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Building and Environment

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Carbon dioxide -- Environmental aspects, Indoor air quality, Hydroxides, X-ray diffraction, Thermogravimetry


Indoor carbon dioxide (CO 2 ) levels serve as an indicator of ventilation sufficiency in relation to metabolic effluents. Recent evidence suggests that elevated CO 2 exposure (with or without other bioeffluents) may cause adverse cognitive effects. In shelter-in-place (SIP) facilities, indoor CO 2 levels may become particularly elevated. This study evaluates four low-cost alkaline earth metal oxides and hydroxides as CO 2 sorbents for potential use in indoor air cleaning applications. Sorbents studied were MgO, Mg(OH) 2 , Ca(OH) 2 and commercially available soda lime. Uncarbonated sorbents characterized with nitrogen adsorption porosimetry showed BET surface areas in the 5.6–27 m 2 /g range. Microstructural analyses, including X-ray diffraction, thermogravimetric analysis and scanning electron microscopy confirmed the carbonation mechanisms and extent of sorption under environmental conditions typical of indoor spaces. Ca-based sorbents demonstrated higher extent of carbonation than Mg-based sorbents. Laboratory parameterizations, including rate constants ( k ) and carbonation yields ( y ), were applied in material balance models to assess the CO 2 removal potential of Ca-based sorbents in three types of indoor environments. Soda lime ( k = [2.2–3.6] × 10 −3 m 3 mol CO 2 −1 h −1 , y = 0.49–0.51) showed potential for effective use in SIP facilities. For example, CO 2 exposure in a modeled SIP facility could be reduced by 80% for an 8-h sheltering interval and to levels below 5000 ppm for an 8-h period with a practically sized air cleaner. Predicted effectiveness was more modest for bedrooms and classrooms


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