Formation of particulate matter in the ambient air of Dhaka city, Bangladesh

The physical and chemical characterizations of airborne particulate matter (PM) in the ambient air of Dhaka, Bangladesh are reported. The daily average concentrations of PM₁₀ and PM_2.5 ranged from 73 to 416 µg/m³ and 44 to 233 µg/m³, respectively. The characterization was performed using Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), inductively coupled plasma mass spectrometry (ICP-MS), thermogravimetric analysis (TGA), and elemental (i.e., CHNS) analysis. In general, PM_2.5 particles were found to be regular in size and stony spherical in shape, whereas PM₁₀ particles displayed a wide array of morphologies, including irregular particle size and shape with sponge morphology. ICP-MS analysis confirmed the presence of trace metals such as V, Mn, Co, Ni, Cu, Zn, As, Sr, Cd, and Pb in the PM samples. The concentrations of metals in PM₁₀ and PM_2.5 were found to be 220 ± 66 mg/g and 453 ± 113 mg/g, respectively. PM₁₀ was found to contain three times more volatile solvents, water, organic compounds, and microbes compared to PM_2.5. Consolidating all findings, a plausible structure for PM was proposed, wherein a metallic core is encapsulated by an organic shell. This study contributes to understand the composition and mechanism for the formation of PM, shedding light on the complex nature of urban air pollution.

Graphical Abstract