Integrating cities with the surrounding environment by incorporating green spaces in creative ways would help counter climate change. We propose a rooftop farm system called BIG GRO where air enriched with carbon dioxide (CO2) produced through respiration from indoor spaces is applied through existing ventilation systems to produce a fertilization effect and increased plant growth. CO2 measurements were taken inside 20 classrooms and at two exhaust vents on a rooftop at Boston University in Boston, MA. Exhausted air was directed toward spinach and corn and plant biomass and leaf number were analyzed. High concentrations of CO2 persisted inside classrooms and at rooftop exhaust vents in correlation with expected human occupancy. CO2 levels averaged 1,070 and 830 parts per million (ppm), reaching a maximum of 4,470 and 1,300 ppm CO2 indoors and at exhaust vents, respectively. The biomass of spinach grown next to exhaust air increased fourfold compared to plants grown next to a control fan applying atmospheric air. High wind speed from fans decreased growth by approximately twofold. The biomass of corn, a C4 plant, experienced a two to threefold increase, indicating that alternative environmental factors, such as temperature, likely contribute to growth enhancement. Enhancing growth in rooftop farms using indoor air would help increase yield and help crops survive harsh conditions, which would make their installation in cities more feasible.

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.