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).

In summary, the objectives of FIRETRACC/100 are as follows:
* To determine the global trends of trace gases relevant to troposphericchemistry over the 20th century. These will include CO, the isotopiccomposition of CO, hydrocarbons, alkyl nitrates, numerous OH-reactivehalocarbons (such as methyl chloride, methyl chloroform, methyl bromide,hydrochlofluorocarbons, etc.), and sulphur gases (COS, CS2, etc.). Trends of longer lived gases will also be determined for dating purposes (CO2, CFCs,SF6, perfluorocarbons, etc.)
* Determine the evolution of inter-hemispheric ratios of OH-sensitive species to constrain modelled global OH fields
* Examine ratios of parent hydrocarbons to alkyl nitrates to place constraints on NOX fields in models
* Elucidate the sources of CO from isotopic studies and use to deconvolute CO/methane coupling in models
* Reconstruct the history of ozone, OH and tropospheric oxidising capacity over the past 100 years using full chemistry 2-D models
* Determine the influence of 20th century industrialisation on the gas phase composition and chemistry of the lower atmosphere

The data consists of ‘primary’ data comprising simple concentration versus depth profiles, and for selected gases also ‘secondary’ data comprising reconstructed historical trends. The firn diffusion model, used in the model reconstruction, is also available through this site.