It's a bit tricky, because anything really corrosive is likely to react fairly rapidly and continuously with corrodible things in the environment and be used up. For instance, acid in the air would react steadily with carbonate rocks and be neutralised, and there is a prodigious quantity of carbonate rock. To keep the air acidic you would have to continue to produce large amounts of sulphate or nitrate even after the disaster had become apparent. Only after producing an astronomical amount of acid to dissolve the astronomical amount of limestone &c. in the planet's crust could you accumulate a permanently corrosive atmosphere that way.
The only thing that springs to my mind is the 1783 eruption of Laki
, a volcanic event that released a lot of hydrofluoric and sulphuric acids, causing global problems. Perhaps something of that character, but on a larger scale and lasting longer (like the K-Pg event
, Triassic-Jurassic mass extinction
, or Permian-Triassic mass extinction event
), might cause an extinction event and come close enough for gaming to a corrosive atmosphere lasting for lifetimes.
It's a bit of a challenge to see what humans might do that could cause a large sustained fluoride-rich basalt flooding event. If fusion power were not so cheap and convenient in Traveller
I might suggest an accident at a large badly-designed geothermal power station might introduce a lot of water into an underground formation, which could become superheated and then, if the pressure would somehow relieved, boil explosively, throw of a lot of overburden allowing more superheated hydrated rock to boil explosively, producing an explosion/eruption that left a large crater/fissure that continued to spew acids for decades or centuries. My only other idea is that a clumsily-handled asteroid, being brought in to orbit to be processed for resources, might have hit the surface and unluckily bullseyed a potential volcanic formation, smashing the crust an releasing a flood of fluorine-rich magma.