FIRETRACC/100: Firn record of trace gases relevant to atmospheric chemical change over 100 years

• Unité de recherche: PCRD EU
• Numéro de projet: 97.0420
• Titre du projet anglais: FIRETRACC/100: Firn record of trace gases relevant to atmospheric chemical change over 100 years

Mots-clé (Anglais)

Firn air; atmospheric chemistry; trace gases; troposphere; global change

Autre Numéro de projet (Anglais)

EU project number: ENV4-CT97-0406

Programme de recherche (Anglais)

EU-programme: 4. Frame Research Programme - 3.1 Environment

Description succincte (Anglais)

See abstract

Partenaires et organisations internationales (Anglais)

UK, F, D, CH

Résumé des résultats (Abstract) (Anglais)

The main objective of FIRETRACC/100 is to examine the impact of 20th century industrialisation on the composition of trace gases in the atmosphere. This can be achieved by deconvoluting the trace gas content of air trapped in deep polar snow (firn), which dates back to the earlier part of the century. The quality of this deconvolution depends heavily on the understanding of the physical and chemical processes in the firn. In order to optimise our resources and to complement the research among the project partners we focused our research on physical effects in the uppermost part of the firn (thermal diffusion, gravitational separation and convective mixing).
Our role within FIRETRACC was to:

· Measure trace gases and isotopes in firn air, specifically: Permanent gases (C02, CH4, N20), Specific isotopic composition of permanent gases, 85Krypton activity

· Model firn air diffusion especially in the upper part of the firn, including thermal diffusion Air samples were returned from the three field expeditions in stainless steel containers.
Additional samples were obtained from inter-laboratory exchange. C02 was measured by infrared laser absorption technique. CH4 and N20 were measured by gascriromatography. Isotopes were analysed by mass-spectrometry on an old Finnigan MAT and a new wide mass range Delta Plus XL. Isotope measurements have been done in collaboration with Laboratoire des Sciences du Climat et de l'Environnement (LSCE), Gif-sur-Yvette, France.

The highlights of the work are as follows:

· In addition to the gravitational settling a fractionation of isotopic ratios by thermal diffusion could be observed

· Observed nitrogen ratios are in agreement with published thermal diffusion coefficients. Measured ratios of other isotopes let us calculate thermal diffusion coefficients based on the comparison with nitrogen isotopes.

· Thermal diffusion was implemented into the firn model. Observed isotopic ratios can be quantitatively interpreted, which strengthens the concept of deconvolution of the trace gas profiles to obtain time series.

· Theoretical studies show that natural convection in firn is possible during winter months.

Références bases de données (Anglais)

Swiss Database: Euro-DB of the
State Secretariat for Education and Research
Hallwylstrasse 4
CH-3003 Berne, Switzerland
Tel. [phone]
Swiss Project-Number: 97.0420