The prospects for alternative energy are rising along with the price of gas, and any discussion of future fuel sources is bound to include hydrogen. Hydrogen-powered cars wouldn’t produce noxious emissions or carbon dioxide—just water. Sounds great, but stratospheric chemist Kristie Boering worries that a “hydrogen economy” might have unforeseen consequences. We caught up with her in her Giauque Hall office, where kinetics equations and her son’s drawings compete for whiteboard space, to see why she’s concerned.
California magazine: Hydrogen’s the most abundant element in the universe. Why worry about a little more on Earth?
Boering: Hydrogen may be the most abundant element in the universe, but Earth is filled with oxygen. Molecular hydrogen (H2) is a reduced gas produced in an oxidizing atmosphere; a lot of that’s in water—it’s in H2O, it’s oxidized already. That we have any molecular hydrogen at all is pretty amazing. If we were to go to a hydrogen fuel cell economy and we produce a lot of hydrogen, and some fraction escapes (because it’s notoriously difficult to contain that small molecule), then we might see emissions equal to or greater than what’s produced naturally. Because it’s such a reactive gas…that could change the balance of chemistry in our atmosphere.
CM: What keeps it in balance now?
B: The atmosphere, and microbes that use H2 as their energy source. Just like we want to use hydrogen as our energy source, particular microbes that live in soils use it as [theirs]. There’s nothing new under the sun, we just need to do what plants and microbes do already. Of the total hydrogen emissions per year, we think about a quarter is coming from human activity and the rest is from natural sources.
CM: So, is hydrogen really a clean alternative to fossil fuel?
B: What’s great, what’s environmentally terrific about hydrogen [technology]—depending on how you produce the hydrogen in the first place—we might be able to dramatically eliminate carbon dioxide emissions to the atmosphere. The other nice thing is, you could reduce…local air pollution. But it might cost some other environmental consequences, and we want to make sure those are minimal.
The analogy I like to make is that burning fossil fuel is great: We don’t have a bunch of horse manure all over the place; gasoline is easy to store, relatively safe. But now we have this CO2 problem with climate change. CFCs were great as refrigerants because they were inert and saved lots of lives because you didn’t have to run your refrigerator using ammonia or something explosive or toxic. The other halogens are used as fire extinguishers. They’re super inert, aren’t flammable, and that’s the beauty of them. But that’s the problem with them. They are so inert they go up to the stratosphere, where they finally break apart and destroy the ozone layer. All these things that seem great wind up having some environmental consequences.
CM: And what might be the consequences of excess hydrogen?
B: One is that if a lot of hydrogen were to escape, it could get into the stratosphere, oxidize, and form water. The stratosphere is dry. That’s important because more water in the stratosphere can destroy ozone. A lot of the modeling suggests it’s not going to be a large effect, but it’s something we want to keep thinking about.
The other thing is that down here in the troposphere, it would start reacting with hydroxyl radicals. Hydroxyl is the detergent of the atmosphere. It reacts with anything that is even slightly chemically reactive and takes it out of the atmosphere. Methane reacts with hydroxyl, and [methane’s] a greenhouse gas. If we put a lot of hydrogen in the atmosphere, we’re going to decrease the ability of the hydroxyl radical to take things like methane out, and might indirectly increase the greenhouse effect.
The atmosphere’s pretty complicated and very nonlinear. So far, we haven’t found something that looks like [hydrogen’s] a no-go. And that’s good. But there are still uncertainties, and we want to make sure there’s not some little feedback here that explodes into something big.