Special issue  

The atmospheric composition of the past is stored in the bubbles of polar ice sheets and glaciers. This archive now reaches back to 800,000 years before present. The last several decades of the atmospheric composition history is not yet occluded in the ice but can be found in the open porous layer at the surface of the ice sheet at high resolution. In this layer a large amount of gas is available which allows for analyses not (yet) possible from the bubble section, and in many cases recovery of atmospheric histories of compounds for which there were no direct measurements in the atmosphere. Within the NEEM deep drilling project in Greenland air was collected from the firn during two very comprehensive field sampling seasons and several surface drillings. Laboratories from Europe, Australia, the US and Japan have measured this air for a suite of components in what is the most extensive set of firn air measurements yet made. In addition, as part of this project an extensive modeling effort is being conducted to better understand the translation from the composition found in the firn to the atmospheric history. The purpose of this issue is to bundle all information from the NEEM measuring campaign and the corresponding modeling attempt at one place. However, we do not want to limit the issue to the NEEM project. We welcome contributions from other ongoing and previous firn air campaigns, and hope that the special issue will provide a comprehensive state-of-the-art view of firn air science.