Re-emissions of polycyclic aromatic compounds from land and sea surfaces in source and receptor areas

Many polycyclic aromatic hydrocarbons (PAHs), along with their nitrated and oxygenated derivatives (NPAHs and OPAHs), are known for their toxicity and ecotoxicity (Bandowe et al., 2014; Rengajaran et al., 2015; IARC, 2019; Nováková et al., 2020). These compounds are co-emitted with PAHs during fossil fuel and biomass combustion, or they form through photochemical and microbiological reactions involving PAHs in the atmosphere and soil (Tsapakis and Stephanou, 2007; Keyte et al., 2013; Bandowe et al., 2017; Wilcke et al., 2021).

While laboratory and field studies have explored the sources, photochemistry, and atmospheric occurrence of these pollutants, their large-scale atmospheric lifetimes and environmental fate remain poorly understood. As semivolatile compounds resistant to biodegradation in soils and surface waters, their potential for long-range transport is further amplified by the "grasshopper effect" (Keyte et al., 2013; Mulder et al., 2014).

We determined the concentration of 25 parent PAHs, 10 OPAHs and 17 NPAHs during summer in air and soils at a rural and near-coastal north European site (Birkenes, southern Norway), a north European forest site (Hyytiälä, southern Finland), a central European rural background site (Košetice, Czech Republic), and in air and surface seawater at two off-shore sites in the Aegean Sea and along transects across the Mediterranean Sea. Directions of diffusive air-soil and air-sea exchanges were derived from the fugacities.

In the source area (central Europe), the diffusive vertical fluxes of most 2-4 ring PAHs, 2-nitronaphthalene and a number of 3-4 ring OPAHs were upward and the carcinogen 1-nitropyrene was found close to phase equilibrium. In the receptor area (northern Europe), acenaphthylene, acenaphthene, benzo(a)anthracene, two 3-4 ring OPAHs, dibenzofuran and 6H-benzo(c)chromen-6-one, were found to volatilise, and 2-nitrofluoranthene close to phase equilibrium (Mwangi et al., 2024). In the Mediterranean Sea, phenanthrene, fluoranthene, pyrene, 2-nitronaphthalene and few 3-4 ring OPAHs were found to volatilise from the sea surface or being close to equilibrium. These findings suggest that land and sea areas even far from the primary sources may indeed act as secondary sources for PAHs, NPAHs and OPAHs in the atmosphere and enable global transport by multihopping.

Secondary emissions may include toxic species, such as e.g., the carcinogenic 1-nitropyrene. Because of neglected re-emissions (secondary sources), PAH emission inventories may be underestimated, in particular in receptor areas.

 

Acknowledgements: Czech Science Foundation (GAČR, grants 07117S, 17534S), the Max Planck Society, the European Commission – H2020, JERICO-S3 (871153), ACTRIS-CZ (LM2023030), RECETOX (LM2023069) financed by the Czech Ministry of Education, Youth and Sports (MŠMT).

 

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