PAST AND FUTURE FOR OZONE-DEPLETING HALOCARBONS IN ANTARCTIC ENVIRONMENT

摘要

Volatile compounds in ice blocks sampled from warm glacier in Western coastal Antarctica were analyzed. The dating of the young ice and air in aged ice probes was performed using quantitative analysis of radioactive isotopes ~(210)Pb and ~(14)C in CO_2. The age of the samples varied from 20 to 4,700 years. The greenhouse (CO_2 and N_2O), sulfur-containing gases (COS, CS_2), 1-propene and halocarbons of natural origin (CF_4, CH_3Cl, C_2H_5Cl, CH_2=CHCl, CH_3Br, CH_2Br_2, CHBr_3, CH_3I, CH_2=CHI and C_2H_5I) were identified in these samples. All these compounds, except CF_4, demonstrate high mixing ratios in comparison with their content in present air. A tendency for the enhancement of the enrichment factors with increasing Henry's law coefficient of the gases was observed for all samples. Possible reason of the enrichment in the warm glacier may be dissolution of the gases in meltwater percolating through the underlying firn layers, subsequent refreezing of the enriched solution during cold season and repeating of the melt-freeze cycles. This study suggests that increased amounts of naturally produced halocarbons, sulfur-containing gases and their resultant halogen and sulfur species may be released to the atmosphere by possible future global warming or by El Nino. This increase may result in a greater contribution by natural halocarbons and sulfur-containing gases to Antarctic tropospheric ozone chemistry and stratospheric ozone depletion.