3 ms·

Half lives are a poor term for this; you are really looking for reaction rates, which are dynamic systems. Methane doesn't just disappear, it reacts with someth

by dexwiz 5y ago

Half lives are a poor term for this; you are really looking for reaction rates, which are dynamic systems. Methane doesn't just disappear, it reacts with something else. A radioactive isotope's decay is relatively self contained, so the half life terminology holds. A microgram or a kilogram of U-235 will decay at about the same rate, making half life a useful number. Methane reacts with OH, which is sourced from different places. Upper levels of the atmosphere get more UV light, which produces all sorts of radicals to react with. But there are also biological and geological sources for radicals which also contribute to reactions. Sum these reactions together and you get something that can be approximated with a half life, but this assumes constant input of reactants. As we increase our output of Methane this changes the reaction rates in the atmosphere and that half life number changes.

ComputerGuru 5y ago
AP Chemistry: the year I took it was the first (only?) year a free response question didn’t feature reaction rates. I learned my lesson on the risks of studying to the historic exam contents!
gertlex 5y ago
As someone whose academic background was in nuclear stuff (but ~10 years ago alas), I had fun read of this article for the considerations like "ohh, a 'half life' with multiple decay modes of varying weights depending on the environment, etc. Gives an itch to dive back into numbers wrangling/plotting! I agree that an accurate description of the (atmospheric in this case) systems over time definitely needs reaction rates, but similar considerations are also needed with nuclear radiation in a lot of situations too: e.g. the overall uhh radioactivity (for lack of recollection of precise terms) is a function of the chain of decay products, which are also often radioactive. That is to say, you might start with half-lives in calculations for dose estimation as a function of time, but you quickly get into more complex things. Also in the nuclear realm, add sources, like a running reactor, or a fresh set of fuel rods, and you get some very interesting effects over time! I think this article was a fair example walkthrough of how things quickly get more complex than the numbers (mis)quoted to the public. I was hoping it would go further, even.

by dexwiz 5y ago

ComputerGuru 5y ago

AP Chemistry: the year I took it was the first (only?) year a free response question didn’t feature reaction rates. I learned my lesson on the risks of studying to the historic exam contents!

gertlex 5y ago

As someone whose academic background was in nuclear stuff (but ~10 years ago alas), I had fun read of this article for the considerations like "ohh, a 'half life' with multiple decay modes of varying weights depending on the environment, etc. Gives an itch to dive back into numbers wrangling/plotting! I agree that an accurate description of the (atmospheric in this case) systems over time definitely needs reaction rates, but similar considerations are also needed with nuclear radiation in a lot of situations too: e.g. the overall uhh radioactivity (for lack of recollection of precise terms) is a function of the chain of decay products, which are also often radioactive. That is to say, you might start with half-lives in calculations for dose estimation as a function of time, but you quickly get into more complex things. Also in the nuclear realm, add sources, like a running reactor, or a fresh set of fuel rods, and you get some very interesting effects over time! I think this article was a fair example walkthrough of how things quickly get more complex than the numbers (mis)quoted to the public. I was hoping it would go further, even.