Repurposing CO2 from Human Respiration Inside Buildings to Enhance Growth in Rooftop Gardens

Abstract Cities face many environmental challenges while providing opportunities for integrating human infrastructure with the surrounding environment. One effort to improve environmental conditions in cities is to increase the amount of green space in creative ways within city limits. Here we propose a unique system taking carbon dioxide (CO2) from indoor spaces and applying it to rooftop gardens or farms through existing ventilation systems with the elevated CO2 levels leading to a fertilization effect that increases plant growth. CO2 measurements were taken inside multiple classrooms as well as at the exhaust vents on a rooftop and air from exhaust was applied to crops and biomass and leaf number were measured. High concentrations of CO2 ([CO2]) persisted inside university classrooms as well as at rooftop exhaust vents in correlation with expected human occupancy and stayed around 1070 ± 70 and 830 parts per million (ppm) CO2 reaching a max of 4470 and 1300 ppm CO2 respectively. Growth in Spinacia oleraceae L. (spinach) grown next to exhaust air increased 4-fold in comparison to plants grown next to a control fan applying atmospheric air. High wind speed decreased growth by approximately 2-fold. Zea mays (corn), a C4 plant, grown next to exhaust experienced a 2 to 3-fold increase, indicating alternative environmental factors additionally playing a part in growth enhancement. Enhancing growth in rooftop gardens using indoor air, could help rooftop plants grow larger and survive harsh conditions. This would make rooftop gardens more viable and better able to provide environmental services and connect urban areas to the surrounding environment.