Aerosols in Northern Morocco (Part 3): the application of three complementary approaches towards a better understanding of PM10 sources

Abstract

This study investigates the sources and characteristics of PM₁₀ pollution in Tetouan city, Morocco, by employing a combination of chemical mass closure, source-receptor modelling (namely positive matrix factorization, PMF), and air mass trajectory statistical analyses (concentration weighted trajectory, CWT). It provides compelling evidence that using such a combination is a powerful approach for studying the composition and sources of PM₁₀ in the Tetouan region. The PMF analysis identifies four PM₁₀ sources, namely Vehicle Exhaust, Secondary Aerosols, Nitrate + Biomass Burning, and Fresh Sea Salt, with distinct seasonal contributions. CWT analysis reveals the Mediterranean Basin as the primary source region, with influences from populated areas in northern Morocco, southern Europe, and marine emissions. PM₁₀ mass closure highlights the abundance of Dust, Particulate Organic Matter (POM), and Water-Soluble Inorganic Ions (WSI), accounting for the majority of the mass. The low OC/EC ratio advocates that carbonaceous aerosols primarily originate from local traffic emissions. Diagnostic of WSI ratios shows that the [NH₄⁺]/[SO₄²⁻] ratio indicated an ammonium-poor environment and suggested an acidic nature of the PM₁₀ aerosols, while the [SO₄²⁻]/[NO₃⁻] ratio reflects the combined influence of stationary and mobile sources, with a partial contribution from industrial activities throughout the year. These findings are expected to shed light on the chemical composition, origin of emission sources, and transport pathways of PM₁₀ in the region, contributing to the understanding of air pollution in the south western Mediterranean.