Occurrence and backtracking of microplastic mass loads including tire wear particles in northern Atlantic air

The study addresses the limited knowledge on the occurrence, composition, size distribution, and sources of atmospheric microplastics (MP), including tire wear particles (TWP), over the marine environment. Prior work suggests atmospheric transport delivers terrestrial MP to oceans and that re-emission from the sea via sea spray may be a major atmospheric source. The authors aim to quantify MP mass loads and composition in northern Atlantic air, including Arctic regions, using active air sampling and mass-based analysis (Py-GC-MS), and to infer source regions using atmospheric transport and dispersion models. The work is important for understanding the ocean-atmosphere leg of the plastic cycle and assessing whether the ocean can act as a source of atmospheric MP, not only a sink.

Existing atmospheric MP studies over marine areas are scarce and largely report particle-number-based concentrations using FTIR or µ-Raman, typically focusing on particles <200 µm with counts up to 85 particles m−3 and minimum identified sizes of 5–10 µm. TWP have generally not been included in those datasets. Several studies suggest significant atmospheric transport of MP (especially PM2.5-sized) to remote regions, including polar areas, and propose sea spray and bubble bursting as mechanisms re-emitting MP from the ocean to the atmosphere. Plastic demand is dominated by common polymers (PE, PP, PS, PET, PVC, PC, PMMA, PA6) and PUR, which are also frequently detected in environmental samples. Comparisons are complicated by differences in sampling and analytical methods and by reporting mass-based versus number-based metrics. The literature generally reports PET/polyester as a dominant polymer type in marine air (29–56% of particles), with PP frequently observed and PS less consistently dominant.

Sampling took place during the HE578 cruise on R/V Heincke (July 2021) along seven transects (T1–T7) from the Norwegian coast to Bear Island and back. Two active sampling approaches were used: (1) Low-volume (LV) samplers provided by NILU with a two-stage filtration cascade capturing size fractions >10 µm and 5–10 µm using stainless-steel meshes (10 µm and 5 µm pore size). LV sampling volumes were 54–417 m³ per sample. LV filter holders (aluminum) and filters were pre-baked (450 °C, 8 h), assembled under clean conditions, and not re-opened onboard. (2) High-volume (HV) samplers (DIGITEL DHA-80) from TUB captured PM10 on standard filters while depositing particles >10 µm onto pre-cleaned aluminum rings (Ø 30 cm) beneath the inlet jets. HV volumes ranged 288–2184 m³. Two identical HV samplers operated in parallel to create duplicates; averages were used. Samplers were mounted on the observation deck (~12 m above sea level) at the bow; sampling occurred only while steaming to minimize ship-related contamination. Operational blanks for both systems were collected after transects 1, 4, and 7 by installing sampling units and running pumps for ~1 min. LV units arrived pre-assembled; HV aluminum rings were exchanged on deck, increasing potential exposure. Sample clean-up used only glass, stainless steel, or PTFE equipment under laminar flow with pre-filtered reagents. Procedural laboratory blanks (n=6 LV; n=12 HV) accompanied processing; positive signals in blanks were subtracted from sample raw data before quantification. LV meshes were sonicated in ethanol (96%) to detach particles, rinsed, and filtrates collected on pre-baked glass fiber filters (15 mm, 0.3 µm). Filter cakes were treated with H2O2 (30%) and petroleum ether (5 min each) to remove organic matter and nonpolar components, then folded into stainless-steel pyrolysis cups. HV aluminum rings were discharged with an antistatic gun, rinsed with ethanol onto glass fiber filters, then treated similarly with H2O2 and petroleum ether and placed in pyrolysis cups. Pyrolysis-GC/MS: A FrontierLabs EGA/Py-3030D pyrolyzer (590 °C) with auto-shot sampler coupled to an Agilent 6890N GC and 5973 MSD (EI 70 eV, 230 °C ion source) using a deactivated retention gap and DB-5MS column. Prior to analysis, 20 µL deuterated polystyrene solution (internal standard for pyrolysis process) and 20 µL TMAH (12.5% in methanol) were added to each cup for on-line derivatization/thermochemolysis. Identification and quantification targeted clusters of common polymers (C-PE, C-PP, C-PS, C-PET, C-PMMA, C-PC, C-PA6, C-MDI-PUR) and tire tread markers (CTT for car, TTT for truck). Calibration used peak area ratios of polymer indicator ions relative to dPS; most polymers were calibrated 0.01–10 µg; C-PP was semi-quantified with a 1-point calibration (0.85 µg) due to low concentrations. Quality control and exclusions: Operational blanks indicated potential contamination for certain clusters. Due to ubiquitous blank signals or sampler-related contamination, C-PMMA (all), C-PC in >10 µm, and C-PP in LV samples were excluded from discussion. C-PVC was excluded due to non-specific naphthalene interference from soot and lack of an applicable marine soot correction. For clusters potentially affected by blanks but without a consistent pattern (e.g., occasional C-PS, and C-PP/C-PET in HV), results were retained but flagged as possibly influenced. LOD/LOQ values and detailed calibration are in SI. Atmospheric transport and dispersion modeling: To infer air mass origins and potential sources, two models were applied. FLEXPART v10.4 (Lagrangian particle dispersion) was driven by ECMWF operational fields (137 levels, 1°×1°, 3-hourly). Particles were released from the moving ship receptor (0–100 m) every 4 h and tracked 30 days backward (retroplume), including gravitational settling for assumed MP density 1234 kg m−3 and size runs at 0.4, 3.0, 8.0, 10, 12, 18, 25 µm; output was footprint emission sensitivity on a 0.5°×0.5° grid. HYSPLIT 4 backward trajectories (24 h and 72 h) used NCEP/NCAR reanalysis (18 levels, 2.5°×2.5°); endpoints at 30 m above sea level at the ship during sampling provided air mass pathways.

• MP were ubiquitous in northern Atlantic marine air, including remote Arctic regions, with total concentrations up to 37.5 ng m−3.
• LV sampler: After excluding affected clusters, MP were present in all >10 µm samples and in five of seven 5–10 µm samples. Total mass loads ranged from below LOQ to 1.82 ng m−3. C-PET dominated (max 1.54 ng m−3), with frequent but lower C-PS (max 0.14 ng m−3). In one case (T7, 5–10 µm), C-PC was 0.28 ng m−3. Generally, >10 µm fractions had higher MP than 5–10 µm.
• HV sampler (>10 µm): All samples contained MP; summed concentrations ranged 0.23–37.5 ng m−3. Very high TWP loads were observed: CTT 35.3 ng m−3 (T1; 94% of total MP) and 13.2 ng m−3 (T3; 87%). When excluding TWP (CTT and TTT), totals never exceeded 2 ng m−3 and matched the LV magnitude for >10 µm.
• Polymer composition (excluding TWP): HV mean relative contributions were C-PET 56%, C-PP 31%, C-MDI-PUR 11%, C-PS ≈3%. LV samples showed C-PET 67% and C-PS 17% on average. PET/polyester clusters were universally present across transects.
• Maximum concentrations by type (from abstract and results): PET cluster up to ~1.5 ng m−3; TWP up to 35 ng m−3; PS/PP/PUR clusters up to ~1.1 ng m−3.
• Comparison with literature: The predominance of PET/polyester aligns with prior marine atmospheric studies reporting 29–56% of particles as PET/polyester; PP also frequent but at lower proportions elsewhere; PUR detected here (avg 11% in HV for some transects) has limited prior reporting.
• Sampler comparison (>10 µm): For C-PET and C-PS, LV and HV showed similar order-of-magnitude mass loads (C-PET typically 0.05–0.41 ng m−3; HV T3 had 0.98 ng m−3 due to visible fibers); C-PS never exceeded 0.1 ng m−3.
• Source attribution (models): FLEXPART footprints and HYSPLIT trajectories indicated some transects (T1, T3, T5, T4 high Arctic) sampled air masses largely from marine areas, while others (T2, T6, T7) had continental influence. High TWP in T1 and T3 despite minimal land contact suggests oceanic re-emission (sea spray) as a source. T7, influenced by mainland, showed elevated C-PET consistent with atmospheric transport of synthetic fibers. T3 and T5 had notable C-MDI-PUR, potentially from ship coating materials re-emitted via sea spray.

The study demonstrates that microplastics, including tire wear particles, are pervasive in marine air along the Norwegian coast into the Arctic, with mass-based concentrations quantifiable by Py-GC/MS. Both low- and high-volume active air sampling approaches produced comparable results for key clusters (C-PET, C-PS) in the >10 µm fraction and revealed complementary strengths: LV reduced direct contamination risk but sampled smaller volumes; HV enabled detection of more diverse polymers and TWP at higher sensitivity. The predominance of PET aligns with prior particle-based literature and supports the hypothesis that synthetic fibers are a major atmospheric MP component over the ocean. Dispersion modeling clarified that both continental transport and oceanic re-emission contribute to observed MP. High TWP loads in air masses with little land influence (T1, T3) suggest sea spray-mediated re-emission from the ocean surface microlayer as an important atmospheric source, while transects influenced by coastal mainland (e.g., T7) showed polymer signatures (PET) consistent with terrestrial fiber emissions transported over sea. Detection of PUR in largely marine-influenced air (T3, T5) is consistent with re-emission of coating-derived particles. Collectively, these findings indicate that the ocean functions not only as a sink but also as an active source of atmospheric MP, closing an important loop in the plastic cycle.

This work provides mass-quantitative evidence for the occurrence, composition, and sources of atmospheric microplastics, including tire wear particles, over the northern Atlantic and into the Arctic. Using active LV and HV samplers with Py-GC/MS analysis, the study found ubiquitous MP with total concentrations up to 37.5 ng m−3 and a dominant contribution of PET/polyester clusters; TWP dominated total loads in specific transects. Dispersion modeling and observations support both continental transport and oceanic re-emission (via sea spray) as significant sources, implying the ocean can serve as a source of atmospheric MP. Future research should prioritize standardized, harmonized sampling and analytical methods (including larger air volumes and consistent size fractionation), deeper investigation of size-resolved distributions to clarify transport and deposition dynamics, and assessment of ecological and health risks associated with atmospheric MP exposure in marine environments.

• Potential secondary contamination: Operational blanks indicated contamination for certain polymer clusters, leading to exclusion of C-PMMA (all), C-PC in >10 µm, and C-PP from LV results. Some retained clusters (e.g., C-PS and C-PP/C-PET in HV) may still contain minor contamination.
• C-PVC was excluded due to non-specificity of the naphthalene indicator and lack of a marine soot correction factor.
• Size fraction coverage was incomplete: HV analyses were available only for >10 µm; LV covered >10 µm and 5–10 µm. Differences in sample volumes and LOD/LOQ may have limited detection of some polymers (e.g., TWP) in LV samples.
• Handling constraints: HV aluminum ring handling onboard increased susceptibility to contamination; large ring handling in the lab was less convenient.
• Comparability with literature is limited due to methodological differences (mass- vs number-based reporting, analytical techniques, and size cutoffs).