Aerosol mass spectrometry of particles containing refractory carbon

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Description

Refractory black carbon (rBC)-containing particles, including energy-derived combustion particles, can affect climate directly by absorbing (and scattering) incoming light depending on particle composition and morphology and indirectly by influencing cloud droplet formation and lifetimes. The uncertainty in the climatic effects of rBC is driven, in part, by several important factors: poorly understood formation, poorly quantified atmospheric processing (e.g., hydrophobic into hydrophilic), and limited information on the UV-VIS-IR optical properties. These uncertainties are complicated by the lack of measurement techniques that can unambiguously measure properties of refractory carbon containing particles.

To help address these uncertainties, we have developed a soot particle aerosol mass spectrometer (SP-AMS) instrument capable of measuring the mass, size, and chemical composition of rBC particles. rBC particles are vaporized by a CW intracavity Nd:YAG laser vaporizer (1064 nm). The volatilized components are ionized by 70 eV electron impact ionization and detected by high resolution time-of-flight mass spectrometry. Laboratory studies demonstrate that the SP-AMS technique provides real-time mass spectra of refractory carbon ion cluster distributions for sampled aerosol particles containing refractory carbon materials. The mass spectra of rBC particles fall into categories that point toward distinct carbon atom bonding and structures from different types of rBC particles, with the potential for source apportionment. In addition, the SP-AMS provide a unique capability for real-time measurements of the amount and chemical composition of nonrefractory components associated with refractory carbon containing particles. These measurements provide an additional constraint on methods for quantifying and modelling the interaction of solar radiation with rBC particles. Results from laboratory and field studies will be presented.