Preprints
https://doi.org/10.5194/amt-2020-303
https://doi.org/10.5194/amt-2020-303

  26 Aug 2020

26 Aug 2020

Review status: a revised version of this preprint was accepted for the journal AMT and is expected to appear here in due course.

Elemental analysis of Oxygenated Organic Coating on Black Carbon Particles using a Soot-Particle Aerosol Mass Spectrometer

Mutian Ma1, Laura-Hélèna Rivellini2, YuXi Cui1, Megan D. Willis3, Rio Wilkie4, Jonathan P. D. Abbatt4, Manjula R. Canagaratna5, Junfeng Wang6, Xinlei Ge6, and Alex K. Y. Lee1,2 Mutian Ma et al.
  • 1Department of Civil and Environmental Engineering, National University of Singapore, Singapore
  • 2NUS Environmental Research Institute, National University of Singapore, Singapore
  • 3Lawrence Berkeley National Lab, Chemical Sciences Division, Berkeley, CA, USA
  • 4Department of Chemistry, University of Toronto, Toronto, ON, Canada
  • 5Aerodyne Research, Inc., Billerica, MA, USA
  • 6School of Environmental Science and Engineering, Nanjing University of Information Science and Technology, Nanjing, China

Abstract. Chemical characterization of organic coatings is important to advance our understanding of the physio-chemical properties and environmental fate of black carbon (BC) particles. The soot-particle aerosol mass spectrometer (SP-AMS) has been utilized for this purpose in recent field studies. The laser vaporization (LV) scheme of SP-AMS can heat BC cores gradually until they are completely vaporized, during which organic coatings can be vaporized at temperatures lower than that of the thermal vaporizer (TV) used in a standard high-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) that employs flash vaporization. This work investigates the effects of vaporization schemes on fragmentation and elemental analysis of known oxygenated organic species using three SP-AMS instruments. We show that LV can reduce fragmentation of organic molecules. Substantial enhancement of C2H3O+/CO2+ and C2H4O2+ signals was observed for most of the tested species when the LV scheme was used, suggesting that the observational frameworks based using HR-ToF-AMS field data may not be directly applicable for evaluating the chemical evolution of oxygenated organic aerosol (OOA) components coated on ambient BC particles. The uncertainties of H:C and O:C determined by the improved-ambient (I-A) method for both LV and TV approaches were similar, with scaling factors of 1.10 for H:C and 0.89 for O:C were determined to facilitate more direct comparisons between observations from the two vaporization schemes. Furthermore, the I-A method was updated based on the multilinear regression model for the LV scheme measurements. The updated parameters can reduce the relative errors of O:C from −26.3 % to 5.8 %, whereas the relative errors of H:C remain roughly the same. Applying the scaling factors and the updated parameters for the I-A method to ambient data, we found that even though the time series of OOA components determined by the LV and TV schemes are strongly correlated at the same location, OOA coatings were likely less oxygenated compared to those externally mixed with BC.

Mutian Ma et al.

 
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Mutian Ma et al.

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Short summary
Chemical characterization of organic coatings is important to advance our understanding of the physio-chemical properties and atmospheric processing of black carbon (BC) particles. This work develops two approaches to improve the elemental analysis of oxygenated organic coatings using a soot-particle aerosol mass spectrometer. Analyzing ambient data with the new approaches indicated that secondary organics that coated on BC were likely less oxygenated compared to those externally mixed with BC.