Seasonal Variation of Mass Concentration and Chemical Composition of PM2.5 and PM10, Source Identification and Human Health Risk Assessment in Meknes City in Morocco

Abstract

In this work, we are interested in the characterization, identification of the sources and seasonal variation of airborne particles in suspension and their chemical compositions as well as their human health risk assessment in Meknes city in Morocco. For this, samples were taken with Gent sampler, making it possible to separate the coarse fractions (PM₁₀) from the fine fractions (PM_2.5). The particles were collected, for a year in the city center in Meknes–Morocco, near the highways with very important automobile traffic and not far from the rail traffic. The concentrations of eight elements (Ca, Cr, Cu, Fe, K, Mn, Pb and Zn) were analyzed using Total Reflection X Rays Fluorescence (TXRF). Some filters were analyzed by Scanning Electron Microscopy coupled to the Energy-Dispersive Spectrometer (SEM–EDS). The statistical approach to pollution sources is carried out by the application of Positive Matrix Factorization (PMF). The results obtained for particulate matter show the importance of terrigenous inputs and soil resuspension, especially in July and August when the coarse fraction reaches the highest levels (increased wind erosion of the soil). European quality standards and WHO recommendations have also been exceeded. While for the chemical composition, the seasonal variations are not significant. It is also noted that the Pb contents are higher than the quality standards. Regarding the sources of pollution, the application of PMF and SEM–EDS show the influence of three major sources: mineral emissions (cement industry), mix of re-suspended soil particles and road traffic and rail traffic. Health risk assessments revealed that non-cancerous hazards were lower than the acceptable level (< 1), hence no significant risk is expected, while, the cancer risk was higher than the acceptable level (10^–6) particularly for Cr. In addition, mortality risk for PM_2.5 and PM₁₀ were higher due to higher ambient concentrations measured in Meknes city.