Particle analysis by laser mass spectrometry (PALMS) studies of ice nuclei and other low number density particles

It has been shown that particles which effectively initiate freezing, known as ice nuclei (IN), are normally found at concentrations less than 10 l−1 in the background atmosphere. The low number density of these particles has presented significant analytical challenges, and determination of the size and composition, and thus the origin, of these particles has historically relied upon electron microscopy (EM). Single particle mass spectrometers can provide better time resolution and reduced sampling artifacts. The modifications to the particle analysis by laser mass spectrometry (PALMS) instrument, a laser desorption/ionization mass spectrometer, required to efficiently size and analyze particles with very low number density, are described here. A comparison to traditional EM studies is made and future applications of this method to solve other contemporary atmospheric problems are also discussed.