Stable isotope analysis for characterization of pollutants at high elevation alpine sites

Variations in the abundance of stable isotope of sulfur, nitrogen and carbon in sulfate, nitrate and organic carbon, respectively, were studied in snow and air samples from high-alpine sites. Their suitability as a tool for characterizing the source regions which contribute to the pollution of the high-alpine areas was investigated. The contributions of different sources to a specific receptor site are generally unknown and depend on emission patterns and meteorological conditions. Measured isotope ratios reflect the actual superposition of the distinct source types under the assumption that no major isotope fractionation occurs during transport and deposition and that post-deposition isotope effects can be excluded. In order to study the relationship between source region and isotopic pattern, daily high-volume samplings of the atmospheric aerosol at Sonnblick (Austrian Alps, 3106 m asl) were combined with twice-daily backtrajectories and evaluated statistically. In addition, vertical snow profiles taken in pits at various locations in the Alps were analyzed. For their interpretation, a so-called snow calendar was constructed which relates specific snow strata to the dates of the respective precipitation events. Furthermore, the isotope ratios of hydrogen and oxygen in the snow samples were used to support the meteorological information. Main findings of the investigations are regional patterns of delta(34)S in airborne sulfates, the seasonality of nitrogen isotope composition in nitrates, and a pronounced isotopic difference in nitrates and sulfates of pre-industrial and modern origin, respectively. This study was parr of EUROTRAC subproject ALPTRAC. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.