run and expose emissions to a breed of rat believed to have health reactions most-closely mirroring human beings.
Also tested without the rats were more tightly controlled post-2010 engines using the same 16-hour special rigorous drive cycle and those reports are available here.
The study exposed the Wistar Han rats to the post-2007 engine exhaust 80 hours a week, for up to 30 months. As per EPA regulations, the engines were fueled by ultra low sulfur diesel, and utilized particulate matter filters and exhaust gas recirculation (EGR) to control NOx. They were run at different levels of intensity to simulate real-world exposure by human populations near roadways where these trucks normally operate.
“Given we wanted to get the health results sooner rather than later, we did use only the 2007 engines in the rat exposures,” said HEI President Dan Greenbaum, “although given that the emissions of the 2010 engines were even lower (with the addition of selective catalytic reduction (SCR) technology) we would have expected even fewer effects if we had used the newer engines.”
In essence, while diesel emissions remain on the World Health Organization’s list of Class 1 carcinogens, and are called out by the California Air Resources Board and the American Cancer Society as carcinogenic, “after treatment” technologies are believed effective.
The study confirmed also that concentrations of particulate matter and toxic air pollutants in new technology diesel exhaust (NTDE) are 90-99 percent lower than emissions from traditional older diesel engines (TDE) – even ones as new as 2004 specification.
“A few mild changes were seen in the lungs, consistent with long-term exposure to NO2, a component of NTDE that has been further substantially reduced in 2010- and later model year engines compliant with U.S. EPA rules,” said the HEI in a statement.
HEI says its findings are expected to be an important consideration in future reviews of the risk of diesel engines by not just the U.S., but also international agencies.
“We are already seeing a transition in America’s roads with over 30 percent of the trucks and buses in use today meeting these new standards and the trend is growing in Europe as well,” said Greenbaum. “These results confirm the great strides that government and industry have made to reduce diesel risk – and argue for even greater efforts to accelerate the replacement of older diesel engines.”
‘Clean Diesel’ – Not An Oxymoron?
Compared to zero-emission technologies, diesel has been sniffed at by environmentally minded advocates as a technology of questionable risk.
In Europe, where diesel passenger vehicles comprise as much as half of new passenger vehicle sales compared to a mere 1 percent or less in the U.S., officials and advocates there are saying their emission controls have not been effective.
But the U.S. EPA’s rules and testing procedures are more stringent, and the HEI study prompted diesel promoters to speak up.
“The significance of this study and its conclusions cannot be overstated,” said the Diesel Technology Forum’s executive director, Allen Schaeffer. “The results of this new study verifies the environmental benefits of the new clean diesel technology, which have near-zero emissions for nitrogen oxides (NOx), hydrocarbons (HC) and particulate matter (PM). And while this study focused on heavy duty truck emissions, the new clean diesel technology has the potential for impacting all sectors, including passenger cars, agriculture, construction, maritime and transportation.”
Looking at more than just cars and trucks, Schaeffer noted diesel technology yet drives a significant portion of the U.S. economy.
“The findings of the ACES study are extremely important because diesel engines are the technology of choice that drives 15 sectors of the global economy ― from agriculture to goods movement, from construction to warehousing,” Schaeffer said. “Clean diesel technology is virtually the power behind America’s domestic and global goods movement.
“This means that the clean air benefits from these clean diesel engines are being experienced in communities throughout the country.”
In years past, environmentalists did have much more to decry and the Natural Resources Defense Council (NRDC), for example, put up a campaign against “dirty diesel,” but despite voices yet questioning it, Schaeffer says accusations have less merit now.
“Diesel technology has undergone a complete transformation in recent years, first, with a move to ultra-low sulfur diesel fuel in 2006 that reduced the fuel’s sulfur content by 97 percent,” Schaeffer said. “This cleaner fuel then enabled refinements in engine technology and the use of emission controls and reduction strategies that are now deployed throughout a wide range of industry, engines and technology.”
NRDC And CARB Weigh In
According to Diane Bailey, a senior scientist for the NRDC who has worked “many years on cleaning up diesel pollution,” the study does indeed validate that strict emission controls are working.
Key is that they are properly maintained, and this has involved more oversight and less hands-on maintenance schedules and servicing by trained technicians – thus higher costs – for fleet and other operators of these electronically controlled vehicles.
We asked her whether we could run a headline “Study Gives Diesel a Clean Bill of Health,” and to this Bailey was not ready to sign off.
“You know you have to put a big fat asterisk on that,” she said.
Beyond zero lung cancer risks discovered amongst the fumigated rats, Bailey retains concerns for other health risks yet associated with diesel exhaust.
At issue is diesel “soot” (particulate matter) and Bailey noted greenhouse gases either from the tailpipe or upstream in the fuel production cycle remain a concern and the study did not address these.
But HEI President Greenbaum said the study has answered many health concerns.
“We tested over 100 health endpoints, including a range of non-cancer effects such as respiratory effects and cardiovascular effects, as well as the cancer testing,” said Greenbaum. “Almost none of the endpoints showed any effects; the only ones that did occur were mild inflammation effects consistent with exposures to NO2 in the exhaust; those exposures have fallen substantially further with the 2010-compliant and later model year engines. We actually compared the lungs of rats exposed to the earlier engines and in earlier NO2 studies in order to make that comparison (the labs had maintained the samples).”
Bailey noted studies in the past have yielded conflicting results leaving open questions about “ultra fine” particulate matter that can transfer from inhaled diesel-exhaust-laced air through the lung-blood barrier into the bloodstream.
It is possible, she said, that an unintended consequence of emissions after treatment could be no mitigation or even an increase in ultra fine particles.
She said she is thus not ready to rest easy that all is well for populations that reside within proximity to major freeways, or for pedestrians on city streets, for example.
Bailey cited health issues including “cardiac illness, heart attack, stroke; it’s just not clear, there are conflicting studies, more research is needed” on these issues as well as respiratory complications including asthma, bronchitis, emphysema, and other potential illnesses besides.
“Typically if you live or go to school or work within a couple hundred feet of a busy freeway your health is seriously impacted – especially if there is heavy diesel truck traffic on that freeway,” Bailey said. “And we hope and expect to see those numbers go down over time as the vehicle fleet in general cleans up. But the studies to date have shown tremendous health impacts on the population closest to the freeways.”
Concerns also were voiced by Public Information Officer Melanie Turner of the California Air Resources Board.
“These engines also emit oxides of nitrogen that contribute significantly to ozone and PM2.5 formation, which lead to respiratory and cardiovascular effects, including premature death,” said Turner. “While emission standards for 2010 and later model year heavy-duty diesel engines reduce NOx emissions also by 90 percent in comparison to pre-2007 technologies, further reductions are needed to attain health-based air quality standards in California.”
How do diesel emission compare to gasoline or natural gas engines? All are fossil fuel, and all have potential health effects. All must meet the same EPA standards, so differences between them may be slight, or difficult to quantify, but diesel remains a concern – particularly the older engines not under the new “near zero” emissions of the latest diesels, as the Diesel Technology Forum describes them.
And ultimately, Bailey said she does have confidence in the scientists that performed the study, and has no reason to question the validity of the findings or conflict of interest.
“I think its an important confirmation that the these pollution controls are working,” said Bailey.
Turner also expressed no criticism of the study.
“The study sponsors were walled off from final decisions on study protocols, review of the final report and interpretation of results,” Turner said.
The Best Solution?
Modern turbocharged diesel engines are the most thermally efficient among internal combustion technology.
Today’s infrastructure and other pre-existent conditions make diesel the technology of choice for many applications, such as long haul trucking and other industries.
There have been efforts to gain traction for natural gas engines – whose manufacturers note they have zero issues with particulates unique to diesel.
Beyond this, Bailey said the NRDC encourages a move away from fossil fuels, as does Turner from the California Air Resources Board.
“California’s climate and clean air goals are driving the need to get transportation sources off of fossil fuels. In fact, Governor Brown’s recent State of the State address clearly laid out our state’s policy goals for petroleum reductions. In his address, the governor called for reducing the petroleum used in cars and trucks by up to 50 percent by 2030,” said ARB’s Turner. “The technologies tested in the study do not address fossil fuel consumption and associated CO2 emissions. Separate actions are needed, and being made, to reduce fossil fuels, including increases in biodiesel and renewable diesel and technologies to improve fuel economy.”
Hybrids, plug-in hybrids and battery electric vehicles are cleaner, and tackle the greenhouse gas issue as well, say proponents. For local route usage, and other applications, there have been inroads into these technologies, and more will continue.
Bailey said she has reservations about hydrogen fuel cells, saying if it’s sourced from renewable energy, that is best.
“We are fully supportive of renewably sourced hydrogen,” she said while noting the technology has more yet to prove, and has been promised for a long time thus far.
The U.S. EPA meanwhile continues to advocate an “all-of-the-above” approach as a tacit acknowledgement that there is no perfect and ready technology that can utterly supersede fossil fuels.
Meanwhile, looking at the market and realities where they are, HEI’s Vice President Bob O’Keefe says its study validates the incumbent technology.
“These results are impressive for what they can mean for reducing exposure in the U.S. and Europe, but also for the promise they hold in the developing countries of Asia and elsewhere in the world,” said of HEI and Chair of Clean Air Asia (Asia’s largest city network dedicated to clean air). “Countries like China are already moving toward implementing the ultra-low sulfur diesel fuel that is required for these new cleaner technologies.”