Investigating Spatial Heterogeneity in Aerosols Chemical Composition and Implications for Physico-Optical Properties over the North Eastern Region of India

Total suspended particulates (TSP) samples were collected using a high-volume sampler in a campaign mode observation over seven selected locations in North-East India, during post-monsoon season of 2023. Scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) system analysis have been performed to understand the morphology, size, and elemental composition of ambient TSP. EDX analysis reveals the presence of C, O, Mg, Si, Na, Al, and K as the significant elements in almost all the samples, and Cr, Cu, Zn, Fe, P, S, Ti, and Ba as minor elements in some of the samples, posing possible threats to human health. These particles are classified into three groups: biogenic, geogenic, and anthropogenic based on the elemental spectrum and morphological features. Fourier Transform Infrared Spectroscopic analysis shows consistent chemical constituents, including calcite, silicate, palygorskite, Illite, and aliphatic hydrocarbons across all the sampling locations. Integrated source apportionment studies like the Enrichment Factor, Pearson Correlation Coefficient, and Principal Component Analysis reveal a mixed source of aerosols originating from both crustal and industrial origins in the eastern part. In contrast, industrial and vehicular emissions primarily influence the middle sector and the western part. SEM analysis confirmed the existence of a wide range of particles with diverse morphologies, mainly spherical and irregular shapes such as rectangles, discs, and cone-like forms, in aerosols across the region, with an abundance of Si. The Discrete Dipole Approximation is further used to simulate the optical properties of these aerosols, considering dust as the constituent but with varying shapes and sizes.