Various people over the past 60ish years have suggested floating habitats in the high-altitude Venusian atmosphere, as the pressure, gravity, and temperature are comparable to Earth. The premise is that there's a high CO₂ concentration which makes an Earth-like atmosphere lighter-than-air, allowing the habitat to float just by virtue of being filled with breathable air.
One such proposal is the HAVOC concept by NASA's Langley Research Center, proposed to float at 50 km / 32 mi altitude, where the pressure is ½ to 1 atmosphere, gravity is about 0.9 gees, and temperature is 27-75 C / 81-167 F, depending on the exact altitude and what source I'm reading.
Facts about the surface are easy enough to find, but I'm having no luck finding useful information about the high-altitude air and its composition. Some sources mention droplets of sulfuric acid and a general lack of oxygen, but that's not very specific.
It seems most people answering questions about the feasibility of such habitats are just assuming the relative compositions are the same at any altitude, but this seems unlikely to me. This plot of Earth shows very different compositions at different altitudes, which leads me to think Venus would have similar differences at higher altitudes.
It's worth noting that the differences really only start around 100 km / 62 mi, where pressures are very low and we're essentially in space. But given the 200:1 pressure differential between the surface and the cloud layers in question, and the various layers of weather phenomenon, I'm not sure that means Venus would also have the same compositions out to the 250 km / 155 mi Kármán line.
Is there any available data on the actual atmospheric composition of Venus at altitudes being considered for the proposed habitats? (50 km / 32 mi) Or is it just the same everywhere and I'm overthinking this?