This data was collected as a result of the FIRETRACC/100 (Firn Record of Trace Gases Relevant to Atmospheric Chemical Change over 100 yrs) project conducted in 1998 and 1999. The FIRETRACC project aimed to determine the history of numerous trace gases of both human (pollution) and natural origin over the 20th century in the global atmosphere. This was achieved by pumping old air out of deep unconsolidated snow (known as firn) that accumulates to depths of around 50 to 100 m on the polar ice caps of both hemispheres. The resulting firn air samples from the Arctic and Antarctic were returned to Europe and the US for multiple gas and isotope analysis in a number of research laboratories. The firn air samples were analysed for well over eighty separate trace gases (halocarbons, non-methane hydrocarbons, alkyl nitrates, sulphur species, etc.), and thirteen different isotopic measurements of CO2, CH4, CO and permanent gases (O2, N2, Ar, Kr).