A twin site study of size-resolved composition, source apportionment and health impacts of aerosol particles in Morocco

This study provides new information on the chemical composition, source contributions, and health implications of size-resolved ultrafine, fine, and coarse mode particles through a comparative assessment at two contrasting sites in Morocco: the rural Atlas Mohammed V (AMV) observatory and the urban city of Fez. During September–October 2019, PM₁₀ concentrations at Fez (32 ± 7.8 μg m⁻³) were nearly three times higher than at AMV (12 ± 6.4 μg m⁻³), with urban ultrafine particles (<0.1 μm) contributing 30 % of PM₁₀ compared to only 12 % at the AMV observatory. Source apportionment results revealed that vehicular exhaust was the main contributor (34 %) to ultrafine particles at FEZ, while a total traffic-related factor, including both exhaust and non-exhaust emissions, dominated at AMV (37 %), indicating long-range transport of urban traffic pollutants. Both sites showed substantial biomass burning influence (ca. 40 %) in fine particles and mineral dust dominance (>50 %) in coarse fractions (1.2–10 μm). Source contributions varied across different air mass origins, suggesting local emissions as primary drivers of pollution, with long-range transport predominantly enhancing background concentrations rather than introducing new source types in the studied regions. Diagnostic ratios indicated that fresh traffic emissions dominated PAH composition in Fez, while mixed petroleum and combustion sources were the dominant sources at AMV. Health risk assessments revealed elevated non-carcinogenic risks in Fez, particularly from traffic-related metals (Ni, Zn). These findings address critical data gaps in North African air quality research and provide essential baseline information to support targeted emission control strategies and public health policies in rapidly urbanizing regions.