Influence of particulate matter air quality on water quality of atmospheric water harvesting

Atmospheric water harvesting (AWH) is a decentralized water technology that dehumidifies air to provide water. When atmospheric water is condensed, other atmospheric particles and gases can enter the liquid water. For AWH to serve as drinking water, it is necessary to understand how these air constituents interact with water as it condenses and the resulting water quality. The objectives of this research were to determine: i) the variation of measured air and water quality contaminants at two sites, and ii) the extent of interaction between particulate matter concentration in the air and the water quality of atmospherically harvested water. This study performed AWH using compressor dehumidifiers at industrial and urban ambient air quality monitoring sites in Albuquerque, New Mexico, USA. Air contamination was greater at the industrial site compared to the urban site (range PM_2.5 urban 1.3 - 33.4 μg/m³, industrial 1.8 - 127.5 μg/m³; range PM₁₀ urban 3.7 - 99.2 μg/m³, industrial 4.4 - 1525 μg/m³). Water trace metals concentrations and turbidity were also greater at the industrial site. Aluminum concentrations ranged 22.9 - 600 μg/L (urban) and 22.1 - 1560 μg/L (industrial); Iron ranged 0.5 - 363 μg/L (urban), 3.4 - 828 μg/L (industrial); Manganese ranged 0.7 - 23.7 μg/L (urban), 1.3 - 69.2 μg/L (industrial); and turbidity ranged 0.3 - 28 NTU (urban), 0.5 - 52 NTU (industrial). Water quality exceeded U.S. EPA regulations for aluminum (39 % of samples at urban site, and 90 % of samples at industrial site > 200 µg/L) and turbidity (96 % at urban site, 100 % at industrial site > 0.3 NTU). A linear mixed-effects statistical model showed water quality was a function of air quality, but for only some parameters. At the industrial site, there was a strong positive relationship between PM_2.5 and some metals (aluminum, calcium, iron [p<0.05]), and marginal significance with other metals (potassium, zinc [p<0.1]). At the urban site, there was only a strong positive relationship between PM_2.5 and calcium. Large variations in PM concentrations and site differences in their characteristics could play an important role in how much of metals in the air enters atmospherically harvested water. Findings from this study can guide research on understanding if air quality can be used to predict AWH water quality, provide insight to further understand the mechanisms of interaction between gas-phase water and particles as they move from the air to condensed water, and drive treatment decisions to meet water quality goals.