The amount of hydrogen gas in the atmosphere increased from 330 to 550 parts per billion between 1852 and 2003. And researchers can’t quite explain that.

Everyone knows that the concentration of greenhouse gases in the atmosphere has increased considerably over the past century and a half. It underlies one of the greatest problems of our time: climate change. But often the focus is on the well-known greenhouse gas carbon dioxide (CO2), which in pre-industrial times had a concentration of about 281 ppm, but almost reached 420 ppm this summer.

hydrogen gas

Much less often you hear about molecular hydrogen (or hydrogen gas) whose atmospheric concentration is also generally believed to have increased significantly since pre-industrial times. “Hydrogen gas is a very simple molecule made up of two hydrogen atoms,” researcher John Patterson explains Scientias.nl from. “And humans produce it mainly by burning fossil fuels (hydrocarbons).”

But where we know fairly accurately how the concentration of a greenhouse gas such as CO2 has changed over the past 150 years, this was unknown for molecular hydrogen. Simply because researchers didn’t know how much hydrogen gas was in the atmosphere in pre-industrial times. A new study, lead author of by Patterson, is changing that.

Ice

Patterson and colleagues turned to the study on air bubbles trapped in the Antarctic ice. Once trapped under freshly fallen snow, those air bubbles are actually like time capsules, which can give us more insight into what the atmosphere was like when the snow fell. Patterson and colleagues sampled air bubbles that formed up to 169 years ago.

In line with expectations

And the research shows that the concentration of hydrogen gas increased by 70 percent between 1852 and 2003. That percentage was in line with expectations, says Patterson. “That’s roughly what we expected based on the increase in atmospheric methane (an important source of hydrogen gas) and the increase in fossil fuel combustion (another important source of hydrogen gas).”

Surprise

But the research also yields a surprise. Because the researchers had expected – based on the decrease in carbon monoxide – that the concentration of hydrogen gas would also decrease slightly in the 20th century. But that’s not the case; the concentration only increases. “Carbon monoxide and hydrogen gas are both released during ‘incomplete combustion’. It’s actually quite simple: if there isn’t enough oxygen available, the combustion of fossil fuels results in carbon monoxide and hydrogen gas instead of carbon dioxide and hydrogen. More pollution control and the introduction of three-way catalytic converters in cars are responsible for the decrease in carbon monoxide. However, we know that three-way catalytic converters also provide a comparable reduction in hydrogen gas in exhaust gases. So we expected that the atmospheric hydrogen gas would react in the same way as atmospheric carbon monoxide (and thus decrease, ed.).” But that is not the case. “There is no evidence that molecular hydrogen emissions have declined in the twentieth century.”

Mystery

How is that possible? “That’s the mystery!” says Patterson. At the moment, everything indicates that there are other, underestimated sources of hydrogen gas besides cars. “But more research is desperately needed.”

Effects

In any case, it is certain that the concentration of hydrogen gas has increased considerably in 150 years. And that is somewhat worrying. “Hydrogen gas is an indirect greenhouse gas,” says Patterson. “It reacts with hydroxyl radicals. Hydroxyl radicals are responsible for breaking down atmospheric methane (an important greenhouse gas). More hydrogen gas that reacts with hydroxyl radicals therefore means that fewer hydroxyl radicals are available to react with methane, increasing methane levels in the atmosphere. Hydrogen gas can also increase the amount of water vapor in the stratosphere (and water vapor is also a greenhouse gas).” The increase in stratospheric water vapor can also lead to an increase in polar stratospheric clouds that contribute to the depletion of ozone.

Hydrogen Economy

Researchers do have ideas about how the atmospheric hydrogen gas concentration will fare in the future. It is expected that this will only increase further – certainly if more and more cars start to run on hydrogen. “Some researchers estimate that if the ‘hydrogen economy’ really takes off, the amount of hydrogen in the atmosphere could increase by a factor of four.”

A good reason to keep a close eye on the concentration in the coming years. “Particularly because of the effects that an increase in hydrogen gas can have on the availability of hydroxyl radicals.” In addition, Patterson would also like to do more research into former atmospheric concentrations of hydrogen gas. Now they are known to us until 1853. “But we can go much further back with ice cores.” The still mysterious source of molecular hydrogen gas, which ensures that the atmospheric concentration continues to rise despite measures such as the introduction of three-way catalytic converters, also deserves more research. “It shows that we do not yet fully understand the biogeochemical cycle of hydrogen gas. More research into this is important, especially because the ‘hydrogen economy’ is likely to disrupt that cycle even further.”