Abstract
Scavenging of gas- and aerosol-phase organic pollutants by rain is an efficient wet deposition mechanism of organic pollutants. However, whereas snow has been identified as a key amplification mechanism of fugacities in cold environments, rain has received less attention in terms of amplification of organic pollutants. In this work, we provide new measurements of concentrations of perfluoroalkyl substances (PFAS), organophosphate esters (OPEs), and polycyclic aromatic hydrocarbons (PAHs) in rain from Antarctica, showing high scavenging ratios. Furthermore, a meta-analysis of previously published concentrations in air and rain was performed, with 46 works covering different climatic regions and a wide range of chemical classes, including PFAS, OPEs, PAHs, polychlorinated biphenyls and organochlorine compounds, polybromodiphenyl ethers, and dioxins. The rain–aerosol (KRP) and rain–gas (KRG) partition constants averaged 105.5 and 104.1, respectively, but showed large variability. The high field-derived values of KRG are consistent with adsorption onto the raindrops as a scavenging mechanism, in addition to gas–water absorption. The amplification of fugacities by rain deposition was up to 3 orders of magnitude for all chemical classes and was comparable to that due to snow. The amplification of concentrations and fugacities by rain underscores its relevance, explaining the occurrence of organic pollutants in environments across different climatic regions.
Highlights
Persistent organic pollutants (POPs) have the potential for long-range atmospheric transport (LRAT) from source to remote regions due to their persistence, semivolatility, or transference to the atmosphere with sea-spray aerosols.[1−3] The study of LRAT and atmospheric deposition has been central in previous assessments of the occurrence of POPs at regional and global scales
Wet deposition by rain and snow is independent of the fugacity gradient between the air and surface but is dependent on the capacity of rain and snow to scavenge atmospheric pollutants.[12−14] These deposition processes can lead to higher concentrations of organic pollutants in water and soils than those derived from airsurface partitioning only, a process named “amplification.” the amplification of organic pollutants has received little attention
Wet deposition by rain or snow[12] scavenges POPs found in the gas and aerosol phases very efficiently and can amplify concentrations of POPs in other environmental compartments, such as in seawater[18−21] or soils.[22−25] This process has been proven to be especially effective for snow scavenging and is one of the main entries of POPs in cold regions, such as highmountain and polar regions.[18,26−28] Partition toward the snowflakes is favored at low temperatures
Summary
Persistent organic pollutants (POPs) have the potential for long-range atmospheric transport (LRAT) from source to remote regions due to their persistence, semivolatility, or transference to the atmosphere with sea-spray aerosols.[1−3] The study of LRAT and atmospheric deposition has been central in previous assessments of the occurrence of POPs at regional and global scales. Wet deposition by rain or snow[12] scavenges POPs found in the gas and aerosol phases very efficiently and can amplify concentrations of POPs in other environmental compartments, such as in seawater[18−21] or soils.[22−25] This process has been proven to be especially effective for snow scavenging and is one of the main entries of POPs in cold regions, such as highmountain and polar regions.[18,26−28] Partition toward the snowflakes is favored at low temperatures This together with the high specific surface area of snow, makes this deposition process crucial to understand the occurrence of a large variety of POPs in polar regions.[17−19,26,27,29] A meta-analysis of the snow−air partition constants (KSA), estimated as the ratio of POP concentrations in snow and air, from previously reported simultaneous field measurements, showed that snow amplification was relevant for diverse families of POPs, independent of their volatility.[18] The same work showed that seawater−air fugacity ratios of polychlorinated biphenyls (PCBs) were
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