Fuel Cell Powered Japanese Trains on Trial in July 295
ScorpFromHell writes "As per this yahoo! news item, "East Japan Railway Co. is to conduct a test run of the world's first fuel-cell-powered train in July.
The fuel cells, which generate power from a chemical reaction between hydrogen and oxygen, will help reduce environmental pollution compared to the existing electric and diesel engines, the company said."
But I wonder how much energy did it consume to produce those huge amounts of Hydrogen & Oxygen? Will it be lesser than the power generated by the reaction between them?
In other words, can this technology be used by countries with not so deep pockets as Japan?"
I think we all know the problem with this (Score:2, Informative)
Centralizing power generation should be more efficient than millions of smaller generators all over the place.
Now, it's just a matter of finding out if generating, transporting, and storing the required hydrogen is environmentally/economically better than diesel or gasoline.
Re:I think we all know the problem with this (Score:5, Informative)
You are half right. Fuel cells are neither an energy storage medium nor an energy source. The source of the electricity used to hydrolyze the water is the energy source. Hydrogen is the energy storage medium The fuel cell is an energy conversion device same as an internal combustion engine except way more efficient.
Re:I think we all know the problem with this (Score:2, Informative)
Not if they produced it from water...
Re:I think we all know the problem with this (Score:3, Funny)
Do you know some secret method for separating oxygen and hydrogen out of water that doesn't require energy? If so, please share it with me, I want to get rich :^)
But to address the question raised in the article: It most certainly did consume more energy to produce the hydrogen and oxygen than the fuel cell can recover from them. To do otherwise would be to break the laws of thermodynamics -- you can't get more energy out of a system than was already in it to start wit
Re:I think we all know the problem with this (Score:2)
Set it out in the sun. Sure, it's using energy, but energy that would have been effectively wasted, anyhow.
Re:I think we all know the problem with this (Score:2)
Re:I think we all know the problem with this (Score:2)
No, I'm not an idiot, and I'm not talking about evaporation.
See: http://www.pureenergysystems.com/news/2004/07/09/
Re:I think we all know the problem with this (Score:3, Insightful)
Sorry for assuming that you were an idiot, but your initial post was light on details and this is slashdot after all.
Re:I think we all know the problem with this (Score:2)
Really? If you distribute your power supply then you can take advantage of cogeneration...heat + power. I think the efficiency of distributed power actually goes up, the cost also goes up though.
Re:I think we all know the problem with this (Score:2)
Re:I think we all know the problem with this (Score:2)
hmmm (Score:3, Insightful)
I think a better question would be "Why isn't the U.S. doing more to be in the forefront of promoting alternative fuel sources?
Steve,
http://tail-f.net/ [tail-f.net]
Re:hmmm (Score:4, Interesting)
What you really should be asking "why isn't the U.S. promoting research and development of alternative fuels capable of meeting the energy needs of a vast industrial economy that are compatible with existing power production facilities." That's a bit of a tougher nut to crack, and the answer won't something as simple as "hydrogen".
Re:hmmm (Score:2)
Perpetuum Mobile is back! (Score:5, Funny)
Re:Perpetuum Mobile is back! (Score:2)
Good echnology applied at the wrong place (Score:5, Interesting)
Fuel cells are useful for energy storage. Perfect to, say, drive a car for a few hours, then dump some more into your energy storage, and drive back, in any direction. Also, they're good to bring energy to remote location. Setup a quick electricity generator in the middle of nowhere. But for trains? They go on tracks, so installing a few wires isn't too expensive or difficult, making the electricity transportation far more efficient trought wires than fitting fuel cells on every locomotive, and then carrying all that hydrogen and
Really, i see this as the wrong match of a technology to a need.
Re:Good echnology applied at the wrong place (Score:5, Interesting)
While you could be right, it's not like wired electrical trains are perfect, that wire infrastructure ISN'T simple to maintain, I witnessed that the other day when a train on my line ripped down the wires for 2 of the 3 tracks.
Also isn't power loss for DC over wires rather large? I'd think if you had an efficient way of storing and extracting that power to just carry it with the train it would be much better.
Also who knows, maybe one day all trains will become electric with this technology, even the ones in the middle of nowhere, I know that electricity had to be generated somewhere but those big power stations have a lot more potential to create clean(ish) energy than those dirty old diesel engine trains.
Re:Good echnology applied at the wrong place (Score:3, Interesting)
Afterall, who says this has nothing to do with environmental goals and simply a way to get their train infrastructure deeper into rural areas while mainting their high level of reliability?
If a fuel-cell train goes down you can still use the track and route around that track portion (given you have enough tracks), but
Re:Good echnology applied at the wrong place (Score:2)
Power loss is described as follows:
P = IV
V = I/R
P = I(I/R)
P = I^2/R
Resistance (in the wires) is pretty much fixed - we can't do much about that. However, we can do something about current. If we transform the power to an insanely high voltage (say, 300-500kV), we minimise transmission loss by reducing current (Remember, P
Re:Good echnology applied at the wrong place (Score:2)
Re:Good echnology applied at the wrong place (Score:2)
After several steps of yes-but.
Power loss for *high current* over wires is high. So you want to transmit at high voltage, which lets you send the same power at lower current. Using AC lets you step the voltage up and down with transformers, which is drop-dead easy. Until fairly recently it was out of the question to get affordable, reliable equipment to change DC voltage at commercial power levels.
Re:Good echnology applied at the wrong place (Score:2)
Re:Good echnology applied at the wrong place (Score:2)
Re:Good echnology applied at the wrong place (Score:5, Informative)
These trains are actually more like busses, they have maybe 2-4 cars and run infrequencly, so electrifying these tracks doesn't make much economic sense; or is just downright ugly and expensive to maintain. They are mostly diesel powered (with the engines located below the passenger compartments, there is no seperate loc).
For these, replacing a noisy diesel engine with much quieter electrical ones makes very good sense.
Re:Good echnology applied at the wrong place (Score:2)
In the end, I'd rather see a diesel-electric hybrid train [thewatt.com] than a fuel cell train and I'd rather see battery electric vehicles [thewatt.com] than fuel cell ve
Re:Good echnology applied at the wrong place (Score:2)
For what its worth, most commuter trains in the US (e.g. Amtrak, Metra, etc.) run on Diesel fuel. The engine burns the fuel to produce electricity for use in an electric transmission. They
Re:Good echnology applied at the wrong place (Score:2)
Take a look at the track lengths in Australia.
My third least favorite thing about Japan (Score:2)
Good lord, bring on the fuel cells.
Btw, if you are wondering about the first two, they are 1: Japanese men are sexist pigs and 2: The "$"#"#$ last train runs around 11:30 pm!
Re:Good echnology applied at the wrong place (Score:2)
electric pollution? (Score:4, Insightful)
hold on a sec.... Electric train engines produce pollution? How is that possible?
Granted, a fair amount of power is lost in the transmission lines, but given that they're run at such a high voltage to begin with, that shouldn't be a huge issue (P=I^2*R). Is more power lost in the transmission process than the process necessary to manufacture and produce all this hydrogen and oxygen?
Fuel Cells are nifty as an energy storage medium, but for trains, they seem wholly inappropriate, especially when electric trains eliminate the need for a storage medium at all (and in a country as densly populated as Japan, this shouldn't be an issue at all)
Re:electric pollution? (Score:5, Informative)
Re:electric pollution? (Score:4, Insightful)
everybody pollutes (Score:2)
Some more details (Score:5, Interesting)
Summarized this is a test vehicle being used on a non-electrified line in a mountainous region. The advantages are less local pollution (which can be a significant issue in mountainous regions where diesel exhaust can linger or even concentrate in valleys) and no large capitol investment in line electrification & maintenance. A side benefit is the advantages of an electrical train without power lines intruding into the landscape.
As a regular user of urban commuter rail service this sounds like an interesting development. The cost of electrifying a rail line is prohibitive yet the all-electric engines are quieter and less polluting, a big sell in expanding service in urban & ex-urban areas. Technology like this could certainly quiet the complaints of many neighbors as well as improve the air quality near central stations.
Re:Some more details (Score:2)
They *could* just do the third-rail trick as per NYC, Chicago, etc. subway systems, and that would eliminate the overhead catenary lines.
Re:Some more details (Score:2)
3rd rail is not an acceptable substitute (Score:2)
Yes, except that would be incompatible with most railway designs whereas the fuel-cell models are drop-in replacements for diesels. Also you'd still be stuck with the huge cost of electrifying the line.
Then there's the problem of many railway lines not being secured along their length like the systems you're referring to. It'd be rather ugly the first time some person
length(Summary)/legth(Article) ... (Score:2)
Editors - how about feeding us some articles with some real info in them? There just might be some technical people in this crowd who'd read them.
Obey the Law!! (of Conservation of Energy) (Score:3, Insightful)
But I wonder how much energy did it consume to produce those huge amounts of Hydrogen & Oxygen? Will it be lesser than the power generated by the reaction between them?
However, I think we should question the efficiency of this. If it takes X amount of energy to run a normal train, but 4X to produce the fuel cell, then is that really a good thing? It's like people saying that electric cars are so much better for the environment. Instead of burning gasoline, you burn coal (or whatever) in the power plants. Is the efficiency of a power plant really so much better than your car?
I don't know the answer to that, but I'm sure there's a
Re:Obey the Law!! (of Conservation of Energy) (Score:2)
Anyway, my real comment is that AFAIK there's going to be very little (energetic) advantage in using a fuel cell train over an electric train. On the one hand, if you need to use power lines to g
Re:Obey the Law!! (of Conservation of Energy) (Score:2)
Re:Obey the Law!! (of Conservation of Energy) (Score:5, Interesting)
Much like biodiesel from recycled french fry oil doesn't scale, this method may not scale either, but it's good to actually have one to see how it pans out in real-world service.
It's no different really than Union Pacific's experiments with gas turbine locomotives, or US and European experiments with steam turbine locos, closed-cycle steam locos, etc.
I think more interesting will be how GE Locomotive's hybrid diesel-electrics work out. If the battery pack had enough amp-hours to replace one locomotive from the consist as a large train tries to power up a mountain grade, then perhaps it'll really justify itself. Of course, it won't work out on lines with multiple grades right after another (Appalachians?), but up places like Cajon Pass it might be beneficial.
Is the efficiency of a power plant really so much better than your car?
Yes, from a thermodynamic perspective it is, as well as economy of scale-wise. The coal plant is running at a steady state, and the average car engine does not. The Otto cycle engine's advantage is its flexible power output curve, which is needed for cars, especially in urban driving. Supplant a smaller displacement Otto-cycle engine that meets the power needs of the car to cruise at 70mph on the flats with an electric assist motor (instant full torque) and battery pack, and you kind of get the best of both worlds without trying to make the gas engine too complicated (i.e., variable displacement, etc).
Re:Obey the Law!! (of Conservation of Energy) (Score:2)
I would think that this is precisely where it would be most useful, provided there's enough power storage. At first thought I would guess that really the only difference between a hybrid diesel-electric train and a normal one is that the hybrid has batteries (or for all I know, a flywheel) and does regenerative braking, thus it has all the hardware that entails. I don't think it will necessarily reduce the number of locomoti
Re:Obey the Law!! (of Conservation of Energy) (Score:4, Insightful)
More energy is still cheaper and more "green" if you are getting it from nuclear, hydro, wind, solar, etc. It's also trivially easy to charge them off-peak, when the energy is cheaper to produce because it's available in excess.
4X wouldn't be a good number, but even 2X would work-out just fine, and there's no reason to assume it's anywhere near that bad, anyhow.
Yes, it certainly is. Even when you count the line losses, charger losses, battery losses, etc., you still come out ahead of burning gasoline directly. Besides that, your car doesn't have complex exhaust filtering and control systems, as power plants do. And, NIMBY should apply here, since the power plants can be far away from you, and polluting where there are far, far fewer people to be affected by it.
Electric cars would likely be charged at night, as well, when a much lower percentage of that power is comming from coal, and more is comming from hydro, wind, etc.
No statistics from me. I've posted them to
Re:Obey the Law!! (of Conservation of Energy) (Score:2)
Re:Obey the Law!! (of Conservation of Energy) (Score:2)
Re:Obey the Law!! (of Conservation of Energy) (Score:2)
What's it called? (Score:3, Funny)
Like a genuine,
Bona fide,
Electrified,
Six-car
Monorail!
Re:What's it called? (Score:2)
Re:What's it called? (Score:2)
hydrogen economy (Score:4, Informative)
Hydrogen is a method of TRANSPORTING and STORING energy. It is not a solution to energy generation. As a storage and transport method, IMSO (S=Scientific), it is not particularly cost effective, and has as much potential for unforseen concequenses as any other untested energy method.
That said, I am highly in favor of fuel cells in general, and am happy to see them adopted more often.
In relation to the question asked about poorer countries, I would also hasten to point out that the fuel cells themselves are expensive, as they require (I believe) a platinum catalyst.
That is all.
Re: (Score:2)
Re:JR and wrong priorities (Score:2)
Thermodynamics (Score:3, Informative)
"But I wonder how much energy did it consume to produce those huge amounts of Hydrogen & Oxygen? Will it be lesser than the power generated by the reaction between them?"
First law of thermodynamics says . . . NO!
And as Homer Simpson put it, "In this house we obey the laws of thermodynamics!"
But... (Score:4, Insightful)
But that's largely irrellevant if the energy to produce them was derived from an energy source that is not exausted by use, such as solar, hydro, or geothermal sources.
Re:But... (Score:2)
Fossile fuels (wait, wouldn't that defeat the purpose?), nuclear (misguided eco-nuts are against it), or solar (I'm pretty sure hampsters on wheels with dynamos are more cost-effective).
I never understood how the mass media has no grasp of thermodynamics. You only need to memorize 2 stinkin words to undertand our energy problems: ENTROPY and CONSERVATION.
1. Entropy: Physics is out to screw over the environment by making EVERYTHING less than 100% e
Re:But... (Score:2)
Nuclear is only a problem for some people... predominantly in the US, who are having a hard time forgetting 3-mile island.
Solar cells may not be very efficient... yet. But the point is that you don't drain its availability by using it. Wind power, by the way, is also a form of solar power, and is in quite common use already at various places around the world.
Geothermal energy and hydro are other sources of energy that are not ex
Re:But... (Score:2)
Well if you want to get technical, alcohol-powered vehicles are actually solar powered, along with hydro.
Why stop there?
The earth came from the a star, right? well I guess that means even geothermal and fossile fuels are solar powered.
Efficacy is as important as efficiency
Rich People should do stupid, inefficient things? (Score:5, Insightful)
What, rich people should do things that are economically stupid?
It's not about this being stupidly inefficient, yet Japan can afford to do it anyway because they're rich. The question is, which is a more efficient use of electricity (or, more generally,. resources), running an electric train, or running a hydrogen/oxygen fuel cell train? Whether you're rich or poor, you should still use the technology that works best for you.
I think it might have occurred to someone in Japan to check and see if this is better than running a conventional electric train in otherwise similar conditions before building it. Although it's quite possible they didn't care. It could be like ethanol [wikipedia.org] in the US, which is used for political reasons, not because it's an efficient way to improve the environment. Depending on who's counting, it generates between .7 and 1.5 times as much power as it consumes to make. We could reduce pollution (including carbon emissions) much more by spending the money we spend on ethanol on nuclear power, solar arrays, or wind power. Ethanol fuel, in it's present state, is government graft to benefit corn farmers and ease the conscience of environmentalists who don't understand it.
I am interested to know if this train really is about a great new technology for saving the environment, or a political ambition.
Re:Rich People should do stupid, inefficient thing (Score:3, Interesting)
My understanding is that it's possible for ethanol production from corn stocks to be energy-positive but it takes expensive equipment. However, it's pretty well-known that there are other stocks from which ethanol can be generated that are more easily energy-positive. You're quite right about the fact that ethanol production from corn stocks in the US is currently just another farm subsidy, though.
Of course, if you're really going to be doing biofuel, you're better off doing biodiesel, which is definite
What did they do? (Score:5, Funny)
What are they on trial for?
Huh? Ohhhhhh....
Re:What did they do? (Score:2)
even if it's a wash.... (Score:3, Insightful)
Even if it takes about the same energy to produce the chemicals, this is ok. Don't think of a fuel cell as an energy producer, it's an energy storage device. This is like a battery. When you charge a battery, you don't get a net increase in energy. You are merely moving electricity that is produced in an electric plant into the battery. The train is the same idea. With something the same size as a train, I can't see any reason not to just use a battery. In fact, you could potentially have a batery car or something like that to store the energy and it would be cheaper than fuel cells. Fuel cells are mainly interesting in automobile applications because their energy storage density is greater than Lithium batteries. Still it's good to see work being done on the fuel cell front.
Re:Chemical Reaction? (Score:5, Insightful)
http://en.wikipedia.org/wiki/Fuel_Cell [wikipedia.org]
Re:Chemical Reaction? (Score:3, Funny)
I hope you took the time to fix the mistake!
Re:Chemical Reaction? (Score:3, Insightful)
Second, your use of the phrase "power plant" implies using combustion to generate heat, which is then used to expand a gas to drive a piston to move a linkage etc. This is called a fuel cell instead because it uses the reaction between hydrogen and oxygen to produce electricity which then drives an electric motor and so forth.
In other words, H2 + O2 -> H2O can be used to drive combustion engines and fuel cells.
Re:Chemical Reaction? (Score:3, Insightful)
Except that fuel cells don't combust per se. Which was my point. The hydrogen acts as the Anode, the Oxygen as the Cathode, and the plates between them strip off the hydrogen electrons to create a voltaic imbalance. The actual combustion of the two is secondary to the energy generation, and is not directly used by the process. The only thing used is the attraction between the hydrogen and oxygen atoms.
A combustion engin
Re:Chemical Reaction? (Score:3, Interesting)
Re:Chemical Reaction? (Score:2)
And all this time I thought it was a race to see who could talk about Nazis first...
[I win!]
Re:Chemical Reaction? (Score:2)
RUN!!
Re:Chemical Reaction? - yes, and a very efficient (Score:5, Informative)
The way a fuel cell works is the same as burning straight Hydrogen. 4 Hydrogen atoms combine with 2 Oxygen atoms to form 2 Water molecules. When you burn Hydrogen, it happens all at once in one big pop (or bang!). In a fuel cell, the atoms dissolve into the water at the electrodes and combine in solution. The reaction is much more controled and generates an electric potential at the electrodes.
As far as efficiency is concerned, the seperation of Hydrogen and Oxygen (by electrolosis) from water and the subsequent recombination in a fuel cell (creating electrical energy) is over 95% efficient. That compares to around 30% for a good diesel engine.
In high school, I actully built a rudementary fuel cell as a science project.
Re:Chemical Reaction? - yes, and a very efficient (Score:3, Interesting)
Re:Chemical Reaction? - yes, and a very efficient (Score:4, Informative)
Re:Chemical Reaction? - yes, and a very efficient (Score:2)
Numbers are wrong. (Score:5, Informative)
OTH, if use a reformer rather than a regular storage system, you lose the bulk of the efficiency (lowers you to 30-40%). Combine that with the 80% motor, and you are in the 24-32% efficiency.
Sadly, an autmobile is around 20% efficiency. [howstuffworks.com] And that is only from the Gas forward. It does not include the previous inefficiencies.
Basically, we are using one of the worse systems possible. It just got developed and marketed first.
Re:Chemical Reaction? - yes, and a very efficient (Score:2)
The one big advangage of fuel cells is that the cycle is essentially the same as a storage battery, not a heat engine. It does
Re:Chemical Reaction? - yes, and a very efficient (Score:2)
A nice graph of fuel cell efficiency.
Practical fuel cell efficiency is around 50% (it is temperature dependent), less if you are using methanol instead of pure hydrogen.
Well to wheels: fuel cell vs. hybrid technologies? (Score:2)
So if w
Re:Chemical Reaction? - yes, and a very efficient (Score:5, Informative)
"As far as efficiency is concerned, the seperation of Hydrogen and Oxygen (by electrolysis) from water and the subsequent recombination in a fuel cell (creating electrical energy) is over 95% efficient."
Whoa! Sure that's the efficiency of electrolysis but then you have to compress and store the hydrogen (hydrogen storage is a whole thing in itself), then you have to feed it to a fuel cell that has an efficiency much less than 95%...usually less than 50% system efficiency. Overall, the total efficiency of hydrogen fuel cells is comparable to a diesel fueled vehicle, maybe even a bit less.
Of course, that's if you make the hydrogen by electrolysis. Most hydrogen comes from natural gas at the moment, which is less efficient and produces CO2.
----
theWattPodcast.com [thewattpodcast.com] - energy news and issues in an mp3
Re:Chemical Reaction? - yes, and a very efficient (Score:2)
As for dissolve... The atoms ionize at the electrodes (H gives up an electron to one electrode and O takes one from the other electrode) and dissolve into the electrolyte (which does not actually have to be liquid... It's usually some sort of gel in practical fuel cells). The electron given up by the O travels through the circuit from one electrode to the other, driving your load (i.e
Re:Chemical Reaction? - yes, and a very efficient (Score:2)
If the system efficiency is near 50% it's a lot better than diesel. Only the most efficient diesel reaches 50% efficiency and it's the size of a house, it's in a container ship. Last I checked it was the most efficient internal combustion engine on the planet. Granted, a turbo diesel is the most efficient internal combustion powerplant for automotive use, but that's not saying much since last I looked it up, the really efficient gasoline engines were hitting around 26%. Not sure where the automotive engine
Re:Chemical Reaction? - yes, and a very efficient (Score:2)
Yes, the initial energy does have to come from somewhere. In the end, it all comes from the sun (diesel is just rotten and compressed plant matter from a long time ago).
Direct solar energy is the ideal source of the energy to separate the water into hydrogen and oxygen.
Re:Chemical Reaction? - yes, and a very efficient (Score:2)
Okay, I'll bite here. Has anyone ever done the math to see how much electrical energy would be required to produce enough hydrogen and oxygen to power a number of fuel cell vehicles that's anywhere close to our current transportation needs? And then gone and multiplied that number by the energy output of the best solar panels? I haven't done the calculation, but I have this feeling that the area would just b
Re:Chemical Reaction? (Score:2)
Re:Chemical Reaction? (Score:2)
Re:Chemical Reaction? (Score:2)
Re:Hum (Score:4, Interesting)
In any case, I think it's worth it. We've researched fossil fuels too much. It's time to research about alternative energy sources.
no it's not worth it. (Score:5, Insightful)
Re:no it's not worth it. (Score:2)
Yeah, we need to look into more efficient hydrogen producing methods. But the market plays a big role in this, too. By having hydrogen-powered vehicles, there will be more demand for cheaper and more effective (and hopefully less polluting) hydrogen production methods - at least compared with our current demand for fossil fuels.
Re:no it's not worth it. (Score:2)
Re:no it's not worth it. (Score:5, Insightful)
Re:no it's not worth it. (Score:2)
Re:no it's not worth it. (Score:2)
Then there's high temperature energy sources - you can generate hydrogen directly through thermolysis. It is very efficient - 70% or so. That's much better than ~50% for electricity generation. Factor in a 70-80% fuel cell e
Re:no it's not worth it. (Score:2, Interesting)
Energy mentioned - so the nuclear advocates came (Score:5, Interesting)
Nuclear wants to be the one true energy monoculture - which is stupid when most of the installed plants are 1950's style economic white elephants and the newer designs like pebble bed lose the thermal energy economy of scale by having small safer units. It's a pity that the nuclear debate ranges between bare faced lies (too cheap to meter) and utter horror with little in between and so few agencies giving out real information. Find a real research reactor (clue - reasearch reactors in places like Indonesia, Pakistan, India, Israel, Nth Korea etc have a military bias) and listen to stuff that comes out of those places - they keep coming up with solutions to major problems that snake-oil salesmen trying to sell nuclear power pretend don't exist in the first place. A reasonable solution for waste storage has been worked out for a tiny fraction of the amount that was spent on advertising that nuclear power is "clean" and the stupid premise that if ash heaps at coal fired plants have traces of radioactivity then it's OK for nuclear power to spread radioactive waste about instead of constructively dealing with the problem.
Re:Hydrogen production (Score:2)
Re:A train or a space ship (Score:2, Informative)
Yes.
Hardly "most", but they certainly seem to be more active than most other countries. I mean, they actually build the things. :-)
Well, there's this [bbc.co.uk] crash [bbc.co.uk]... (It wasn't doing more than about 100 km/h (60 mph) at the time though)
Re:Alternative fuels are energy transport, not sou (Score:2)
More people die every year due to accidents in coal mining and accidents at coal-burning power plants than have died due to all the nuclear accidents put together.
More nuclear material is released into the atmosphere every year due to the burning of coal for electrical power alone (not counting heating) than has been released by all the nuclear accidents that have ever occurred. In 2000, the US alone released around 1250 metric tons of uranium and 5000 metric tons of thorium. Want another fucked up stat
Re:Fuel cell water vapor by product is a pollutant (Score:3, Informative)