An automatic recorder for air/firn transfer studies of chemical aerosol species at remote glacier sites

In order to gain year round information on the relationship between major ions in atmospheric aerosol and deposited snow at ice core drill sites, an automatic station for filter pack sampling and for monitoring of snow height changes by vertical temperature profile readings was developed. The station was deployed for two years at a high elevation ice core drill site in the Alps (Colle Gnifetti, 4450 m asl) and thoroughly tested during several unattended campaigns for its long term reliability. Both devices showed a good long-term field performance, despite harsh environmental conditions, with the exception of data logger break downs induced by strong thunderstorms. Snow height evaluations from the vertical temperature profiles and their temporal changes provided a depth resolution of less than 5 cm and agreed well with concurrent readings from an ultra-sonic distance meter. Measurement of major ions in the autonomously sampled filter packs revealed (1) enhanced field blanks for nearly all species but no important increase of the NH+4 to SO2-4 ratio during storage of exposed filters, (2) a nearly complete remobilisation of NO-3, Cl- and Br- from the front quartz filters and (3) a sufficiently large retention of gaseous NO-3, Cl- and Br- species on the back up nylon filters to allow quantification of the total concentration of these ions. Except for Na+, K+ and Mg2+ the (field blank controlled) detection limits allowed to evaluate year round atmospheric concentrations although mid-winter levels have been as low as in central Greenland during summer. The pattern and summer–winter means of atmospheric concentrations were found to be consistent with year round observations performed at a lower Alpine site as well as with the chemical snow properties at Colle Gnifetti.