Passive Strategies for Reducing the Impact of Outdoor Air Pollutants on Indoor Air Quality: A Combination of CAM Plants and Hydrogel Filters

Abstract

Water and plants absorb 55% of the carbon dioxide and pollutants introduced into the atmosphere (Ref?). This absorption of carbon dioxide, along with the production of oxygen, is recognized as the largest operation in nature (NASA, 2011), which has significant implications for improving the indoor air quality (IAQ) of built environments. Thus, this study hypothesizes that a natural ventilation system comprising filtration through plants and saturated hydrogels is effective for improving IAQ by decreasing the amount of airborne pollutants entering interior spaces from the urban environment. Various plant types were analyzed to compare their efficiency in reducing CO2 and other air pollutants. Of these, plants that utilize Crassulacean acid metabolism (CAM) were found to be the most efficient. The saturated hydrogels within the filtration system maintain spacing to allow hot-dry outdoor air to pass through and thus simultaneously diffuse water vapor while adsorbing volatile organic compounds (VOCs) and particulate matter of different sizes (PM10 and PM2.5). The hypothesis was tested via two methods. First, the efficiency of a solar chimney in creating airflow inside a room was studied via computer simulations. Second, a physical model was subsequently created to test how plants, a hydrogel filter, and their combination affect IAQ, measured by air quality through sensors inside and outside the model. The study was conducted in March in Tucson, Arizona, which has a typical hot, arid climate. The results of the testing indicate the proposed solutions can lower the indoor temperature via evaporative cooling and increase humidity levels to 46%, as recommended by a recent IAQ study (Razjouyan, et al., 2020). The results also reveal a significant reduction in levels of VOCs, CO2, PM10, and PM2.5. Thus, the proposed ventilation system has significant implications for future designs seeking to ensure optimum IAQ via natural ventilation strategies.