Author links open overlay panelMatthew Russell ab
, Alex Webster c
, Carl Abadam bd
, Katelin Fisher b
, Stephanie Campbell bd
, Carmen Atchley bd
, Kana Radius bd
, Paris Eisenman bd
, Ashley Apodaca-Sparks bd
, Astrid Gonzaga bd
, Rui Liu e
, Patrick Hudson f
, Anjali Mulchandani abdShow moreAdd to MendeleyShareCite
https://doi.org/10.1016/j.watres.2025.124213Get rights and content
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Abstract
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 PM2.5 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 PM2.5 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 PM2.5 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.
Graphical abstract
Keywords
Dehumidification
Condensation
Aerosols
Water vapor
Pollutants
1. Introduction
Global warming and the increased variability and intensity of natural disasters (e.g., floods, droughts, wildfire) are a continuing concern to water supplies. Any of these natural disasters can impact municipal water supplies and limit access for weeks to months. The atmosphere is an alternative freshwater reservoir that contains 12,900 km3 of water (Shiklomanov, 1991), is universally accessible, and can serve as a water source when other supplies are inaccessible. Atmospheric water harvesting (AWH) can condense this available water vapor to provide access to water for communities in need during emergencies (Gayoso et al., 2024; Mulchandani and Westerhoff, 2020).
There are few studies on AWH water quality, and the relationship between air quality and water quality has only been minimally investigated for both condensation and sorption-based systems (Mulchandani et al., 2022; Zeng et al., 2024). These AWH water quality studies are often performed at a single site for around 12 months (Mulchandani et al. 2022), while few have studied AWH across multiple sites and months (Xia et al., 2015). These studies find turbidity, aluminum, iron, and manganese concentrations above United States Environmental Protection Agency (U.S. EPA) and World Health Organization (WHO) drinking water regulations in untreated AWH water, and aluminum and iron above regulatory values in treated AWH water (Zeng et al., 2024). As more studies are performed, it is apparent that there may be large variability in concentrations of metal and organic contaminants over space and time. The concentration of these contaminants may be impacted by variability in air quality, but this influence is not well studied. Xia et al. (2015) studied the relationship between particulate matter (PM) and ion contaminants in condensation-based atmospherically harvested water and found high concentrations of Cl–, SO42-, NH4+ and Ca2+ in industrial areas associated with soil dust and exhaust. This study was performed in a temperate climate (relative humidity ranged 60–80 %), and it is unknown whether these results are transferable or universal for all climate zones and pollution sources, specifically those experienced in more arid regions. For AWH to be considered a viable drinking water source in multiple regions, more data is needed to understand the extent and nature of air quality influence on AWH water quality. Spatial and temporal analysis across environments (e.g., arid with heavy agricultural and urban emissions sources, vs humid with heavy industrial emissions) is needed to determine the full range of potential water quality.
Air quality is influenced by natural and anthropogenic emissions of trace gases and aerosols as well as meteorological factors such as temperature, wind speed, and humidity. As such, air quality can vary across a geographic region and changes throughout the day (Hosein et al., 1977). The U.S. EPA classifies and measures outdoor air pollution by 6 criteria pollutants: ozone (O3), carbon monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), lead (Pb) and particulate matter (PM) pollution (US EPA, 2015a). Of these pollutants, PM may be most likely to influence chemical makeup of AWH water quality due to the interaction between PM and gas phase water in the atmosphere.
Fig. S1 shows how PM and gas-phase water interact in the atmosphere. PM is formed through nucleation, accumulation and coarse modes. In nucleation mode, particles are freshly formed through combustion or atmospheric reactions from emissions sources such as traffic, industry and burning (EPA, 2023). These particles grow through coagulation with water vapor and other constituents to get to accumulation mode. As small particles stick together, the total particle number decreases, and the mass and surface area of each coagulated particle increase. Lastly, coarse mode generally consists of mechanically separated particles that may be resuspended from surfaces. PM is classified as fine (<2.5 m) and coarse (<10 m) and is often made up of clusters of different constituents depending on the emissions that influence the air quality (EPA, 2019). PM2.5 typically contains crustal material comprising of metal compounds (Al, Cu, Fe, K, Mn, etc.), soil, small liquids, elemental carbon, volatile organic compounds and various ions (SO42- and NO3–) (Chemical Elements, Minerals, Rocks, 2024; EPA, 2023; Hasheminassab et al., 2014). PM10 is typically produced by surface abrasion, sea spray, biological materials, and road, crop and livestock dust (EPA, 2023). Water vapor in the air continue to interact with particulates, which may partition with water vapor into condensed AWH waters. We theorize that when this water vapor condenses within an AWH system, particles of all sizes from various sources (e.g., traffic, industry and burning) containing constituents such as metals, carbon and gases will be collected in the harvested water and impact water quality.
Currently, there is a knowledge gap regarding the relationship between PM concentrations and characteristics, and subsequent water quality of AWH, particularly as it varies by space and time to determine site specific impacts. These relationships may vary as a function of location, climate, and air quality. Closing this gap can provide key insight on the level and type of treatment required to make AWH a viable drinking water source. If there is a significant relationship between air quality measured as PM and water quality, air could be pre-filtered to remove PM before harvesting. Alternatively, post-harvesting water treatment may be applied to remove both particles and dissolved constituents.
The objectives of this research were to determine: i) the variation of measured air and water quality contaminants by site, and ii) the extent of interaction between particulate matter concentration in the air and the water quality of atmospherically harvested water. Condensation-based AWH devices were operated in a semi-arid high-desert metropolitan city. AWH devices were co-located with air quality monitoring instrumentation to directly compare air quality with AWH water quality. The air was not pre-filtered, and AWH water samples were not filtered or treated in order to gain a full understanding of the impact of PM on water quality. We hypothesized that air pollution and AWH water pollution would be greater at the industrial site compared to the urban site. Secondly, we hypothesized that there would be a positive linear relationship between both PM10 and PM2.5 and total organic carbon and metal concentrations, the nature of which may be specific to each site. Findings from this study can guide research on understanding if PM 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.
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https://www.sciencedirect.com/science/article/pii/S0043135425011200?via%3Dihub
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