# Elemental analysis of oxygenated organic coating on black carbon particles using a soot-particle aerosol mass spectrometer

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 the 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 Cinline-formula2Hinline-formula3Oinline-formula $M3inlinescrollmathml{}^{+}/$ 14pt14ptsvg-formulamathimgfe7e56fecca5364a5a87c8fbcfe3d012 amt-14-2799-2021-ie00001.svg14pt14ptamt-14-2799-2021-ie00001.png COinline-formula $M4inlinescrollmathml{}_{normal 2}^{+}$ 8pt15ptsvg-formulamathimgd7f2ee209205b974ae323652b1975b71 amt-14-2799-2021-ie00002.svg8pt15ptamt-14-2799-2021-ie00002.png and Cinline-formula2Hinline-formula4Oinline-formula $M7inlinescrollmathml{}_{normal 2}^{+}$ 8pt15ptsvg-formulamathimgfb80c4c6e16db439d7ccc2ddca26875a amt-14-2799-2021-ie00003.svg8pt15ptamt-14-2799-2021-ie00003.png signals was observed for most of the tested species when the LV scheme was used, suggesting that the observational frameworks based on the use of 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 inline-formulaH:C and inline-formulaO:C determined using the improved-ambient (I-A) method for both LV and TV approaches were similar, and scaling factors of 1.10 for inline-formulaH:C and 0.89 for inline-formulaO: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 inline-formulaO:C from inline-formula−26.3 % to 5.8 %, whereas the relative errors of inline-formulaH: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 using 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.

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Ma, Mutian / Rivellini, Laura-Hélèna / Cui, YuXi / et al: Elemental analysis of oxygenated organic coating on black carbon particles using a soot-particle aerosol mass spectrometer. 2021. Copernicus Publications.

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