A 15-year atmospheric record of intentionally produced persistent organic pollutants in Spain: Spatial gradients, thermodynamic fractionation, and temporal trends.

Abstract

This study presents a comprehensive 15-year (2009-2023) assessment of persistent organic pollutants (POPs) in the Spanish atmosphere to evaluate the Stockholm Convention's effectiveness. Polyurethane foam passive samplers were deployed across 23 sites to monitor legacy pesticides and industrial chemicals. Results reveal a concentration hierarchy dominated by hexachlorobenzene (HCB), which accounted for a median of 41% of the ∑POP concentrations and displayed a remote-enriched spatial pattern characteristic of global distillation. In contrast, legacy pesticides and indicator polychlorinated biphenyls (iPCBs) were influenced by temperature-dependent secondary volatilization from historically contaminated soils, as indicated by Clausius-Clapeyron analyses. These compounds frequently exhibited an unexpected urban enrichment likely associated with heat island effects, while polybrominated diphenyl ethers (PBDEs) displayed a pronounced urban gradient (a 35-fold increase from remote baselines) driven by the late-regulated BDE-209. Long-term temporal analyses underscore a sharp regulatory dichotomy. Early-banned compounds, such as endosulfan, HCB and dichlorodiphenyltrichloroethane (DDT), and lighter PBDEs, are experiencing rapid environmental depletion, with significant annual declines of up to -33%. Conversely, pentachlorobenzene (PeCB), iPCBs, and BDE-209 show stalled or locally increasing trends (up to +20%), sustained by unintentional combustion, active consumer goods, and regulatory lag times. Altitudinal profiling across Tenerife sites highlights this divergence: coastal areas reflect local secondary emissions, whereas high-altitude observations confirm the progressive clearance of the global free troposphere. Overall, these findings provide new insights into the spatial and temporal dynamics of atmospheric POPs, reaffirming the role of long-term monitoring in guiding international abatement strategies.