ATOFMS characterization of individual model aerosol particles used for exposure studies

Given growing concerns over the observed relationship between ultrafine particles and adverse human health effects, there is a major need in the community performing human/animal exposure studies for methods that can be used for the generation of high concentrations of ultrafine particles (< 100 nm) with controllable compositions. The Palas spark discharge generator (Palas GFG 1000) is commonly used to generate soot-like particles for such studies. However, before such methods can be used routinely in the lab, it is important to assess the chemical variability and reproducibility of the ultrafine particles produced using such techniques. The goal of this study involves performing the on-line assessment of the chemical variability of individual ultrafine and fine (50-300 nm) particles produced by a Palas generator. The aerodynamic size and chemical composition of C-12 and C-13 elemental carbon (EC) composite iron-carbon (Fe-C-12), and welding particles were analyzed using aerosol time-of-flight mass spectrometry, and in general highly reproducible single-particle mass spectra were obtained. When using pure graphite (C-12) electrodes, EC particles were produced with sizes peaking in the ultrafine mode and 96% of the mass spectra containing distinct C-n(+) (n = 1-3) envelopes at m/z 12, 24, and 36. In contrast, the size mode of the particles generated from isotopically labeled C-13, graphite electrodes peaked in the accumulation mode, with 73% of the particles producing EC carbon ion cluster patterns at m/z 13 (C-13(+)), 26(C-13(2)+), and 39 (C-13(3)+), with additional organic carbon species at m/z 15 (CH3+), 27 (C2H3+/CHN+), 43 (C3H7+/CH3CO+), m/z 58 (C3H8N+), and 86 (C5H12N+). Observed differences between the C-12 and C-13 particle spectra are most likely due to their different surface properties, with C-13 particles more effectively adsorbing semivolatile organic species originating in the particle-free dilution air. Homogeneous metal particles were also generated from Fe-C-12 and welding rods with almost all (92% and 97%, respectively) of the spectra showing reproducible Fe/Mn/Cr and Fe/C-12 ion ratios.