Hydrogen economy could impact the stratosphere

According to conventional wisdom, hydrogen-fuelled cars are environmentally friendly because they emit only water vapour - a naturally abundant atmospheric gas. But new research shows that leakage of the hydrogen gas that fuel such cars could potentially cause problems for the upper atmosphere.

Researchers from the California Institute of Technology report that the leaked hydrogen gas that would inevitably result from a hydrogen economy, if it accumulates, could indirectly cause as much as a 10% decrease in atmospheric ozone.

If hydrogen were to replace fossil fuel entirely, the researchers estimate that 60 to 120 trillion grams of hydrogen would be released each year into the atmosphere, assuming a 10-to-20% loss rate due to leakage. This is four to eight times as much hydrogen as is currently released into the atmosphere by human activity.

Because molecular hydrogen freely moves up and mixes with stratospheric air, the result could be the creation of additional water at high altitudes and, consequently, an increased dampening of the stratosphere. This in turn would result in cooling of the lower stratosphere and disturbance of ozone chemistry.

The question of whether or not hydrogen is actually bad for the environment hinges on whether the planet has the ability to consume excess hydrogen. Man-made hydrogen will either be absorbed in the soil - a process that is still poorly understood but likely free of environmental consequences - or react with other compounds in the atmosphere.

The balance of these two processes is important. If the soil absorption process dominates, a hydrogen economy might have little effect on the environment. But if the atmosphere is the big player, the stratospheric cooling and destruction of ozone are more likely to occur, according to the research.

'Understanding the effects of hydrogen on the environment now should help direct the technologies that will be the basis of a hydrogen economy. If hydrogen emissions present an environmental hazard, then recognising that hazard now can help guide investments in technologies to favour designs that minimise leakage,' said physics research scientist Tracey Tromp.

'On the other hand, if hydrogen is shown to be environmentally friendly in every respect, then designers could pursue the most cost-effective technologies and potentially save billions in needless safeguards.'

'Either way, it's good for society that we have an emission scenario at this stage,' says Assistant Professor of Geochemistry John Eiler. 'In past cases - with chlorofluorocarbons, nitrogen oxides, methane, methyl bromide, carbon dioxide, and carbon monoxide - we always found out that there were problems long after they were in common use. But this time, we have a unique opportunity to study the implications of a new technology before it's even a problem.'