Decoding Biomass Smoke in Rural India: A Multi-Technique Analysis of Particulate Matter and Ash from Cooking Fuels

The use of solid biomass fuels for cooking in rural Indian households produces significant particulate emissions with implications for indoor air quality and human exposure. This study characterises the physico-chemical properties of particulate matter (PM) and combustion ash emitted from commonly used biomass fuels to provide a detailed understanding of their composition, morphology, and elemental profiles.

Particulate and ash samples were collected from real-world kitchens and controlled combustion of biomass fuel under simulated household conditions. The average particle size distribution of emitted PM was dominated by fine and ultrafine fractions, with a large proportion below 2.5 µm.
The samples were analysed using Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDX), X-ray Diffraction (XRD), and Raman spectroscopy to identify surface morphology, elemental composition, crystalline phases, and carbon structure. Morphological analysis showed that PM from biomass combustion formed irregular, porous agglomerates, as well as soot-like formations with branches or chain-like structures. EDX analysis indicated that potassium, calcium, silicon, and iron were the major elements, with trace amounts of sodium, zinc, aluminium, and magnesium also detected. Elemental analysis revealed presence of heavy metals, including arsenic, cadmium, chromium, lead, and zinc from biomass burning. Mercury was found only in PM samples from cooking. Raman spectra of PM and ash samples exhibited distinct D and G bands, indicating the presence of amorphous carbon structures, with higher ID/IG ratios, suggesting incomplete combustion. Carbonaceous analysis revealed that around 80% of the carbon in PM was organic carbon (OC), while only 30% of the carbon in ash was OC. The predominance of elemental carbon (EC) in the remaining 70% suggests substantial formation of black carbon or soot due to incomplete combustion of biomass fuels. Volatile analysis was carried out for both particle-bound and gaseous phase samples, where benzene-derivatives were found to be the highest. Common compounds found in the samples include naphthalene derivatives as well as long-chain and cyclic silanes and siloxanes, which cause chronic health effects in addition to being classed as carcinogenic compounds or developmental toxins.

This study demonstrates a replicable approach that combines personal exposure monitoring with a six-stage Andersen cascade impactor to collect particulate samples representative of their deposition potential in the human respiratory tract, followed by detailed physico-chemical characterisation. These findings contribute to understanding source-specific emission profiles from rural cooking practices and can support emission inventory development, exposure assessment, and mitigation strategies targeting household biomass combustion.