Hydrogen fuel is hostile to stratospheric ozone

by using hydrogen fuel cells -- the best alternatives to fossil fuels -- we may be heading towards another environmental disaster. This is the theory of researchers from the California Institute of Technology, usa. As per their investigation, large-scale use of hydrogen may disturb the balance of atmospheric chemistry and widen the ozone hole. Therefore, an extensive hydrogen economy should be designed carefully, else it may increase our problems instead of solving them. Furthermore, since hydrogen is a microbial nutrient, a change in its levels may have unforeseen effects on the microbes.

Naturally, a very minute quantity of hydrogen is present in the atmosphere, as it participates in the chemical cycles of water, pollutants and greenhouse gases, and thereafter gets oxidised into water. Although the photochemical reactions and absorption by soil determine the atmospheric levels of the gas, anthropogenic emissions like car exhaust also influence its concentration.

Problems can arise if large amounts of hydrogen are emitted due to inefficient production, storage, transport and use. According to the study, if all the current technologies (based on fossil fuel combustion) were to be replaced by hydrogen fuel cells, then its emissions would be roughly four to eight times more than the present rates. This would result in the doubling or tripling up of the atmospheric concentration of the gas.

Because molecular hydrogen freely moves up and mixes in the stratospheric air, the result would be the creation of additional water at high altitudes. This would lead to more dampening of the stratosphere, where most of the beneficial ozone is found. The excess humidity would cool the lower stratosphere and thereby disturb the ozone layer.

To estimate the anticipated effects, the researchers used a model called the Caltech/jpl 2-d. The simulations show that an increase in stratospheric water content caused by a quadrupling of hydrogen levels at the Earth's surface would result in a negligible change in stratospheric ozone concentration, but would have several indirect consequences, such as affecting the temperature of the lower stratosphere. An increase of 0.5 parts per million by volume in stratospheric water content will cool the lower stratosphere by 0.5c. The cooling would create more polar stratospheric clouds and hence delay the breaking up of the polar vortex, which plays a crucial role in ozone formation. The delay would mean that the ozone hole would become deeper, larger and more persistent. The model also predicts that a rise in the levels of hydrogen near the Earth's surface will alter the average hydroxyl ion (oh) concentration in the troposphere and the stratosphere, which in turn will affect the lifetimes of other trace gases like methane and carbon monoxide that react with oh.

The researchers admit their predictions are far from exact. Moreover, though soil is said to be one of the main 'sinks' for the gas, there is a lack of understanding about its mechanism and variation as regards to time and location. Consequently, scientists are not certain about how it will respond to an increase in the concentration of hydrogen.

According to the authors, the current situation is unique as the society has an opportunity to understand the potential environmental impact well ahead of the growth of a hydrogen economy. This contrasts with the cases of carbon dioxide, methyl bromide and lead, all of which were released into the environment before their effects were understood. "We most certainly have an unprecedented opportunity this time," says Tracey Tromp, the lead researcher.

If the gas is indeed bad for the ozone layer, should the transition to hydrogen-fuelled cars be abandoned? Not necessarily, Tromp asserts. "If it's the best way to provide a new energy source, then we can, and probably should, do it," she says, adding: "If we had the perfect foreknowledge of the effects of carbon dioxide a hundred years ago, would we have abandoned the internal combustion engine? Probably not; but we might have begun the process of controlling carbon dioxide emissions much earlier than we did."

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