Abstract
Direct atmospheric carbon capture is increasingly vital to mitigating global climate change, yet terrestrial carbon capture systems are constrained by severe land and water footprints. Here, we present a radical paradigm for carbon sequestration: the integration of micro-algal bioreactors directly into the flexible, multi-layered envelope skins of high-altitude balloons operating in the lower stratosphere (18–25 km). By exploiting the extreme, uninterrupted solar irradiance available above the troposphere, we demonstrate that psychrophilic microalgal strains, such as Chlamydomonas nivalis, cultured within transparent, microfluidic polyurethane skin channels, can achieve remarkable photosynthetic rates. Thermal homeostasis is maintained passively through the controlled absorption of solar radiation by pigmented biomass combined with gas-phase insulation layers, elevating internal fluid temperatures to sustainable growth regimes (+5°C to +15°C) despite ambient stratospheric temperatures of -55°C. Gas exchange is facilitated via lightweight, high-flux hydrophobic poly(tetrafluoroethylene) membranes, which passively concentrate sparse atmospheric CO2. Simulated stratospheric chamber testing indicates a carbon fixation yield of 14.2 g C/m² of balloon surface per day, representing a three-fold increase over optimal terrestrial microalgal raceway ponds. This work establishes the technical feasibility of bio-functionalized high-altitude atmospheric platforms as a scalable, dual-use technology for high-efficiency carbon drawdown and high-altitude research.
