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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union

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Atmos. Meas. Tech., 9, 6117-6137, 2016
https://doi.org/10.5194/amt-9-6117-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
22 Dec 2016
Effect of secondary organic aerosol coating thickness on the real-time detection and characterization of biomass-burning soot by two particle mass spectrometers
Adam T. Ahern1, Ramachandran Subramanian1, Georges Saliba1, Eric M. Lipsky1,2, Neil M. Donahue1, and Ryan C. Sullivan1 1Center for Atmospheric Particle Studies, Carnegie Mellon University, Pittsburgh, PA, 15213, USA
2Penn State Greater Allegheny, 4000 University Drive, McKeesport, Pennsylvania 15132, USA
Abstract. Biomass burning is a large source of light-absorbing refractory black carbon (rBC) particles with a wide range of morphologies and sizes. The net radiative forcing from these particles is strongly dependent on the amount and composition of non-light-absorbing material internally mixed with the rBC and on the morphology of the mixed particles. Understanding how the mixing state and morphology of biomass-burning aerosol evolves in the atmosphere is critical for constraining the influence of these particles on radiative forcing and climate. We investigated the response of two commercial laser-based particle mass spectrometers, the vacuum ultraviolet (VUV) ablation LAAPTOF and the IR vaporization SP-AMS, to monodisperse biomass-burning particles as we sequentially coated the particles with secondary organic aerosol (SOA) from α-pinene ozonolysis. We studied three mobility-selected soot core sizes, each with a number of successively thicker coatings of SOA applied. Using IR laser vaporization, the SP-AMS had different changes in sensitivity to rBC compared to potassium as a function of applied SOA coatings. We show that this is due to different effective beam widths for the IR laser vaporization region of potassium versus black carbon. The SP-AMS's sensitivity to black carbon (BC) mass was not observed to plateau following successive SOA coatings, despite achieving high OA : BC mass ratios greater than 9. We also measured the ion fragmentation pattern of biomass-burning rBC and found it changed only slightly with increasing SOA mass. The average organic matter ion signal measured by the LAAPTOF demonstrated a positive correlation with the condensed SOA mass on individual particles, despite the inhomogeneity of the particle core compositions. This demonstrates that the LAAPTOF can obtain quantitative mass measurements of aged soot-particle composition from realistic biomass-burning particles with complex morphologies and composition.

Citation: Ahern, A. T., Subramanian, R., Saliba, G., Lipsky, E. M., Donahue, N. M., and Sullivan, R. C.: Effect of secondary organic aerosol coating thickness on the real-time detection and characterization of biomass-burning soot by two particle mass spectrometers, Atmos. Meas. Tech., 9, 6117-6137, https://doi.org/10.5194/amt-9-6117-2016, 2016.
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The SP-AMS exhibited a different sensitivity to black carbon vs. potassium as more SOA mass was condensed onto biomass burning particles. The SP-AMS's sensitivity to BC mass did not plateau following successive SOA coatings, despite achieving high OA : BC mass ratios > 9. A laser ablation single-particle mass spectrometer exhibited a positive correlation to the condensed SOA mass on individual soot particles, demonstrating its ability to obtain mass quantitative measurements from complex matrices.
The SP-AMS exhibited a different sensitivity to black carbon vs. potassium as more SOA mass was...
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