Project Atmospheric Mirror V2.2: Sub-Stratospheric Photophoretic Calcite Particle Dispersion Framework

Context: Solar Radiation Modification (SRM) strategies targeting the upper atmosphere are increasingly evaluated as temporary mechanisms to limit global thermal overshoot. Traditional stratospheric sulfate aerosol injection (SO2) introduces significant side effects, including lower stratospheric heating, ozone layer depletion via heterogeneous halogen chemistry, and short atmospheric residence times driven by rapid gravitational settling. Methods: This paper presents Project Atmospheric Mirror (V2.2), an open-source technical architecture utilizing sub-stratospheric photophoretic micro-structured calcite (CaCO3) aerosols. By exploiting photophoretic levitation forces—where thermal gradients across the particle surface counteract gravitational settling—the micro-particles operate at reduced deployment altitudes (12–15 km) relative to traditional stratospheric proposals. The alkaline composition naturally neutralizes anthropogenic acidic species (HCl, HNO3, H2SO4), suppressing halogen-driven ozone depletion pathways. Results: Radiative transfer and aerosol transport modeling demonstrate that an engineered sub-stratospheric calcite layer achieves an operational shortwave scattering yield corresponding to a net radiative forcing of -1.20 W/m² (equivalent to a global mean surface cooling yield of approximately -0.827°C). Photophoretic dynamics extend mean atmospheric residence time to ~45 days, optimizing particle mass delivery requirements while providing secondary ocean-alkalinity buffering benefits upon post-tropospheric deposition. Governance & Open Science: Formulated as a non-proprietary reference design, this technical framework is placed under the Creative Commons Attribution 4.0 International (CC BY 4.0) license to provide a citable, reproducible baseline for independent modeling by atmospheric scientists, intergovernmental bodies, and international research organizations evaluating solar geoengineering risk profiles.