The Nitrogen Problem

[NNadir]

18. The title of your post borders on an oxymoron.

They didn't give Haber the Nobel Prize because he saved a few cents over a great process, however.

There are, believe it or not, many tens of thousands of references on the topic other than Wikipedia, if you look.

Smil's book gives an excellent account of the entire situation with nitrogen fixation at the beginning of the 20th century. It may be better to read Smil's book than to provide popular links to popular websites. If you are truly interested in this issue, I would suggest you read it. It's an excellent work, highly regarded and often cited in the primary scientific literature. (The Wikipedia page, by contrast, is not.)

There was a reason that the Chilean saltpeter mines were considered in the early part of the 20th century, and there was a reason that Germany was very interested in having BASF (Bosch) work with Haber to scale his process up. Trust me, it's not because the Caro process was workable. The issue is discussed in the first chapter of Smil's book.

Nitrous oxide has always been a feature of the nitrogen cycle, and always will be. However, in terms of concentration, this is driven by thermodynamic equilibrium and kinetics, it's a little glib to say "it may solve itself." It's, um, not solving itself. Further, of note, the process in the ionosphere by which nitrous oxide is decomposed is a chain radical process that destroys ozone, much as the CFC's banned under the Montreal protocol does. The concentration is rising rather rapidly, not because the sun has broken down and no longer irradiates the upper atmosphere with high energy UV radiation.

It is not broken down by infrared radiation at all, and therefore the remark about "NOT reflected into space" has no meaning.

Now, different groups have been working on TiO₂ based (and other) catalysts that might help catalyze this reaction in visible light, but it is very difficult to imagine how one might utilize such a catalyst in such a way as to make a difference to the entire atmosphere. The photolysis wavelengths for the decomposition of nitrous oxide are given in a paper that is available in open access: Atmos. Chem. Phys., 10, 6137–6149, 2010. In this paper the photolysis wavelengths are given as between 195 and 230 nm for both N₂O and CCl₄. These are UV wavelengths, high energy radiation, very different from infrared.

The rate of decomposition and its balance in pre-industrial and present day times is nicely covered in a paper that I happen to have in my files, but may not be public access: Nature Geoscience 2, 659 - 662 (2009)

Here's an excerpt from the introductory text that addesses the point:

Estimates of the stratospheric sink of N₂O are reasonably well constrained2,7,so the global source strength can be inferred from knowledge of the sink and the rate of N₂O accumulation in the atmosphere. For the period before the industrial revolution, when primarily natural N₂O sources and sinks were approximately in balance, each at about 10.2 Tg N₂O_N yr?1, N₂O production from natural terrestrial and coastal ecosystem sources was 4-5% of the estimated natural rate of N fixation by lightning and biological N fixation7.Similarly, in the 1990s, after adjusting the growth of atmosphericN₂O for estimated industrial sources, the annual increase was equal to 3-5% of the sum of estimated anthropogenic sources of new N fixation7. Crutzen et al. concluded that a reasonable approximation of N₂O production, both before and after the industrial revolution, from terrestrial and coastal systems is about 4%+/- 1%) of annual new N fixation (natural and anthropogenic) in the biosphere7.

The paper's first paragraph declares that the rate of growth of N₂O, is linear, about 0.26% a year.

It is not clear that we can reduce the amount of applied fertilizer and still feed seven billion people, not at least without genetically engineering most food crop plants to increase their nitrogen efficiency. That, however would take a lot of time, more time than we actually have.

The climate forcing of nitrous oxide is non-trivial, and is not really "a distant third," accounting for roughly 4% of the forcing.

Have a nice day tomorrow.