Introduction: Organosulfur (OS) compounds are essential for life as we know it, yet our knowledge of abiotic formation pathways is limited. Recent experiments suggest that simple atmospheric photochemistry is a compelling route towards synthesis of these compounds (DeWitt et al., 2010, Reed et al., 2020, 2022, 2025). These results also challenge our understanding of the Archean sulfur cycle. It is traditionally thought that photochemistry of atmospheric sulfur gases (H2S, SO2) resulted in sulfuric acid (H2SO4) and elemental sulfur (S8) aerosols. These two reservoirs would have preserved the sulfur mass-independent isotope fractionation (S-MIF) signature in the geologic record that has been interpreted as evidence for an anoxic atmosphere during the Archean Eon (~4.0-2.5 Gya). OS as an atmospheric sulfur sink would transform both our understanding of S-MIF and delivery to the Earth’s surface of OS molecules useful for life. However, our understanding of the relative importance of S8, H2SO4, and OS in the Archean is limited. We sought to determine if there are conditions under which all three reservoirs are formed, and if those conditions are relevant to the Archean atmosphere. We performed UV photochemistry experiments of CO2/H2S/N2 mixtures without methane (CH4) to investigate sulfur speciation and potential organic aerosol formation from inorganic precursors as a function of CO2 mixing ratio (0-1%). Aerosols were measured online using scanning mobility particle sizing and aerosol mass spectrometry and offline using thermal desorption chemical ionization mass spectrometry. Results: No aerosol was produced for mixtures of CO2 (0.1 or 1%) in N2 without H2S. With 5 ppmv H2S, the aerosol particle volume produced increased as a function of the initial CO2 mixing ratio, with ~12000 µm3/cm3 of aerosol being produced at 1% CO2. Aerosol composition. With only 5 ppmv H2S in N2, the aerosol was composed of S8 particles. When CO2 was included, OS was formed at all CO2 mixing ratios investigated. In terms of inorganic sulfur speciation, S8 dominated below 0.025% CO2 and H2SO4 dominated above that value. At 0.025% CO2, all three reservoirs contributed approximately equally to the sulfur aerosol signal. The OS aerosol included organosulfur compounds such as methyl sulfate, ethyl sulfate, and methanesulfonic acid. In addition to OS, non-sulfur containing organic aerosol (OA) was also produced. The OA consisted of small organic acids such as oxalic acid and malonic acid. Implications: These experiments challenge the idea that S8 and H2SO4 were the main sulfur reservoirs in the Archean Eon. Estimates of atmospheric CO2 range from ~0.01-80% (Catling and Zahnle, 2020), thus only at the lower end of this range would S8 be a significant sulfur sink for our conditions. Taken together with results from experiments including CH4 (Reed et al., 2022), which was present during the Archean, and using SO2 rather than H2S (DeWitt et al., 2010), both of which show a lack of S8 formation under plausible Archean analog scenarios, these findings suggest that the understanding of S8 as a major sulfur reservoir should be revisited. Instead, organosulfur aerosol should be considered as a significant sulfur reservoir in the Archean Eon. This has implications for prebiotic chemistry, as sulfur is essential for life. Photochemistry represents an abiotic pathway for the formation of complex organic molecules, even in the absence of organic precursors, which could be deposited on the surface and utilized by existing or emerging life. Formation of organic molecules in the absence of CH4 expands our knowledge of the types of atmospheres that could support organic haze, with implications for habitability and exoplanet characterization. References: Catling, D. C., Zahnle, K. J., 2020, Sci. Adv., 6, 9, doi: 10.1126/sciadv.aax1420 DeWitt, H. L., Hasenkopf, C. A., Trainer, M. G., et al., 2010, Astrobiology, 10, 8, doi: 10.1089/ast.2009.9455 Reed, N. W., Browne, E. C., Tolbert, M. A. 2020, ACS Earth Space Chem, 4, 6, doi: 10.1021/acsearthspacechem.0c00086 Reed, N. W., Wing, B. A., Tolbert, M. A., et al., 2022, Geophys. Res. Lett., 49, 9, doi: 10.1029/2021GL097032 Reed, N. W., Christensen, C. M., Surratt, J.D., et al., 2025, Proc. Natl. Acad. Sci. U.S.A., 122, 49, doi: 10.1073/pnas.251677912