This data set includes gas ratios in polar firn air: O₂/N₂, ¹⁵N/¹⁴N, ⁴⁰Ar/N₂, ⁴⁰Ar/³⁶Ar, ⁴⁰Ar/³⁸Ar, ⁸⁴Kr/³⁶Ar, ¹³²Xe/³⁶Ar, and ²²Ne/³⁶Ar. Investigators sampled air from the permeable snowpack (firn) layer at two sites: Siple Dome, Antarctica in 1996 and at the South Pole in 2001. They observed and modeled the processes of gravitational settling, thermal fractionation, and preferential exclusion of small gas molecules from closed air bubbles. The purpose of this study was to understand these physical processes, which affect the composition of bubbles trapped in ice. By measuring these gas ratios in the ancient air preserved in bubbles trapped in ice, researchers can determine past atmospheric composition and local temperature changes along with the relative timing and magnitude of such events.