Influence of source contributions and seasonal variations on particle-associated polycyclic aromatic hydrocarbons and cancer risks in a rapidly urbanizing South American City (Fortaleza, Brazil)

Particulate matter (PM) was recently classified as a Group 1 (carcinogen to humans), marking a significant step forward in prioritizing the monitoring of airborne particles in urban environments. In this sense, the primary objective was to evaluate the cancer risk associated with PM10 and polycyclic aromatic hydrocarbons (PAHs) levels, with a focus on the contribution of different source types and seasonal variations in a highly urbanized city located in the tropical semiarid region of South America, where air quality studies and understanding remain scarce. The PM was collected using a Hivol sampler, and the PAHs contained within were extracted using Soxhlet extraction and analyzed by gas chromatograph with mass spectrometery. The PM10 levels ranged from 8.9 to 33.3 µg/m³ and from 17.2 to 33.2 µg/m³, in the rainy and dry season, respectively, while the ΣPAHs ranged from 0.18 to 2.03 ng/m³ (wet season) and from 0.14 to 0.64 ng/m³ (dry season). The ratio of PM10 levels between wet and dry periods remained relatively stable throughout the year, consistently staying below 1 across most parts of the city. However, in areas with higher traffic flow, classified as moderate to deep urban canyon zones, levels were significantly higher during the dry period. The sources appointment indicates that the contribution of the vehicle fleet is geographically predominant, followed by contributions from the burning of coal and wood, and, more succinctly, the influence of the existing industrial sectors in the region. Compared to other urban and industrial regions worldwide, Fortaleza's risk levels are moderate to relatively low. However, the relative cancer risk is approximately 22% higher for smokers compared to nonsmokers.