TOF-SIMS analysis of sea salt particles: imaging and depth profiling in the discovery of an unrecognized mechanism for pH buffering

Abstract

As part of a broader effort at understanding the chemistry of sea salt particles, we have performed time-of-flight secondary ion mass spectroscopy (TOF-SIMS) analysis of individual sea salt particles deposited on a transmission electron microscopy (TEM) grid. Scanning electron microscopy (SEM) and TOF-SIMS analysis have, in conjunction with OH exposure studies, led to the discovery of an unrecognized buffering mechanism in the uptake and oxidation of SO 2 in sea salt particles in the marine boundary layer. This chemistry may resolve some discrepancies in the atmospheric chemistry literature. Several challenges during the acquisition and interpretation of both imaging and depth profiling data on specific particles on the TEM grid identified by the SEM were overcome. A description of the analysis challenges and the solutions ultimately developed to them is presented here, along with an account of how the TOF-SIMS data were incorporated into the overall research effort. Several issues unique to the analysis of high aspect ratio particles are addressed.