Abstract: Atmospheric (PM2.5) is a critical indicator of air quality, with substantial implications for human health. Polycyclic aromatic hydrocarbons (PAH) and their oxygenated (OPAH) derivatives represent one of the largest contributors to the harmful effects attributed to PM. The objective of this study was to assess the concentrations of PAHs and OPAHs in PM2.5 collected at five cities on three continents: Stockholm (Sweden), Kyoto (Japan), Limeira, Ribeirão Preto, and Cáceres (Brazil), in order to identify the main sources of particulate air pollution at these cities during the winter/dry seasons. PM2.5 sampling campaigns were carried out in 2020, 2021, and 2022, using high-volume air samplers. PAHs and OPAHs were extracted and determined by gas chromatography coupled to mass spectrometry (GC/MS) following the methodology described by Santos et al. (2016). The highest mass concentrations of PM2.5 were found in Ribeirão Preto (49.5 ± 18.4 μg m-3 ; n = 6) and Limeira (33.7 ± 17.9 μg m-3 ; n = 9), followed by Stockholm (19.7 ± 6.3 μg m-3 ; n = 5), and the lowest in Kyoto (9.9 ± 4.9 μg m-3 ; n = 9). Cáceres exhibited the highest variability in PM2.5 levels, ranging from 2.2 to 122.3 μg m-3 (n = 6) showing occasional high inputs. Comparisons with WHO short-term air quality guideline (AQG 24 h: 15 μg m-3 ) revealed several exceedances of the threshold, particularly in the Brazilian cities. Winter/dry season sampling indicated higher PM2.5 levels compared to annual means reported by local agencies, with all cities surpassing the WHO annual AQG. This underscores the need for continuous monitoring, especially in regions lacking a comprehensive air quality network. Limeira had the highest median of total PAHs (Σ16PAH) (11.8 ng m-3 ), followed by Ribeirão Preto (5.50 ng m-3 ), Stockholm (2.07 ng m-3 ), Kyoto (1.68 ng m-3 ), and Cáceres (1.29 ng m-3 ). Cáceres exhibited the lowest Σ16PAH median but displayed high variability, correlating with the observed variability in PM2.5 levels. Since the site in Cáceres is located at a remote area, the main drivers of the elevated concentrations detected in certain samples were occasional PM2.5 inputs by biomass burning, as evidenced by the high concentrations of retene, associated with biomass burning. Among the individual PAHs, human exposure to high-molecular-weight PAHs (HMW-PAHs) are of special health concern due to their higher mutagenic and carcinogenic activity compared to smaller PAHs. A prevalence of HMW-PAHs was observed in Ribeirão Preto, Limeira, and Kyoto samples, with benzo[b]fluoranthene (BbF) and benzo[ghi]perylene (BPer) being the most abundant. The carcinogenic activity of PAHs mixtures, measured in terms of benzo[a]pyrene equivalent (BaPeq) concentrations, was notably elevated in Brazilian cities. In Ribeirão Preto, the BaPeq concentrations reached up to 13.5 ng m-3 , highlighting the city’s susceptibility to heightened risk due to biomass burning, as previously demonstrated (Scaramboni et al., 2024). In contrast to Σ16PAH, total oxygenated PAHs (Σ4OPAH) showed different patterns, with Cáceres having nearly twice the concentrations of Σ4OPAH compared to Kyoto and Stockholm. In Cáceres, 2-methylanthraquinone was the predominant OPAH, exhibiting a median concentration 2-8 times greater than that observed in other cities. The primary source of this compound is attributed to the teak tree, widely cultivated in the city. However, the specific emission processes, whether through burning or biogenic emissions, remain to be investigated. In all five cities studied, diagnostic ratios (DRs) consistently indicated a dominance of pyrogenic sources over petrogenic sources in the measured PAHs, aligning with expectations given the prevalence of pyrogenic sources in air samples compared to petrogenic sources associated with sediment deposition from petroleum activities. DRs also suggested that the pyrogenic sources were a combination of vehicle emissions and biomass combustion. The BaP/BPer ratio, associated with traffic-related emissions, was highest in Stockholm, in line with its proximity to a highway. The BaP/(BaP + BeP) ratio indicated fresh PM emissions in Cáceres > Ribeirão Preto > Limeira > Stockholm and more aged particles in Kyoto, aligning with fire spots in Cáceres and long-range air mass trajectories from China and South Korea to Kyoto. Brazilian cities showed a notable influence of biomass burning, likely attributable to widespread Amazon and Cerrado wildfires added to local fires. Our results support the importance of improving the air quality especially during the emission-intense winter/dry season to reach air quality standards and limit human health effects from air pollution.

Keywords: Particulate Matter, Biomass Burning, Monitoring.