Composition of firn air at the North Greenland Ice Core Project (NGRIP) site

Reconstructions of the past variations of atmospheric composition are important for better understanding of the changes of climate and atmospheric chemistry. While direct observations of atmospheric composition and isotope ratios are currently available, ice core analyses revealed those in the pre-industrial era. Porous compacted snow layers (firn) over ice sheets also archive air up to 100 years older than that at surface. Depth profiles from firn air measurements are therefore useful for reconstructing historical variations of trace gas species over times about century back in time. They are also helpful for improving firn air transport models toward better understanding of snow densification and interpretation of ice core data. Here we present depth profiles of air composition in the firn at a Greenland site of NGRIP (North Greenland Ice Core Project). Various greenhouse gases, halocarbons and isotope ratios were analyzed from air samples collected from the NGRIP firn by using combination of high-precision measurement systems.重建过去大气成分的变化，对于深入理解气候与大气化学的演变进程具有重要意义。当前虽已具备大气成分与同位素比值的直接观测数据，但冰芯分析可揭示工业革命前的大气状况。冰盖上方的粒雪（firn，经压实的多孔雪层）同样可封存比地表空气年长可达百年的空气样本。因此，基于粒雪空气测量得到的深度剖面，可用于重建近百年尺度内痕量气体组分的历史变化情况。此类剖面还有助于优化粒雪空气运移模型，进而深化对雪层压实过程的理解，并为冰芯数据的解译提供支撑。本研究针对格陵兰地区NGRIP（North Greenland Ice Core Project，北格陵兰冰芯项目）站点的粒雪层，公布了其空气成分的深度剖面数据。研究团队通过多套高精度测量系统的联用，对从NGRIP粒雪层采集的空气样本中的多种温室气体、卤代烃以及同位素比值进行了分析测定。