06 Apr 2021

06 Apr 2021

Review status: this preprint is currently under review for the journal ACP.

First insights into Northern Africa high-altitude background aerosol chemical composition and source influences

Nabil Deabji1,2, Khanneh Wadinga Fomba1, Souad El Hajjaji2, Abdelwahid Mellouki3, and Hartmut Herrmann1 Nabil Deabji et al.
  • 1Leibniz Institute for Tropospheric Research (TROPOS), Atmospheric Chemistry Department (ACD), Permoserstraße 15, 04318, Leipzig, Germany
  • 2LS3MN3E-CERNE2D, Faculty of Science, Mohammed V University in Rabat, 4 Avenue Ibn Battouta, B.P. 1040, 10100 Rabat, Morocco
  • 3Institut de Combustion Aérothermique Réactivité et Environnement/OSUC-CNRS, 1C Avenue de la Recherche Scientifique, 45071 Orléans Cedex 2, France

Abstract. Field measurements were conducted to determine aerosol chemical composition in a newly established remote high-altitude site in North Africa to investigate the variations in aerosol composition useful in assessing global and regional changes in atmospheric composition. Particulate matter (PM10) filter samples (200) were collected at the Atlas Mohammed V atmospheric observatory (AM5) located in the Middle-Atlas Mountains in Morocco using a high-volume (HV) collector in a 12 h sampling interval from August to December 2017. The chemical composition of the samples was analyzed for trace metals, ions, elemental carbon, organic carbon, aliphatic hydrocarbons, and polycyclic aromatic hydrocarbon (PAHs) content.

The results indicate that high-altitudes aerosol composition is influenced by both regional as well as trans-regional transport of emissions. However, local sources play an important role, especially during low wind speed periods, as observed for November and December. Despite the proximity of the site to the Sahara Desert, its influence on the atmospheric composition at this high-altitude site was mainly seasonal and accounted for only 14 % of the sampling duration. Background conditions at this remote site are characterized by low wind speeds (Av. 2.5 m/s) and mass concentrations in the range of 9.8 and 20 µg/m3. The chemical composition is found to be dominated by inorganic elements, mainly suspended dust (47 %) and ionic species (16 %), followed by organic matter (15 %), water content (12 %), and indeterminate mass (9 %). Biogenic organics contributed up to 7 % of the organic matter with high contributions from compounds such as Nonacosane, Heptacosane, and 2-Pentadecanone. The AM5 site is dominated by four main air mass inflow, which often leads to different aerosol chemical compositions. Mineral dust influenced was seasonal and ranged between 20 and 70 % of the PM mass with peaks observed during the summer and was accompanied by high concentrations of SO42− of up to 1.3 µg/m3. During winter, PM10 concentrations are low (< 30 µg/m3), the influence of the desert is weaker, and the marine air masses (53 %) are more dominant with a mixture of sea salt and polluted aerosol from the coastal regions (Rabat and Casablanca). During the daytime, mineral dust contribution to PM increased by about 42 % because of road dust resuspension. In contrast, during night-time, an increase in the concentrations of PAHs, ketones, and anthropogenic metals such as Pb, Ni, and Cu was found due to variations in the boundary layer height. The results provide first insights into typical North African high-altitude background aerosol chemical composition useful for long-term assessment of climate and regional influence of air pollution in North Africa.

Nabil Deabji et al.

Status: open (until 01 Jun 2021)

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Nabil Deabji et al.

Nabil Deabji et al.


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Short summary
Mountain and high altitude sites provide representative data for the lower free troposphere and various pathways for aerosol interactions, changing boundary layer heights useful in understanding atmospheric composition. However, few studies exist in African regions despite its diversity in both natural and anthropogenic emissions. This study provided detailed atmospheric studies in the North African high-altitude region.