Enhancing crop growth in rooftop farms by repurposing CO2 from human respiration inside buildings

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.