Thanks for the welcome and the excellent analysis Ptah! Both are greatly appreciated. I'm glad my little message stimulated some thought. This is a magnificent place!
I love the idea of a CO taint; IIRC it was the reason for the taint on one of the Sword Worlds (Gram?) and the reason was volcanism. Based upon my volcanological knowledge (passable but not IMO extensive) CO is a notable, but not a huge outgassing product (in fact, in every case of CO production, CO2 was present in higher concentrations). But your knowledge and points about its stability indicate that it could easily be an especially dangerous taint. I also especially like the H2S taint; not only is it a deadly gas (as you pointed out, deadlier than HCN!) but smells horrible and would make a seemingly garden world a miserable, and potentially deadly place (hold on to that filter mask a little tighter...)
CO presents a big problem in that (at least at the time of my experience) almost no masks will filter it out (I remember any time we dealt with carbon monoxide, SCBA was necessary). I could be wrong on that. ANyway, I myself would rule that any higher tech masks will filter CO (unless someone knows as fact that it cannot be filtered). I wonder about insidious atmospheres because in the far future (TL10+ ?) I imagine heat and pressure (and some very exceptional other causes, e.g. extremely high radiation) will be the most likely causes for failure of protective equipment. I do not include H2, though, as I believe that it would escape from a world rather than form a thick exotic atmosphere (perhaps a trace would exist, but that doesn't seem to me enough for an "insidious" atmosphere). The idea of a CO leak even in a merely tainted atmosphere is a terrifying thought however; no odor, quick incapacitation and death.
Cyanogen... I once read that this is one of the many components of a comet's "tail". Based upon my experience with hazardous chemicals, I'm sure it was real fun to play with that!
-and I know Cyanogen Chloride was a war gas. Very good point about the explosivity/flammability of many of these substances (their toxicity is well known, it seems their other dangers are not as readily discussed). As for HCN I'd imagine if there is just enough to be dangerous (but not so much that it's San Quentin) the world might not be a red zone, but would be pretty damn nasty nonetheless (A stern TAS alert about that little stop on the Spinward Main!). I have read (and heard) that HCN exposure will destroy most mask filters. I imagine in the far future that will not be the case, but for lower tech worlds is a consideration (does H2S do this as well???)
I like your point about low O2 not being a taint. THat would probably best be considered a type of exotic atmosphere that just had enough life to create some O2. The danger of fire on a high-O2 world could be a very interesting concern for travellers on an otherwise pleasant (all things considered) planet.
Nitrogen compounds...oops forgot to list those
Very glad you reminded me. You did teach me the fascinating bit about the microorganism-generated nitrous oxide (I love volcanism but it does get tiring if the ONLY causes are volcanism and infectious agents). It's nice when many plausible options exist.
Great point about the Aral Sea. After taking your direction and examining the (terrible) problem, I'm now convinced, and shall add suspended dust/particles to the list.
The danger after the first couple of years isn't so much from the stuff floating around but the radioactive isotopes (some with half lives reaching into the 1000's of years) in the water, soil, animals. Some isotopes, such as isotopes of Cobalt and Iodine, will get incoproated into the body where there radioactive decay can cause serious damage.
I still would call the fallout/residual radiation problem (isotopes) more an overall danger rather than an atmospheric taint. I can easily see a world with an atmosphere of standard non-tainted (code 6 in most traveller systems) with high levels of dangerous isotopes in the environment (plants, animal flesh and bone, soil, etc). For a few years after a war, the atmosphere (as you pointed out) would probably be coded "tainted" but gradually would return to non-tainted (just don't eat the plants!).
So I've got: infectious or otherwise dangerous microorganisms, toxic biological products (such as pollen, spores, etc), volcanic gasses (one, two or most likely a mix of SO2, nitrogen compounds, H2S, HCN, HCl, CO, CO2, ...), biologically-produced poisons or asphyxiant gasses (N2S, ...), suspended particulate matter (salts, ash, dust, ...) recent nuclear war products, high O2 levels, ...
The Twelve Days of Christmas, Traveller style!
