Pollution de l'air par les particules acides à Alger et influence de l'aérosol marin

The study presents the levels of air pollution by fine particulate matters PM₁₀ and PM₃ and the associated acid pollution in the great area of Algiers. Sampling site is located at the campus of Ecole Nationale Polytechnique, at 10 Km in the east of Algiers-city. Samples are taken using a high volume sampler, HVS-PM–₁₀ instrument equipped with a Sierra-Andersen cascade impactor with four stages. Sampling equipment was located at 4 meters high and at a few meters in the proximity of the national traffic road RN-5. The results reveal that air pollution by fine particles is very high and exceeds the European and WHO guidelines. The average content of PM₁₀ rises up to 78,8 μg/m³. The respirable particles (PM₃) average content is 45,2 μg/m³ which constitute approximately 50 % in mass of the PM₁₀. The ratio PM₃/PM₁₀ is a characteristic of an urban area influenced by road traffic.
In the PM₁₀, the average contents of acid compounds, particulate sulphates and nitrates, rise respectively up to 5,0 μg/m³ and 3,6 μg/m³. In the PM₃, the respective levels reached are of 4,4 μg/m³ and 2,6 μg/m³. The acid component contributes to approximately 21 % of PM₃ and 17 % of PM₁₀. The study of the size distribution shows that the major part of sulfates and nitrates transported by the particles are in PM₃ (80 % for sulfates and 60 % for nitrates).
Significant correlations between these ionic species and the fine particles were established.
The average contents of chlorides rise up to 3,2 μg/m³ in the PM₁₀ and 3 μg/m³ in the PM₃. The study of atmospheric chlorides made it possible to discuss the influence of the marine aerosol on the composition of the acid aerosol.
In Algeria, the vehicle fleet (4 million vehicles in 2008) is rather old with a low level of maintenance. In urban area, it is the major source of high pollutant emissions of fine particles associated to high levels content of acid particles.