That's honestly the less important part. Even if the atmosphere were pure hydrogen (whether protium or deuterium or tritium) you would not build a hydrogen bomb without its own encapsulated hydrogen fuel source.

The black magic of a hydrogen bomb is that it focuses the explosive energy of a fission bomb to ignite a fusion explosion. Doing so requires a very specific configuration; any hydrogen on the outside of the bomb, regardless of its concentration, would not reach the appropriate temperature/pressure to fuse.

Yes but that part needs a 10th grade understanding of science.

H2 is an assumption you've made. When talking about a nuclear explosion. There is hydrogen in a number of compounds (notably water and hydrogen sulfide) present in the atmosphere that could be relevant sources. The ppm being incidental is another issue. You've been unnecessarily condescending to an honest question.

That's an odd thing to "know" considering that the amount of water vapor in the atmosphere is measured in parts per hundred, and a substantial portion of water vapor is hydrogen.

Just as that person was 1 of 10,000 learning something for the first time today, I hope that today you learned that not everyone has exactly your set of knowledge. Also consider that it is quite likely that person is an expert in several things you have never even heard of.

XKCD 10,000: https://xkcd.com/1053/

Don’t overestimate education systems and peoples ability to learn from them :-)

Edit: now I'm puzzled why this is collecting downvotes. :-)