Plants play important roles in maintaining air quality and biogeochemical cycles, although many mechanisms remain poorly understood. Recently, spontaneous production of hydrogen peroxide (H2O2) has been reported from the condensation of water vapor as microdroplets. Here, we report detection of H2O2 in proximity to plants undergoing photosynthesis in a closed environment, confirmed using commercial peroxide test strips and spectrophotometric titration. Our results have potential major implications for the role of plant-mediated atmospheric cleansing, climate change, and urban and indoor air quality.