Salyut space stations atmosphere

[AegeanBlue]

I have been trying to answer a question but the (english speaking) internet generally has been lacking in authoritative sources. What was the atmospheric composition and pressure of the Salyut space stations? So far as I can see they had surface pressure and composition, unlike Skylab which had a 75% Oxygen atmosphere. Did they have the same atmospheric composition across the 7 or 8 (including DOS-2) stations? Why did they take that  approach when Skylab chose a simpler lower pressure mostly oxygen atmosphere, especially before Salyut 6 which was the first to receive resupply?

[AnalogMan]

This document:

Designing For Human Presence in Space: An Introduction to Environmental Control and Life Support Systems (ECLSS) Appendix I, Update—Historical ECLSS for U.S. and U.S.S.R./Russian Space Habitats

Gives atmospheric details for Salyut in table 2 on document page 18.

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060005209.pdf

Bibliographic info:

https://ntrs.nasa.gov/search.jsp?R=20060005209

[whitelancer64]

Simple answer: the space stations (both Salyut and Skylab) were designed to use air pressure / composition compatible with their existing crew vessels.

Apollo CM was pressurized to 5 PSI with a 100% Oxygen atmosphere, so Skylab was likewise pressurized at 5 PSI. However, to improve fire safety, Nitrogen was added to the air mix, but to provide the same amount of Oxygen at 5 PSI to the crew that a 21% Oxygen atmosphere does at sea level pressure, it needed a 72% Oxygen atmosphere.

note: a table of US spacecraft atmospheric information is on page 6 of the document linked above.