<p>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 determination of Organic Volume Fraction (OVF) from STXM data and to determine the level of associated error. Using the mixture of sodium chloride and sucrose as one system and ammonium sulfate and sucrose as another, three solutions each were made with 10:1, 1:1, and 1:10 mass ratios (inorganic to organic). The OVF 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 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 adipic acid is assumed rather than sucrose, and a much larger (up to 25 %) difference if sodium chloride is assumed instead of ammonium sulfate. These results show that, with attention paid to ensuring quality data, an OVF value within 1 % of the theoretical value can be determined.</p>