Reduced Uptake of Airborne Organic Pollutants in Salt-Based Atmospheric Water Harvesting

High water yield and low energy requirements make sorption-based atmospheric water harvesting (SAWH) a promising approach for decentralized freshwater production. Salts such as lithium chloride (LiCl) and calcium chloride (CaCl2) are commonly used in these systems. This study evaluates the chemical quality of SAWH-produced water, focusing on the uptake of volatile organic compounds (VOCs) from polluted air. Experiments were conducted in a controlled system where humid air with known VOC concentrations was contacted with hygroscopic salts. Water was harvested via sorption and thermal desorption, and VOC content analyzed using gas chromatography. VOC transfer into salt-harvested water was significantly lower than in other AWH methods, including silica gel, atmospheric water generators (AWGs), and passive condensation. Under extreme exposure (12,500 μg/m3), BTEX compounds (benzene, toluene, ethylbenzene, xylene) remained below 5 μg/L in salt-harvested water, compared to 47, 5, and 10 μg/L in water from silica gel, AWG, and condensation, respectively. For 1-butanol, levels were approximately 1000 μg/L, versus 20,000, 7000, and 38,000 μg/L in the alternatives. At typical urban and industrial VOC levels (10–100 μg/m3), the impact on harvested water quality was negligible. VOCs tended to concentrate in the initial aliquot of collected water, highlighting a consideration for practical implementation. The extent of VOC uptake depended on compound polarity and hydrogen bonding capacity. Overall, SAWH using hygroscopic salts demonstrates minimal interaction with airborne organic pollutants and offers a promising route for cleaner water production in polluted environments.