This study presents a comprehensive characterization of aerosols across selected Eurafrican stations over a decade (2010–2019), utilizing Aerosol Optical Depth (AOD) and Angstrom Exponent (AE) data from the surface-based AERONET Version 3, Level 2 dataset. The main objective is to understand the spatial and seasonal variability of aerosols and their relationship with regional meteorological patterns, with particular focus on how different aerosol types dominate across varied geographic and climatic regions.
Four stations were selected for analysis, representing both eastern and western parts of the Eurafrican domain: Cairo_EMA_2 (Egypt) and Tamanrasset_INM (Algeria) in the east, and IER Cinzana (Mali) and Cape Verde in the west. To ensure accurate and reliable comparisons across sites, the AOD data were first detrended to remove inherent seasonal trends. Validated AOD and AE values were then employed to classify aerosol types and assess their seasonal behavior, providing insight into the dominant aerosol sources and their temporal dynamics.
Aerosol Type Classification and Key Findings
The results confirm that Saharan dust is the dominant aerosol type at the eastern stations of Cairo and Tamanrasset. This is evidenced by AOD values less than 1 and AE values less than 1, which indicate the prevalence of large, coarse particles typical of desert dust. In contrast, the western stations of IER Cinzana and Cape Verde display both AOD and AE values greater than 1, signifying finer aerosol particles. These finer particles are likely influenced by sources such as biomass burning and anthropogenic pollution, which are common in these regions.
Seasonal analysis further revealed that the monsoon season is the period of highest dust activity. Conversely, the winter season exhibited lower AOD values at the eastern stations, highlighting the strong seasonal influence of regional meteorological cycles on aerosol loading and type. The seasonal cycles show that the monsoon not only drives dust transport but also affects aerosol optical properties through changes in humidity, wind patterns, and atmospheric mixing.
Linear regression analysis between AOD and AE was conducted for the various sites. At Tamanrasset_INM, an inverse relationship was observed, with AE mean and standard deviation of approximately 0.01 ± 0.28, supporting the dominance of dust aerosols driven by strong surface winds. This inverse coupling between AE and AOD is significant because fine-mode aerosols generally have AE > 1, while coarse-mode aerosols show AE < 1. The root mean square error (RMSE) and mean absolute error (MAE) for regression fits were low, indicating good agreement and reliable characterization of aerosol optical properties.
Detrending of AOD time series was necessary to separate seasonal variations from longer-term trends. Seasonal patterns can otherwise mask relative changes in aerosol loading. This approach enables a more precise understanding of aerosol behavior over time and across regions.
Seasonal cycles were examined in detail, classifying data into winter, premonsoon, monsoon, and postmonsoon periods, which collectively represent about 25% of the dataset. The study found that AOD spectral dominance begins in the premonsoon and extends through the monsoon season, with characteristic dust loading. AE values during this period ranged from 0.22 to 0.33, all below 1, further confirming the coarse dust particle presence.
Winter was characterized by drier local conditions, with AE values peaking at 0.33 and showing typical dust aerosol peaks in AOD. These results emphasize the key role that local meteorology and atmospheric chemistry play in influencing aerosol concentrations. For instance, low-pressure regions tend to have higher AOD loading due to enhanced aerosol uplift and transport.
The inverse correlation between AE and AOD was again confirmed for Cairo_EMA_2, with seasonal variations clearly indicating that different aerosol types dominate at different times of the year. Winter spectral means showed negative deviations in AOD and AE, consistent with dust dominance, whereas premonsoon periods exhibited more varied aerosol properties.
The spatial trends highlight the asymmetric AOD variations, particularly pronounced in the eastern region after detrending. This asymmetry may result from additional aerosol types such as black carbon or other absorbing aerosols contributing to the optical depth.
The comprehensive decadal analysis across the Eurafrican stations revealed distinct regimes of aerosol sources and types, including dust, biomass burning, and urban pollution, each with unique optical and physical-chemical properties. These sources are affected by long-range transport and seasonality, demonstrating the complex nature of aerosol dynamics in the region.
The findings provide a clearer understanding of the spatial heterogeneity and seasonal shifts in aerosol properties across Eurafrican regions. Saharan dust remains the principal aerosol type in eastern stations, while western stations show more influence from finer aerosols related to biomass burning and human activities. The study confirms the monsoon season as a major driver for dust transport and highlights how meteorological cycles shape aerosol characteristics.
The study link is here: Recent study in aerosol distribution