Critical Thinking
Recent Berkeley Study on Diesel Fuel versus Gasoline Requires More Critical Thought
A study completed by University of California at Berkeley researchers reports that diesel exhaust contributes 15 times more of a smog-causing chemical than gasoline engines, per liter of fuel burned. Although I haven’t been able to look at the entire study, I started reading the supplementary material available online. And from the first page of that supplemental material, I can already see major pitfalls for unwary editors and reporters who don’t look more critically at the study.
According to the supplementary material, samples for the study were taken at a tunnel on Highway 24 in Oakland, Calif. “Emissions from gasoline and diesel vehicles were measured as part of a field sampling campaign to characterize on-road mobile sources. Measurements were made July 13-29, 2010, at the Caldecott tunnel, on Highway 24 in Oakland, Calif. Sampling for the data presented here was taken in the uphill eastbound traffic bore with all vehicle types and traffic rates of approximately 2,000 light-duty vehicles and 30-140 medium and heavy-duty trucks per hour running on a mixture of gasoline and diesel fuel.”
It would be interesting to know what the average age of the trucks were. I suspect because of the recent downturn in the economy, a number of them were older trucks most likely with pre-2007 U.S. Environmental Protection Agency-compliant emission technology engines. Perhaps even with pre-2004 EPA-compliant emission technology engines.
In the summer of 2010, I doubt many operators would have had the latest in truck emission technology - the 2010 EPA-compliant engine or the aftermarket exhaust retrofits now largely required for operating in California. As many of you may know, the California Air Resources Board in 2008 approved regulations that require truck operators to install exhaust retrofits that capture pollutants in emissions. But the regulations established a timetable for accomplishing this starting Jan. 1, 2011. The regulations also established a staggered implementation schedule that requires over the next several years eventual replacement of all heavy-duty diesel-fueled trucks with units equipped with engines that meet the EPA’s 2010 emission standards.
To infer from this study that diesel is worse than gasoline ignores the fact that there have been monumental changes in emission regulations for diesel engines in California since the testing for this study was first done in the summer of 2010.
Even if you can’t get a look at the full study, be sure to take a closer look at the supplemental material. Also take a look at another study conducted by the University of California-Riverside and funded by the South Coast Air Quality Management District and the San Joaquin Valley Air Pollution District. That study looked at the emissions of newer technology engines and the effects of the shift to ultra-low sulfer diesel fuel available since 2006. The UC-Riverside study finds that an 18-wheel diesel engine-powered truck would have to drive 143 miles on the freeway to put out the same mass of particulates as a single charbroiled hamburger patty.
Would you like fries with that?
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