AMS and Microprobe Analysis of Combused Particles in Ice and Snow

Abstract

Ice cores and snow pits of the cryosphere contain particles that detail the history of past atmospheric air compositions. Some of these particles result from combustion processes and have undergone long-range transport to arrive in the Arctic. Recent research has focused on the separation of particulate matter from ice and snow, as well as the subsequent analysis of the separated particles for 14C with accelerator mass spectrometry (AMS) and for individual particle compositions with laser microprobe mass analysis (LAMMA). The very low particulate concentrations in Arctic samples make these measurements a challenge. The first task is to separate the particles from the ice core. Two major options exist to accomplish this separation. One option is to melt the ice and then filter the meltwater. A second option is to sublimate the ice core directly, depositing the particles onto a surface. This work demonstrates that greater control is obtained through sublimation. A suite of analytical methods has been used for the measurement of the carbon in snow and ice. Total carbon was analyzed with a carbon/nitrogen/hydrogen (CHN) analyzer. AMS was used for the determination of carbon isotopes. Since source identification of the carbonaceous particles is of primary importance here, the use of LAMMA was incorporated to link individual particle molecular-structural patterns to the same group of particles that were measured by the other techniques. Prior to this study, neither AMS nor LAMMA had been applied to particles contained in snow. This paper discusses the development and limitations of the methodology required to make these measurements.