SEM, SEM-EDX, µ-ATR-FTIR and XRD for urban street dust characterisation

Street dust, which is deposited from the atmosphere, reflects the quality of the environment. In this study, a collection of non-destructive qualitative and semi-quantitative techniques was exploited to characterise urban street dust samples from Khamees-Mushait city, Saudi Arabia. The collection included scanning electron microscope-energy dispersive X-ray spectroscopy (SEM-EDX), µ-attenuated total reflectance-Fourier transform infrared (µ-ATR-FTIR) and X-ray diffraction spectrometry (XRD). Sixty dust samples were collected from 20 sites. The particle-size of <100 µm was considered for characterisation. SEM analysis showed different heterogeneity levels of particle-size and particle-shape reflecting different origins. The particle-size distribution revealed that the dominant fractions of particle-size were 20–43 and 40–63 μm followed by <10 and 63–100 μm. Additionally, fly ash and soot particles were also detected. The principal component analysis and hierarchical cluster analysis classified sampling sites into three categories, which were linked with functional sites in the study area. µ-ATR-FTIR and XRD revealed that different types of silicate minerals were the dominant in the study area. µ-ATR-FTIR also revealed selective functional groups (ammonium, aliphatic, sulphate, water/n-alkanoic/n-alkanols and organonitrate) and minerals (smectite, kaolinite) in specific sampling sites. EDX analysis showed the following descending order of element percentages: O ≫ C ≫ Si > Fe ≈ Al ≫ Ca > Mg > Na > Ba > K. The GIS maps showed homogenous spatial distribution of C, K contents, and to some extent O, Ca and Mg contents while Al, Fe and Si contents showed high spatial heterogeneity. The major and dominant minerals in all sites were quartz, sodium calcium aluminium silicate, calcium aluminium silicate, calcite and kaolinite as recorded by XRD analysis.