Quantitative capabilities of STXM to measure spatially resolved organic volume fractions of mixed organic ∕ inorganic particles

Authors

Matthew Fraund, University of the PacificFollow
Tim Park, University of the Pacific
Daniel Bonanno, University of the Pacific
Don Q. Pham, University of the Pacific
Ryan C. Moffet, University of the PacificFollow

Document Type

Article

Publication Title

Atmospheric Measurement Techniques

Department

Chemistry

ISSN

1867-1381

Volume

12

Issue

3

DOI

10.5194/amt-12-1619-2019

First Page

1619

Last Page

1633

Publication Date

3-12-2019

Abstract

Scanning transmission X-ray microscopy coupled with near-edge X-ray absorption and fine structure (STXM-NEXAFS) spectroscopy can be used to characterize the morphology and composition of aerosol particles. Here, two inorganic ∕ organic systems are used to validate the calculation of organic volume fraction (OVF) and determine the level of associated error by using carbon K-edge STXM data at 278, 285.4, 288.6, and 320 eV. Using the mixture of sodium chloride and sucrose as one system and ammonium sulfate and sucrose as another, three solutions were made with 10:1, 1:1, and 1:10 mass ratios (inorganic to organic). The OVFs of the organic-rich aerosols of both systems deviated from the bulk OVF by less than 1%, while the inorganic-rich aerosols deviated by approximately 1 %. Aerosols from the equal mass mixture deviated more (about 4 %) due to thick inorganic regions exceeding the linear range of Beer's law. These calculations were performed after checking the data for poor image alignment, defocusing issues, and particles too thick to be analyzed. The potential for systematic error in the OVF calculation was also tested by assuming the incorrect composition. There is a small (about 0.5 %) OVF difference if the organic is erroneously assumed to be adipic acid rather than the known organic, sucrose. A much larger difference (up to 25 %) is seen if sodium chloride is assumed instead of ammonium sulfate. These results show that the OVF calculations are fairly insensitive to the organic while being much more sensitive to the choice of inorganic.

Creative Commons License

This work is licensed under a Creative Commons Attribution 4.0 International License.

Recommended Citation

Fraund, M., Park, T., Yao, L., Bonanno, D., Pham, D. Q., and Moffet, R. C.: Quantitative capabilities of STXM to measure spatially resolved organic volume fractions of mixed organic ∕ inorganic particles, Atmos. Meas. Tech., 12, 1619-1633, https://doi.org/10.5194/amt-12-1619-2019, 2019.