Analysis and classification of individual ambient aerosol particles with field-deployable laser-induced breakdown spectroscopy platform

Abstract

Studying the elemental composition of aerosol particles on a single particle level is of importance when determining the internal and external mixing state of the aerosol population. We present a field-deployable platform for the elemental analysis of ambient single particles using laser-induced breakdown spectroscopy (LIBS). The platform utilizes a wideband spectrometer for simultaneous multi-element detection and size-amplification-aided aerosol charging (SAAC) for efficient particle focusing via a linear electrodynamic quadrupole (LEQ). Carefully designed emission collection system allows minimization of the plasma background emission, which allows us to use short gate delays for increased yield of analyte emission. Performance evaluation with a set of well-defined salt aerosols show excellent capability in determining the relative mass percentage and absolute mass of elements spanning multiple orders of magnitude on a single particle level. Limits of detection for Mg, Na and K were determined to be approximately 2 fg, 40 fg, and 70 fg, respectively. An outdoor aerosol sample was analyzed in the size range of 1–3 µm in diameter, and the particles were classified into distinct categories based on their elemental composition. The maximum analysis speed is about 20 particles per minute and the minimum detectable particle size is, depending on the constituent elements, about 300–800 nm. Emission signals of Al, B, C, Ca, Cu, Fe, K, Mg, Na, Si, and Ti were detected during the measurements of generated or outdoor aerosols.