Investigation of Desert Dust Contribution to Source Apportionment of PM10 and PM2.5 from a Southern Mediterranean Coast

ABSTRACT

In order to identify the source apportionment of particulate matter PM₁₀ and PM_2.5 in the southern Mediterranean coast of Tunis (Tunisia), three different sites characterized respectively by traffic, industries and being an urban background area are studied. The chemical characterization included a gravimetric determination of atmospheric particles mass concentration, measurements of the major anions (SO₄^2–, NO₃^–, Cl^–) and cations (Ca²⁺, Mg²⁺, K⁺, NH₄⁺) concentrations in the aerosol samples by ion chromatography and analysis of 18 elements by energy dispersion X-ray fluorescence. Aerosol ion balance of various PM₁₀ constituents are used to identify possible sources of the particulate matters. Thanks to these analysis, the particulate masses were reconstructed from the main possible constituents: crustal matter, primary and secondary pollutants, marine aerosols and organic matter. Wherever PM₁₀ and PM_2.5 were studied, PM₁₀ crustal elements and sea salt aerosols were mainly associated with the coarse fraction whereas primary and secondary anthropogenic pollutants as well as organic matter rather compose PM_2.5 fraction. In all the sites, PM₁₀ mass was mainly composed of crustal matter (41–50%) and poorly of sea salt (3–4%). And so aerosols chemical composition is heavily affected by dust winds from Sahara desert, with some contribution of local traffic and industries and only a slight direct impact of the nearby Mediterranean sea.