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At a global scale, the "rains out of the atmosphere" bit mostly covers it. Condensation and evaporation processes tend to make water vapor largely self-regulati

At a global scale, the "rains out of the atmosphere" bit mostly covers it. Condensation and evaporation processes tend to make water vapor largely self-regulating, shifting around quantities of water that dwarf human factors. However, where does the article mention water vapor? They're doing electrolysis, i.e., cracking water molecules apart. The desired result is the liberated hydrogen; the waste is oxygen--hopefully O2, or if you're unlucky O3, which is a pollutant in the lower atmosphere.

pyre 17y ago
I was under the impression that when using hydrogen for fuel, the by-product was water (at least in automobiles). The article just triggered the question, I wasn't necessarily commenting on the technology. > At a global scale, the "rains out of the atmosphere" bit mostly covers it. Condensation and evaporation processes tend to make water vapor largely self-regulating, shifting around quantities of water that dwarf human factors. I was thinking more on a local level. I realize that water vapor will dump out of the atmosphere (unlike CO2) so it for the most part will not be a greenhouse gas. My question was on whether or not large amounts of water vapor being released from cars will cause local ecosystem changes. (i.e. If every vehicle in NYC or Los Angeles ran on hydrogen, would it cause average rainfall in the immediate or surrounding areas to increase? What about yearly average ratio of cloudy vs sunny days?) Obviously people in middle-America (for example) probably won't cause much of a local impact, but what about major urban centers?
- donaq 17y ago
  As I understand it, they're getting the hydrogen from water in the first place, so...
  - pyre 17y ago
    Who says that will be locally though? I doubt they will be turning water into hydrogen fuel locally in places like the US Southwest where they already have issues with getting in fresh water?
    - donaq 17y ago
      I see what you mean. However, I wonder if they could utilize used water for conversion to hydrogen. And if so, whether it would be enough.
- camccann 17y ago
  I was under the impression that when using hydrogen for fuel, the by-product was water (at least in automobiles). The article just triggered the question, I wasn't necessarily commenting on the technology. Oh, sorry! Yes, burnt hydrogen is water. My question was on whether or not large amounts of water vapor being released from cars will cause local ecosystem changes. (i.e. If every vehicle in NYC or Los Angeles ran on hydrogen, would it cause average rainfall in the immediate or surrounding areas to increase? Well, large urban areas already have significant impacts on the local climate--e.g., the heat island effect: http://en.wikipedia.org/wiki/Urban_heat_island http://en.wikipedia.org/wiki/Urban_heat_island The significant factor, I'd think, would be the amount of water being introduced, which in relative terms would be trivial amounts for most climates. New York is already plenty humid, for instance. I'd guess that any impact from increased ambient humidity would be swamped by the heat island and other such effects, except perhaps in an extremely arid climate.
- wglb 17y ago
  Gasoline-powered ICEs also produce water vapor. One might assume that the water vapor output produced by hydrogen-powered vehicles is on the same order as the ICE that is replaced.
  - pyre 17y ago
    I realize that water is produced by burning gasoline too, but since the only by-product of burning hydrogen is water (IIRC) I assume that the amount is larger.
    - ars 17y ago
      Most of the energy from burning gasoline is from the hydrogen in the gasoline. It's about a 1 to 2 ratio of carbon to hydrogen. (i.e. 2 hydrogens for each carbon). So twice as much water as carbon dioxide when burning gasoline. And on top of that the hydrogen releases more energy than the carbon (for each atom). So if you have no carbon, just hydrogen it might be 25% more water (just a guess off the top of my head).

pyre 17y ago

I was under the impression that when using hydrogen for fuel, the by-product was water (at least in automobiles). The article just triggered the question, I wasn't necessarily commenting on the technology. > At a global scale, the "rains out of the atmosphere" bit mostly covers it. Condensation and evaporation processes tend to make water vapor largely self-regulating, shifting around quantities of water that dwarf human factors. I was thinking more on a local level. I realize that water vapor will dump out of the atmosphere (unlike CO2) so it for the most part will not be a greenhouse gas. My question was on whether or not large amounts of water vapor being released from cars will cause local ecosystem changes. (i.e. If every vehicle in NYC or Los Angeles ran on hydrogen, would it cause average rainfall in the immediate or surrounding areas to increase? What about yearly average ratio of cloudy vs sunny days?) Obviously people in middle-America (for example) probably won't cause much of a local impact, but what about major urban centers?

donaq 17y ago
As I understand it, they're getting the hydrogen from water in the first place, so...
- pyre 17y ago
  Who says that will be locally though? I doubt they will be turning water into hydrogen fuel locally in places like the US Southwest where they already have issues with getting in fresh water?
  - donaq 17y ago
    I see what you mean. However, I wonder if they could utilize used water for conversion to hydrogen. And if so, whether it would be enough.
camccann 17y ago
I was under the impression that when using hydrogen for fuel, the by-product was water (at least in automobiles). The article just triggered the question, I wasn't necessarily commenting on the technology. Oh, sorry! Yes, burnt hydrogen is water. My question was on whether or not large amounts of water vapor being released from cars will cause local ecosystem changes. (i.e. If every vehicle in NYC or Los Angeles ran on hydrogen, would it cause average rainfall in the immediate or surrounding areas to increase? Well, large urban areas already have significant impacts on the local climate--e.g., the heat island effect: http://en.wikipedia.org/wiki/Urban_heat_island http://en.wikipedia.org/wiki/Urban_heat_island The significant factor, I'd think, would be the amount of water being introduced, which in relative terms would be trivial amounts for most climates. New York is already plenty humid, for instance. I'd guess that any impact from increased ambient humidity would be swamped by the heat island and other such effects, except perhaps in an extremely arid climate.
wglb 17y ago
Gasoline-powered ICEs also produce water vapor. One might assume that the water vapor output produced by hydrogen-powered vehicles is on the same order as the ICE that is replaced.
- pyre 17y ago
  I realize that water is produced by burning gasoline too, but since the only by-product of burning hydrogen is water (IIRC) I assume that the amount is larger.
  - ars 17y ago
    Most of the energy from burning gasoline is from the hydrogen in the gasoline. It's about a 1 to 2 ratio of carbon to hydrogen. (i.e. 2 hydrogens for each carbon). So twice as much water as carbon dioxide when burning gasoline. And on top of that the hydrogen releases more energy than the carbon (for each atom). So if you have no carbon, just hydrogen it might be 25% more water (just a guess off the top of my head).