Size-resolved aerosol composition and source apportionment in Morocco: Contrasting urban and remote sites 

Aerosol particles are complex mixtures of organic and inorganic compounds suspended in the atmosphere that significantly impact the climate, human health, and the environment. Understanding their composition and sources is crucial for developing effective air pollution control policies. Although some studies have been conducted on the chemical composition of PM and the sources of PM in Moroccan urban areas, a knowledge gap exists regarding the organic composition and chemical processes across different-sized bins. A detailed study was conducted in September and October 2019 at two distinct sites in Morocco: Atlas Mohammed V (AMV) and the urban city of FEZ. Size-resolved aerosol samples were collected using a 5-stage Berner impactor. Analyses included PM mass, organic carbon (OC)/elemental carbon (EC), trace metals, water-soluble ionic species, and a broad range of organic species. The results show strong regional variations in PM mass, with FEZ (32 µg m-3) showing approximately three times the PM level of AMV (11 g m-3). Coarse particles within the 3.5-10 µm size range made up 35% of the PM mass at AMV and 32% at FEZ. The PM3.5/PM10 ratio at both sites was comparable, with an average of 0.65±0.037. However, the chemical composition analysis revealed a strong urban-remote contrast. FEZ showed higher concentrations of fine-mode pollutants such as OC, EC, and sulfates. At the same time, the remote AMV site exhibited higher coarse-mode OC and nitrates, suggesting different sources and formation processes influenced the PM composition at both sites. The organic compound profiling identified a dominance of alkanes (12±6.8 ng m-³) and PAHs (1.9±2.5 ng m-³), such as Benz(a)pyrene, Benzo(k)fluoranthene, Phenanthrene, and Retene, with the urban FEZ site revealing significantly higher concentrations, particularly in the 0.42-1.2 µm size range. In contrast, at AMV, these compounds were more evenly distributed across all particle sizes, reflecting the influence of both natural and anthropogenic sources on their abundances. According to the Positive Matrix Factorization (PMF) model, we identified four and six particle emission sources at AMV and FEZ, respectively. Mineral dust (36-55%) was the predominant component in the coarse mode at both sites, while road dust mixed with local pollutants was significant (up to 44%) in smaller particles (1.2-3.5 µm) in FEZ. At AMV, mixed anthropogenic emissions (21-45%) and secondary aerosols (26-61%) significantly impacted the ultra-fine and acceptable modes, while in FEZ, traffic exhaust (18-34%) and biomass burning (17-41%) dominated the fine mode. Diagnostic ratios of polycyclic aromatic hydrocarbons (PAHs) indicated a blend of fresh and aged particles at AMV, predominantly from petroleum and combustion sources with long-range anthropogenic influence. In contrast, FEZ showed a predominance of fresh emissions from traffic-related sources affecting all particle sizes. These results explore the chemical composition and source apportionment, highlighting the need to control anthropogenic traffic-related emissions to improve urban air quality in North Africa.