The polar ice sheets are sensitive indicators of our current climate, and are natural archives of evidence of past climate. Because instrumental records of atmospheric chemistry do not exist very far into the past, we must make the best possible use of natural archives of past atmospheric composition. This collaborative project aims to improve the understanding of the processes by which evidence of past atmospheric composition is archived in the firn to become trapped in bubbles in the underlying ice. We aim to establish quantitative relationships between firn structure and interstitial processes at Summit, which will also enable us to understand mechanisms that may impact firn air composition at other sites.