The best thing about the Prius is that it achieves its high fuel economy without sacrificing size or performance and, most importantly for global warming, without being a diesel. There seems to be a lot of confusion on this point, so let me elaborate.
Bottom Line: If you care about global warming, don't buy a diesel car (certainly not in this country), and if you must buy a diesel, only get a new one with a very good particle trap. [Does this mean that Europe's massive switch to diesel was not good for the climate? In a word,"probably."]
First, diesel fuel has a considerably higher carbon content than gasoline, so burning a gallon of diesel emits 22.2 pounds of CO2 vs. 19.4 for gasoline (see here). A diesel car with the same mpg as a gasoline car would have considerably higher carbon dioxide emissions per mile. [This is offset one third by the fact that diesel has fewer upstream emissions, which, if I did the math right, takes total life-cycle CO2 emissions from a gallon of diesel to 25.8 pounds vs. 24.2 for gasoline (see here).]
Second, and more importantly, we have known for a number of years that black carbon (BC) or small soot particles are a major greenhouse gas -- and that diesel engines are a major source of BC. A March 2008 review article published in Nature Geoscience, (subs. req'd, abstract below), "Global and regional climate changes due to black carbon," found that BC may be as much as 55% as potent in total greenhouse warming as CO2.
In October, the House held "a hearing to examine the climate change and other impacts of black carbon emissions" (testimony and transcript here). Dr. Mark Jacobson, Co-founder and Director of the Atmospheric Energy Program at Stanford University's Department of Civil and Environmental Engineering, testified directly on how BC emissions significantly reduce the climate benefits from diesel cars (here):
It is generally thought that diesel vehicles obtain better gas mileage and emit less carbon dioxide than equivalent-class gasoline vehicles and, therefore, using more diesel vehicles will address the climate problem. However, this concept ignores the larger emissions of fossil-fuel soot from diesel than gasoline vehicles and the resulting climate effects. It also ignores the fact that the addition of control devices to diesel vehicles to reduce their soot and nitrogen oxide emissions, required to meet California and EPA Tier 2 Permanent Bin emission standards and to address the climate problem of soot, reduces the gas mileage of the diesel vehicles. Finally, it does not consider that, in the United States, the lowest-carbon-emitting vehicles in 2006 were gasoline and gasoline-electric hybrid vehicles, not diesel vehicles [See Table 7 in testimony]. The addition of particle traps to the best diesels sold in 2006 in the U.S. would reduce the standing of the diesels further.
[Note: Jacobson explains "the addition of a trap decreases the mileage, thus increases the carbon dioxide emissions from such vehicles by 3.5-8.5%."]
Also, the addition of a particle trap to diesel increases the NO2:NO ratio in diesel exhaust increases, exacerbating photochemical smog. Finally, even with a particle trap, diesel vehicles still emit more particles than do gasoline vehicles.
Jacobson provides analysis and figures to show that
when diesel vehicles have 30% better mileage than gasoline vehicles, diesel vehicles emitting particles continuously at a particulate matter emission standard of 40 mg/mi or 80 mg/mi may warm climate more than gasoline vehicles for more than 100 yr for a CO2 lifetime of 30 years…. However, diesel emitting at 10 mg/mi (Tier 2, bins 2-6 emission standard) may
warm climate relative to gasoline for about 10 yr at 30% higher mileage.
However, because no diesel vehicle available in the U.S. in 2006, 2005, or 2004 emitted less CO2 than did the best gasoline vehicle available, the 30% scenario in not applicable to the best available vehicles in the United States. As such, 2006 and earlier diesel vehicles sold in the U.S. all caused more global warming than did the best gasoline cars available, over a 100-year period.
And Jacobson also explains ...
... when diesel vehicles have 15% better mileage than gasoline vehicles, the diesel vehicles cause more global warming over 100 years, regardless of whether they are emitting fossil-fuel soot at a particulate matter emission standard of 10 milligrams per mile (mg/mi), 40 mg/mi, or 80 mg/mi and regardless of the atmospheric lifetime of carbon dioxide (30 or 50 years). This conclusion applies to diesel vehicles having 0-15% better mileage as well.
I did not see anything in the testimony of the other experts that called into question these conclusions.
To repeat the bottom line: If you care about global warming, don't buy a diesel car (certainly not in this country), and if you must buy a diesel, only get a new one with a very good particle trap. And the corollary -- unless you need a much bigger car, you just can't beat the Prius for total greenhouse gas emissions in this country.
Here is the abstract of "Global and regional climate changes due to black carbon":
Black carbon in soot is the dominant absorber of visible solar radiation in the atmosphere. Anthropogenic sources of black carbon, although distributed globally, are most concentrated in the tropics where solar irradiance is highest. Black carbon is often transported over long distances, mixing with other aerosols along the way. The aerosol mix can form transcontinental plumes of atmospheric brown clouds, with vertical extents of 3 to 5 km. Because of the combination of high absorption, a regional distribution roughly aligned with solar irradiance, and the capacity to form widespread atmospheric brown clouds in a mixture with other aerosols, emissions of black carbon are the second strongest contribution to current global warming, after carbon dioxide emissions. In the Himalayan region, solar heating from black carbon at high elevations may be just as important as carbon dioxide in the melting of snowpacks and glaciers. The interception of solar radiation by atmospheric brown clouds leads to dimming at the Earth's surface with important implications for the hydrological cycle, and the deposition of black carbon darkens snow and ice surfaces, which can contribute to melting, in particular of Arctic sea ice.
Ask Umbra on green moving companies
EPA affirms California’s right to set tougher automobile emissions standards
Ask Umbra’s video advice on sunscreen
Comments
View as Flat
robertogreen Posted 11:55 am
19 May 2008
not to keep hammering away at the same point..
but it seems to me that it is a moral imperative for those who can afford it to buy prii and make them plug-ins. if you can spend 70 gs on a BMW, you can spend less to get a fully plugged-in prius getting well over 100 mpgs. today.
Permalink
GreenMom Posted 2:07 pm
19 May 2008
Is the same thing true...
...of B100?
I could buy a diesel car and join a local biodiesel coop selling B100. How would that stack up on carbon emissions vs. the Prius I currently own?
Thanks.
Permalink
dehada Posted 2:52 pm
19 May 2008
diesel will -- and should -- have a place
This is an interesting post, but one that does not adequately address the complexity of the issue.
The Prius is indeed a remarkable achievement, and perhaps the most remarkable thing about it is how "unremarkable" it is: you just get in and drive, and while it won't win any awards for performance or fun, it goes down the road just fine and produces very low emissions at the tailpipe.
But to elevate the Prius (and by association, Toyota) to deity because it gets 45ish mpg and isn't a diesel takes the praise too far. First of all, Toyota earns good CAFE credits for each model -- credits that can offset the poor performance of their much more profitable trucks and SUVs. Not counting its Lexus devision, Toyota sells six SUV models in the US, (more than Chevrolet or Ford) and is just pulling the wraps off its latest "Sequoia," a monster that is finally comparable in its excesses to the much-derided full-size American utes. From a business perspective, having the thrifty Prius to support sales of the thirsty Sequoia is great foresight, indeed.
It's also true that diesel produces more greenhouse gasses per gallon than gasoline, and this is because, on a volume basis, it packs more potential energy than a gallon of gas. But even adjusted for the higher emissions intensity of the fuel, the efficiency of the high-compression Diesel cycle trumps that of the spark-ignition Otto, particularly in the types of driving where hybridization shows the biggest gains (idling and stop-and-go) and also in the types of driving where hybrids produce no advantage (sustained high speeds and towing). Over-the-road trucks don't use diesel because it's macho, but because it is so much more efficient than gasoline. Look no further than the geniuses at Toyota, who will soon be installing diesel engines into their US versions of the Tundra and Sequoia. For many, many, years, they have sold diesels overseas.
The point about the climate effects of "carbon black" is particularly troublesome to me because you're the bold takeaway from your post portrays the science behind the issue in the same light as the well-documented science behind the climate effects of CO2. Even calling the particulate matter from diesel engines "carbon black" is a term that, like "Dihydrogen Monoxide," sounds like something we should automatically reject. Meanwhile, our understanding of particulate emissions is ever-evolving. Most of the stuff comes from things like volcanoes, crop burning, cowpie stoves, barbeques, etc. instead of diesels. Even gasoline engines, whose particulate emissions are now thought to be much, much greater than previously assumed - just in much smaller particles that could rise higher in the atmosphere than their diesel counterparts.
The pollution controls for diesels are finally coming into their own, now that we've cleaned up the dirty fuel that precluded them in the US until 2007. It's true that some take an efficiency toll, but this is nothing like the huge hits gasoline engines took in the late 1970s when their emissions equipment became standard. In fact, the latest engines from Volkswagen, Mercedes, BMW, and even the relative newcomer, Honda, will produce fewer particulates than gasoline engines, without any discernable fuel economy penalty. Many of these cars will be much better suited to the type of highway driving many Americans do. While we all wish our driving patterns were different, it does make sense to use the technology that is best for the task. Give diesel emissions controls a chance to mature - just a decade after catalytic converters became standard on gas engines, their performance and cost penalties became negligible.
Finally, it's worth mentioning that diesel, by virtue of its much lower vapor pressure, has some inherent advantages over gasoline in evaporative emissions and safety.
None of this is to diminish the Prius, which is for many people an excellent choice, if they have to drive at all. But to count among its strengths "it's not a diesel," and to credit that strength to a benevolent and forward-thinking auto company is a stretch. If we're really serious about cutting the environmental impacts of human transportation, we'll have to combine massive paradigm shifts with a full suite of promising technologies. The Prius alone won't do it: hybrids will join diesels, biofuels, lightweight materials, and a host of other promising technologies as parts of a complex solution to a complex problem.
Permalink
Phillip Huggan Posted 3:22 pm
19 May 2008
sot as CO2e
The logical conclusion of the March 24 2008 soot article, if the research is verified or if such verification takes to long, is for environmentalists to lobby the UNFCCC, UNEP, EPA and other such agencies to include soot as a CO2e in existing and future GHG reduction frameworks.
By far the cheapest way to prevent near-term lung disease and long-term starvation/dehydration deaths in this regard is to rapidly induce (fund) the 3rd world to switch to clean burining stoves.
Permalink
moehrlei Posted 12:36 am
20 May 2008
Throwing out the baby with the bath water
I own a VW Jetta (diesel) that gets 45mpg highway. Granted, I love a Prius, but to only compare diesel to a Prius is simply ignoring the rest of the pack. You're stacking the deck.
Compare diesel to non-hybrids and the numbers change. Not everybody can buy a Prius!
I've also heard VW is making a 69mpg diesel hybrid soon (but not selling it in the US, go figure). I'm betting a 69mpg diesel hybrid will beat the Prius. So then we'll have to junk our Prius and buy all new... Well, you see where I'm going...
No individual raindrop ever considers itself responsible for the flood.
Permalink
enki Posted 12:43 am
20 May 2008
One Step Further
It would be possible to improve the fuel economy of any internal combustion vehicle (cars, trucks, ships, trains) by 30 to 60 percent. Even jet aircraft could probably be converted to run this way.
This would reduce CO2 emissions by 30 to 60 percent. If we did it on a worldwide basis we could solve (or at least postpone) our climate crisis as well as stretching out our fuel supply for many years.
This would be able to be achieved by putting a steam reformer on vehicles. This device takes water and a carbon or hydrocarbon and combines the two producing CO and H2. The vehicle runs on this CO/H2 Synfuel.
A reformer was developed by the Pacific Northwest Labs and successfully used in Iraq by the US Army to produce H2 fuel for fuel cell generators on the battlefield. They lost their funding for the project though and now it is more or less mothballed.
Dual Fuel systems are on the market which, although intended for natural gas, would allow vehicles to be converted to run on this Synfuel.
For that matter, in areas of the world where petroleum resources are limited, this same CO/H2 synfuel could be made from coal or any other source of carbon such as charcoal or torrified plant materials. You wouldn't have to go through the extra steps involved in the coal to liquids process in that case.
So a real solution to the climate crisis does exist. Unfortunately the oil companies won't support it because it would cut their oil sales in half and enviros won't support it because it doesn't totally abandon carbon fuels.
Mike Johnston
Permalink
amazingdrx Posted 12:52 am
20 May 2008
Throw out diesel?
Another alternative is to convert them to run on biogas. That would be good with trains, trucks, construction equipment, tractors, and even ships.
Certainly don't build or buy anymore diesel powered cars though.
Converting existing diesel cars to methane is a good alternative, but converting all cars to plugin hybrid is far better.
http://amazngdrx.blogharbor.com/blog
Permalink
moehrlei Posted 12:54 am
20 May 2008
No Diesel Hybrid
I did some more digging and spoke too soon. VW has a diesel hybrid Golf demo vehicle, but have recanted and will not produce it. Too expensive. Sad.
No individual raindrop ever considers itself responsible for the flood.
Permalink
amazingdrx Posted 12:55 am
20 May 2008
Sorry enki
It was/is a scam. Widely exposed, but still circulating on the net. It was too good to be true, a perpetual motion type scam.
Like the majic hydrogen economy, it is merely diversion.
http://amazngdrx.blogharbor.com/blog
Permalink
Biodiversivist Posted 1:34 am
20 May 2008
GreenMom
"Is the same thing true of B100? I could buy a diesel car and join a local biodiesel coop selling B100. How would that stack up on carbon emissions vs. the Prius I currently own?"
B100 emits roughly 50% less "soot" than diesel, but that is roughly 50% more "soot" than a new gasoline powered car (especially a Prius).
As for greenhouse gases, we are talking mostly CO2. The CO2 coming from the tail pipe of B100 is roughly the same as diesel. On a lifecycle basis, B100 will release roughly half as much CO2 only if you ignore crop displacement effect and nitrous oxide (300 times worse than CO2) release from agriculture.
In the end, it all comes down to biodiversity. Poison Darts--Protecting the biodiversity of our world
Permalink
enki Posted 1:36 am
20 May 2008
excuse me?
Hi amazingdrx,
What was a scam? Nothing I talk about is unproven or even fringe science and certainly not an internet scam. Perhaps you are confusing what I am talking about with something else.
There is a device which originated with pseudoscience/free energy types. This is an on-board electrolyzer which uses the electrical energy of the vehicle to produce H2 from water. This device doesn't work as described. It can't. I spent a lot of time on energy related newsgroups and such so I know about most of the scams (even the well intentioned ones).
What I am describing is something totally different and I can provide you with plenty of hard science to back me up. I would really like to get more public awareness of this concept going because I think it is a valuable addition to our energy portfolio which is being neglected at present.
Mike Johnston
Permalink
amazingdrx Posted 1:56 am
20 May 2008
Ooops
You are right enki, I took the steam reformer plan as another perpetual motion hydrogen scam. That's very different then, never mind.
Another alternative does this without the need for the steam reformer.
A solid oxide fuel cell that is inexpensive, anti-fouling and runs on multiple fuels without a reformer. This extracts 50% of the energy from the fuel, directly as electricity. A cogeneration gas turbine generator is added to claim another 25% from the hot gases exiting the cell.
This technology is cost competitive and scalable. A backup generator for a car of maybe 10 kw up to a 100mw power plant running on biogas to backup a renewable power grid.
1000 pound hypercars the same size as a Prius could use a 10 kw fuel cell, lithium ion nano batteries, and a 40 hp electric motor, run on biogas/gasoline flex fuel. And get 60 miles on a plugin battery charge.
That is technologically feasible at this time. mass produced in the millions they could be sold to consumers for 15 k. When will China build them? Detroit sure isn't. Toyota has a hypercar demonstrator similar to this, without the solid oxide fuel cell.
http://amazngdrx.blogharbor.com/blog
Permalink
Erik Hoffner Posted 2:06 am
20 May 2008
biodiesel coop selling B100
GreenMom, Biodiversivist is right in part, but it's all about the feedstock. It's possible that your possible coop's fuel has little climate impact to do with 'conversion' of cropland, but look into it. (But biodiesel beats fossil in most pollution categories by a goodly margin, except NO2)
In western Mass we can buy biodiesel from 100% waste/non-food sources, which is the best case scenario, and in which case, Mr Romm is off target with this post. I don't know of any recycled gasoline running in a Prius.
Erik
The Orion Grassroots Network: 1,200+ grassroots groups working for conservation & more
Permalink
meander Posted 2:09 am
20 May 2008
Diesel complexity
Professor Jacobson's analysis is interesting, if somewhat overly complicated. I hope we see many other analyses of diesel vs. gasoline as the new clean diesels are released in the future so that consumers can make informed decisions.
Jacobson's comparison of a very efficient gasoline car with a diesel car makes some sense, but it is also worthwhile considering a like-for-like substitution: someone buying the diesel model instead of the gasoline model. For example, the diesel Jetta (50-60 mpg) instead of the gasoline Jetta (25-30 mpg). Or a diesel pickup instead of a gasoline one.
Regarding dehada's point about "carbon black" being an oversimplification: diesel particulate matter (PM) is indeed tremendously complex, but is essentially black carbon at its core. Diesel PM is composed of thousands of compounds and is emitted in a range of sizes. The core of diesel PM is made up of tiny particle that are almost pure carbon. These carbon particles -- which are the part of diesel PM that is "black carbon" -- are coated with various hydrocarbons and sulfur compounds in liquid or solid form. Professor Jacobson and other researchers have done some work examining the effect of PM composition on its climate change impact. (Some good background on diesel PM can be found at the South Coast Air Quality Management District.)
As for dehada's complaint that "[t]he point about the climate effects of 'carbon black' is particularly troublesome to me because you're the bold takeaway from your post portrays the science behind the issue in the same light as the well-documented science behind the climate effects of CO2," black carbon receives significant coverage in the IPCC reports. While its role is not as clearly understood as CO2's -- the IPCC rating for "level of scientific understanding rating" is "medium to low" (Figure TS-5 in the Technical Summary (PDF)) -- recent research, like the paper cited by Romm in the post, indicate that the problem of black carbon is even worse than the IPCC assessed.
Phillip Huggan makes a good point about international agreements, but there are numerous challenges to adding black carbon. The biggest is that unlike CO2, the nature of the PM -- what fraction is black carbon, the particle size, etc. -- depends highly on its source. The PM from a cookstove is not the same as the PM from a diesel engine (and the PM from a Chinese diesel is different from an Indian or American diesel). Furthermore, it is quite a bit harder to do an emissions inventory. With CO2, you can multiply the fuel consumption by a conversion factor and get the emission of CO2, but it's not so simple with PM (an article on p. 2214 of the 9/27/02 issue of Science explains this clearly). A recent paper by Professor Tami Bond of the University of Illinois explores the topic in depth and concludes that even with all of the uncertainty it's possible to add black carbon to international negotiations.
As the commenters above point out, the current model year of diesel trucks and the next model year of diesel passenger cars will have pollution control technology that nearly eliminates the PM emissions. But there are still millions of trucks and pieces of off-road equipment in the U.S. without PM emission controls. Technology exists to make dramatic reductions on the in-use equipment, with California taking the lead. EPA also has funding this year to help pay for the equipment. With trucks and construction equipment having long lifetimes -- often 20 to 30 years -- cleaning up their exhaust can have significant health and climate benefits.
Permalink
enki Posted 2:25 am
20 May 2008
fuel cells n such
I agree that solid oxide fuel cells are great as are fuel cells in general. But these do nothing for vehicles already on the road. Perhaps the best application for the steam reformer would be on existing vehicles. This would give new fuel efficiency to such things as large ships, mass transportation systems and perhaps most importantly diesel trucks.
The amount of diesel fuel burned by heavy trucks each year worldwide is tremendous. In the US pretty much every item that a consumer buys has been on a truck at some point. The average diesel truck gets only 5-6 mpg and travels 100 to 140 thousand miles per year. That is roughly 25,000 gallons of diesel fuel per year per truck. Imagine the impact of doubling the fuel mileage of those vehicles!
On a different note, earlier this year I was asked to evaluate one of the "scam" systems you were talking about for a group of Danish investors. The on board electrolysis systems are being developed and marketed by several companies in the US and one in Canada and are actually being sold. One of these companies is currently on the 25 hot tech stocks list.
After reviewing the system and independent lab data on it I soon realized that there is no way these things work as described. There are models for passenger cars as well and the way that these show an increase in fuel mileage is that most require you to remove the oxygen sensor and thereby force the engine to run lean. So it SEEMS as though you are saving fuel but whatever savings you see are just because the engine is running lean and has nothing to do with the tiny amount of H2 being produced by the on board electrolyzer.
Mike Johnston
Permalink
Phillip Huggan Posted 6:56 am
20 May 2008
soot sources and computer models
Good point meander, about the soot sources. I suggested soot from inefficient 3rd world stoves be addressed because I read a 2006 paper that claimed soot from this source is twice as bad as soot from, say, forest fires. It isn't just soot that would be difficult to calculate as a CO2e. C02 from airplanes is 2-4x as bad as from other sources. Planting coniferous trees may result in a positive temperature forcing because of the reduced winter snow cover. It is known hydro dams in northern or mid latitudes are generally okay, but in the tropics are "bad" (I think because carbon in tropical soils gets unsequestered). Even something as basic as cloud climate forcing is dramatically affected by altitude. I guess this is a warning for administrative structures to adapt to new scientific findings fast.
The last time I attempted a layman's guess at unresolved science I was wrong (I thought fast melting Bering Sea ice cover was because of altered ocean currents but it was really changes in cloud cover), but I'll try again. This new computer model: http://news.bbc.co.uk/2/hi/science/nature/7376301.stm
suggests surface temperatures should be following the green dotted line. But they are higher. I'll hypothesize they are higher because of the soot underaccounting. The scary thing about this graph is that it doesn't extend beyond 2025. Beyond 2025, I think the ocean circulation pattern would cause a dramatic warming beyond what previous computer models suggested. Another scary thing is the model suggests global climate is very sensitive to ocean currents, and most/all computer models underrepresent the amount of freshwater that will be delivered into oceans in the decades ahead.
I also suggested focusing upon sooty stoves because of the health benefit, the 2x soot multiplier over other soot sources, and soot in general because it only lingers in the air for a few weeks; for this emissions source, the warming could immediately be reduced.
Permalink
Biodiversivist Posted 1:39 pm
20 May 2008
Partially right
I'm with Eric, if you are going to burn biodiesel, make sure it is made from waste products, and not from something that displaces crops or carbons sinks.
However, gasoline tailpipe emissions are less than biodiesel regardless of feedstock. Biodiesel pollutants (CO2 is a greenhouse gas, not a pollutant regulated because of health concerns) are quite a bit higher than an equivalent gasoline car.
"But biodiesel beats
fossil[diesel] in most pollution categories by a goodly margin, except NO2"Biodiesel beats regular diesel, not an equivalent gasoline car. The following chart compares the 2006 gasoline Jetta to the 2006 diesel Jetta.
If burning biodiesel, NOx would be about 10% higher and particulate matter (PM, or soot) about 50% lower than the values listed for the diesel Jetta.
Cleaner diesels are on the way.
http://home.comcast.net/~russ676/biodiesel/img5.gif
In the end, it all comes down to biodiversity. Poison Darts--Protecting the biodiversity of our world
Permalink
dehada Posted 4:28 am
21 May 2008
those are limits, not results
Note that the values in that chart are the limits for each category, not test results.
The diesel may have much lower CO emissions than the gas, for example.
Permalink
Erik Hoffner Posted 5:13 am
21 May 2008
neutral
True, dehada. And regardless of whether gasoline emits less CO2 than biodiesel, if your fuel is waste-derived, it's virtually carbon neutral.
There is no reused gasoline.
Erik
The Orion Grassroots Network: 1,200+ grassroots groups working for conservation & more
Permalink
Biodiversivist Posted 12:51 am
22 May 2008
That argument swings both ways , dehada
They are limits for gasoline cars as well, not results. Gasoline car emissions are also often well below the limits when new. As cars age their emissions go up. The diesels will approach their limits as will the gasoline cars.
There is no doubt, Eric that biodiesel from waste grease is better from a CO2 perspective than gasoline. I was just clearing up the misconception that regulated tail pipe emissions are lower for biodiesel than regular gas. It's a trade off, but one that should go away when new generation diesels show up with better pollution controls.
In the end, it all comes down to biodiversity. Poison Darts--Protecting the biodiversity of our world
Permalink
paulanthony212 Posted 5:50 am
23 May 2008
I had to resort to creating my own hybrid..sort of
This gas crisis is so out of hand, that I've resorted to drastic measures. Recently I converted my 04 Cadillac to utilize water as fuel from an easy to install kit, I obtained online from a company called Water4fuel.info
Permalink